Untitled - Palazzoli

Untitled - Palazzoli
INTRODUCTION page53
Chap.1 THE HISTORY 1.1 - HISTORICAL FACTS AND CURIOSITIES
Chap.2 TECHNICAL ASPECTS
2.1EXPLOSION
2.2 EXPLOSIVE ATMOSPHERE FROM GAS
2.2.1 Limits of inflammability
2.2.2 Minimum ignition energy
2.2.3
Flash point
2.2.4
Autoignition temperature
2.2.5 Gas classification in ATEX according to IEC/EN 60079 standards
2.3
EXPLOSIVE ATMOSPHERE FROM DUST
2.3.1
Explosibility limits
2.3.2 Minimum ignition energy
2.3.3 Ignition temperature and glowing temperature
2.3.4
Electrical resistivity
2.3.5 Dust classification in ATEX according to IEC/EN 60079 standards
2.4
ELECTRICAL IGNITION SOURCES
2.4.1
Electric arc
2.4.2
Surface temperature
2.4.3
Electrostatic discharge
page54
page
54
page56
page56
page 57
page
57
page
57
page
58
page59
page59
page
60
page
61
page61
page
61
page
62
page62
page
62
page
62
page63
page63
page63
Chap.3 ZONES AND PROTECTION LEVELS
3.1 SOURCES OF RELEASE AND ZONE CLASSIFICATION
3.2 EQUIPMENT PROTECTION LEVEL-EPL
page65
page
65
page
68
Chap.4 TYPES OF PROTECTION
4.1 TYPES OF PROTECTION
4.1.1 Flameproof enclosures Ex-d
4.1.2 Increased safety Ex-e
4.1.3 Intrinsic safety Ex-i
4.1.4
Encapsulation Ex-m
4.1.5 Type of protection nA-nC-nR
4.1.6 Oil immersion Ex-o
4.1.7 Powder filling Ex-q
4.1.8 Pressurized enclosure Ex-p
4.1.9 Protection by enclosures Ex-t
4.1.10 Protection by “combined” types of protection
page70
page
70
page
72
page
72
page
73
page74
page
75
page
77
page
77
page
78
page
78
page
79
Chap.5 REQUIREMENTS FOR EX DEVICES
5.1 CLASSIFICATION OF ELECTRICAL EQUIPMENT FOR GAS ACCORDING TO IEC/EN 60079-0
5.2 CLASSIFICATION OF ELECTRICAL EQUIPMENT FOR DUST ACCORDING TO IEC/EN 60079-0
5.3 GENERAL REQUIREMENTS FOR ELECTRICAL EQUIPMENT
5.3.1 Thermal and impact resistance and IP rating 5.3.2
Gasket sealing
5.3.3 Resistance to light
5.3.4
Electrostatic charges
5.3.5 Characteristics of plastic and elastomeric materials
page80
page
80
page
82
page
82
page
83
page85
page
85
page86
page
88
Chap.6 ATEX DIRECTIVES AND EX PRODUCT MARKING
6.1 DIRECTIVE 99/92/EC
6.2 DIRECTIVE 94/9/EC
6.2.1 Equipment groups and categories
6.3 NEW 2014/34/EU DIRECTIVE AND DIFFERENCES WITH 94/9/EC
6.4 EX PRODUCT MARKING
6.4.1
CE marking
6.4.2 Marking according to the ATEX directive
page89
page
89
page
90
page
91
page
93
page
95
page95
page
96
Cap.7 CERTIFICATIONS
7.1 CONFORMITY ASSESSMENT
7.2 THE TECHNICAL DOCUMENTATION 7.2.1 Safety instructions, use and maintenance
7.2.2 Ignition risk analysis document
7.2.3 EU declaration of conformity
7.2.4
EU-type-examination certificate
page101
page
101
page 102
page 103
page 104
page 104
page106
50
Chap.8 ATEX vs IECEx
8.1 THE IECEx SCHEME
8.2 DIFFERENCES BETWEEN ATEX DIRECTIVES AND IECEx SCHEME 8.3 IECEx MARKING
8.4 WORLD MAP WITH ATEX-IECEx-OTHER SCHEMES
page108
page 108
page 108
page 111
page 112
Chap.9 AREA CLASSIFICATION
9.1INTRODUCTION
9.2 HAZARDOUS AREA CLASSIFICATION PROCEDURE
9.2.1 Procedures to classify hazardous areas
9.3 DEFINITIONS AND INFORMATION
9.3.1
Explosive atmosphere
9.3.2 Source of release
9.3.3 Grade of release
9.3.4 Dusts – levels of housekeeping
9.3.5
Zones
9.4GARAGES
9.4.1 Locate the environment
9.4.2
Flammable substance
9.4.3 Sources of release
9.4.4 Grades of release
9.4.5 Load of release
9.4.6 Type of zone
9.4.7
Hazardous distance
9.4.8 Hazardous area classification
9.5 CAR REPAIR SHOPS
9.5.1 Locate the environment
9.5.2
Flammable substances
9.5.3 Sources of release
9.5.4 Grades of release
9.5.5 Load of release
9.5.6 Type of zone
9.5.7 Hazardous distance 9.5.8 Hazardous area classification
9.6 NATURAL GAS THERMAL PLANTS
9.6.1 Locate the environment
9.6.2
Flammable substances
9.6.3 Sources of release
9.6.4 Grade of release
9.6.5 Load of release
9.6.6 Type of zone
9.6.7
Hazardous distance
9.6.8 Hazardous area classification
9.7CARPENTRIES
9.7.1 Locate the environment
9.7.2
Flammable substances
9.7.3 Sources of release
9.7.4 Grade of release
9.7.5 Load of release
9.7.6 Type of zone
9.7.7
Hazardous distance
9.7.8 Hazardous area classification
9.8 AGRICULTURAL INDUSTRIES
9.8.1 Locate the environment
9.8.2
Flammable substances
9.8.3 Sources of release
9.8.4 Grade of release
9.8.5 Load of release
9.8.6 Type of zone
9.8.7
Hazardous distance
9.8.8 Hazardous area classification
page113
page 113
page 113
page 114
page
114
page114
page 114
page 115
page 115
page115
page 116
page 116
page117
page 117
page 118
page 118
page 118
page119
page 119
page 120
page 120
page120
page 121
page 121
page 121
page 121
page 122
page 122
page 123
page 123
page123
page 124
page 124
page 124
page 124
page125
page 125
page 126
page 126
page126
page 127
page 128
page 128
page 128
page129
page 129
page 130
page 130
page130
page 131
page 131
page 131
page 131
page133
page 133
Chap.10 INSTALLATION METHODS
10.1GENERALITIES
10.2 TERMS AND DEFINITIONS
10.3 BRIEF GENERAL INFORMATION
10.3.1
Overload
page134
page 134
page 135
page 135
page135
51
10.3.2
Short-circuit
10.3.3
Electric arc
10.3.4
Dangerous sparks
10.3.5
Static electricity
10.3.6
Thermal effects
10.4 GARAGES
10.4.1
Generalities
10.4.2
Explosion
10.4.3
Fire
10.4.4
External influences
10.4.5 Selection and installation of electrical components
10.5 CAR REPAIR SHOPS
10.5.1
Generalities
10.5.2
Explosion
10.5.3
Fire
10.5.4
External influences
10.5.5 Selection and installation of electrical components
10.6 THERMAL PLANTS
10.6.1
Generalities
10.6.2
Explosion
10.6.3
Fire
10.6.4
External influences
10.6.5 Selection and installation of electrical components
10.7 CARPENTRIES
10.7.1
Explosion
10.7.2 Fire and external influences
10.7.3 Selection and installation of electrical components
10.8 AGRICULTURAL INDUSTRIES
10.8.1
Generalities
10.8.2
Explosion
10.8.3
Fire
10.8.4
External influences
10.8.5 Selection and installation of electrical components
page136
page137
page137
page137
page138
page 138
page138
page138
page139
page139
page 139
page 140
page140
page141
page141
page141
page 141
page
145
page145
page145
page146
page146
page 146
page 147
page147
page 148
page 148
page
150
page150
page150
page150
page151
page 151
Chap.11 PROCEDURE FOR TEMPORARY TESTS
11.1GENERALITIES
11.2 INSPECTION AND MAINTENANCE
11.3INSULATION
11.4 EQUIPMENT WITHOUT MARKING
11.5DOCUMENTATION
11.6PERSONNEL
11.7 INSPECTION TABLES
page153
page 153
page
153
page 154
page
154
page 154
page 155
page155
52
INTRODUCTION
In the vast majority of industrial processes flammable substances or combustibles are stocked,
handled or transported.
Excluding explosive or unstable chemical substances for which the danger is well recognized in
nature, there is a high number of “unsuspected” elements that present characteristics able to
create an explosion, under specific circumstances.
As a matter of fact, if the danger in some sectors such as the chemical or petrochemical is well
known, it can be difficult to realize it in some working places that we could define as “ordinary”,
such as agricultural industries, metalworking factories, carpentries, distilleries, sugar refineries,
battery charging places, etc.
Actually, the major accidents happen in these places.
In recent history, the most significant case took place in Georgia (USA), in the Imperial Sugar
factory where a whole sugar refinery was destroyed causing the death of 14 people and the
injuries of 36 due to a blast triggered by the apparently harmless sugar dust.
Picture 1: blast of a sugar refinery
Unfortunately, as often happens, only these accidents can make the general opinion aware about
possible situations or problems of risk.
The safety of working places is an example of this and in the last years we are witnessing an
international massive campaign of arrangements and legislations aiming at improving the worker
conditions and prevent these dangerous events as much as possible.
In this context the ATEX Directives regulate the manufacturing of equipment for use in potentially
explosive atmospheres and worker safety conditions in those areas.
53
Chap.1: THE HISTORY
1.1 – HISTORICAL FACTS AND CURIOSITIES
The first discovered dangerous zone was inside coal mines where there was a double risk: the
presence of methane and coal dust.
When the methane – air mixture was triggered, a minor explosion took place and this was enough
to trigger a second and more violent explosion caused by the dust cloud which was created by the
first one.
The first solution adopted by miners to solve these problems was to use a long pole with embers
placed on the top to trigger the gas every day, so that there was not the possibility for the gas to
accumulate in such a quantity to create an explosion that could produce a bigger one.
However, this solution to provoke “controlled explosions”, as easily understandable, represented
many risks and soon the list of miners willing to make this procedure shortened. At first they
recruited prisoners and then animals, which were sprinkled with water and equipped with a
particular seat with a candle and sent over the mines with the hope to create only small blasts.
Picture 2: controlled explosions to avoid the accumulation of dangerous gas concentrations inside mines
The first type of protection inside mine industries was to ventilate the mines in order to markedly
dilute the flammable gas and, as a consequence, reduce the limits of the explosion.
Regarding coal mines, in 1815 Sir Humphrey Davy invented what was called the “Davy lamp”, a
particular oil lamp, that worked as a gas (firedamp) detector.
54
Picture 3: Davy lamp
If there was presence of fire damp, it overpassed the metal grille and came in contact with a small
flame creating an increase of gas inside the lamp and a consequently gradual extension of the
flame up to the switch-off, thus warning the miner about the danger.
The metal grille was very thin, in order not to allow the flame propagation through the screen.
Then, some low voltage signalling sirens were introduced in mines in order to control the
functioning of the elevators. Since they worked at 12 V dc they were thought to be safe; but in
1912 and 1913 two disastrous explosions inside mines were caused by these devices.
The particular attention in the design of safer signalling sirens was the first step towards the
development of an electrical equipment series suitable to be installed in potentially explosive
atmospheres.
The first German regulation “Protection of electrical installations in dangerous areas” was
published in 1935 as a guide line to the installation of electrical equipment inside hazardous areas.
A major change took place in 1938, dividing the regulation in two parts: one regarding the
essential installation requirements and the other the principal requirements in product design.
The regulation concerning the product design included the fundamental concepts of the types of
protection such as flameproof enclosure, oil immersion and increased safety.
All the components were designed in order to be protected and encased inside industrial
enclosures that were resistant to atmospheric agents and weather conditions; this fact then
brought to the development of flameproof components installed inside increased safety
enclosures.
The devices designed to be in compliance with these normative requirements were marked with
the Ex symbol for the first time.
In the sixties, the European Community was founded to set a free trade of products inside Europe;
to achieve this target, the technical standards needed to be harmonised and for this reason they
created the CENELEC.
This new system of European Standards (EN 50014 - EN 50020) published in 1972, was based on
the Zone classification system of the IEC 60079-10.
The European Standards thus replaced the various National Standards and then the guidelines for
application in Zone 0 (EN 50284) and Zone 2 (EN 50021) were issued.
In 1975 the first European Directive for equipment in hazardous areas was published and named
“Explosion Protection Directive”.
55
Chap.2: TECHNICAL ASPECTS
2.1 - EXPLOSION
An explosion is an oxidation-reduction reaction that provokes the formation of heat (highly
exothermic reaction), usually combined with a visible flame.
The reaction happens only if there are the three following components present at the same place
and time:
• Fuel: reducing agent, usually substances in the form of gases, vapours, dusts and fibers
with specific physical properties and in definite volume concentration.
• Combustive agent: oxidative agent, typically the oxygen present in the air.
• Ignition source: any source of energy able to trigger the reaction.
IGNITION
Picture 4: fire triangle
This situation is schematically represented by the fire triangle shown in Picture 4.
A relevant characteristic of an explosion is the high speed of reaction: once the reaction is
triggered, a flame front is created and is physically expressed as a wave of pressure spreading in
space and moving from the combusted mixture to the non-combusted surroundings.
The shorter is the distance from the explosion point the bigger is the effect: for this reason if an
explosion happens in a confined volume, it will multiply its danger.
However, not all the fuel-combustive mixtures create a potentially explosive atmosphere: the
conditions for a potential environment explosiveness are influenced by the physical and chemical
characteristics of the fuels and trigger properties (energy of ignition) related to the fuel type.
56
2.2 – EXPLOSIVE ATMOSPHERE FROM GAS
2.2.1 – LIMITS OF INFLAMMABILITY
Any substance in the form of gas, vapour or mist can create an explosive atmosphere only when
its concentration in the air is in a certain range between two limits, defined as lower and upper
explosion levels which are expressed in volume percentage:
•
•
LEL or Lower explosion level under which the combustible substance is in concentration in
the air not enough to create an explosion, even if ignited.
UEL or Upper explosion level above which the combustible substance is in concentration in
the air not enough to create an explosion, even if ignited.
Picture 5: ignition area
The range between the two limits is defined as explosive or flammable range and corresponds to
the potential ignition of the explosive atmosphere.
In Table 1, explosive limits of some flammable gases and vapours are quoted.
Substance
Etane
Methane
Propane
Butane
Ethylene
Propylene
LEL [%Vol]
3
5
2,1
1,8
2,7
2,4
UEL [%Vol]
12,4
15
9,5
8,4
37
11
Substance
Acetylene
Benzene
Ethyl alcohol
Ammonia
Hydrogen
Acetone
LEL [%Vol]
2,5
1,3
3,3
15
4,0
2,6
Table 1: inflammability limits of some substances
UEL [%Vol]
100
7,9
19
28
75
31
2.2.2 – MINIMUM IGNITION ENERGY
As said, one of the necessary elements of the explosion is the ignition source.
In order to ignite the atmosphere it is necessary a certain quantity of energy that varies according
to the combustible concentration present in the mixture, with a parabolic pattern that tends to a
minimum in correspondence with the stoichiometric concentration, defined as Minimum Ignition
Energy (M.I.E.), and noticeably increases close to the inflammability limits.
The Minimum Ignition Energy, quoted in mJ, is thus the minimum energy which is necessary to
trigger a potentially explosive mixture and is a characteristic of each substance.
57
Picture 6: ignition areas of hydrogen and propane
Picture 6 represents the typical patterns of the ignition energy for hydrogen and propane
according to the substance volume concentration in air; as it can clearly be inferred, the danger of
hydrogen is much bigger as it has a wider explosive range and needs lower ignition energy to
trigger the mixture.
Substance
Hydrogen
Benzene
Acetylene
Methane
Acetone
MIE [mJ]
0,018
0,22
0,02
0,28
1,15
Substance
Metanhol
Carbon oxide
Ethylene
Propane
Ammonia
MIE [mJ]
0,215
0,1
0,096
0,25
>100
Table 2: minimum ignition energy of some substances
2.2.3 – FLASH POINT
If the explosive atmosphere is created by combustibles in the form of liquids, the parameter that
must be taken into consideration is the flash point.
This is the minimum temperature at which vapours can be formed in such a quantity to mix with
oxygen present in the air, creating a potentially explosive atmosphere.
This temperature value, of which some examples for flammable liquids are quoted in Table 3,
usually corresponds approximately to the LEL, because these values are in some way linked to
each other.
Substance
Diesel
Benzene
Petroleum
Tinf [°C]
+55
-11
-20
Substance
Acetone
Ethyl alcohol
Methyl alcohol
Tinf [°C]
-17
+12
+11
Table 3: flash point of some substances
58
2.2.4 – AUTOIGNITION TEMPERATURE
The Autoignition Temperature, as the name suggests, is the minimum temperature at which the
combustible-combustive mixture ignites without the need of a third source of energy.
This specific value of the substance, together with the Minimum Ignition Energy, is essential in the
gas classification, which is detailed in the next paragraph, and so in the selection of the suitable
electrical equipment.
Even though the assessment of this value is highly influenced by the methods of testing and
ambient conditions at which it is obtained, it is possible to find in literature some tables with
illustrative values for each substance.
Substance
Gas oil
Petrol
Wood
Tacc [°C]
220
250
220-250
Substance
Acetone
Hydrogen
Methyl alcohol
Tacc[°C]
540
560
455
Table 4: Autoignition Temperature of some substances
2.2.5 – GAS CLASSIFICATION IN ATEX ACCORDING TO IEC/EN 60079 STANDARDS
To exactly know the basic characteristics of an electrical equipment for not igniting an explosive
atmosphere, it is necessary to clearly define it according to the type of combustible substance.
This is possible thanks to the gas classification detailed in Sheet 1.
IEC/EN 60079 standards classify the gases in groups based on the Minimum Ignition Energy and
assigns temperature classes according to the Autoignition Temperature.
Sheet 1: Gas classification according to IEC/EN 60079
59
2.3 – EXPLOSIVE ATMOSPHERE FROM DUST
If the danger related to gas, or anyway flammable liquids, is well known by everyone, maybe it is
not so intuitive to connect the risk of an explosion with the presence of dust or combustible
particles.
This is even more emphasized as the combustible dust often comes from the working, handling or
stocking of materials, such as aluminium, which are clearly non-flammable at the solid state.
A dust is defined as a combination of solid particles that can deposit because of the weight or can
stay suspended in the air for a certain period of time.
Not all the dusts can be combustible. Generally the dusts having particle size less than 0,5 mm can
react with oxygen present in atmospheric condition once they are suspended in the air.
The danger linked to combustible dust increases in an inversely proportional way to the particle
size and can be due to:
•
formation of a dust cloud
In this case, the dust suspended in the air forms a combustible cloud that, helped by the
dimensions, tends to mix with oxygen creating a potentially explosive atmosphere. This is the
typical case of the industrial sector during normal operations of a production cycle, from the
removal of a bit of wood to the machine cleaning.
•
formation of a dust layer
In this case, the dust deposited because of the weight can create layers that, if not removed, can
reach thicknesses of tens of millimeters.
A dust layer can principally be hazardous for two reasons:
o it can raise and create a cloud caused by an air movement or, in the worst case, as an
effect of a previous explosion. As a matter of fact, the wave of pressure generated by an
explosion caused by a dust cloud can usually raise the deposited layers in the
surroundings determining new clouds that immediately ignite, creating a dominoes effect
with potentially devastating consequences;
o it can contribute to decrease the thermal dissipation of an equipment, with a consequent
increase of temperature and ignition danger.
For dusts, the concept of the fire triangle is extended, picture 7, as the necessary conditions for
creating an explosion are more than three:
o
o
o
o
o
60
the dust must be combustible
it must be spread in the air to create a cloud – presence of oxygen (combustive)
it must have a certain particle size (less than 0,5 mm)
the concentration must be within the range of a defined explosive range
it needs an ignition source
Picture 7: fire pentagon
2.3.1 – EXPLOSIBILITY LIMITS
As already mentioned, also dusts are defined within an explosive range according to the
concentration in air.
The limit concentrations are defined LEL and UEL as for gases but are expressed in mass for air
volume unit (g/mm3) and defined in atmospheric conditions. For concentrations lower than the
LEL the distances between particles are so high that the heat caused by the oxidation-reduction of
one of them is not enough to ignite those of the surroundings.
The limit of lower explosion level of dusts is usually a value between 20g/mm3 and 100g/mm3.
Anyway, when the dust concentration does not exceed 10g/m3 it is considered a safety condition
and thus it is a reference LEL in potentially explosive atmosphere assessment.
2.3.2 – MINIMUM IGNITION ENERGY
Dusts, as gases, require a Minimum Ignition Energy to trigger an explosion: in this case it depends
on the chemical and physical properties and particle size of the dust.
It is typically quoted in some tens of mJ and thus presents bigger values than gases.
Dusts
Coffee
Active carbon
Cellulose
Wood
Polyethylene
MIE [mJ]
25
100
45
20
20
Dusts
Magnesium
Vitamine B1
Aspirin
Sugar
Sulphur
MIE [mJ]
30
35
15
45
35
Table 5: Minimum Ignition Energy for some combustible dusts
2.3.3 – IGNITION TEMPERATURE AND GLOWING TEMPERATURE
In the case of dusts, there are two important temperature values:
• Tci (IT ignition temperature) - minimum ignition temperature of a dust cloud
• Tl (GT glowing temperature) - minimum ignition temperature of a dust layer with “I”
thickness (usually considered 5 mm) on a hot surface.
Both these values are important to define the temperature limit that a surface of an electrical
equipment can reach in order to increase safety.
61
2.3.4 – ELECTRICAL RESISTIVITY
The solid material producing dust can be electrically conductive.
In order to be considered conductive, a dust must have a resistivity value lower or equal to 103Ωm.
In potentially explosive areas, the presence of conductive dusts on the surface of an electrical
equipment enclosure or in its internal can be dangerous as it tends to condition the dielectric
characteristics favouring:
− the formation of an electric arc between parts with different potential, caused by the
reduction of insulating distances in air
− surface discharge phenomena
− tracking phenomena (the dust is deposited on the surface and for its characteristics
produces a conductive track that allows the current flowing).
For these reasons, the electrical resistivity of a dust is an important parameter that, as we will see
in the next paragraph, is the base for dust classification as per IEC/EN 60079 standards.
2.3.5 - DUST CLASSIFICATION IN ATEX ACCORDING TO IEC/EN 60079 STANDARDS
Same as for gases, IEC/EN 60079 standards regulate the dust classification in groups, according to
conductivity properties as per the visual scheme of Sheet 2.
Sheet 2: dust classification according to IEC/EN 60079
2.4 – ELECTRICAL IGNITION SOURCES
The ignition risk of an explosive atmosphere for an electrical equipment is in the ordinary
operation. As a matter of fact, the energy levels which are normally produced are much bigger
than the value of the minimum ignition energy of gases, liquids and dusts.
In order to protect an electrical equipment from the surrounding environment the habit is to use
enclosures that, other than reducing the risks of direct contact with live parts, also offer protection
against mechanical solicitations and undesired penetrations of liquids or dirt.
For this reason, the enclosure of the equipment becomes central in potentially explosive
atmospheres as it is the element between what it contains and the surroundings. Thus, the
62
mechanical and thermal characteristics of the enclosure material become the main elements to
avoid the ignition of an explosive atmosphere.
The main ignition sources produced by an electrical device are:
•
•
•
formation of electric arc
surface temperature
electrostatic discharge
2.4.1 – ELECTRIC ARC
An electrical equipment designed to control or insulate the circuits of an electrical plant can
produce an electric arc, both in normal operation or in case of fault, and this is principally due to:
•
•
•
•
shortcircuits
overvoltages
surface deterioration and insulation weakening (tracking)
use of MCBs
All these elements produce energy levels much higher than the minimum values of ignition for
gases and dusts, and so the risk is very high.
An electrical equipment which can produce an electric arc in normal operation or in case of fault is
called “sparking”.
2.4.2 – SURFACE TEMPERATURE
The increase of temperature, generated by the Joule effect of an electrical current flow, causes
the warming of the electrical equipment.
During the normal operation or in case of fault (as it can be a short-circuit, overvoltage or bad
contact) the temperature of the enclosure increases and can become dangerous in presence of an
explosive atmosphere.
The temperature increase can become the ignition source if the achieved value is higher than the
Autoignition Temperature of the mixture.
2.4.3 – ELECTROSTATIC DISCHARGE
The electrical equipment material is very important for what concerns the accumulation of
electrostatic charges.
As a matter of fact, where there is an accumulation of electrostatic charge the contact with parts
with different potential, as people or moving machines, provokes an electrostatic discharge
physically represented by a spark that can ignite a potentially explosive mixture.
Researches confirmed that the static electricity accumulated by a person can reach 135 mJ, value
which is enough to ignite the vast majority of explosive mixture between air and gas or air and
dust.
63
Some examples of industrial operations with charge separation and then potentially electrostatic
discharge are:
o charge and discharge or cleaning operations (by means of water or high-pressure vapour)
of tanks or silos that contain flammable liquids or combustible dusts
o working processes such as metal sandblasting
o movement of liquids or dusts on transport system with speed higher than 1m/s.
64
Chap.3: ZONES AND PROTECTION LEVELS
3.1 – SOURCES OF RELEASE AND ZONE CLASSIFICATION
The notion of zone, the base of hazardous area classification, has been introduced in order to
simplify the selection and installation of safe electrical equipment inside environments where
there is the possibility of an explosive atmosphere due to the presence of gas and/or combustible
dusts.
In an installation or environment with potential explosion risk, a source of release is a point from
which a flammable substance can be emitted in such a way that can produce an explosive
atmosphere, both during normal operations or predictable faults.
This is defined according to how frequently the source can emit the hazardous substance. For this
reason, in the years some mathematical models have been created based on the interaction of the
ambient parameters (temperature, pressure, ventilation, etc.) and operative conditions that
involve the hazardous substance, as times, means and temperatures of release.
IEC standards system, particularly IEC 60079-10 establishing basic rules for the classification of
hazardous areas both in presence of gases or combustible dusts, refers to a particular calculation
model, defined IEC zone system.
This model is based on explosive atmosphere formation probability and duration that become
thus the basic parameters to classify dangerous zones.
The zones acquire different numbers in case of presence of gases or combustible dusts as shown
in Tables 6 and 7.
65
ZONE 0
An area in which an
explosive atmosphere,
consisting of a mixture
with air and flammable
substances in the form of
gas, vapour or mist, is
present continuously or
for long periods or
frequently.
ZONE 1
An area in which an explosive
atmosphere, consisting of a
mixture with air and
flammable substances in the
form of gas, vapour or mist, is
likely to occur in normal
operation occasionally.
ZONE 2
Area in which an explosive
atmosphere, consisting of a
mixture
with
air
and
flammable substances in the
form of gas, vapour or mist is
not likely to occur in normal
operation but, if it does occur,
will persist for a short period
only.
Preferred
symbols
IEC 60079-10-1
GAS EXPLOSIVE
ATMOSPHERE
> 1.000 h/year
USA CAN
Explosive atmosphere duration
DIVISION 1
10 ÷ 1.000 h/year
0,1 ÷ 10 h/year
DIVISION 2
Table 6: definition of zone - GAS
ZONE 20
An area in which an
explosive dust atmosphere,
in the form of a cloud of
dust in air, is present
continuously, or for long
periods or frequently.
ZONE 21
An area in which an explosive
dust atmosphere, in the form
of a cloud of dust in air, is
likely to occur in normal
operation occasionally.
ZONE 22
An area in which an explosive
dust atmosphere, in the form
of a cloud of dust in air, is not
likely to occur in normal
operation but, if it does occur,
will persist for a short period
only.
Preferred
symbols
IEC 60079-10-2
DUST EXPLOSIVE
ATMOSPHERE
> 1.000 h/year
USA CAN
66
Explosive atmosphere duration
DIVISION 1
10 ÷ 1.000 h/year
Table 7: definition of zone - DUST
0,1 ÷ 10 h/year
DIVISION 2
The zone classification according to IEC 60079 standards applies internationally and has been
harmonised by CENELEC as European standards (EN 60079-10-1 for gas, EN 60079-10-2 replacing
EN 61241-10 for dust).
North-American countries such as USA and Canada follow the guidelines by National Electrical
Code (NEC) e Canadian Electrical Code (CEC), with rules which are different but present some
similarities:
CLASS I
CLASS II
CLASS III
flammable gases, vapours or mists
combustible dusts
ignitable fibers or flyings
The classification of hazardous areas according to North-American Standards presents only two
zones, called divisions.
DIVISION 1
DIVISION 2
Area in which hazardous concentrations
of combustibles are present
continuously
Area in which hazardous concentrations
of combustibles are not present
continuously
The article 505 of the NEC provides the possibility of classification according to IEC standards and
products in compliance with IEC 60079 standards but the equivalence is not always exact and
accepted: products certified for zone 1 for example do not automatically meet requirements for
Division 1 as this includes also zone 0 of the IEC scheme.
Some typical examples of zones, classified according to IEC zone system, are analyzed in chapter
10.
Picture 8: zones and divisions
67
3.2 – EQUIPMENT PROTECTION LEVEL-EPL
The safety level of an electrical equipment is substantially the ability to avoid the ignition under
specific operating conditions.
In order to do this, an electrical equipment must:
•
•
•
not spark or provoke electric arc
avoid dangerous surface temperature
be made of materials which do not accumulate electrostatic charge
The capability to satisfy these characteristics must be maintained in time and be evaluated in the
following conditions, to be declared by the manufacturer:
•
•
•
normal operation
in presence of a predictable fault
in presence of a second fault (rare), depending on the previous one.
According to the danger of the area for which the equipment is intended, there are different
Equipment Protection Levels, EPL, that substantially express what said before with the use of an
acronym, composed of a first letter that identifies the type of substance present in the explosive
atmosphere (G for Gas and D for Dust) and a second letter that characterizes the protection level
(“a”, “b” or “c”).
The following sheet clarifies it and shows the link between zone and protection level.
The protection level is very important as it allows to immediately understand in which hazardous
zone an EX product can be installed.
68
Sheet 3: EPL – zone correspondence
69
Chap.4: TYPES OF PROTECTION
4.1 – TYPES OF PROTECTION
How does an electrical device reach the Equipment Protection Level explained in the previous
chapter?
By the way it is necessary to introduce the types of protection: they are substantially construction
methods for equipment (electrical or not) that involve the selection of materials, dimensions and
the designing of enclosures and internal components, aiming to minimize the possibility to ignite
an explosive atmosphere.
The types of protection are different according to the type of equipment, explosive atmosphere
and ways in which the ignition is avoided. Moreover, since they are the basic principles to define
the protection levels, they are characterized according to their operating conditions (normal
operation, predictable fault, rare fault).
Types of protection, levels of protection and hazardous zones are closely related to each other, as
shown in Sheet 4.
The types of protection are defined inside IEC/EN 60079 standards (from part 1 on) and can be
divided in three macro-families according to the techniques which are used to avoid the explosion,
as shown in Table 8.
CONTAINMENT
It allows the explosion to
occur inside the enclosure
but not to propagate
outside
Example:
“d” – flameproof
enclosures
TYPES OF PROTECTION
SEGREGATION
It avoids the contact
between hot points and
potentially explosive
atmospheres
Examples:
“m” - encapsulation
“o” – oil immersion
“p”- pressurization
“t” – by enclosure
Table 8: division of types of protection
PREVENTION
It increases the reliability
of electrical components,
limiting hot points and
sparks
Examples:
“e” – increased safety
“i”- intrinsic safety
“n”
They are indicated with small letters (“d”, “e”, “m”, “n”, “i”, “p”, “o” for gas and “i”, “m”, “t”, “p”
for dust) preceded by the letters Ex indicating the compliance with IEC/EN 60079 standards.
In some cases, the identification letters of the types of protection are followed by those relative to
protection levels.
Regarding the characteristics of each type of protection, the standards (IEC/EN 60079-1 and
followings) establish the design requirements and the tests that must be done on the equipment
to check the protection efficiency.
In the following paragraphs, all these types of protection will be detailed with examples of
materials used and possible applications.
70
Sheet 4: types of protection - EPL – zones correspondence
71
4.1.1 – FLAMEPROOF ENCLOSURES Ex-d
The type of protection Ex-d provides the use of particular enclosures that can contain non-Ex
marked components (sparking or not) and allows not only the ingress of explosive atmospheres (in
this case Gas) but also the ignition of it.
These enclosures, generally made of metallic material (aluminium alloys, steel or cast iron),
guarantee the resistance to the pressure generated by the explosion and are designed in such a
way that the joints (named as flameproof joints) are long and have interstice enough not to permit
the outgoing of flames, avoiding the ignition of the explosive atmosphere, Picture 9.
Picture 9: type of protection Ex d
As it can easily be inferred, the level of protection that can be guaranteed is high, EPL Gb, that
makes the equipment suitable to be installed in zone 1.
Some typical installations are low voltage equipment such as electrical distribution boards,
switches, transformers, low and medium voltage motors and all those devices that, during the
normal operation, can spark or cause high temperatures.
The reference standard is IEC/EN 60079-1.
4.1.2 – INCREASED SAFETY Ex-e
The type of protection Ex-e or increased safety applies only to non-sparking equipment, as to say
those that do not produce arcs or sparks during the normal operation, with rated voltage lower
than 11 kV dc/ac.
Some additional measures are provided (longer insulating distances in air, use of specific and Exmarked components, etc.) to offer an increased safety against the production of arcs or sparks or
the possible reaching of high temperatures.
In this case, the ignition is avoided even if the explosive atmosphere is in contact with the internal
elements, and thus the type of protection is suitable for all kinds of gases.
The temperature class of the equipment is defined according to the maximum temperature that
any part (external or internal) can reach during the type examination, as per IEC/EN 60079-7
standard.
The equipment enclosure is required to be minimum IP54 rated, avoiding the ingress of solid
bodies or water that could reduce the insulating distances between the components.
72
Picture 10: type of protection Ex e
The components that can be used with these products must be ATEX marked with a type of
protection suitable for the increased safety.
Even in this case the guaranteed protection level is high, EPL Gb, and allows to safely install the
equipment in zone 1.
The enclosures are usually made of plastic or metal with gasket in elastomer to keep the IP rating.
Typical examples of this type of protection are junction or terminal boxes, terminals and terminal
boards, electromagnets, coils and rotating electrical machines.
4.1.3 – INTRINSIC SAFETY Ex-i
The type of protection with intrinsic safety Ex-i is based on the limitations of energy that the
circuit can generate so that it will not ignite the explosive atmosphere.
The intrinsic safety equipments are suitable for all kinds of gases. According to the gas, and thus to
the minimum energy ignition, it is necessary to define the dedicated intrinsic safety type of
protection. It is not a type of protection relative to a single equipment but to a whole system that
is generally composed of two parts:
• an equipment or a single component with intrinsic safety placed inside the hazardous area
• a combined electrical device (that can be placed inside or outside the hazardous area and
is usually connected with a multi-pole cable), named safety barrier, used to supply the
equipment, keeping a reduced value of energy produced. If it is placed in an hazardous
area, it requires a type of protection suitable for the zone in which it is installed.
Picture 11: type of protection Ex i
73
It is a type of protection that can guarantee all the three protection levels; thence both for gas and
for dust the letter “i” which stands for intrinsic safety is combined with another letter (“a” “b” or
“c”) which identifies the protection level.
Interesting application examples are mainly in measuring tools and electronic components, such
as sensors, transducers, monitoring and control circuits, etc.
4.1.4 - ENCAPSULATION Ex-m
The type of protection by means of encapsulation Ex-m, reference standard IEC/EN60079-18,
concerns both dust and gas.
The parts or components of the equipment that can potentially ignite an explosive atmosphere are
encapsulated by means of resins, typically thermoplastic, thermosetting or epoxide, so that they
insulate the hazardous atmosphere.
The resin must stand the operating temperature declared for the equipment and is tested in
climatic chamber to verify the maintaining of the characteristic after ageing.
Picture 12: type of protection Ex m
Even though this type of protection guarantees a good electric insulation and discrete
characteristics of mechanical protection, it is not possible to make any maintenance; in fact in case
of fault it is necessary to replace the whole equipment.
As for the intrinsic safety, even the encapsulation is a type of protection that can guarantee all the
three levels of protection; for this reason both in gas and dust, the letter m of the encapsulation is
followed by the three letters (“a” “b” or “c”) according to the level of protections.
74
4.1.5 – TYPE OF PROTECTION nA-nC-nR
The types of protection “n” can guarantee the protection against a gas explosive atmosphere only
during normal operation and are thus suitable only for Zone 2.
The three types of protection described by IEC/EN 60079-15 standard are:
•
•
•
nC or sparking electrical devices or components
nA or non-sparking electrical devices or components
nR or electrical devices with restricted-breathing enclosure
nC- sparking electrical devices or components
It is a type of protection suitable for sparking components and includes:
− nC- hermetically sealed: the protection is guaranteed by the enclosure that is sealed in
order to avoid the ingress of explosive atmosphere; the main protection is the sealing that,
together with the enclosure, must guarantee the maintaining of the operation in time at
the temperature declared for the device.
− nC- enclosed break: the ingress of explosive atmosphere is prevented, but the external
explosive mixture must not be triggered; for this reason they are tested to verify the
functioning (the standard prescribe 10 On-Off for the device).
− nC- non-incendive components: they are substantially similar to the previous ones but the
tests are harsher (the standard prescribes 50 On-Off for the device). It is not suitable for all
the kinds of gases and according to the type of tested mixture, it is necessary to declare the
group II to which it refers.
Picture 13: type of protection Ex nC (hermetically sealed)
Picture 14: type of protection Ex nC (enclosed break)
75
nA- non-sparking electrical devices or components
It is a type of protection indicated only for non-sparking components.
The containing enclosure of the device must guarantee a minimum IP54 protection rating for the
powered parts, to avoid the ingress of external bodies or water.
Picture 15: type of protection Ex nA
The ingress of explosive atmosphere is prevented and the protection is guaranteed by the intrinsic
characteristics of internal components and the maintaining of the insulating distances.
It is suitable for all the kinds of gases of group II and typical examples of application are lighting
devices, terminal boards and junction or terminal boxes.
nR- electrical devices with restricted-breathing enclosure
It is a type of protection that can be used both for sparking and non-sparking components, and the
protection is guaranteed by the limitation of power dissipation (and then the temperature delta
between the device and the surrounding environment), so that the created depression once it is
de-energized delays the ingress of explosive atmosphere for a limited time prescribed by the
standard.
Picture 16: type of protection Ex nR
A restricted-breathing device requires a testing port (both for standard and field test) and is
generally inserted in a case that needs detailed maintaining inspections, especially for the gaskets.
76
4.1.6 – OIL IMMERSION Ex-o
Ex-o is a type of protection for gas that consists of immersion of electrical devices or parts in a
protection liquid (usually mineral oil) in order to prevent the ignition of the explosive atmosphere
externally or internally. The reference standard is IEC/EN 60079-6.
Picture 17: type of protection Ex o
It is applied to components or Ex devices that without oil do not spark or trigger an explosive
atmosphere during the normal operation (for example devices with type of protection nA) and
with the adding of a liquid they can guarantee protection in case of a first fault and with Gb
protection level, suitable to be installed in zone 1.
Anyway, it is not one of the most diffused type of protection due to the difficult maintaining.
4.1.7 – POWDER FILLING Ex-q
Ex-q is a type of protection for gas that consists of fulfilling of components or parts of the electrical
device with a material in order to prevent the ignition of the explosive atmosphere outside or
inside the enclosure, that must be minimum IP54 rated.
The ingress of explosive atmosphere in this case is prevented through the presence of the filling
material, because the flame cannot propagate externally.
It is suitable for zone 1 and applies to electrical devices and Ex components with rated current
equal to or less than 16 A, rated voltage equal to or less than 1000 V and rated power equal to or
less than 100 W.
The powder filling is rarely used for the same reasons of the oil immersion.
Picture 18: type of protection Ex q
77
4.1.8 – PRESSURIZED ENCLOSURE Ex-p
Ex-p is a type of protection used for electrical equipment of big dimensions and high power, such
as motors or generators, power switchboards, electrical cabins, control systems for industrial
processes, etc.
The ingress of explosive atmosphere is prevented by the presence of a protective gas (for example
air) inside the enclosure kept at constant pressure higher than the external atmosphere.
The internal components do not need to be ATEX marked.
A device protected by internal pressurization is typically composed of the following elements:
−
−
−
−
a casing
protective gas supply unit
protective gas discharge unit
control unit for washing and pressure (that must be protected by one or more types of
protection suitable for the zone where it is installed, or not protected if installed in a safe
area)
Picture 19: type of protection Ex p
This type of protection can be divided in three different ways according to the conditions for the
prevention of the ignition:
•
•
•
px – inner pressurization that reduces the classification within the enclosure from Zone 1
to a safe area (Epl from Gb to non-hazardous)
py - inner pressurization that reduces the classification within the enclosure from Zone 1 to
Zone 2 (Epl from Gb to Gc)
pz - inner pressurization that reduces the classification within the enclosure from Zone 2 to
a safe area (Epl from Gc to non-hazardous)
4.1.9 – PROTECTION BY ENCLOSURES Ex-t
The protection by enclosure Ex-t is a type of protection for dust suitable for any kind of electrical
device (sparking or not during normal operation) and dangerous zone (20, 21, 22 according to
specific requirements that the enclosure must satisfy).
78
The internal components can be standard as the ingress of explosive atmosphere (combustible
dust) can be prevented through particular attention to the parts of the enclosure that are the
interface between the enclosure and the surrounding environment (joints, cable entries, etc.).
Picture 20: type of protection Ex t
According to the zone and the type of combustible dust, the protection against the entry of
explosive atmosphere is guaranteed through the minimum requirement of IP rating, as per Table
9.
Epl
ta
tb
tc
IIIA - combustible flyings
IP6X
IP5X
IP5X
Group III
IIIB - non-conductive dust
IP6X
IP6X
IP5X
Table 9: minimum IP rating required as per type of zone
IIIC - conductive dust
IP6X
IP6X
IP6X
The reference standard is IEC/EN 60079-31.
In this case, it is crucial the choice of the materials (both for the enclosure and the gaskets) that
must ensure the characteristics of mechanical, thermal and light resistance in order to guarantee
the maintaining of the IP rating.
4.1.10 – PROTECTION BY “COMBINED” TYPES OF PROTECTION
The above explained types of protection can be also combined with each other.
There are many electrical equipments with two or more different types of protection applied to
different parts of the same device.
For this reason, there are also complex devices where each part or component must satisfy the
essential requirements of each reference standard.
In this case, the symbols of the type of protection must be reported in alphabetical order. Some
indicative examples are flameproof (Ex-d) control devices inserted in increased safety (Ex-e)
enclosures that together are marked Ex d e.
Another common example is when a powder-filled component (Ex-m) is installed inside an
increased safety device (Ex-e) that together are marked Ex e mb.
79
Chap.5: REQUIREMENTS FOR EX DEVICES
The requirements that must be respected by all the electrical devices intended to be used in
potentially explosive atmospheres can be found in IEC/EN 60079-0 standard.
It is not only described how to classify different devices according to the type of explosive
atmosphere, but also the characteristics that the material must have to prevent the ignition.
This “general” rule applies then to the specific type of protection, where it is re-called in some
requirements.
Some of the main standard requirements will be detailed in the following paragraphs.
5.1 – CLASSIFICATION OF ELECTRICAL EQUIPMENT FOR GAS ACCORDING
TO IEC/EN 60079-0
The electrical equipment intended for use in “gas” potentially explosive atmosphere are divided in
groups (GROUP I, GROUP II) and subgroups according to the gas classification described in chapter
2 and reported in Table 10.
EQUIPMENT GROUPS
Electrical equipment intended for use in mines susceptible to firedamp.
Electrical equipment intended for use in places with an explosive gas
atmosphere:
IIA
IIB
IIC
Propane, methane,
Etylene
Hydrogen, Acetylene
benzene ecc.
I
II
Table 10: classification of equipment as per IEC/EN 60079-0 - GAS
As it can easily be inferred, the equipment which is suitable to be installed in the most hazardous
area with presence of a gas from group IIC (the most dangerous) will be suitable for the same zone
also when there is a gas from groups IIB and IIA; it is not possible the contrary, as shown in Table
11.
Group of flammable
substances
I
IIA
IIB
IIC
Groups and subgroups
of Ex equipment
Table 11: correspondence between the groups of substances and equipment
I
IIA, IIB, IIC
IIB, IIC
IIC
Other than being divided in groups and subgroups, in IEC/EN 60079-0, the devices are classified
according to the maximum surface temperature that they can generate during their operation
declared by the manufacturer.
For an Ex equipment the maximum surface temperature is the maximum temperature reached by
its surface parts when powered with electrical parameter harsher than the operating ones.
This temperature is the necessary parameter to define the temperature class where the
equipment is classified and must be declared in the marking.
80
Table 12 clearly shows the equipment temperature class according to the ignition temperature of
gases, other than the maximum surface temperature allowed to be safe and avoid ignition of the
gas (considering a small safety margin).
GROUP II
Equipment temperature class
Maximum surface temperature
Gas ignition temperature
T1
T2
T3
T4
T5
T6
450°C
300°C
200°C
135°C
100°C
85°C
>450°C
>300°C
>200°C
>135°C
>100°C
>85°C
Table 12: correspondence between the temperature class and the gas ignition temperature
As for the groups, also for the temperature class when an equipment is classified as T6, it means it
is suitable also for all the other classes (from T5 to T1) while the contrary is not valid, as indicated
in Table 13.
Substance temperature
class
T1
T2
T3
T4
T5
T6
Ex equipment
temperature class
from T1 to T6
from T2 to T6
from T3 to T6
from T4 to T6
T5 and T6
T6
Table 13: correspondence between the substance temperature class and the equipment temperature class
The electrical equipments of Group I are not divided in temperature classes but the maximum
surface temperature must be always declared and must not overpass:
•
•
450°C where the coal dust is not expected to create a layer
150°C where the coal dust is expected to create a layer
81
5.2 - CLASSIFICATION OF ELECTRICAL EQUIPMENT FOR DUST
ACCORDING TO IEC/EN 60079-0
The electrical equipments intended to be installed in presence of a “dust” potentially explosive
atmosphere are classified in GROUP III and divided in subgroups, according to the classification of
dusts as explained in chapter 2 and reported in table 14.
EQUIPMENT GROUP
Electrical equipments intended for use in places with an explosive dust
atmosphere other than mines with firedamp:
IIIA
IIIB
IIIC
Combustible flyings
Non-conductive dusts
Conductive dusts
III
Table 14: classification of equipments as per IEC/EN 60079-0 - DUST
Also in this case, the same table shown for gases can be extended to Group III dusts:
Subgroups of
combustible substances
IIIA
IIIB
IIIC
Subgroups of Ex
equipment
Table 15: relation between substance groups and equipment groups
IIIA, IIIB, IIIC
IIIB, IIIC
IIIC
The combustible dusts are not classified in temperature classes as for the gases. Anyway it is
always necessary to indicate in the marking the maximum surface temperature, distinguishing if in
presence of a layer or not, as shown in Table 16.
MAXIMUM SURFACE TEMPERATURE
Without a layer of dust
For a certain thickness of dust TL
in mm that surrounds all the
sides of the equipment
Ex. T 100°C
Ex. T400 140°C
Table 16: maximum surface temperature
5.3 – GENERAL REQUIREMENTS FOR ELECTRICAL EQUIPMENT
In IEC/EN 60079-0 standard there are paragraphs concerning some of the technical requirements
that must be respected by the electrical equipment intended to be installed in potentially
explosive atmosphere, in order to contribute to guarantee the prevention of the ignition.
Among others, there are the mechanical and thermal resistance of the electrical equipment
(mainly the enclosure), the sealing of the gasket/cable entry (IP rating), the accumulation of
electrostatic charge, the earthing, the technical characteristics of the materials used for the
enclosure, etc.
In the following paragraphs, some of the essential requirements will be detailed directly referring
to IEC/EN 60079-0 standard.
82
5.3.1 – THERMAL AND IMPACT RESISTANCE AND IP RATING
The standard prescribes that both for gas and dust the enclosures in metallic or non-metallic
material with non-metallic gaskets must pass without any damage a cycle of tests evaluating
thermal and mechanical resistance and IP rating.
These harsh laboratory tests guarantee the maintaining of the characteristics of the equipment in
time, simulating the typical conditions of ageing of the materials.
For what concerns the cold and hot thermal resistance, the equipment must be tested at the
maximum operating service +20K for 672h at 90% of humidity and for 24h at the minimum
operating temperature -5/10 K.
Picture 21: example of conditioning in climatic chamber
Then, the mechanical resistance against impact is tested: the standard requires that the
equipment (or better the enclosure) must resist at an impact generated by a weight of 1, kg
(the head impactor must be made of tempered steel and with hemispheric form with 25 mm
diameter) dropped vertically from an height, specified in Table 17 that defines the field of
application of the equipment.

Drop height ℎ,
GROUP I
GROUP II or III
HIGH
LOW
HIGH
LOW
2m
0,7 m
0,7 m
0,4 m
0,7 m
0,4 m
0,4 m
0,2 m
0,4 m
0,2 m
0,2 m
0,1 m
EQUIPMENT GROUP
RISK OF MECHANICAL DANGER
“Enclosures and external accessible parts of enclosures
(different from the light-transmitting ones)” such as
junction boxes, sockets, etc.
"Guards, protective covers, fan hoods, cable glands"
"Light-transmitting parts without guards " such as glasses,
displays and monitors
"Light-transmitting parts with guard having individual
2
2
openings from 625 mm to 2 500 mm (tested without
guard)” such as lighting fixture with cage
Table 17: drop height for impact test related to equipment type and risks
As shown in Table 17 there are two types of mechanical risk: it is the manufacturer who decides if
the device must resist to a high or a low risk.
When the manufacturer declares the electrical equipment has been tested with low risk, it has to
be marked with an “X” which identifies the specific condition of use.
83
Picture 22: impact test
After thermal and mechanical conditioning, the IP rating is tested, in compliance with IEC/EN
60529 standard to verify the resistance against the penetration of solid bodies or water as per
Table 18.
st
0
1
2
3
4
5
6
1 digit of IP rating: solid bodies
IP RATING
Non-protected
Protected against solid objects with dimensions >50mm
Protected against solid objects with dimensions >12,5 mm
Protected against solid objects with dimensions >2,5 mm
Protected against solid objects with dimensions >1 mm
Dust-protected
Dust-tight
0
1
2
3
4
5
6
7
8
2nd digit of IP rating: water
Non-protected
Protected against vertically dripping of water
Protected against dripping of water (15° tilted)
Protected against spraying of water
Protected against splashing of water
Protected against jetting of water
Protected against powerful jetting of water
Protected against temporary immersion
Protected against continuous immersion
Table 18: IP protection degrees
Picture 23: IP test - DUST
84
Picture 24: IP test - WATER
5.3.2 – GASKET SEALING
Where the degree of protection provided by the enclosure depends on a gasketed joint which is
intended to be opened for installation or maintenance, gaskets must be attached or secured to
one of the mating faces to prevent loss, damage or incorrect assembly.
The gasket material other than not adhering to the other joint face must guarantee an operating
temperature range compatible with the operating temperature of the device.
Picture 25: example of a gasket attached to a joint side
The adhesives or materials used for attaching the gasket to the joint side must have the same
thermal characteristics of the gasket material and be compatible with the materials with which
they are attached without damaging.
5.3.3 – RESISTANCE TO LIGHT
The resistance to light of enclosures, or parts of enclosures, of non-metallic materials must be
satisfactory, as defined in IEC/EN 60079-0 standard. Materials meeting the ultraviolet light
exposure requirements (f1) in ANSI/UL 746C are considered satisfactory and do not need any
further test.
Where not otherwise protected from exposure to light, a resistance test of the material to
ultraviolet light must be made if the enclosure or parts of the enclosure, upon which the type of
protection depends, are made of non-metallic materials. The test is done on normalizeddimension bars.
Picture 26: examples of samples for testing the resistance to ultraviolet light
For Group I equipment, the test applies to luminaires only.
85
If the equipment is protected from light (for example, daylight or light from luminaires) when
installed, and, in consequence, the test is not carried out, the equipment shall be marked by the
symbol “X” to indicate this specific condition of use.
Sheet 5 resumes the situation of light requirements for enclosures in non-metallic material.
Sheet 5: light requirements for enclosures in non-metallic material
5.3.4 – ELECTROSTATIC CHARGES
One of the main requirements that an electrical device must respect is to avoid the ignition risk
due to the presence of surface electrostatic charges.
This requirement must be satisfied by means of one of the following methods for products of
Group I and II:
•
86
by suitable selection of the material so that surface resistance complies with either of the
limits given below:
resistance of ≤ 10 Ω (1GΩ) measured at 50 ± 5 % relative humidity or
≤ 10 Ω measured at 30 ± 5 % relative humidity
•
the limitation of surface of non-metallic material, according to group and zone and to
Table 19. The surface is defined with the following method:
- for sheet materials, the area is the exposed (chargeable) area
- for curved objects, the area is the projection of the object giving the maximum area.
GROUP I
10000
Epl
Ga
Gb
Gc
Maximum surface area [mm2]
GROUP II
IIA
IIB
5000
2500
10000
10000
10000
10000
Table 19: Maximum surface of non-metallic parts according to group and zone
IIC
400
2000
2000
NB: the values for surface area can be increased by a factor of four if the exposed area of
non-metallic material is surrounded by and in contact with conductive earthed frames.
Alternatively, for long parts with non-metallic surfaces, such as tubes, bars, or ropes,
the surface area needs not to be considered, but the diameters or widths shall not exceed
the values shown in Table 20.
GRUPPO I
30
•
IIC
1
20
20
by limitation of a non-metallic layer bonded to a conductive surface, such as a layer of
powder coating. The thickness of the non-metallic layer shall not exceed the values shown
in Table 21.
2
•
IIB
3
30
30
Table 20: Maximum diameters or widths according to group and zone
GROUP I
•
Epl
Ga
Gb
Gc
Maximum diameter or width [mm]
GRUPPO II
IIA
3
30
30
Epl
Ga
Gb
Gc
Maximum thickness [mm]
GROUP II
IIA
2
2
2
IIB
2
2
2
Table 21: Maximum thickness according to group and zone
IIC
0,2
0,2
0,2
by provision of a conductive coating. The equipment must be marked “X” and the
documentation must provide guidance on the use of the product.
for fixed installations where the installation is intended to minimize the risk from
electrostatic discharge, by marking the equipment X”. The instructions must provide
guidance for the user to minimize the risk from electrostatic discharge.
For products of Group III this requirement can be satisfied by means of one of these solutions:
•
by suitable selection of the material so that surface resistance complies with the limits
given below:
87
•
•
resistance of ≤ 10 Ω (1GΩ) measured at 50 ± 5 % relative humidity or
≤ 10 Ω measured at 30 ± 5 % relative humidity
by a breakdown voltage ≤4 kV (measured across the thickness of the insulating material
according to the method described in IEC 60243-1)
by a thickness ≥8 mm of the external insulation on metal parts.
5.3.5 – CHARACTERISTICS OF PLASTIC AND ELASTOMERIC MATERIALS
The essential requirements that must be respected by non-metallic enclosures or parts of them,
on which depends the type of protection, are fundamental.
The specification for plastic material must contain:
•
•
•
•
•
name or trademark of the manufacturer
identification of the material, type, color, eventual percentage of reinforcements, fillings or
additives
possible surface treatments such as varnishes
the Temperature Index TI, corresponding to the 20.000h point on the thermal endurance
graph without loss of flexural strength exceeding 50%, determined in accordance with IEC
60216-1 and IEC 60216-2 and based on the flexing property in accordance with ISO 178. As
an alternative to the TI, the relative thermal index (RTI – mechanical) may be determined in
accordance with ANSI/UL 746B
when applicable information about resistance to UV rays.
The specification for the elastomeric material must contain:
•
•
•
•
•
88
name or trademark of the manufacturer
identification of the material, type, color, eventual percentage of reinforcements, fillings or
additives
possible surface treatments such as varnishes
the Continuous Operating Temperature (COT)
when applicable information about resistance to UV rays.
Chap.6: ATEX DIRECTIVES AND EX PRODUCT
MARKING
In the previous chapter the main topic were the safety principles that are necessary to achieve in
order to avoid the possibility of an explosion, which means to minimize the probability to create
an explosive atmosphere and, at the same time, reduce the presence of potential ignition sources.
In Europe there are two Directives issued to translate in a juridical way what said in the previous
chapters, establishing Essential Safety Requirements (ESR) without giving any indication on how to
achieve it.
The manufacturer, or generically those to which the Directives are addressed, is free to decide
technical procedures to use in order to satisfy the compliance with ESR. He can invent or respect
what the harmonised standards prescribe. As a matter of fact, the harmonised standards, such as
IEC/EN 60079, are applicable to the Directive and guarantee the presumption of conformity.
Harmonised standards are published on the Official Journal of the European Union (the OJ),
directly from the European Commission.
6.1 - DIRECTIVE 99/92/EC
The Directive 99/92/EC, become effective on 1st July 2003, concerns worker health and safety
when exposed to the risk of explosive atmospheres and, in this case, refers to EHSR (Essential
Health Safe Requirements) rather than ESR.
The aim of the Directive is to assess the risk of an explosion, the technical measures used to
minimize the formation of an explosive atmosphere and the probability of an ignition.
In order to achieve this, the Directive provides specific dispositions that must be complied in
hazardous areas, both for gas and dust.
This becomes an operative obligation for the employer to classify his area and select suitable
equipment for safe installation inside the same.
This reflects the IEC zone system explained in chapter 2; as a matter of fact, the European
Commission established presumption of conformity with this Directive for the IEC/EN 60079-10-1
and IEC/EN 60079-10-2 harmonised standards.
The Directive provides in detail all the obligations for the employer to improve the worker health
and safety; and some of them are:
•
•
risk assessment document (based on the probability and duration of explosive
atmospheres and ignitions, installation and process characteristics, substances which are
present and used, predictable effects, assessment of non-hazardous areas connected to
hazardous areas)
subdivision in hazardous zones identifying for each one the safety minimum prescriptions
(personnel training, giving detailed instructions about dangerous work operation, providing
ways to release gas and dust toward safe areas, providing for workers suitable equipment
to avoid electrostatic discharge, etc.).
89
•
document about protection against explosions (done before the plant begins to work to
locate and assess explosion risks, take preventions to satisfy the directive requirements,
such as areas with safety minimum prescriptions, indicate work tools and areas designed as
safe, etc.)
Moreover, the Directive 99/92/EC requires that the areas with possibility of explosion atmosphere
must be identified with the proper triangular symbol, Picture 27.
Picture 27: signal that identifies areas with possibility of an explosive atmosphere
In order to avoid fines, workplaces with possibility of explosive atmospheres used for the first time
(or transformed in hazardous places from non-hazardous) after 30th June 2003 must satisfy the
Directive requirements immediately. Hazardous places already present and used before this day
had 3 years in order to be in compliance with the new directive (within 30th June 2006, so the
time is over!)
6.2 - DIRECTIVE 94/9/EC
If the Directive 99/92/EC can be defined as social, since the aim is worker health and safety, by
classifying hazardous areas in zones the Directive 94/9/EC focuses more on the essential
requirements that the equipment or protection systems must ensure in order to be installed in
potentially explosive atmospheres.
The 94/9/EC mainly addresses the manufacturers, importers and all those that place on the
European Community market a product intended to be installed in explosive atmosphere.
As the Directive 99/92/EC provides Essential Safety Requirements attached to the text without
giving any technical indications on the product.
This Directive:
•
•
•
•
•
90
contains electrical and non-electrical products
considers all the potential ignition sources
subdivides equipment in groups and categories that guarantee the safety against ignition
according to their functioning
establishes conformity procedures that must be complied by the manufacturer according
to the group and category danger (see chapter 7)
contains the CE marking with visual symbol of the products which are in compliance (see
following chapters).
Here below Table 22 helps to understand which are the application fields of the Directive.
YES
DIRECTIVE 94/9/EC APPLICATION
Equipments: machines, materials, fixed and mobile
devices, control devices, detecting tools and systems
that, alone or combined, are intended for production,
transport, storage, measurement, control and conversion
of energy and transformation of material that can create
an explosion caused by potential ignition sources
Safety systems: safety, control and regulation devices
intended to be used out of hazardous areas, but
necessary or useful for the functioning of the above
devices (Ex-i barriers)
Protection systems: devices whose function is to prevent
explosions and/or circumscribe the area where it
occurred, placed on the market with autonomous
functions
Components: essential parts for the safe functioning of
equipment and protection systems, with no autonomous
function
NO
Medical devices for use in medical environment
Equipment with ignition risk due to explosive or unstable
chemical materials
Equipment intended for use in domestic environments
Personal protective equipment
Equipment used on board of seagoing vessels or
offshore mobile units
Means of transport
Table 22: directive 94/9/EC application
6.2.1 – EQUIPMENT GROUPS AND CATEGORIES
The Directive 94/9/EC divides the equipment in groups based on their use:
•
•
GROUP I: equipment intended for use in mines with firedamp
GROUP II: equipment intended for use in explosive atmosphere in surface.
As it can be inferred from the below Tables, 23 and 24, each group is subdivided in categories.
CATEGORY
M1
M2
GROUP I
Protection level
Very High
Two means of protection
Two faults
High
Guaranteed in normal operation
and in case of more severe
operating conditions
Functioning conditions
Energized in the event of an
explosive atmosphere
De-energized in the event of an
explosive atmosphere
Table 23: division in categories of equipment in group I
91
GROUP II
CATEGORY
1
2
3
Protection level
Very High
Two means of protection
Two faults
High
One mean of protection
One fault
Normal
Guaranteed in normal
operation
Explosive atmosphere
presence and
duration
GAS
ZONE
Always, often of for
long periods
0
20
Probable
1
21
Rare
2
22
DUST
Table 24: subdivision in categories of equipment in group II
To the category number it is necessary to add the letters G and D according to the presence of Gas
or Dust (if both the letters are present, it means that the device is suitable for both gas and dust).
As it can be inferred, there is a direct correspondence among Directive groups and categories and
protection levels, and consequently hazardous areas.
EPL (harmonised standards) and GROUPS/CATEGORIES (directive) CORRESPONDENCE
IEC/EN 60079
ATEX 94/9/EC
GROUP
ATMOSPHERE
EPL
PROTECTION
GROUP AND
INSTALLATION
LEVEL
CATEGORY
ZONE
VERY HIGH
Ma
I M1
/
MINE
I
FIREDAMP
HIGH
Mb
I M2
/
VERY HIGH
Ga
II 1G
Zone 0
GAS
HIGH
II
Gb
II 2G
Zone 1
(IIA IIB IIC)
NORMAL
Gc
II 3G
Zone 2
VERY HIGH
Da
II 1D
Zone 20
DUST
HIGH
III
Db
II 2D
Zone 21
(IIIA IIIB IIIC)
NORMAL
Dc
II 3D
Zone 22
Table 25: correspondence between groups/categories and EPL
A category 1 equipment is suitable for all the hazardous zones, while it is not the same for
category 2 and 3 which respect the following Table 26.
HAZARDOUS ZONES
Zone 0 - 20
Zone 1 - 21
Zone 2 - 22
EQUIPMENT CATEGORY
Category 1
Category 1 or Category 2
Category 1 or Category 2 or Category 3
Table 26: relation between the hazardous zone and equipment category that can be installed
It is important to underline that category 3 equipments, suitable to be installed in zone 2-22, are
the most installed and represent around the 80% of those installed in ATEX areas.
92
6.3 - NEW 2014/34/EU DIRECTIVE AND DIFFERENCES WITH 94/9/EC
The new ATEX Directive regarding equipment, named 2014/34/EU, became effective on 30th
March 2014.
It is substantially a recast, or a replacement of the Directive 94/9/EC that will be abrogated on 20th
April 2016.
The new Directive does not bring substantial changes if compared with technical specifications of
94/9/EC; the field of application and exclusions, the conformity assessment procedures and the
subdivisions in groups and categories are the same.
The main difference with the old Directive is the increased evidence on the obligations of the
economic operators, such as manufacturers, authorized representatives, importers and
distributors; with the support of Table 27, we will see the most important ones:
Economic
operator
Duties of economic operators according to Directive 2014/34/EU
Definition
Manufacturer
Any natural or legal person who
manufactures a product or has a product
designed or manufactured, and markets
that product under his name or trade
mark or uses it for his own purposes
Authorised
representative
Any natural or legal person established
within the EU who has received a written
mandate from a manufacturer to act on
his behalf in relation to specified tasks
Obligations
Design and manufacture in accordance
with the essential health and safety
requirements.
Draw up the technical documentation and
carry out the relevant conformity
assessment procedure.
Draw up an EU declaration of conformity
and affix the CE marking.
Keep the technical documentation and the
EU declaration for 10 years after the
product has been placed on the market.
Ensure that procedures are in place for
series production to remain in conformity
with this Directive.
Ensure that product which they have
placed on the market bear a type, batch or
serial number allowing their identification.
Accompany the product with instructions
and safety information in a language which
can be easily understood by end-users.
When realising that a product which they
have placed on the market is not in
conformity with the Directive, the
necessary corrective measures must be
taken, such as withdraw it or recall it.
It does not have to draw up the technical
documentation.
Perform the tasks specified in the mandate
received form the manufacturer.
Keep the EU declaration of conformity for
10 years after the product has been placed
on the market.
93
Importer
Any natural or legal person established
within the EU who places a product from
a third country on the Union market
Distributor
Any natural or legal person in the supply
chain, other than the manufacturer or the
importer, who makes a product available
on the market
Place on the market only products in
conformity, ensuring that the
manufacturer has done the appropriate
conformity assessment procedure and has
drawn up the technical documentation.
Ensure that the product bears the CE
marking and is accompanied by the EU
declaration of conformity.
Indicate on the product their name,
registered trade mark or, where it is not
possible due to the dimensions, on the
packaging.
Ensure that the product is accompanied by
instructions and safety information in a
language which can be easily understood
by end-users.
Ensure that the storage or transport
conditions do not jeopardise its compliance
with the requirements.
Keep a copy of the EU declaration of
conformity for 10 years after the product
has been placed on the market.
If they realise that a product which they
have placed on the market is not in
conformity with the Directive, the
necessary corrective measures must be
taken, such as withdraw it or recall it.
The Directive does consider as a
Manufacturer who places a product on the
market under his name, or trade mark, and
has the same duties.
Ensure that the product bears the CE
marking, that is accompanied by the EU
declaration of conformity, the safety
instructions in a language which can be
easily understood by end-users.
Ensure that the storage or transport
conditions do not jeopardise its compliance
with the requirements.
If they realise that a product which they
have placed on the market is not in
conformity with the Directive, the
necessary corrective measures must be
taken, such as withdraw it or recall it.
The Directive does consider as a
Manufacturer who places a product on the
market under his name, or trade mark, and
has the same duties.
Table 27: obligations of economic operators according to the Directive 2014/34/UE
Moreover, with the new Directive, EC declarations of conformity and EC type test certificates
change their name and become EU declarations of conformity and EU type test certificates.
94
Anyway, the certificates issued by a Notified Body according to the ATEX Directive 94/9/EC are still
valid according to the new Directive, as the harmonised standards that guarantee the presumption
of conformity to the directive remain the same.
Even though the new Directive has been formally effective since 30th March 2014, the important
day is 20th April 2016. Starting from that day, it will be compulsory to be in compliance with the
new Directive, unless eventual delays in the receipt of the Member States inside their National
Rules.
6.4 – EX PRODUCT MARKING
Since the first half of the 90s inside the European Community the national barriers have been
cancelled and the goods are free to move. In this field, all the products that satisfy the essential
health and safety requirements defined in each applicable Directive must bear a mark that
represents it.
6.4.1 – CE MARKING
The graphic symbol used is the CE marking, that must be present on all the EX products (except for
the components, for which the marking is not compulsory), Picture 28.
The CE marking :
•
•
•
•
•
Picture 28: graphic symbol of the CE marking
is affixed on the product or on the label in a visible way, easy to read and indelibly. In case
the dimensions of the product do not allow it, the marking must be affixed on the
packaging and on the documents that accompany the product
is affixed on the product before being placed on the market
must be followed by the identification number of the Notified Body, when that body is
involved in the production control phase
in case of ATEX products, is accompanied by the specific mark of explosion protection, the
symbols of group and category of the equipment
the information above may be followed by other indications signalling a special use or risk.
95
6.4.2 – MARKING ACCORDING TO THE ATEX DIRECTIVE
As anticipated by the previous paragraph, the ATEX directive, other than the classic CE marking,
requires the presence of a further graphic symbol represented by an hexagon with inside the
letters epsilon-x, that must respect specific dimensions, Picture 29.
Picture 29: graphic symbol that identifies the EX products
The meaning of affixing a definite marking to an ATEX product is to communicate to those who
buy, install or make any operation of maintenance or inspection, that the device satisfies the
essential safety requirements of the Directive.
Said that, a product suitable to be installed in places with potentially explosive atmosphere can be
in compliance with the ATEX Directive:
•
•
because it is in compliance with the IEC/EN 60079 harmonised standards, that have
presumption of conformity with the ESR of the Directive
because it is in compliance with different laws and safety principles against the explosion,
not mentioned inside the IEC/EN 60079 harmonised standards.
According to the above, there are two different types of marking: one prescribed by the Directive,
that identifies the conformity, and another one that we can define as complete, containing all the
indications relative to conformity with IEC/EN 60079 harmonised standards.
Marking according only to the Directive
The marking which satisfies only the requirements of the ATEX Directive must contain the
following information:
•
•
•
•
96
CE marking
identification number of the Notified Body that assesses the Quality System of the ATEX
production (for example 0051 is the identification number of IMQ)
N.B. this identification number is compulsory for those products where a Notified Body
made the type examination (see Chapter 7), so for all the category 1 and 2 equipment
the epsilon-x marking
the equipment group and category followed by the letter D if for dust and G if for Gas
Sheet 6: example of marking according to the ATEX Directive – CATEGORY 1 and 2
For the category 3 equipment, since the Notified Body is not compulsory, the marking in
compliance with the Directive can also be without the identification number (“0051” in the
previous example).
Sheet 7: example of marking according to the ATEX Directive – CATEGORY 3
Marking in compliance with the Directive and IEC/EN 60079 harmonised standards
On the contrary, if the conformity with the ATEX Directive is obtained through the conformity with
IEC/EN 60079 harmonised standards (presumption of conformity with ESR of the Directive), the
marking requires further information, contained in the Ex marking.
97
Sheet 8: example of marking in presumption of conformity with ATEX Directive because in compliance with IEC/EN 60079
harmonised standards
Anyway, the labels affixed on the ATEX products must contain also further information to identify
unambiguously both the equipment and the manufacturer which is responsible for the same.
The needed data are:
• Name and address of the manufacturer
• Product part number
• Number of the EU/EC-type-examination certificate
• Batch identification number (serial number or week/year of production)
• Technical data that characterize the product (voltage, frequency, current, polarity, IP
rating, insulation class, particular operating temperature, etc.)
Picture 30 shows in detail the marking of a Palazzoli interlocked socket, in which you can see the
presence of all the needed information.
98
Picture 30: label example of a Palazzoli ATEX interlocked socket
99
100
Cap.7: CERTIFICATIONS
As seen in the previous chapter, the ATEX Directive 94/9/EC (2014/34/EU) for the equipment
provides the subdivision of Ex products in groups and categories, according to their suitability for
the use in zones.
According to the category, the Directive prescribes different procedures for the conformity
assessment of a product.
7.1 – CONFORMITY ASSESSMENT
For the equipment of GROUP I CATEGORY M1 and GROUP II CATEGORY 1 (G or D), it is necessary
the certification by a third party, a Notified Body, for what concerns both the product conformity
assessment and the production. The procedures are the following:
•
•
•
•
The Notified Body must do the EU type examination and release the EU-type-examination
certificate
The Notified Body must certify the production quality system of the manufacturer for
ATEX, releasing a notification, that is a sort of company certificate allowing the
manufacturer to produce ATEX devices
The manufacturer must guarantee the exact correspondence between the tested and
certified prototype and each single piece produced. The test to assess the conformity of
the prototype must be done by the Notified Body responsible of the certification, that
releases a certificate of conformity
At the end, the manufacturer draws up the EU declaration of conformity and affixes the CE
marking on the product.
Also for the equipment of GROUP I CATEGORY M2 and GROUP II CATEGORY 2 (G or D), it is
necessary to get the certification by a third party, a Notified Body, for what concerns both the
product conformity assessment and the production. The procedures are the following:
•
•
•
•
The Notified Body must do the EU type examination and release the EU-type-examination
certificate
The Notified Body must certify the production quality system of the manufacturer for
ATEX, releasing a notification, that is a sort of company certificate allowing the
manufacturer to produce ATEX devices
The manufacturer must guarantee the exact correspondence between the tested and
certified prototype and each single piece produced. The test to assess the conformity of
the prototype must be done by the Notified Body responsible of the certification, that
releases a certificate of conformity
At the end, the manufacturer draws up the EU declaration of conformity and affixes the CE
marking on the product.
101
It is different when we consider the equipment for GROUP II CATEGORY 3 (G or D), intended for
use in ZONES 2-22. As a matter of fact, this is the only case where the intervention of a Notified
Body is not necessary. The procedures, in this case, are the following:
•
•
the manufacturer performs an internal control on the device, guaranteeing autonomously
that the production process is in compliance with the Directive requirements, making a
self-certification
the manufacturer can then proceed with the drawing up of an EU declaration of conformity
and the affixing of the CE marking on the product.
Even though the equipments of group II category 3 (suitable for zones 2-22) do not require the
compulsory intervention of a third party, Palazzoli submits the conformity assessment also for
these products to a Notified Body, applying the same procedure of the equipments with group II
category 2 (suitable for zone 1-21).
7.2 – THE TECHNICAL DOCUMENTATION
In this text the technical documentation has been mentioned many times. The aim of this
paragraph is to clarify this aspect, clearly explaining which are the elements and information that
must be present.
The technical datasheet explains the technical, functional and protection characteristics of the
project in compliance with the essential safety requirements of the ATEX Directive and the relative
conformity assessment procedure.
The aims are:
102
•
placement and classification of the product for use suitable for the destination
•
principles for the coding according to the ATEX directive
•
a list of the standards, completely or partially applicable
•
general description of the devices
•
satisfaction of essential requirements of the ATEX Directive
•
main technical information, design drawings and manufacturing of the product
•
datasheet and/or trademark of the main used material
•
descriptions and explanations to understand drawings and operation of the equipment
•
ignition risk analysis of the equipment (normal and abnormal conditions according to the
destination) with the description of the solutions used to satisfy the safety requirements of
the ATEX Directive
•
laboratory test reports
•
CE marking and applied procedures for CE marking
•
conformity marking for the reference standards of the specific type of protection
•
copy of the conformity declaration
The most significant documents are the safety instructions, ignition risk analysis and conformity
declaration.
7.2.1 – SAFETY INSTRUCTIONS, USE AND MAINTENANCE
The instructions for use are important because their correct application is the necessary condition
to respect the essential safety requirements.
The instructions must be in the language of the end-users or in a language that can be easily
understood and they must contain:
− each necessary indication to assess the conformity of the product for predictable use
conditions
− technical parameters such as electrical, thermal, etc.
− essential characteristics of the parts that can be integrated in the products
− instructions for a safe placing in service, mounting and dismounting operations, installation
and/or replacing of eventual components and maintenance
− legend for the indications reported on the markings.
Picture 31: example of a safety datasheet
CAM-EX isolator switch
Picture 32: example of a safety datasheet
TAIS-EX interlocked socket
103
7.2.2 – IGNITION RISK ANALYSIS DOCUMENT
Another important document is the one relative to the ignition risk analysis that the manufacturer
prepares in order to show the conformity to the essential safety requirements of the Directive.
It contains a list of the standards completely or partially applied, harmonised and non,
accompanied by the technical solutions used to satisfy the essential safety requirements.
It is a document with legal value, through which the manufacturer shows to the relevant Bodies
(such as the Magistracy) to have correctly behaved for what concerns the design and
manufacturing of the product.
In Picture 33 it is possible to find an extract of the document for the ignition risk analysis of a
Palazzoli ATEX product.
Picture 33: example of ignition risk analysis document
7.2.3 – EU DECLARATION OF CONFORMITY
The EU declaration of conformity is the document that the manufacturer has to draw up to assess
the conformity to the Directive and together with the safety, use and maintenance instructions
they are the only documents which must accompany the product.
The EU declaration of conformity must contain:
• name or trademark of identification, accompanied by the address of the manufacturer
• a brief description of the device
• all the relevant dispositions that the equipment satisfies
104
•
•
•
eventual name, number of identification and address of the Notified Body that makes the
EU-type-examination and certifies the quality production, and the number of the EU-typeexamination certificate
identification of the signer who has the power to commit the Company (Manufacturer or a
delegate inside European Community)
eventual reference to harmonised standard and technical specifications used and other
applied Community Directives.
Picture 34 shows an example of a declaration of conformity for a Palazzoli ATEX product.
Picture 34: example of a declaration of conformity
105
7.2.4 – EU-TYPE-EXAMINATION CERTIFICATE
As seen in the previous paragraphs, for the equipment of GROUP I CATEGORY M1 and M2 and
GROUP II CATEGORY 1 and 2 (G or D), it is necessary the intervention of a Notified Body, both for
the conformity assessment of the product and the production.
By the way, it is reported an analysis of a type-examination certificate in order to show how it is
structured and which information it must contain:
106
Sheet 9: type examination certificate analysis
N.B.: Both the declaration of conformity and the certificate are mentioned with the EC symbol
referring to 94/9/EC standard as up to the day of national receipt it is not possible to draw up
documentation in conformity with the new 2014/34/EU Directive.
107
Chap.8: ATEX vs IECEx
8.1 –THE IECEx SCHEME
If in Europe ATEX reference standards are the Community Directives, internationally, or more
precisely out of Europe, all this is not enough.
As a matter of fact, in this case it is necessary to follow the IECEx scheme, which is the result of a
multilateral agreement among Countries and Certification Bodies, based on the use and
compliance with requirements of some international standards (IEC).
Picture 35: IEC and IECEx symbols
The IECEx scheme aim is to abolish the barriers among different Countries to facilitate the free
movement of electrical equipments that can be installed in potentially explosive atmospheres and
have one single scheme, recognized and valid at an international level, keeping an adequate safety
level.
For this reason, the IECEx scheme provides that ACBs (Accepted Certification Bodies also said
ExCBs) test and assess the conformity of electrical equipments used in explosive atmospheres by
means of international standards about product safety, releasing certificates and test report
recognized in the vast majority of the Countries in the world.
8.2 – DIFFERENCES BETWEEN ATEX DIRECTIVES AND IECEX SCHEME
Even though the devices are the same, there are some differences between ATEX Directives and
IECEx international scheme that are important to be known.
In the following Table 28, some of the fundamental aspects of the IECEx scheme are mentioned,
and for each of them, there is a comparison with what is prescribed by ATEX Directives.
ASPECT
Certification
procedure
108
IECEx
ExCBs emit:
• IECEx TR (test reports)
• IECEx QAR (quality system
assessment reports)
• IECEx CoC (certificate of
conformity).
The certificates of conformity are
officially registered in the IECEx website
and can be completely seen by anyone.
ATEX
The Notified Bodies emit the EU type
certificates and notifications about the
production quality (group I category M1
M2 and group II category 2)
Conformity
assessment
Aim
Validity
Field of application
The procedure is the following:
IECEx TR + IECEx QAR = IECEx CoC
IECEx TR: document emitted by an
ExTL (laboratory of an ExCB that
performs tests according to the
IECEx scheme) which contains a
register of performed tests and
shows that the examined product is
in conformity with reference
standards.
IECEx QAR: document that presents
the results of an assessment in place
of the production quality system by
an EXCB according to the IECEx
scheme.
The QAR is necessary for any type of
products and self certifications are
not allowed.
A summary of the QAR is published
on the official website of IECEx:
www.iecex.com
IECEx CoC: certificate of conformity
assessing the conformity of the
product with the specific reference
standards.
Also for CoC self certifications are
not allowed for any type of
products.
One single certificate valid for each
product that can be installed in
potentially explosive atmospheres,
recognized and considered valid at
international level.
Keep an adequate safety level.
Reduce certification costs and times.
One single international database.
The products certified according to
the IECEx scheme are accepted in
many Countries of the world.
Electrical and non-electrical
products and systems.
Places with explosion risk caused by
Gas or combustible Dust.
Also service industries.
The manufacturer draws up the EU
declaration of conformity through
which he declares to have all the
documents and test reports in
conformity with the Directive.
The Notified Body intervenes only for
products of group I category M1 M2
and group II category 1 and 2.
For the products in category 3 it is
allowed a self-certification by the
manufacturer, both for the production
quality and the conformity of the
product with the Directive.
Remove commercial barriers for
products intended to be installed in
potentially explosive atmospheres and
improve equipment and worker safety.
The ATEX Directives are laws inside the
Countries of the European Community
and thus they are mostly accepted in
Europe.
Electrical and non-electrical products
and systems.
Places with explosion risk caused by
Gas or combustible Dust.
Only equipment.
109
Reference
standards
Only international standards, the
conformity is compulsory.
Manufacturer
surveillance
Workplace
requirements
The ExCB keeps the validity of the
Coc according to the QAR.
None, the references are to the
standards of the different Member
States.
Each accepted standard that can prove
the compliance with essential safety
requirements of the Directive.
Anyway, EU approves a list of
harmonised standards and the
conformity with these standards
guarantees also the compliance with
the essential safety requirements: the
compliance with these standards is not
compulsory but they are almost always
used to certify the products.
Notified Bodies perform periodic
controls of the manufacturers.
The Directive 99/92/EC contains special
necessities for what concerns the
worker health and safety requirements.
Table 28: differences ATEX - IECEx
For what concerns the process of conformity assessment, the Sheet 10 can be used as a reference
as it clarifies the single necessary steps to get an IECEx TR, IECEx QAR and IECEx CoC:
Sheet 10: necessary steps to get IECEx QAR, IECEx TR and IECEx CoC
110
8.3 – IECEX MARKING
For what concerns the IECEx marking, since the scheme does not provide any subdivision in groups
and categories as the ATEX Directive, it refers to Equipment Protection levels - EPL.
As a matter of fact, the EPLs are enough to classify the products in terms of possible installation
zones, as shown in Table 29, making the same function of groups and categories of the ATEX
Directive.
EPL (harmonised standards) and GROUPS/CATEGORIES (directive) CORRESPONDENCE
IEC 60079
ATEX 94/9/EC
GROUP
ATMOSPHERE
EPL
PROTECTION
GROUP AND
INSTALLATION
LEVEL
CATEGORY
ZONE
VERY HIGH
Ma
I M1
/
MINE
I
FIREDAMP
HIGH
Mb
I M2
/
VERY HIGH
Ga
II 1G
Zone 0
GAS
HIGH
II
Gb
II 2G
Zone 1
(IIA IIB IIC)
NORMAL
Gc
II 3G
Zone 2
VERY HIGH
Da
II 1D
Zone 20
DUST
HIGH
III
Db
II 2D
Zone 21
(IIIA IIIB IIIC)
NORMAL
Dc
II 3D
Zone 22
Table 29: groups/categories and EPL correspondence
For this reason, the marking according to the IECEx scheme is only of this type:
Sheet 11: example of marking in conformity with IECEx scheme
111
8.4 – WORLD MAP WITH ATEX-IECEX-OTHER SCHEMES
The IECEx international scheme is one of the most diffused in all the world.
According to statistics of 2012 there are 30 Countries that rely on and recognize this certification
scheme, as shown in Table 30.
Australia
Brazil
Canada
China
Croatia
Czech Republic
Denmark
Finland
France
Germany
Countries which are part of the IECEx system
Hungary
Italy
India
Japan
Republic of Korea
Malaysia
Netherlands
Norway
New Zealand
Poland
Table 30: list of Countries which recognize the IECEx scheme
Romania
Russia
Singapore
Slovenia
South Africa
Sweden
Switzerland
Turkey
United Kingdom
USA
Even though the vast majority of the Countries in the world recognize and accept the IECEx
international scheme, some States tend to privilege specific certification schemes, as seen for
example for the North-American States (Usa and Canada).
In order to clarify the concept, here below you can see a map of the world with the symbols of
different certification schemes.
Picture 36: map of the world with different certification schemes
112
Chap.9: AREA CLASSIFICATION
9.1 - INTRODUCTION
Area classification: why?
The danger is present in each working activity, no exclusion. As a matter of fact, a research done in
2013 by the Italian National Institute of Statistics asserts that 714.000 people declared to have
suffered an injury while they were at work or during the way house-work.
In the world ILO International Labour Organization showed in the press release of 28th April 2013
that 2.000.000 people died for accidents or sicknesses connected to their work.
Different national standards provide the indications that must be followed by the employer to
reduce the danger in workplaces.
Among these dangers there is also the creation of an explosive atmosphere, so the area
classification is a section of law to highlight the dangers that an explosive atmosphere could cause.
9.2 – HAZARDOUS AREA CLASSIFICATION PROCEDURE
Fixed the term “classification of areas” the question could be:
Classification of areas: which is the procedure to follow?
This is a typical procedure that can be followed:
− locate environment and relative conditions
− locate flammable substances or combustibles and their relevant characteristics
− locate sources of release (later indicated as SR) verifying the possibility to eliminate or limit
them as much as possible
− establish for each SR the grade of release, verifying the possibility to reduce the load
− for each SR calculate the load of release in precautionary conditions
− for each SR establish the type of hazardous zone
− for each SR calculate the hazardous distance to define the shape of the dangerous volume
− classification of the hazardous area is obtained by the single hazardous zones.
113
9.2.1 – PROCEDURES TO CLASSIFY HAZARDOUS AREAS
It is important to specify that the classification does not depend only on the activity performed in
that environment,
− for example: thermal plant = ZONE 2.
If it was so, it would have been useless to describe such a procedure, a table was enough; but the
result at the end of the procedure does not necessarily cover the whole area but it could be that:
− one hazardous zone or no hazardous zone for all the environment
− one or more type of the same hazardous zone limited to one or more points of the environment
− more type of hazardous zones for different areas of the environment.
The conclusion is that an assessment must be performed for each environment.
At this point it is necessary to clarify that:
− provided that who is in charge of the procedure of classification must be an expert (a skilled
person with knowledge of the relevant characteristic of the hazardous substances), to build an
electrical plant is easy for skilled people, but it will be dangerous for those who do not have any
knowledge about electricity
− there are environments (some of them will be introduced in the next paragraphs) for which the
classification is simple and thus can be solved with few reasoning and data
− there are environments for which the production processes require a more complex reasoning
and more data.
In the end, for each environment it is necessary to make a dedicated assessment.
9.3 – DEFINITIONS AND INFORMATION
For each environment that we will analyse there are terms which have common definitions; so, in
order not to repeat them every time, here below there are some definitions of the main terms.
9.3.1 – EXPLOSIVE ATMOSPHERE
Mixture with air, in atmospheric conditions, of flammable substance in the form of gas, vapours,
dusts, fibers or flyings that after the ignition allow the self sustaining of the flame propagation.
9.3.2 – SOURCE OF RELEASE
A source of release (later indicated as SR) is a point or part of the containment system from where
a flammable substance/combustible can be released in air creating an explosive atmosphere. An
SR can release either during normal operation and maintenance or in case of a fault.
114
9.3.3 – GRADE OF RELEASE
There are three fundamental grades of release.
Here below they are indicated in decreasing order of explosive atmosphere probability for the
presence of gas:
− Continuous grade a release which is continuous or is expected to occur for long periods
− Primary grade
a release which can be expected to occur periodically or occasionally during
normal operation
− Secondary grade
a release which is not expected to occur in normal operation and if it does
occur, it is likely to do so only infrequently and for short periods
9.3.4 - DUSTS – LEVELS OF HOUSEKEEPING
An adequate housekeeping in places with presence of combustible dusts allows to exclude the
presence of sources of release caused by dust layers.
The IEC/EN 60079-10-2 standard identifies three levels of housekeeping
LEVEL 1 – GOOD
The housekeeping is considered GOOD when dust layers are kept to negligible thickness, or are
non-existent. In this case, the risk of the occurrence of explosive dust clouds from layers and the
risk of fire due to layers have been removed.
LEVEL 2 – FAIR
The housekeeping is considered FAIR when dust layers are not negligible but are short-lived (less
than one shift). The dust is removed before any fire can start.
LEVEL 3 – POOR
The housekeeping is considered POOR when dust layers are not negligible and persist for more
than one shift. The fire risk may be significant, any conditions that can create a dust cloud (for
example, someone entering the room) shall be considered in the hazardous area classification.
9.3.5 - ZONES
According to the frequency of formation and duration of explosive atmosphere for the presence of
gas, hazardous areas are classified in zones.
This topic has been explained in chapter 3.
When beside the definition of ZONE the acronym NE (negligible extension) is added, it identifies a
theoretical zone where, under specific conditions, the extension can be ignored.
115
9.4 – GARAGES
9.4.1 – LOCATE THE ENVIRONMENT
To locate the environment we can refer to the definition indicated by the standards for the fire
prevention.
Garages: covered area dedicated to shelter, parking and movement of vehicles provided
with related services. There are some spaces which are not considered car parks, such
as areas covered with roof, open on at least two sides, those where each car place is
accessible directly from places in open air, and spaces dedicated to exhibition or sale if
the vehicles are without fuel or with limited fuel only for movement inside the
exhibition area. They can be public or private.
From this definition we can deduce some useful information:
− the garage is a closed space, the natural ventilation is less than the open air; the ventilation
influences the capacity to disperse the gas in the atmosphere
− a public garage is often open air, as to say without any separating element of the internal spaces,
even this influences the evaluation of the ventilation
− a showroom where car are exposed with a limited amount of fuel is not hazardous.
Moreover, for the fire prevention standards the area dimensions are important for the following
reasons:
− garages, public or private, with a surface up to 300 m² are not subject to fire prevention control
116
As we will see in paragraph 9.4.3 this does not influence the classification.
9.4.2 – FLAMMABLE SUBSTANCE
In a garage the flammable substances are the fuels present in the vehicle tanks. The standards
particularly consider the following substances:
− gasoline
− liquefied petroleum gas (LPG)
− compressed natural gas (CNG)
Area classification: and the diesel?
The diesel is a flammable substance whose flash point is at more than 65 °C.
The flash point of the substances above listed is under 0 °C.
To have an explosive atmosphere with diesel the ambient temperature should be more than 65 °C
which is not considered normal. A particular situation that could make diesel dangerous is the
possibility that this substance is vaporized in the environment; but again this is not considered a
normal situation in a garage.
9.4.3 – SOURCES OF RELEASE
In a garage the sources of release are present in case of anomalies that involve the release of fuel
from a tank.
Regarding LPG
1. The parking of vehicles, fueled by liquefied petroleum gas, equipped with safety
system in compliance with ECE/ONU 67-01 standard is allowed in floors over the ground
and in the first floor under, even though they have more than one.
Practically the LPG system in compliance with ECE/ONU 67-01 standard is considered a system
with negligible release, so now the parking is allowed even where it was forbidden in the past.
Regarding CNG
Even in this case the release is considered negligible, the eventual outgoing of gas is considered a
catastrophic fault (CNG is stocked in tanks with pressure of 200 bar).
The cases identified as “catastrophic fault” are not included in the classification procedure of the
hazardous area as it would establish zones with huge width according to the event considered
highly improbable.
Regarding Gasoline
Anomalies considered:
− it could be assumed that a fuel delivery tube breaks, is pierced or detaches from its place and
consequently the liquid can outflow. If the vehicle was moving, the fuel would keep outflowing
117
till the noticing of the problem; if the vehicle was still, the outflowing would be limited to the
liquid contained in the tube
− it could be assumed that the tank breaks, for example for a small crack; anyway this would
happen after a violent choke that the driver could not ignore and consequently it would be
immediately noticed and neutralized.
Assuming the formation of a puddle caused by the breaking of the fuel delivery tube, the most
likely source of release is the surface of the liquid. In this situation, based on careful assessments,
the quantity of fuel dispersed could be about 0,05dm³.
Taking the final part of the paragraph 9.4.1 (regarding the fire prevention), the source of release is
an unexpected fact that can happen to any vehicle. For this reason, the area of the garage
influences only the risk analysis: more vehicles mean higher probability that the unexpected event
happens.
9.4.4 – GRADES OF RELEASE
Base on the definitions given in 9.3.3, the SR that can be present in a garage are classified as
SECONDARY GRADE.
9.4.5 – LOAD OF RELEASE
The load of a puddle depends on different factors:
− the puddle surface
− the speed of ambient air and the efficiency factor of the ventilation
− the molar mass and pressure value of the flammable substance
− the atmospheric pressure
− and other different elements
If we consider the release of gasoline, based on the evaluations done by skilled people, we can
estimate a load of release of about 0,005 mg/s. With this load, the gasoline concentration in air is
so little that it can be considered negligible.
9.4.6 – TYPE OF ZONE
Based on the definitions of the chapter 3 the SR in a garage can determine a ZONE 2. Anyway,
considering these values:
− the load of release
− the load of ventilation in environment close to the SR
− the air change in the environment and close to the SR
− the hypothetical volume of the explosive atmosphere and concentration in air
the ZONE 2 can be downgraded to ZONE 2 NE, as to say a theoretical zone where, with the specific
conditions, the extension is negligible.
118
9.4.7 – HAZARDOUS DISTANCE
If the extension is negligible the hazardous distance is negligible.
9.4.8 – HAZARDOUS AREA CLASSIFICATION
Analysed the points of the previous paragraphs it is now possible to make an area classification.
In the garage described at 9.4.1, the considered SR considered determine a ZONE 2 NE and, as the
conditions declared by the employer are the same, the extension is negligible. Practically, there is
no danger of explosion as the eventual explosive atmosphere has a limited extension. There is
anyway the major risk in case of fire because of the high number of vehicles.
119
9.5 – CAR REPAIR SHOPS
9.5.1 - LOCATE THE ENVIRONMENT
Car repair shops can be divided in two categories:
− category A: car repair shops where there are not activities on the fuel, no hot working and no
underground pit; for example a car electrical repair shop, a shop of an installer of burglar alarm
or some particular sound systems, the tire repair shop, etc.
− category B: car repair shop where there are activities on the fuel, hot workings (welding or
working on the vehicle components that can be a source of ignition) or underground pits.
In order to assess the explosion danger, in this chapter we exclude:
− the car body repair shops with painting departments
− the car repair shop specialized in vehicles with LPG or CNG, where there are activities on the
high pressure system with full tanks and where it is allowed the access to vehicles with visible
breaks on the high pressure system.
9.5.2 – FLAMMABLE SUBSTANCES
In a car repair shop the flammable substances are the fuels present in the vehicle tanks. The
standards particularly consider the following substances:
− gasoline
− liquefied petroleum gas (LPG)
− compressed natural gas (CNG)
120
9.5.3 – SOURCES OF RELEASE
In the examined car repair shops the sources of release are either during normal operation or in
case of anomalies that involve outflowing of fuel from the containment system.
LPG and CNG releases are not considered for the same reason of the previous chapter.
Sources of release during normal operation can be:
− washing of mechanical parts using flammable substances (this procedure is used less and less
preferring products with a similar efficiency but non-flammable)
− inspections and test of the injectors or the circuit of fuel delivery when this involves a controlled
outflowing
− tank emptying operations
− battery recharging
Sources of release caused by anomalies:
− it could be assumed that a fuel delivery tube breaks, is pierced or detaches from its place and
consequently the liquid can outflow. If the vehicle was moving, the fuel would keep outflowing
till the noticing of the problem. If the vehicle was still, the outflowing would be limited to the
liquid contained in the tube
− another anomaly could be that a clumsy movement of the mechanic could cause the outflowing
of the flammable substance.
9.5.4 – GRADES OF RELEASE
Based on the definitions of the paragraph 9.3.3 the SR that can be found in a car repair shop can
be classified as PRIMARY and SECONDARY GRADE.
9.5.5 – LOAD OF RELEASE
Differently from the previous case – garages – it is not possible to establish a generic load of
release, since the cases when the fuel can be out of the containment system are different, and the
same for the ambient conditions. In these cases it is needed to make a punctual calculation, which
is not possible here.
9.5.6 – TYPE OF ZONE
In the car repair shops of category A the ZONE 2 can be downgraded to ZONE 2 NE, as to say in a
theoretical zone where the extension is negligible. The recommendations are:
− carefully avoid the release of flammable substances
− immediately remove eventual gasoline puddle to reduce the duration, for example by means of
sand or neutralising substances.
In the car repair shops of category B in order to eliminate or reduce the extension of ZONE 1,
eventually reducing them to ZONE 2 or ZONE 2 NE, the recommendations are:
− use of skilled personnel in all the operations that involve fuel: tank emptying, inspections of
injectors, washing of mechanical parts
− tank emptying operations in circumscribed areas of the shop
− testing of the injectors using dedicated benches designed in order not to disperse the fuel
− washing of mechanical parts using dedicated pools with an opening lid and placed under a
121
injectors, washing of mechanical parts
− tank emptying operations in circumscribed areas of the shop
− testing of the injectors using dedicated benches designed in order not to disperse the fuel
− washing of mechanical parts using dedicated pools with an opening lid and placed under a
correctly dimensioned extraction equipment; moreover the position of the pool must be far
from sources of heat, arcs and sparks
− eventual battery rechargers must be placed in a well ventilated area and the position must be far
from sources of heat, arcs and sparks
− the operations that specifically interest the high pressure circuits of the vehicles with LPG or
CNG must be with empty tanks and closed intercept valves.
9.5.7 – HAZARDOUS DISTANCE
Neither for the hazardous distance, as for the load of release, it is possible to give a generic
dimension, so we refer to the results produced by who classifies the area. Assuming to dedicate
precise dedicated working areas of the shop, it will be probably confined inside these areas; it will
unlikely involve the whole shop.
9.5.8 – HAZARDOUS AREA CLASSIFICATION
Resuming the previous paragraphs:
− In the areas where the vehicles are parked to be repaired (excluding the fuel delivery circuit,
tank included) the danger is the outflowing for an anomaly of the containers; considering the
continuous presence of skilled people and the immediate remove of puddles, we configure a
ZONE 2 NE.
− In the areas where dedicated machines are used as for example: test benches for injectors, pools
with lid and extraction for washing mechanical parts and tools, we assume that there are
releases only in case of anomalies; so, in this case, we can configure a ZONE 2.
− In the areas where there are activities like tank emptying, in specific cases, we can configure a
ZONE 1.
− In the areas intended for battery recharging, generally not more than one meter in all directions
starting from the cells of the accumulators, we configure a ZONE 1.
122
9.6 – NATURAL GAS THERMAL PLANTS
9.6.1 – LOCATE THE ENVIRONMENT
For this classification we assume the following entry data:
− room over the ground exclusively dedicated for thermal plant
− the thermal plant uses natural gas as combustible
− the operation rated pressure is between 20 mbar and 500 mbar
− aeration openings realized and placed in order to avoid the formation of gas locks
− the room is equipped with two openings, each with a surface of 1500 cm² (60x25 cm) for a total
of 3000 cm²
− the activities in the thermal plant are performed by people properly skilled about explosive
atmosphere risk, ignition sources and means of prevention and protection.
9.6.2 – FLAMMABLE SUBSTANCES
The flammable substance present in the examined thermal plant is:
− natural gas
The natural gas is a substance lighter than air (even if a little) and thus we would expect a
dispersion towards above.
123
9.6.3 – SOURCES OF RELEASE
In a natural gas thermal plant the sources of release are present only in case of anomalies and are
identified in discontinuity points of the pipes with insertion of connecting devices (flanges, joints,
couplers and others) or control elements (valves, manometers, pressure switches and others):
− Flanges with fiber gaskets: assuming the collapsing of the sealing or the breaking of a flange
gasket, there would be the outflowing of natural gas
− Valves: assuming the collapsing of the sealing or the breaking of a flange gasket, there would be
the outflowing of natural gas.
The way of release, in this case, consists in dispersion of the flammable substance in air.
9.6.4 – GRADE OF RELEASE
Based on the definitions of the paragraph 9.3.3 the SR that can be found can cause a SECONDARY
GRADE release.
9.6.5 – LOAD OF RELEASE
The load of release from a hole that can be accidentally created on a sealing device depends on:
− the hole surface
− the molar mass and pressure value of the flammable substance
− the atmospheric pressure and pressure inside pipes
− and other different elements.
Generally we could expect a load of release of:
− about 0,01 g/s flanges with gasket different from the compressed fibers
− about 0,1 g/s flanges with gasket in compressed fibers.
With the load of 10 mg/s there would be a negligible volume of explosive atmosphere; while with
the load of 100 mg/s the volume must be considered.
9.6.6 – TYPE OF ZONE
Based on the definition of ZONE reported in chapter 3 the SR determine a ZONE 2; as a matter of
fact, they are predictable releases only in case of fault or anomalies.
Considering the following parameters:
− load of release
− load of ventilation in the environment and close to SR
− air change in the environment and close to SR
− hypothetical volume of the explosive atmosphere and concentration in air, the situation could
change.
124
Generally:
− in case of release from a flange gasket in compressed fibers the ZONE 2 is confirmed
− in case of release from a flange gasket different from the compressed fibers (for example the
spiral wound or in Teflon or with metal ring on metal) the ZONE 2 can be downgraded to ZONE 2
NE.
9.6.7 – HAZARDOUS DISTANCE
If the extension is negligible, the hazardous distance is about 50 cm.
It is a rounded value to give an idea of the dimension, the correct value must be calculated with a
punctual analysis of each case.
9.6.8 – HAZARDOUS AREA CLASSIFICATION
After having examined the points of the previous chapters, it is now possible to make a
classification.
In the thermal plant with pipes jointed with flanges with a gasket in compressed fibers, the
examined SR determine a ZONE 2 that extends from the SR for 0,5 m in all the directions. Different
values can bring to different results.
125
9.7 - CARPENTRIES
9.7.1 – LOCATE THE ENVIRONMENT
They are places for the wood working – cutting, milling, planning, and drilling – with machine tools
equipped with extraction fans. Also small repairing works that do not involve big quantities of saw
dust are included in this activity.
In those installations where there can be dusts able to create an explosive mixture, there must be
dedicated systems of extraction for each type of gas, vapour or dust, or some other measures
must be taken to avoid the danger of explosion.
The machine tools can be reciprocating saws with horizontal movement, band saws, circular saws
with swinging table or similar, planing machines, surfacers, millers.
Specific case for the example:
To simulate a specific case we assume the following data:
− in the carpentry three air changes are ensured every hour
− the fire prevention standards are respected
− the flammable substances are those indicated in the next paragraph.
9.7.2 – FLAMMABLE SUBSTANCES
In a carpentry the main element of working is wood and it is natural to think about this material as
the only combustible substance; but in many carpentries there is a painting department and an
area where glues are used.
126
In this example, we will focus only on wood.
The process of woodworking creates the following rejects:
− sawdust and woodchips, as to say particles that cannot be defined as combustible dust
− dust with particles bigger than 500 µm (as to say 0,5 mm); these rejects are partially not
removed by the extraction system and deposit on the floor, machines and installation.
− dust with particles smaller than 0,5 mm, same as above.
According to the definition of the technical standard, the combustible dust is made of solid
particles with dimensions equal to or smaller than 0,5 mm.
Some working – particularly during finishing operations – produces particles that can be defined
dust.
But the problems are more, because according to the type of tree (pear tree, walnut, beech and
others) the characteristics of wood do change.
Characteristics of the beech sawdust (approximate, there are no absolute values):
− Lower explosion level ............................................................... 40 g/m³
− Ignition temperature for a layer of 5 mm ............................... 310 °C
− Ignition temperature of the cloud ........................................... 490 °C
− Maximum overpressure of explosion ...................................... 9 bar
− Limit concentration of oxygen .................................................. 5%
− Minimum ignition energy ......................................................... 30 mJ
Other needed data for the classification depend on the type of working and state of the dust, so
for the example we assume:
− a dimension of less than 0,5 mm as a medium size
− a volume unit mass of 1000 kg/m³. The volume unit mass is the volume in a cubic meter which is
occupied by compact particles without considering internal vacuoles and is measured in kg/m³.
The beech, as the black locust, sessile oak, cherry-tree has a specific weight of 1 ton for cubic
meter
− humidity present in the dust equal to 3,5%
In order to have precise values, when needed, you must ask to a specialized laboratory.
9.7.3 – SOURCES OF RELEASE
The source of release is a point from which the dust can be released or raised (if it is a layer)
creating an explosive atmosphere. In a carpentry there can be:
− layers of combustible dust in open containers
− layers of dust deposited out of containers (on the floor or machines) that can be frequently
disturbed
− opening towards the environment of machines that produce combustible dusts
− bag emptying points and/or small containers
− not hermetically sealed bags
− discontinuity points of machines and pipes.
127
9.7.4 – GRADE OF RELEASE
Based on the definitions of the paragraph 9.3.3 the SR that can be found can cause FIRST and
SECONDARY GRADE release.
9.7.5 – LOAD OF RELEASE
Neither in this case is it possible to establish a generic load of release, as the cases in which the
dust can be out of the containment systems are different so as the ambient conditions. In these
cases you must proceed each time with a punctual calculation, which is not possible here.
9.7.6 – TYPE OF ZONE
As indicated in chapter 3 there are three types of zone: ZONE 20; ZONE 21; ZONE 22.
Zone 20
Generally there is a ZONE 20 inside the containment systems in which a part of the dust contained
stays suspended in air, for example:
− inside the extraction line system (ducts)
− in the surroundings of the tools that during all the working day treat wood, producing small
particles of dust (such as the polishing or sizing machines) without an adequate extraction
system.
In this second case, we specify that in working areas the presence of ZONE 20 – continuous
presence of dust that would be breathed by the operator – is forbidden and thus this eventuality is
not considered.
One of the ignition dangers in ZONE 20 is the movement of dust, inside transport systems, with
speed higher than 1 m/s; in these cases there is an accumulation of electrostatic charge (ex.
pneumatic conveying of dust).
Zone 21
It is a ZONE 21 when:
− conditions are similar to those of the second example of the previous paragraph of ZONE
20, but for a short period of the working day. Also in this case the main measure to take is
an adequate extraction system
− caused by a wood dust cloud that is formed emptying the sacks of the extractors combined
with machines producing tiny particles.
Zone 22
It is a ZONE 22 each time it is possible to disperse the dust in air caused by an anomaly or a
distraction of the operator, for example:
− extraction system out of use for a fault; from the moment of the fault to its individuation
128
and block of the production there will be a short period in which an explosive atmosphere
can occur
− in many cases the extraction system brings the dust in bags that, once full, are emptied
manually. During this operation one of the bags can slip through the hands of the operator
and fall, break or other and, consequently, be dispersed in air. For a short period the dust
can create an explosive atmosphere
− the breaking of a connecting duct made of textile material – they are couplers between
tubes or between tubes and extraction system devices – could cause that the contained
dust goes out and creates an explosive atmosphere
− the deposited dust accidentally raised from the ground – for example using compressed air
– and mixed with air could create an explosive atmosphere
9.7.7 – HAZARDOUS DISTANCE
The cases in which the dust can be dispersed in air are very different and it is not possible to
estimate a size. For this reason, the reference in such case will be the results produced by who
classifies the area.
9.7.8 – HAZARDOUS AREA CLASSIFICATION
Resuming the previous paragraphs:
− considering the presence of an adequate extraction system or the presence of closed machines
to reduce at minimum the dispersion of dust, ZONE 20 and 21 are considered unlikely in a
carpentry
− considering cases of anomalies, the cleaning frequency (removing the dust from the surfaces,
not only the floor) in the working areas, the probability of ZONE 22 is not negligible.
129
9.8 – AGRICULTURAL INDUSTRIES
9.8.1 – LOCATE THE ENVIRONMENT
In this paragraph we will analyse the industries of the primary sector, those that deal with cereals,
legumes, peanuts, cocoa, coffee, sugar and other agricultural products.
In these places, during the movement and deposit of the above mentioned products, clouds are
created; as to say, tiny particles with dimensions equal to or less than 0,5 mm.
Same as explained in the previous chapter for carpentries, places where there can be dusts able to
create an explosive atmosphere must be equipped with extraction systems.
9.8.2 – FLAMMABLE SUBSTANCES
The dust created by cereals, legumes, peanuts, cocoa, coffee, sugar and other agricultural
products, if mixed with air creates an explosive atmosphere.
In the following table there are quoted some values of these elements: the listed substances
present very different characteristics; the minimum ignition energy of rice is 5 mJ, while for cocoa
is 20.000 times higher.
130
Rice
Sugar
Corn
Cocoa
30 g/m³
60 g/m³
60 g/m³
125 g/m³
Ignition temperature for a cloud
380 °C
310 ÷ 480 °C
370 °C
560 °C
Ignition temperature for a layer of 5 mm
290 °C
380 ÷ 460 °c
290 °C
NC
Maximum overpressure of explosion
8,6 bar
8,2 bar
9,3 bar
6,7 bar
5 mJ
10 mJ
60 mJ
100 J
Lower explosion level
Minimum ignition energy
9.8.3 – SOURCES OF RELEASE
The source of release is a point from which the dust can be released or raised (if it is a layer)
creating an explosive atmosphere:
− layers of combustible dust in open containers
− layers of deposited dust (on the floor or machines) that can be frequently disturbed; a particular
case could be the conveyor belt because it moves and is easier to “disturb the deposited dust”.
The movement then increases the extension of the hazardous area
− opening towards the environment of open machines that produce combustible dusts
− bag emptying points and/or small containers
− not hermetically sealed bags
− discontinuity points of machines and pipes
Pictures 36 and 37 refer to potential ignition sources.
9.8.4 – GRADE OF RELEASE
Pictures 36 and 37 show examples of CONTINUOUS, PRIMARY and SECONDARY GRADE releases.
9.8.5 – LOAD OF RELEASE
Neither in this case is it possible to establish a generic load of release, as the cases in which the
dust can be out of the containment systems are different so as the ambient conditions. In these
cases you must proceed each time with a punctual calculation, which is not possible here.
9.8.6 – TYPE OF ZONE
In these places there are three types of zone: ZONE 20; ZONE 21; ZONE 22.
131
Picture 37: in this case there are more than one source of release;
one is the release tube, another is the dust surface inside the
container, another one the opening of the container.
Picture 38: the source of release is the connecting duct made of
textile material when for an anomaly it loses the sealing.
Zone 20
Generally there is a ZONE 20 inside containers, mixers, dryers, hoppers, dust ducts. Practically
inside containment systems where part of the dust is suspended in the air.
There could be also ZONE 20 out of the containment systems but, in working areas, this condition
is forbidden and thus, once located, must be removed.
Zone 21
Generally there is a ZONE 21 close to the containment systems, especially when there are
operations of transfer from a containment system to another, as for example: in the surroundings
of the hopper openings, during transfer operations of containers done without dust extraction
system; around the trench for truck emptying; around the container openings as shown in Picture
37.
Zone 22
It is a ZONE 22 each time it is possible to disperse the dust in air caused by an anomaly or a
distraction of the operator, for example:
− extraction system out of use for a fault; from the moment of the fault to its individuation
and block of the production there will be a short period in which an explosive atmosphere
can occur
132
− in many cases the extraction system brings the dust in bags that, once full, are emptied
manually. During this operation one of the bags can slip through the hands of the operator
and fall, break or other and, consequently, be dispersed in air. For a short period the dust
can create an explosive atmosphere
− the breaking of a connecting duct made of textile material – they are couplers between
tubes or between tubes and extraction system devices – could cause that the contained
dust goes out and creates an explosive atmosphere
− the deposited dust accidentally raised from the ground – for example using compressed air
– and mixed with air could create an explosive atmosphere.
9.8.7 – HAZARDOUS DISTANCE
The cases in which the dust can be dispersed in air are very different and it is not possible to give
an estimated size. For this reason, the reference in such case will be the results produced by who
classifies the area.
9.8.8 – HAZARDOUS AREA CLASSIFICATION
In this environment – we mean only those with presence of combustible dust – the level of
housekeeping is considered poor (see chapter 9.3.4).
This means that a big part of the areas where there is dust (moving or deposited) can be classified
as ZONE 21 and ZONE 22.
133
Chap.10: INSTALLATION METHODS
10.1 - GENERALITIES
In this chapter we will refer to all the information of the previous ones in order to develop
installation methods for some specific activities. Particularly the paragraphs are closely linked to
those of chapter 9.
After the classification is done and the danger in different areas of the factory is assessed, the
employer – for the law who takes decisions and has spending power in the factory – must take all
the preventing measures to avoid an explosion.
The main measure is to avoid the creation of an explosive atmosphere; when this is not possible,
all the potential ignition sources must be removed.
In chapter 2 we explained that an explosion occurs if there is contemporary presence of an
explosive atmosphere and an ignition source.
The electrical plant could be an ignition source and for this reason all the protection measures
must be taken in order to reduce the explosion hazard to an acceptable level.
There are different types of protection (chapter 4) for the electrical equipment in hazardous areas.
In this chapter we will give some indications to select and assemble electrical installation in
explosive atmospheres, in the places examined in the previous chapter.
When you do an electrical plant you must do all the possible to prevent any danger linked to the
use of materials and equipment. Particularly the electrical plant must not cause:
A) damages to living beings
B) material damages
C) fault of electrical and electronic plants
MAIN DANGER THAT THE ELECTRICAL PLANT CAN CAUSE
CONSEQUENT EFFECTS
burns
respiratory arrest
heart fibrillation
direct contacts
indirect contacts
overcurrents
burns
fire ignition
explosion ignition
electrical plant inopportunely out of voltage
electric arc
thermal effects
overvoltage due to atmospheric conditions or wrong operations
external influences due to
- atmospheric agents: sun, rain, wind…
- impacts, vibrations
- corrosive agents
material damages of components
that consequently could cause the above
listed dangers
Table 31: main dangers that the electrical plant can cause and consequent effects
134
10.2 – TERMS AND DEFINITIONS
Component of the installation
Each element used for production, transformation, transmission or electric energy
distribution such as machines, transformers, equipment, measuring tools, protection
devices, pipes.
Group of an equipment for explosive atmosphere
Classification of an electrical equipment according to the explosive atmosphere for
which it is intended.
Hazardous area
Area where an explosive atmosphere is or can be present in such a quantity that
requires particular measures for realization, installation and use of equipment.
10.3 – BRIEF GENERAL INFORMATION
By the way, the following information refers to points that could trigger an explosive atmosphere.
Information is general and synthetic.
10.3.1 - OVERLOAD
The overload is a fault current, is a current of bigger intensity than the rated one and happens in a
healthy circuit.
There is an overload when the circuit rated current overpasses the conductor rated load
and the rated current is the maximum value expected in the project calculations.
There can be temporary overloads (starting of a system component that requires a high
breakaway starting current) or permanent or persistent overloads (for example system
components used over their rated value).
Here below there are some cases where an overload can occur:
Circuits with sockets
A circuit that connects a series of sockets is never dimensioned for the value of the sum of the
rated currents of all the sockets present in the installation. It is usually calculated with a
coincidence factor, a factor that reduces the maximum possible value to a value more adequate to
what is expected. When the real current overpasses the expected, for different reasons, there is an
overload.
If a circuit has only one socket, dedicated to a precise user device, the eventual overload is caused
by an anomaly in this device.
Circuits that power motors
When the motors are subject to a bigger effort than the one for which they are intended (improper
use of the equipment), they require a higher current than the rated one and create an overload.
135
Circuits that power transformers
When the load connected to the secondary of a transformer overpasses the rated power, it creates
an overload.
− Overload: how to defend yourself?
In an electrical circuit a protection device must be installed in order to intervene every time the
current takes values able to cause a dangerous heating for the insulation of the conductors,
connections, terminals and surrounding environment.
The general rule is the following:
− the load of the conductors (Iz) must be bigger than (or equal to) the rated current of the
protection device (In) that must be bigger than (or equal to) the rated current (IB).
What above can be expressed with the formula:
− Overload: conclusions
 ≥  ≥ 
In the end, an overload could be the cause of the ignition of an explosive atmosphere.
In the classified areas, a wrongly dimensioned protection device could be the cause of an
undesired ignition.
10.3.2 – SHORT-CIRCUIT
Overcurrent that occurs after a fault of negligible impedance between two points that
have voltage in normal operating current.
Differently from the overload, the short-circuit is an overcurrent that occurs due to a fault and this
is a valid reason to interrupt it. Moreover, it is usually an overcurrent much higher than the one
that can be created by an overload.
− Short-circuit: conclusions
To conclude, if the overload could cause the trigger of an explosion, the short-circuit will definitely
occur. Also in this case, it is necessary to install a protection device that can interrupt the current
to bring the conductor temperature to an acceptable limit.
In order to do it, this principle must be followed: the energy that the MCB allows to pass before
opening must not overpass the maximum allowed by the conductors.
What above is expressed by the formula:
where:
 ≤   
− I²t specific energy that passes through the protection device
− K factor whose value depends on the conductor material, insulation, initial and final
temperature that the cable can withstand without damaging
136
− S section of the conductor
10.3.3 – ELECTRIC ARC
This aspect has already been examined in chapter 2; here below some other observations are
added.
An electric arc sometimes is a desired event (for example it is produced for welding), some other
times it is an undesired event (interesting case for us). An electric arc can be ignited for different
reasons and, consequently, the solutions to avoid this event are different.
Some examples for which adequate measures must be taken:
− an arc that could be triggered by an overvoltage caused by atmospheric agents
− an arc that could be triggered by an overvoltage caused by opening and closing of protection
and control devices
− an arc that could be triggered by loosened connection terminals creating the condition of two
far electrodes (less than one millimeter).
10.3.4 – DANGEROUS SPARKS
The use of components in insulating material according to the type and specific conditions create
electrostatic discharges, sparks that could (according to the energy produced) ignite an explosive
atmosphere.
An immediate solution could be to use components with metallic external parts; but also in this
case there are some dangers to consider: if the metallic components suffer impacts or frictions,
they can create dangerous sparks.
The components must not contain in mass more than:
group II - gas or vapours
group III - dust
EPL “Ga”
EPL “Da”
10% in total for aluminium, titanium or zirconium
EPL “Ga” e “Gb”
7,5% in total for aluminium, titanium or zirconium
EPL “Gc”
no particular requirements
7,5% in total for magnesium, titanium or zirconium
EPL “Db”
7,5% in total for magnesium, titanium or zirconium
EPL “Dc”
no particular requirements
Table 32: maximum percentage allowed of some substances according to groups and EPL
10.3.5 – STATIC ELECTRICITY
To connect with the previous chapter, an arc could be triggered by an effect of electrostatic charge
accumulation. Being a discharge that happens in a very limited period, more than the arc, we can
define the electrostatic discharge as a spark.
In the insulating materials, differently from the conductors (usually made of metal), the
electrostatic discharge are stable in time (static) and when they charge, for example for rubbing,
they keep the charge.
137
In metallic materials the positive and negative charges are free to move and do not accumulate.
Practically an earth connection favours the disposal of the electrical charges.
In case of contact between positively charged elements with negatively charged elements an
electrostatic discharge occurs. By the way, the electrostatic discharge accumulated by a person
can reach 135 mJ, value bigger than the majority of the minimum ignition energies of explosive
atmosphere air-gas/vapour and air-dust.
For other information regarding electrostatic discharge you can also read chapter 2.
10.3.6 – THERMAL EFFECTS
One of the unavoidable consequences of the passage of an electrical current in a circuit is the
increase of temperature. The Joule effect (heating) in an electrical equipment occurs due to:
− rated current flowing (normal functioning)
− overcurrents (shortcircuit, overload – see previous chapters)
− fault of earth current
− bad contacts (terminals that can loosen with time).
Even if the equipment is protected by a case, part of the heating is transferred also to the case
which takes a temperature that, during normal functioning, stabilizes only when it reaches the
thermal regime.
When the temperature of the equipment overpasses the limit of ignition for an explosive mixture,
it can become the trigger of the explosion.
10.4 - GARAGES
10.4.1 - GENERALITIES
For garage it is intended a place where vehicles are sheltered and, in this specific case, other
activities which are sometimes present are excluded, such as: refueling areas, areas with car repair
activities.
Different types of garage are identified in the previous chapter; according to the type, the
selection and installation of the components may be different.
10.4.2 - EXPLOSION
From the point of view of the explosion, in a garage the undesired event is the ignition of the fuel
contained in the vehicles released for a fault. As seen in the previous chapter, the probable release
of fuel can cause a zone 2 on the floor which is generally with negligible extension.
138
10.4.3 - FIRE
From the point of view of fire, in a garage the undesired event is proportional to the number of
vehicles present. A fire will obviously last more in the case that is fuelled by a higher number of
vehicles.
10.4.4 – EXTERNAL INFLUENCES
Regarding external influences, in a garage one of the dangers to consider is the damage that an
electrical component could suffer after an impact with a vehicle. As described above, a damaged
component could be the cause of a short-circuit or an overtemperature that could then provoke a
fire.
Among the external influences, then, the ambient temperature must be considered; as a matter of
fact, the garages even though they are covered in winter months must withstand temperatures
below zero.
10.4.5 – SELECTION AND INSTALLATION OF ELECTRICAL COMPONENTS
Provided that it is assessed the persistence of all the conditions expressed in the previous chapter,
conditions which leaded to exclude a danger of explosion, the fire hazard assessment is still to be
done.
The main theme of this book is not fire hazard but it is useful to give some synthetic information, a
warning that gives a particular attention in the construction of the electrical plants in these places.
When the number of the vehicles present in a garage is high (for example when the surface
reaches 1000 m²) a fire causes a risk bigger than a normal environment.
In common cases a private garage contains a small number of vehicles and for this it is not
included in the example above.
In a private garage the electrical equipment is generally composed of lighting devices, control
points to switch the lamps, sockets and connecting tubes.
But the main risk of a fire can be found in public garages, for example the underground parking of
a commercial center.
In public garages, the electrical equipment is composed of lighting devices and connecting tubes.
In places with fire hazard due to the presence of flammable substances (in this case the fuel of the
vehicles) the electrical components must be placed inside enclosures with protection rating not
less than IP4X.
Domestic sockets and lighting control devices are exceptions.
In order to reduce the danger of damages caused by moving vehicles, the electrical equipment
must be placed in appropriate positions:
− components such as switches, sockets and others, must be placed inside niches, where walls
create an angle or out of action zones, as to say in places where the vehicles cannot impact. The
installation height must be more than the vehicle bumpers (generally is the most prominent part
if we do not consider the wing mirrors). Moreover, to facilitate disable people that uses
wheelchairs, the height must be more than 140 cm from the ground.
139
When the danger of damage is an event to be considered – impacts of small strength –
components with a high mechanical protection degree must be considered: IK 10 (the component
can withstand an impact of a weight of 5 kgs dropped from a height of 0,4 m).
For example, these products satisfy all these requirements (IP rating, operating temperature, IK
rating):
Component
IP
IK
T
distribution board TAIS CUBE series
66
10
-30 °C ÷ + 100 °C
junction boxes TAIS series
67
10
-40 °C ÷ + 70 °C
control devices (switches) RONDO' series
55
10
-25 °C ÷ + 70 °C
lighting fixtures RINO series
66
9
-25 °C ÷ + 50 °C
where:
Table 33: characteristics of some Palazzoli products that allow a safe use
− component: product of Palazzoli S.p.A.
− IP: protection rating against the penetration of solid bodies and the damaging effects of the
water penetration
− IK: impact resistance
− T: operating temperature.
For the non-flushed tubes with vertical run from ceiling to floor, where possible, it is
recommended the installation in angles and, where not possible, the use of multipole cables with
sheath in protective hard shell classification code 5557.
Crushing resistance
Impact resistance
5
4000 N
5
20 J (IK10)
Minimum operating
temperature
5
-45 °C
Maximum operating
temperature
7
+400 °C
Table 34: explication of the classification code 5557
10.5 – CAR REPAIR SHOPS
10.5.1 - GENERALITIES
Car repair shops can be divided in two categories:
− category A: car repair shops where there are not activities on the fuel, no hot working and no
underground pit; for example a car electrical repair shop, a shop of an installer of burglar alarm
or some particular sound system, the tire repair shop, etc.
− category B: car repair shop where there are activities on the fuel, hot workings (welding or
working on the vehicle components that can be a source of ignition) or underground pits.
140
10.5.2 - EXPLOSION
From the point of view of the explosion, in a car repair shops of category A the undesired event is
the ignition of the fuel contained in the vehicles released for a fault. As seen in the previous
chapter, the probable release of fuel can cause a zone 2 on the floor which is generally with
negligible extension.
In a car repair shop of category B the danger is the ignition of the fuel contained in the vehicles
released for a fault or accidentally spilt by the operator during tank fulfilling and emptying
operations or interventions on the fuel circuit.
10.5.3 - FIRE
From the point of view of fire, in a car repair shop the undesired event is proportional to the
number of vehicles present and the type of working done; for example in the car repair shops
where fuel circuit is repaired, if adequate measures were not taken, there would be a higher
probability of fire than, for example, a car wash.
10.5.3 – EXTERNAL INFLUENCES
In a car repair shop – both of category A and B – one of the dangers to consider is the damage that
an electrical component could suffer after an impact with a vehicle. As for garages, a damaged
component could be the cause of a short-circuit or an over temperature that could then provoke a
fire.
10.5.3 - SELECTION AND INSTALLATION OF ELECTRICAL COMPONENTS
In the car repair shops of category A, for the continuous presence of personnel and following the
indications for the garages, the place is not considered hazardous.
For the selection and installation of electrical components general principles for an industrial area
must be followed, considering the danger of possible impacts caused by moving vehicles.
In the car repair shops of category B it is recommended to establish an area of the shop dedicated
to the workings on the fuel circuits.
In this area, the classification could identify ZONES 1 and ZONES 2.
Zone 1
In ZONES 1 all the measures must be taken to limit the extension as much as possible; doing so it
becomes more feasible the purpose not to install electrical components that could ignite the
explosive atmosphere and, consequently, increase the safety.
In the examined case the component to install must be marked according to the Directive ATEX
94/9/EC with the following data or with data that indicate a higher protection.
141
in a ZONE 1 caused by gasoline, LPG o CNG
in a ZONE 1 caused by hydrogen
II 2G Ex-e IIA T3 Gb
II 2G Ex-e IIC T1 Gb
II
places with presence of explosive atmosphere
different from the mines
II
places with presence of explosive atmosphere
different from the mines
2
equipment designed to operate in conformity
with the parameters established and
guarantee a high protection level
2
equipment designed to operate in conformity
with the parameters established and
guarantee a high protection level
G
gas
G
gas
EX e increased safety type of protection
EX e increased safety type of protection
IIA
IIC
group of the hydrogen and acetylene
T1
gas ignition temperature >450 °C; maximum
surface temperature allowed 440 °C
Gb
the equipment do not ignite during normal
operation and in case of a fault
T3
Gb
group of the gas (for the example case:
gasoline, LPG, CNG)
gas ignition temperature >200 °C; maximum
surface temperature allowed 195 °C
the equipment do not ignite during normal
operation and in case of a fault
For the ZONE 1 and ZONE 2 the following components are recommended:
boxes in aluminium alloy ALUPRES-EX series
boxes in thermosetting (GRP) TAIS-EX series
II 2G Ex e IIC Gb
NOTE: on the left a picture of the box in thermosetting (GRP)
TAIS-EX series
142
cable glands UNI-EX series
II 2G Ex-e II
adapters UNI-EX series
II 2G Ex-d IIC
Zone 2
In the ZONES 2, generally more extended than ZONE 1, the electrical components must be marked
according to the Directive ATEX 94/9/EC or one that indicates a higher protection:
in a ZONE 2 caused by gasoline, LPG or CNG
II 3G Ex-n IIA T3 Gc
II
places with presence of explosive atmosphere
different from the mines
3
equipment designed to operate in conformity
with the parameters established and
guarantee a normal protection level
G
gas
EX n type of protection n
IIA
group of the gas (for the example case:
gasoline, LPG, CNG)
T3
gas ignition temperature >200 °C; maximum
surface temperature allowed 195 °C
Gc
the equipment do not ignite during normal
operation
An aspect to be remembered is the use of mobile, portable and personal equipment. These
devices could be temporary introduced in an hazardous area and be an ignition source. These
objects are not part of the electrical plant but it is useful to emphasize also this aspect, particularly
the devices that are connected to the sockets. Once assessed that the mobile or portable devices
are adequate for that hazardous zone, they must be equipped with a plug with the same marking
of the socket installed.
These components are recommended:
switched sockets with mechanical interlock with
enclosure in antistatic thermosetting (GRP), IP66
protection rating, TAIS-EX series
II 3G Ex-nR IIC T6 Gc
NOTE: on the left a picture of 463126EX wall mounted
switched interlocked 2P+E, 16 A, 230 V
143
switched sockets with mechanical interlock with
enclosure in aluminium alloy, IP 66 protection rating,
ALUPRES-EX series
II 3G Ex-nR IIC T6 Gc
NOTE: on the left a picture of 465136EX wall mounted
switched interlocked 3P+E, 16 A, 400 V
isolator switches in aluminium alloy, IP66 protection
rating, CAM-EX series
II 3G Ex-nR IIC T6 Gc
small control devices in antistatic thermosetting (GRP),
IP 66 protection rating, TAIS MIGNON-EX series
small control devices in aluminium alloy, IP 66
protection rating, RONDO'-EX series
TAIS MIGNON EX
RONDO' EX
II 3G Ex-nR IIC T6 Gc
lighting fixtures in stainless steel AISI 304, diffuser in
tempered glass, IP 66 protection rating, G13 T8
lampholder, RINO-EX series
II 3G Ex-nA IIC T4 Gc
Other useful information for all the areas of the shop
The electrical components must be used within their rated power, current, voltage and frequency
declared by the manufacturer.
144
For example the socket in the picture has the following characteristics:
Palazzoli code
Rated current
470126
16 A
Rated voltage
Poles
230 V
2P+E
It is a socket with 16A rated current, this means that it is predisposed to receive plugs with 16A
but this does not exclude that the load can overpass this limit. For this reason it is necessary to
install a protection device, such as an MCB.
10.6 – THERMAL PLANTS
10.6.1 - GENERALITIES
The thermal plant is composed of one or more rooms connected to each other, exclusively
intended for heat production.
10.6.2 - EXPLOSION
From the point of view of explosion, in a thermal plant the danger is represented by a thermal
plant and more precisely the undesired event is the ignition of the fuel – in the specific case the
natural gas – released because of a discontinuity of the gas circuit (flanges, electrovalves, threaded
joints, etc..).
The gas release is an abnormal event and includes faults, non-correct use or distractions of the
operator; events that can be considered as rare.
Discontinuity points are the probable sources of release; in the particular cases listed here below,
the releases cause hazardous zones with negligible extension, ZONE 2NE:
− the plants are realized and supervised in compliance with laws and technical standards
− the activities in the thermal plant are performed by people properly skilled about explosive
atmosphere risk, ignition sources and means of prevention and protection
− the operation rated pressure is between 20 mbar and 500 mbar
− the dimensions of the release holes do not overpass 0,25 mm².
145
In case of thermal plant where there are flanges with compressed fibers gasket, it is
recommended to assume a release hole of 2,5 mm² dimensions; in this case since one of the
conditions above is not respected, we configure a ZONE 2.
10.6.3 - FIRE
From the point of view of fire, in a thermal plant the undesired event is proportional to the power
of the thermal plant.
10.6.4 – EXTERNAL INFLUENCES
In a thermal plant there are no particular dangers due to external influences.
It is practically a closed environment where the negative effects of atmospheric agents, plants and
animals are excluded.
It is a covered, close space. The only permanent connections with the external are the fix openings
which are standardized by the law. To avoid the ingress of animals, some grilles are applied on the
openings. They allow only small insects or dust.
10.6.5 – SELECTION AND INSTALLATION OF ELECTRICAL COMPONENTS
Generally, all the technical measures for building an ordinary electrical plant are valid. Particularly
since it is a technical environment to improve the maintenance and identification of the
components in the installation, a wall-mounted installation is recommended. Considering the
openings, it is also recommended a protection rating not less than IP44.
In case of thermal plants there is the possibility of ZONE 2, the components to install must be
marked according to the Directive ATEX 94/9/EC or one that indicates a higher protection level.
in a ZONE 2 caused by natural gas
II 3G Ex-n IIA T1 Gc
These components are recommended:
small control devices in antistatic thermosetting (GRP),
IP 66 protection rating, TAIS MIGNON-EX series
small control devices in aluminium alloy, IP 66
protection rating, RONDO'-EX series
II 3G Ex-nR IIC T6 Gc
TAIS MIGNON EX
146
RONDO' EX
lighting fixtures in stainless steel AISI 304, diffuser in
tempered glass, IP 66 protection rating, G13 T8
lampholder, RINO-EX series
II 3G Ex-nA IIC T4 Gc
10.7 - CARPENTRIES
10.7.1 - EXPLOSION
In order that an explosion occurs, there must be the following conditions:
− presence of dust
− dispersion of dust in air (cloud with minimum density of 40 g/m³)
− the oxygen
− the ignition source (minimum ignition energy 30 mJ).
In a carpentry the dust is generally produced using machines that perform finishing workings, such
as finishing or sizing machines; circular saws, for example, mainly produce wood chips and small
quantities of dust.
In the factories that work wood the probability of a ZONE 20 or ZONE 21 is low, but it is more likely
to identify potential ZONE 22 where, during normal activity, the quantity of dust is not sufficient to
create an explosive atmosphere but in case of an anomaly – stop of the extraction system, a
distraction or carelessness of the operator – this condition could happen.
Zone 21
In the classified volumes with danger of explosion it is preferred not to install electrical
components, but this is not always possible. In the volumes classified as ZONE 21, if it is not
possible to remove all the electrical components, it is better to limit only to ducts and junction
boxes.
Zone 22
Generally (it is not a rule) the ZONE 22 is a volume of about 10 m³, this is to say that it is rare to
find all the working areas as ZONE 22 but only parts.
ZONE 22 is usually close to the machines that for type of working do not produce wood chips but
sawdust (finishing machines, sizing machines and similar).
In volumes classified as ZONE 22 the electrical components that can be found are junction boxes
and industrial sockets.
147
10.7.2 – FIRE AND EXTERNAL INFLUENCES
In a carpentry elements are supposed to move; for their dimension, they could escape the
operator control and cause damages to the devices (danger of impacts with consequent
mechanical damage). A damaged component, as already written, could be the cause of a shortcircuit or an overtemperature that could provoke a fire.
10.7.3 – SELECTION AND INSTALLATION OF ELECTRICAL COMPONENTS
In the examined case the components to install must be marked according to the ATEX Directive
94/9/EC with the following characteristics or one that indicates a higher protection level:
in a ZONE 21 caused by sawdust
in a ZONE 22 caused by sawdust
II 2D Ex-tb IIIB T200 °C Db
II 3D Ex-tc IIIB T200°C Dc
II
places with presence of explosive atmosphere
different from the mines
II
places with presence of explosive atmosphere
different from the mines
2
equipment designed to operate in conformity
with the parameters established and
guarantee a high protection level
3
equipment designed to operate in conformity
with the parameters established and
guarantee a normal protection level
D
dust
D
dust
tb
protection by enclosure
tc
protection by enclosure
IIIB
non-conductive dust
IIIB
non-conductive dust
T200 °C (note 1)
T200 °C (note 1)
Db
Dc
normal protection level + one fault
normal protection level
note 1) the selection of the maximum surface temperature has been made considering the ignition temperature of a
layer of sawdust (310 °C) reduced of 75 °C and rounded down.
The following components are recommended and suitable both for ZONE 21 and ZONE 22:
boxes in thermosetting (GRP) TAIS-EX series
II 2D Ex-tb IIIC Db
NOTE: since they are boxes without electrical devices
there is no indication on the maximum surface
temperature
148
switched sockets with mechanical interlock with
enclosure in antistatic thermosetting (GRP), TAIS-EX
series
II 2D Ex-tb IIIC 115 °C Db IP66
Note: the sockets must be equipped with an interlock; and since the dusts are non-conductive the protection rating
must not be less than IP55.
Major risk in case of fire
Once assessed that in the factory there is an environment with fire hazard for the presence of
flammable substances (in this case wood under working or deposited) the electrical components
must be placed inside enclosures with a protection rating not less than IP 4X.
When the danger of damage is an event to be considered – impacts of small strength –
components with a high mechanical protection degree must be considered: IK 10 (the component
can withstand an impact of a weight of 5 kgs dropped from a height of 0,4 m).
For example, these products satisfy all these requirements (IP rating, operating temperature, IK
rating):
Component
IP
IK
T
distribution board TAIS CUBE series
66
10
-30 °C ÷ + 100 °C
junction boxes TAIS series
67
10
-40 °C ÷ + 70 °C
control devices (switches) RONDO' series
55
10
-25 °C ÷ + 70 °C
lighting fixtures RINO series
66
9
-25 °C ÷ + 50 °C
where:
Table 35: characteristics of some Palazzoli products that allow a safe use
− component: product of Palazzoli S.p.A.
− IP: protection rating against the penetration of solid bodies and the damaging effects of the
water penetration
− IK: impact resistance
− T: operating temperature.
149
10.8 – AGRICULTURAL INDUSTRIES
10.8.1 - GENERALITIES
In this paragraph we will analyse the industries of the primary sector, those that deal with cereals,
legumes, peanuts, cocoa, coffee, sugar and other agricultural products.
In these places, during the movement and deposit of the above mentioned products, clouds are
created; as to say, tiny particles with dimensions equal to or less than 0,5 mm.
10.8.2 - EXPLOSION
In order that an explosion occurs, there must be the following conditions:
− presence of dust
− dispersion of dust in air (cloud with minimum density of 40 g/m³)
− the oxygen
− the ignition source (minimum ignition energy 30 mJ).
Differently from the carpentries where the only element is wood, here the elements are many
more and each one with different characteristics.
In the table taken from Chapter 9 some data of these elements are quoted:
Rice
Sugar
Corn
Cocoa
30 g/m³
60 g/m³
60 g/m³
125 g/m³
Ignition temperature for a cloud
380 °C
310 ÷ 480 °C
370 °C
560 °C
Ignition temperature for a layer of 5 mm
290 °C
380 ÷ 460 °c
290 °C
NC
5 mJ
10 mJ
60 mJ
100 J
Lower explosion level
Minimum ignition energy
Table 36: some characteristics of flammable substances
As it is possible to see in the table, the minimum ignition energy for RICE or SUGAR is very small if
compared with the one of COCOA.
In order to select the electrical components it is important to consult the classification of the
hazardous zones.
10.8.3 - FIRE
From the point of view of fire the following cases must be considered:
− mills for cereals or other materials to be grinded with a daily potentiality of more than 20 tons;
cereal deposits and other products with a daily mass of more than 50 tons
− plants for drying cereals and vegetables with deposit of dried products with quantities in mass of
more than 50 tons
− sugar factories and sugar refineries
− bakeries and rice mills with a daily production of more than 50 tons.
150
10.8.4 – EXTERNAL INFLUENCES
There are industrial environments with outdoor areas, areas with roofs and closed areas; as to say
different areas that require different evaluations.
Outdoor areas are influenced by atmospheric agents, such as sun, rain, hail, snow, wind, plants
and animals.
In indoor areas, if without heating, the low temperatures must be considered. Indoor areas with
standard ambient conditions, explosion and fire must be considered.
10.8.5 – SELECTION AND INSTALLATION OF ELECTRICAL COMPONENTS
Zone 20
Generally there is a ZONE 20 inside containers, mixers, dryers, hoppers, dust ducts; practically
inside containment systems where part of the dust is suspended in the air.
In these volumes, electrical components are rare; they are control elements such as level sensors,
elements that use intrinsic safety as type of protection.
Zone 21
In the classified volumes with danger of explosion it is preferred not to install electrical
components, but this is not always possible. In the volumes classified as ZONE 21, if it is not
possible to remove all the electrical components, it is better to limit only to ducts and junction
boxes.
Zone 22
In volumes classified as ZONE 22 the electrical components that can be found are junction boxes
and industrial sockets.
Marking
In the examined case the components to install must be marked according to the ATEX Directive
94/9/EC with the following characteristics or one that indicates a higher protection level.
Among the different factors to consider there is the ignition temperature of the cloud, that is
different according to the type of material:
− for the cocoa the T of the marking can be 480 °C
− for the rice 300 °C
− for the sugar the following table must be reported
151
in a ZONE 21 caused by sugar dust
in a ZONE 22 caused by sugar dust
II 2D Ex-tb IIIB T200 °C Db
II 3D Ex-tc IIIB T200°C Dc
II
places with presence of explosive atmosphere
different from the mines
II
places with presence of explosive atmosphere
different from the mines
2
equipment designed to operate in conformity
with the parameters established and
guarantee a high protection level
3
equipment designed to operate in conformity
with the parameters established and
guarantee a normal protection level
D
dust
D
dust
tb
protection by enclosure
tc
protection by enclosure
IIIB
non-conductive dust
IIIB
non-conductive dust
T200 °C (note 1)
T200 °C (note 1)
Db
Dc
normal protection level + one fault
normal protection level
note 1) the selection of the maximum surface temperature has been made considering the ignition temperature of a
layer of sugar dust (310 °C) reduced of 75 °C and rounded down.
The following components are recommended and suitable both for ZONE 21 and ZONE 22:
boxes in thermosetting (GRP) TAIS-EX series
II 2D Ex-tb IIIC Db
NOTE: since they are boxes without electrical
devices there is no indication on the maximum
surface temperature
switched sockets with mechanical interlock with
enclosure in antistatic thermosetting (GRP), TAIS-EX
series
II 2D Ex-tb IIIC 115 °C Db IP66
Note: the sockets must be equipped with an interlock and since the dusts are non-conductive the protection rating
must not be less than IP55.
152
Chap.11: PROCEDURE FOR TEMPORARY TESTS
11.1 - GENERALITIES
The evolving of the state of an electrical plant must be constantly monitored to evaluate the
maintaining in time of the characteristics of safety and reliability of the components.
This means that periodic inspections must be performed in order to individuate anomalies or
traces of possible future anomalies; once the potential irregularities have been found,
maintenance has to be guaranteed.
IEC EN 60079-17 standard, article 3.6 - inspection
action comprising careful scrutiny of an item carried out either without dismantling, or
with the addition of partial dismantling as required, supplemented by means such as
measurement, in order to arrive at a reliable conclusion as to the condition of an item.
IEC EN 60079-17, article 3.7 - maintenance
combination of any actions carried out to retain an item in, or restore it to, conditions in
which it is able to meet the requirements of the relevant specification and perform its
required functions.
The reference standard of this topic is the IEC EN 60079-17.
11.2 – INSPECTION AND MAINTENANCE
In the IEC EN 60079-17 there are three different levels of inspection:
− visual
− close
− detailed.
Generally the visual and/or close inspections can be done with equipment under voltage because
this intervention does not jeopardize the type of protection.
The intervention between inspections cannot be standardized; the maintaining in time of the
characteristics of safety and reliability of the components is closely linked to the type of working
done in the factory.
Some industrial processes, because of the products used or the movement of objects difficult to
handle, could cause a quick deterioration to the components of the installation.
To establish the intervention time it is recommended at the beginning a period of six months.
After the first one, verified the deterioration of the equipment and the variation from the previous
inspection, the time can be shifted to one year; in any case the inspection time must not exceed
three years.
Procedure
To ensure that the installations are maintained in satisfying conditions, the procedure is the
following:
153
− perform an inspection of close type (after the first complete inspection)
− after that, it can be evaluated if an increase of the inspection time can be justified
− in any case the inspection time must not be more than three years
− consider if the intervention of skilled personnel is necessary.
Types of inspection
− The initial inspections (the production process is not started yet) must be detailed and on all the
electrical plant. The initial inspections must assess the correspondence with the project.
− The periodic inspections according to the specific cases can be visual, close or detailed. Unless
particular warnings the inspection can be done on samples.
11.3 - INSULATION
For the detailed inspections, the majority of the cases requires that the plant is out of voltage.
In areas that require EPL Gc or Dc (ZONE 2 or ZONE 22) the work can be done taking preventing
measures for a non-hazardous area, but respecting the following safety conditions:
− prepare the maintenance in order to guarantee the absence of sparks that can ignite, during the
working
− the circuits are designed in order to exclude the production of sparks
− the hot surfaces of the equipment cannot create an explosion.
11.4 – EQUIPMENT WITHOUT MARKING
It is not rare that the markings placed on the equipments protected against explosion are missing
or non-legible. On a device installed in places in which the type of working can erase the marking
(for example factories that produce inks or particular resins), additional markings can be placed.
The additional markings must not compromise the integrity of the equipment.
11.5 - DOCUMENTATION
To perform inspection or maintenance skillfully, the documentation of the installation must be
available. The documentation must contain:
− the classification of the area.
− NOTE: the factory plant layout with the indication of the hazardous zones. This document
will allow for the maintainer to locate whether the position of the interventions is inside or
close to a classified area, or if it is in a safe area
− the Equipment Protection Level of the devices (see paragraph 3.2)
− the marking according to the ATEX directive (see paragraph 6.4.2)
− NOTE: if the maintenance requires the replacement of a component damaged or close to
deterioration, this must be compatible with the rest of the installation and in conformity
with the hazardous zone
− the documentation of the component to be maintained
154
−
the manufacturer generally supplies the instructions on how to maintain in order to keep
the conformity with the type of protection of the component
−
register copy of the previous initial and periodic inspections
−
the register will allow to identify the objects already replaced and eventual notes regarding
anomalies for which an intervention has been required. According to the dispositions of the
standard the general conditions of the equipment must be noted in order to plan adequate
corrective measures.
11.6 - PERSONNEL
The personnel in charge of inspection and maintenance of the installation must be skilled. An
approximate maintenance is a high risk for the factory.
Even if skilled, an adequate and continuous training – documented and available – will favour the
preparation of the personnel and decrease consequently the probability of an accidental event.
11.7 – INSPECTION TABLES
The following tables are based on the IEC EN 60079-17 standard.
The aim of these tables is to show the complexity of this activity and the reason for which the
standard requires that the personnel are skilled.
In the standard for each voice of the table additional indications on how to perform the specific
inspection are provided. For this reason, those who intend to try inspections are recommended to
consult the standard.
155
TYPE OF PROTECTION Ex d / Ex e
Periodic inspection according to IEC EN 60079-17 standard
Place:_____________________________ Installation:____________________
(D = Detailed, C = Close, V = Visual – YES = positive inspection, NO = negative inspection)
D = identifies defects such as loosened internal connections
C = identifies defects such as loosened bolts also with the use of stairs and tools
V = identifies defects visible at naked eye without stairs and tools
X = inspection required
GRADE
OF INSPECTION
D
C
V
X
A
GENERAL (ALL EQUIPMENT)
1
Equipment is appropriate to the EPL/Zone requirements of the location
X
X
2
Equipment group is correct
X
X
3
Equipment temperature class is correct
X
X
4
Equipment circuit identification is correct
X
5
Equipment circuit identification is available
X
X
X
X
X
X
X
X
X
X
6
7
Degree of protection (IP grade) of equipment is appropriate for the level of protection/group/
conductivity
There is no evidence of ingress of water or dust in the enclosure in accordance with the IP
rating
X
8
Enclosure, glass parts and glass-to-metal sealing gaskets and/or compounds are satisfactory
X
9
There is no damage or unauthorized modifications
X
10
There is no evidence of unauthorized modifications
11
Bolts, cable entry devices (direct and indirect) and blanking elements are of the correct type
and are complete and tight
Physical check
X
X
Visual check
12
Joint surfaces are clean and undamaged and gaskets, if any, are satisfactory and positioned
correctly (only for Ex d)
X
X
Only for Ex d
Dimensions of flanged joint gaps are:
13
- within the limits in accordance with manufacturer’s documentation or
X
X
- within maximum values permitted by relevant construction standard at time of installation or
- within maximum values permitted by site documentation
14
15
16
Only for Ex e
Electrical connections are tight
Only for Ex e
Unused terminals are tightened
Only for Ex e
Flameproof components are undamaged
X
X
X
B
LIGHTING EQUIPMENT
1
Only for Ex e – Fluorescent lamps are not indicating EOL effects
X
X
X
2
HID lamps are not indicating EOL effects
X
X
X
3
Lamp type, rating, pin configuration and position are correct
X
156
RESULT
YES
NO
?
X = inspection required
GRADE
OF INSPECTION
C
1
D
C
V
X
X
X
X
X
Motor fans have sufficient clearance to the enclosure and/or covers, cooling systems are
undamaged, motor foundations have no indentations or cracks
The ventilation airflow is not impeded
X
3
Insulation resistance (IR) of the motor windings is satisfactory
X
D
INSTALLATION
1
Type of cable is appropriate
X
2
There is no obvious damage to cables
X
X
X
3
Sealing of trunking, ducts, pipes and/or conduits is satisfactory
X
X
X
X
X
X
5
6
Only for Ex d
Stopping boxes and cable boxes are correctly filled
Integrity of conduit system and interface with mixed system maintained
X
X
sfactory (for example connections are tight and conductors are of sufficient cross-section)
X
Visual check
7
Fault loop impedance (TN systems) or earthing resistance (IT systems) is satisfactory
X
8
Insulation resistance is satisfactory
X
9
Automatic electrical protective devices operate within permitted limits
X
10
Automatic electrical protective devices are set correctly (auto-reset not possible)
X
11
Specific conditions of use (if applicable) are complied with
X
12
Cables not in use are correctly terminated
X
13
Obstructions adjacent to flameproof flanged joints are in accordance with IEC 60079-14
X
X
14
Variable voltage/frequency installation complies with documentation
X
X
E
HEATING SYSTEMS
1
Temperature sensors function according to manufacturer’s documents
X
2
Safety cut off devices function according to manufacturer’s documents
X
3
The setting of the safety cut off is sealed
X
X
4
Automatic recovery is not possible
X
X
5
Reset of a heating system safety cut off possible with tool only
X
6
Safety cut off independent from control system
X
7
Level switch is installed and correctly set, if required
X
8
Flow switch is installed and correctly set, if required
X
F
MOTORS
G
1
2
NO
Earthing connections, including any supplementary earthing bonding connections are satiPhysical check
1
YES
?
MOTORS
2
4
RESULT
Only for Ex e
Motor protection devices operate within the permitted tE or tA time limits
X
ENVIRONMENT
Equipment is adequately protected against corrosion, weather, vibration and other adverse
factors
No undue accumulation of dust and dirt
X
X
X
X
X
X
157
TYPE OF PROTECTION Ex n
Periodic inspection according to IEC EN 60079-17 standard
Place:_____________________________ Installation:____________________
(D = Detailed, C = Close, V = Visual – YES = positive inspection, NO = negative inspection)
D = identifies defects such as loosened internal connections
C = identifies defects such as loosened bolts also with the use of stairs and tools
V = identifies defects visible at naked eye without stairs and tools
X = inspection required
GRADE
OF INSPECTION
D
C
V
X
A
ELECTRICAL EQUIPMENT
1
Equipment is appropriate to the EPL/Zone requirements of the location
X
X
2
Equipment group is correct
X
X
3
Equipment temperature class is correct
X
X
4
Equipment circuit identification is correct
X
5
Equipment circuit identification is available
X
X
X
X
X
X
X
X
X
X
6
Degree of protection (IP grade) of equipment is appropriate for the level of protection/group/
conductivity
7
There is no evidence of ingress of water or dust in the enclosure in accordance with the IP rating
X
8
Enclosure, glass parts and glass-to-metal sealing gaskets and/or compounds are satisfactory
X
9
There is no damage or unauthorized modifications
X
10
There is no evidence of unauthorized modifications
11
Bolts, cable entry devices (direct and indirect) and blanking elements are of the correct type
and are complete and tight
Physical check
X
X
Visual check
X
12
Electrical connections are tight
X
13
Unused terminals are tightened
X
14
Enclosed-break and hermetically sealed devices are undamaged
X
15
Encapsulated components are undamaged
X
16
Restricted breathing enclosure is satisfactory – (type “nR” only)
X
17
Test port, if fitted, is functional– (type “nR” only)
X
18
Breathing operation is satisfactory– (type “nR” only)
X
19
Breathing and draining devices are satisfactory
X
X
B
LIGHTING EQUIPMENT
1
Fluorescent lamps are not indicating EOL effects
X
X
X
2
HID lamps are not indicating EOL effects
X
X
X
3
Lamp type, rating, pin configuration and position are correct
X
C
MOTORS
X
X
X
X
X
1
Motor fans have sufficient clearance to the enclosure and/or covers, cooling systems are undamaged, motor foundations have no indentations or cracks
2
The ventilation airflow is not impeded
X
3
Insulation resistance (IR) of the motor windings is satisfactory
X
158
RESULT
YES
NO
?
X = inspection required
GRADE
OF INSPECTION
D
C
V
D
INSTALLATION
1
Type of cable is appropriate
X
2
There is no obvious damage to cables
X
X
X
3
Sealing of trunking, ducts, pipes and/or conduits is satisfactory
X
X
X
4
Integrity of conduit system and interface with mixed system maintained
X
X
X
5
X
6
Fault loop impedance (TN systems) or earthing resistance (IT systems) is satisfactory
X
7
Insulation resistance is satisfactory
X
8
Automatic electrical protective devices operate within permitted limits
X
9
Automatic electrical protective devices are set correctly (auto-reset not possible)
X
10
Specific conditions of use (if applicable) are complied with
X
11
Cables not in use are correctly terminated
X
12
Variable voltage/frequency installation complies with documentation
X
X
X
X
X
X
X
X
2
NO
sfactory (for example connections are tight and conductors are of sufficient cross-section)
Visual check
1
YES
?
Earthing connections, including any supplementary earthing bonding connections are satiPhysical check
E
RESULT
ENVIRONMENT
Equipment is adequately protected against corrosion, weather, vibration and other adverse
factors
No undue accumulation of dust and dirt
Observations________________________________________________________________________________________________________________________
___________________________________________________________________________________________________________________________________
___________________________________________________________________________________________________________________________________
Date_______________________________Inspector________________________________________________________________________________________
159
TYPE OF PROTECTION Ex t
Periodic inspection according to IEC EN 60079-17 standard
Place:_____________________________ Installation:____________________
(D = Detailed, C = Close, V = Visual – YES = positive inspection, NO = negative inspection)
D = identifies defects such as loosened internal connections
C = identifies defects such as loosened bolts also with the use of stairs and tools
V = identifies defects visible at naked eye without stairs and tools
X = inspection required
GRADE
OF INSPECTION
D
C
V
X
A
ELECTRICAL EQUIPMENT
1
Equipment is appropriate to the EPL/Zone requirements of the location
X
X
2
Equipment group is correct
X
X
3
Equipment maximum surface temperature is correct
X
X
4
Equipment circuit identification is correct
X
5
Equipment circuit identification is available
X
X
X
X
X
X
X
X
X
X
6
7
Degree of protection (IP grade) of equipment is appropriate for the level of protection/group/
conductivity
There is no evidence of ingress of water or dust in the enclosure in accordance with the IP
rating
X
8
Enclosure, glass parts and glass-to-metal sealing gaskets and/or compounds are satisfactory
X
9
There is no damage or unauthorized modifications
X
10
There is no evidence of unauthorized modifications
11
Bolts, cable entry devices (direct and indirect) and blanking elements are of the correct type
and are complete and tight
Physical check
X
X
Visual check
X
12
Electrical connections are tight
B
LIGHTING
1
Fluorescent lamps are not indicating EOL effects
X
X
X
2
HID lamps are not indicating EOL effects
X
X
X
3
Lamp type, rating, pin configuration and position are correct
X
C
MOTORS
X
X
X
X
X
1
Motor fans have sufficient clearance to the enclosure and/or covers, cooling systems are
undamaged, motor foundations have no indentations or cracks
X
2
The ventilation airflow is not impeded
X
3
Insulation resistance (IR) of the motor windings is satisfactory
X
160
RESULT
YES
NO
?
X = inspection required
GRADE
OF INSPECTION
D
C
V
D
INSTALLATION
1
Type of cable is appropriate
X
2
There is no obvious damage to cables
X
X
X
3
Sealing of trunking, ducts, pipes and/or conduits is satisfactory
X
X
X
4
Integrity of conduit system and interface with mixed system maintained
X
X
X
5
NO
sfactory (for example connections are tight and conductors are of sufficient cross-section)
X
Visual check
6
Fault loop impedance (TN systems) or earthing resistance (IT systems) is satisfactory
X
7
Insulation resistance is satisfactory
X
8
Automatic electrical protective devices operate within permitted limits
X
9
Automatic electrical protective devices are set correctly (auto-reset not possible)
X
10
Specific conditions of use (if applicable) are complied with
X
11
Cables not in use are correctly terminated
X
12
Variable voltage/frequency installation complies with documentation
X
E
HEATING SYSTEMS
1
Temperature sensors function according to manufacturer’s documents
X
2
Safety cut off devices function according to manufacturer’s documents
X
F
ENVIRONMENT
2
YES
?
Earthing connections, including any supplementary earthing bonding connections are satiPhysical check
1
RESULT
Equipment is adequately protected against corrosion, weather, vibration and other adverse
factors
No undue accumulation of dust and dirt
X
X
X
X
X
X
X
Observations________________________________________________________________________________________________________________________
___________________________________________________________________________________________________________________________________
___________________________________________________________________________________________________________________________________
Date_______________________________Inspector________________________________________________________________________________________
161
TYPE OF PROTECTION Ex i
Periodic inspection according to IEC EN 60079-17 standard
Place:_____________________________ Installation:___________________
(D = Detailed, C = Close, V = Visual – YES = positive inspection, NO = negative inspection)
D = identifies defects such as loosened internal connections
C = identifies defects such as loosened bolts also with the use of stairs and tools
V = identifies defects visible at naked eye without stairs and tools
X = inspection required
GRADE
OF INSPECTION
D
C
A
ELECTRICAL EQUIPMENT
1
Circuit and/or equipment documentation is appropriate to the EPL/Zone
X
X
2
Equipment installed is that specified in the documentation
X
X
3
Circuit and/or equipment category and group correct
X
X
4
IP rating of equipment is appropriate to the Group III material present
X
X
5
Equipment temperature class is correct
X
X
6
Installation is clearly labelled
X
X
7
There are no unauthorized modifications
X
8
There is no evidence of unauthorized modifications
V
X
X
X
X
Diode safety barriers, galvanic isolators, relays and other energy limiting devices are of the
9
approved type, installed in accordance with the certification requirements and securely ear-
X
thed where required
10
Electrical connections are tight
X
11
Printed circuit boards are clean and undamaged
X
12
The ambient temperature variation field and the equipment operating temperature is correct for
the installation
X
X
13
Condition of enclosure gaskets is satisfactory
X
14
The maximum voltage Um of the associated apparatus is not exceeded
X
B
INSTALLATION
1
Cables are installed in accordance with the documentation
X
2
Cable screens are earthed in accordance with the documentation
X
3
There is no obvious damage to cables
X
X
X
4
Sealing of trunking, ducts, pipes and/or conduits is satisfactory
X
X
X
5
Point-to-point connections are all correct (initial inspection only)
X
X
X
X
X
6
Earth continuity is satisfactory (e.g. connections are tight, conductors are of sufficient crosssection) for non-galvanically isolated circuits
X
7
Earth connections maintain the integrity of the type of protection
X
8
Intrinsically safe circuit earthing is satisfactory
X
9
Insulation resistance is satisfactory
X
10
Separation is maintained between intrinsically safe and non-intrinsically safe circuits in common distribution boxes or relay cubicles
X
11
Short-circuit protection of the power supply is in accordance with the documentation
X
12
Specific conditions of use (if applicable) are complied with
X
13
Cables not in use are correctly terminated
X
162
RESULT
YES
NO
?
X = inspection required
GRADE
OF INSPECTION
D
C
1
2
C
V
X
X
RESULT
YES
?
NO
ENVIRONMENT
Equipment is adequately protected against corrosion, weather, vibration and other adverse
factors
No undue accumulation of dust and dirt
X
X
Observations________________________________________________________________________________________________________________________
___________________________________________________________________________________________________________________________________
___________________________________________________________________________________________________________________________________
Date_______________________________Inspector________________________________________________________________________________________
163
GLOSSARY
Combustibility
The dust combustibility is an attitude to burn in layer and is determined through
laboratory tests.
Combustive agent
It is an oxidative agent, usually oxygen present in the air.
EPL
ATEX Equipment Protection Level.
ESR
Essential Safety Requirements that ATEX equipments have to respect in order to be
used in hazardous areas.
Explosibility
The dust explosibility is its capacity to explode in a cloud and is verified through
laboratory tests.
Flash point
The lowest temperature at which a liquid can generate vapours in such a quantity
as to generate an explosion.
Fuel
Substances in the form of gas, vapour, fog or dust.
Ignition sources
Any event (spark, flame, temperature, etc.) that is a source of energy.
IT
Ignition Temperature is the minimum temperature of a hot surface at which it can
ignite.
LEL
Lower Explosion Level: concentration of gas, vapour or dust, below which the
atmosphere is not explosive.
MIE
Minimum Ignition Energy: quantity of minimum energy that can ignite an explosive
atmosphere.
SE
Sources of Emission: each point of an installation from which an inflammable
substance can be emitted and mix with air in standard environmental conditions.
Temperature of autoignition
The temperature of autoignition is the lowest temperature at which the combustiblecombustive mixture needs to be brought, so it ignites itself automatically.
UEL
Upper Explosion Level: concentration of gas, vapour or dust, over which the
atmosphere is not explosive.
164
ATEX 2015-2016
SOLUTIONS FOR EXPLOSIVE ATMOSPHERES
ZONES 1-2 GAS, 21-22 DUST
168
catalogo ATEX 2015
SOLUZIONI PER ATMOSFERA ESPLOSIVA
Palazzoli range for ATEX zones
GAS
Industrial plugs in antistatic material
CEE-EX
for zones
2-21-22
Interlocked sockets in antistatic thermosetting (GRP)
TAIS-EX
for zones
2-21-22
JUNCTION
Boxes in antistatic thermosetting (GRP)
Boxes in aluminium alloy
CONTROL - SIGNALLING
Cable glands and adaptors
ALUPRES-EX
for zones
1-2-21-22
UNI-EX
for zones
1-2-21-22
Rotary control devices in aluminium alloy
CAM-EX
for zones
2-21-22
Sirens and bells
ALARM-EX
for zones
2-21-22
Oval and round bulkhead lamps in aluminium alloy
Lighting fixtures in stainless steel
SOLUTIONS FOR EXPLOSIVE ATMOSPHERES
TAIS-EX
for zones
1-2-21-22
CAM-EX
for zones
2-21-22
Small control devices in aluminium alloy
ATEX catalogue book 2015-2016
ZONE 22
ALUPRES-EX
for zones
2-21-22
Rotary control devices in antistatic thermosetting (GRP)
Small control devices in antistatic thermosetting (GRP)
ZONE 21
TAIS MIGNON-EX
for zones
2-22
RONDO’-EX
for zones
2-22
RINO-EX
for zones
2-21-22
RINO-EX
for zones
1-2-21-22
Palazzoli S.p.A. Via F. Palazzoli, 31 - 25128 Brescia - Italy - Tel. +39 030 2015.1 - Fax +39 030 2015.258 - www.palazzoli.com - [email protected]
SOLUTIONS FOR EXPLOSIVE ATMOSPHERES 2015-2016
Interlocked sockets in aluminium alloy
LIGHTING
ZONE 2
55556
POWER SUPPLY
ZONE 1
DUST
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertisement