Product Bulletin
Hazardous Area Classifications
9.2:001
June 2012
D103222X012
Hazardous Area Classifications and
Protections
The intent of this document is to provide a broad
overview of hazardous area classifications and the
types of protection techniques involved. The
information provided in this bulletin is for educational
purposes and should not be used in place of any other
source or governing documents.
Not all approvals are covered in this bulletin. Contact
your Emerson Process Management sales office for
information on approvals not covered in this bulletin.
Contact your Emerson Process Management sales
office for product specific hazardous area approval
information or visit our website at www.Fisher.com.
1. Class—The Class defines the general nature (or
properties) of the hazardous material in the
surrounding atmosphere which may or may not be in
sufficient quantities.
a. Class I—Locations in which flammable gases or
vapors may or may not be in sufficient quantities to
produce explosive or ignitable mixtures.
b. Class II—Locations in which combustible dusts
(either in suspension, intermittently, or
periodically) may or may not be in sufficient
quantities to produce explosive or ignitable
mixtures.
c. Class III—Locations in which ignitable fibers may
or may not be in sufficient quantities to produce
explosive or ignitable mixtures.
Hazardous Area
Classifications
When electrical equipment is used in, around, or near
an atmosphere that has flammable gases or vapors,
flammable liquids, combustible dusts, ignitable fibers
or flyings, there is always a possibility or risk that a fire
or explosion might occur. Those areas where the
possibility or risk of fire or explosion might occur due
to an explosive atmosphere and/or mixture is often
called a hazardous (or classified) location/area.
Currently there are two systems used to classify these
hazardous areas; the Class/Division system and the
Zone system. The Class/Division system is used
predominately in the United States and Canada,
whereas the rest of the world generally uses the Zone
system.
2. Division—The Division defines the probability of the
hazardous material being able to produce an explosive
or ignitable mixture based upon its presence.
a. Division 1 indicates that the hazardous material
has a high probability of producing an explosive or
ignitable mixture due to it being present
continuously, intermittently, or periodically or from
the equipment itself under normal operating
conditions.
b. Division 2 indicates that the hazardous material
has a low probability of producing an explosive or
ignitable mixture and is present only during
abnormal conditions for a short period of time.
3. Group—The Group defines the type of hazardous
material in the surrounding atmosphere. Groups A, B,
C, and D are for gases (Class I only) while groups E, F,
and G are for dusts and flyings (Class II or III).
a. Group A—Atmospheres containing acetylene.
Class/Division System
Hazardous locations per the Class/Division system are
classified according to the Class, Division, and Group.
www.Fisher.com
b. Group B—Atmospheres containing a flammable
gas, flammable liquid-produced vapor, or
combustible liquid-produced vapor whose MESG is
less than 0.45 mm or MIC ratio is less than 0.40.
Product Bulletin
Hazardous Area Classifications
9.2:001
June 2012
Typical gases include hydrogen, butadiene,
ethylene oxide, propylene oxide, and acrolein.
c. Group C—Atmospheres containing a flammable
gas, flammable liquid-produced vapor, or
combustible liquid-produced vapor whose MESG is
greater than 0.45 mm but less than 0.75 mm or
MIC ratio is greater than 0.40 but less than 0.80.
Typical gases include ethyl either, ethylene,
acetaldehyde, and cyclopropane.
d. Group D—Atmospheres containing a flammable
gas, flammable liquid-produced vapor, or
combustible liquid-produced vapor whose MESE is
greater than 0.75 mm or MIC ration is greater than
0.80. Typical gases include acetone, ammonia,
benzene, butane, ethanol, gasoline, methane,
natural gas, naphtha, and propane.
c. Zone 2—Ignitable concentrations of flammable
gases or vapors which are not likely to occur under
normal operating conditions and do so only for a
short period of time.
Group—Electrical equipment used in gas atmospheres
is divided into two groups.
n Group I—Equipment used in mines with
atmospheres containing methane or gases and
vapors of equivalent hazard.
n Group II—All other equipment; which is further
subdivided into three subgroups.
- Group IIA—Atmospheres containing
propane, or gases and vapors of equivalent
hazard.
e. Group E—Atmospheres containing combustible
metal dusts such as aluminum, magnesium, and
their commercial alloys.
- Group IIB—Atmospheres containing
ethylene, or gases and vapors of equivalent
hazard.
f. Group F—Atmospheres containing combustible
carbonaceous dusts with 8% or more trapped
volatiles such as carbon black, coal, or coke dust.
- Group IIC—Atmospheres containing
acetylene or hydrogen, or gases and vapors of
equivalent hazard.
g. Group G—Atmospheres containing combustible
dusts not included in Group E or Group F. Typical
dusts include flour, starch, grain, wood, plastic, and
chemicals.
Zone System
Hazardous locations per the Zone system are classified
according to its Zone which can be gas or dust. For gas
atmospheres electrical equipment is further divided
into Groups and Subgroups.
Zone—The Zone defines the probability of the
hazardous material, gas or dust, being present in
sufficient quantities to produce explosive or ignitable
mixtures.
1. Gas
a. Zone 0—Ignitable concentrations of flammable
gases or vapors which are present continuously or
for long periods of time.
b. Zone 1—Ignitable concentrations of flammable
gases or vapors which are likely to occur under
normal operating conditions.
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D103222X012
2. Dust
a. Zone 20—An area where combustible dusts or
ignitable fibers and flyings are present continuously
or for long periods of time.
b. Zone 21—An area where combustible dusts or
ignitable fibers and flyings are likely to occur under
normal operating conditions.
c. Zone 22—An area where combustible dusts or
ignitable fibers and flyings are not likely to occur
under normal operating conditions and do so only
for a short period of time.
Protection Techniques and
Methods
Various protection techniques and methods have been
developed and employed, thus reducing or minimizing
the potential risks of explosion or fire from electrical
equipment located in hazardous locations. Not all
methods are listed.
Hazardous Area Classifications
Product Bulletin
9.2:001
June 2012
D103222X012
Class/Division system
n Explosion-proof—A type of protection that utilizes
an enclosure that is capable of withstanding an
explosive gas or vapor within it and or preventing
the ignition of an explosive gas or vapor that may
surround it and that operates at such an external
temperature that a surrounding explosive gas or
vapor will not be ignited thereby.
n Intrinsically Safe—A type of protection in which the
electrical equipment under normal or abnormal
conditions is incapable of releasing sufficient
electrical or thermal energy to cause ignition of a
specific hazardous atmospheric mixture in its most
easily ignitable concentration.
n Intrinsically Safe—A type of protection in which the
electrical equipment under normal or abnormal
conditions is incapable of releasing sufficient
electrical or thermal energy to cause ignition of a
specific hazardous atmospheric mixture in its most
easily ignitable concentrations. This type of
protection is referred to as “Ex i”.
n Increase Safety—A type of protection in which
various measures are applied to reduce the
probability of excessive temperatures and the
occurrence of arcs or sparks in the interior and on
the external parts of electrical apparatus that do not
produce them in normal service. Increased safety
may be used with flame-proof type of protection.
This type of protection is referred to as “Ex e”.
n Dust Ignition-proof—A type of protection that
excludes ignitable amounts of dust or amounts that
might affect performance or rating and that, when
installed and protected in accordance with the
original design intent, will not allow arcs, sparks or
heat otherwise generated or liberated inside the
enclosure to cause ignition of exterior
accumulations or atmospheric suspensions of a
specified dust.
n Type n—A type of protection applied to electrical
equipment such that in normal operation it is not
capable of igniting a surrounding explosive
atmosphere. This type of protection is referred to as
“Ex n”.
n Non-incendive—A type of protection in which the
equipment is incapable, under normal conditions,
of causing ignition of a specified flammable gas or
vapor-in-air mixture due to arcing or thermal effect.
Zone system
n Flame-proof—A type of protection in which an
enclosure can withstand the pressure developed
during an internal explosion of an explosive mixture
and that prevents the transmission of the explosion
to the explosive atmosphere surrounding the
enclosure and that operates at such an external
temperature that a surrounding explosive gas or
vapor will not be ignited there. This type of
protection is referred to as “Ex d”.
Temperature Code
(T Code)
A mixture of hazardous gases and air may be ignited by
coming into contact with a hot surface. The conditions
under which a hot surface will ignite a gas depends on
surface area, temperature, and the concentration of
the gas. The same can be said about combustible
dusts. The T code of a product denotes the maximum
surface temperature that a given product will not
exceed under a specified ambient temperature. For
example, a product with a T code of T3 means that its
maximum surface temperature will not exceed 200_C
provided it is operated in a ambient temperature
defined by the manufacturer.
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Product Bulletin
Hazardous Area Classifications
9.2:001
June 2012
D103222X012
Table 1. Approval Agencies
Approvals(1)
Approval Agencies Used(2)
Approvals Accepted
FM
FM—Factory Mutual
North America
CSA
CSA—Canadian Standards Association
North America
ATEX
Baseefa—British Approvals Service for Electrical Equipment in Flammable Atmospheres
KEMA—NV tot Keuring van Elektrotechnische Materialen
LCIE—Laboratorie Central des Industries Electriques
European Union
IECEx
CSA—Canadian Standards Association
Baseefa—British Approvals Service for Electrical Equipment in Flammable Atmospheres
International
SAA
SAA—Standards Association of Australia
NEPSI
TIIS
INMETRO
GOST-R
Australia
NEPSI—National Supervision and Inspection Centre for Explosion Protection and Safety of
Instrumentation
China
TIIS—Technology Institution of Industrial Safety
Japan
INMETRO—National Institute of Metrology, Standardization and Industrial Quality
Brazil
GOST—GOSSTANDART
Russia
1. Fisherr products may carry additional approvals. Contact your Emerson Process Management sales office for additional approval information.
2. Fisher product approvals may be certified by other agencies. Contact your Emerson Process Management sales office for additional information.
Nomenclature
Class/Division system
Approved equipment is marked according to which
Class (I, II, or III), Division (1 or 2), Group (A, B, C, D, E,
F, or G), and temperature code (T1 through T6) that it
is rated for. For intrinsically safe equipment the words
“Intrinsically Safe” or “IS” will precede the actual
approval marking to indicate it as being intrinsically
safe. Examples are listed below:
Class I Division 1 Group B,C,D T5
CL I Div 2 GP ABCD T5
IS CL I,II,III Div 1 GP ABCDEFG
CL II,III Div 1,2 GP EFG T4
Zone system
Approved equipment is marked according to the
protection concept for which it has been designed (Ex
i, Ex d, Ex n, and etc.), the gas group (I, IIA, IIB, or IIC),
and temperature code (T1 through T6) that it is rated
for. For the United States it will be preceded by which
Class and Zone it is approved for. Examples are listed
below:
Ex ia IIC T5
Ex d IIB+H2 T6
Ex nA IIC T6
Class I Zone 2 AEx nC IIC T5
4
Additional Terminology
Although the following terminology is not permitted
for markings it is commonly used to describe the
various types of approvals or when speaking of them.
XP—Flameproof approval for Class I Division 1
EXP—Flameproof approval for Class I Division 1
NI—Non-incendive approval for Class I Division 2
DIP—Dust Ignition Proof approval for Class II
Division 1
S—“Suitable For” for Class II Division 2
IS—Intrinsically Safe
Approval Agencies
Generally speaking, most countries require that
products intended for installation in a hazardous
location be approved by a recognized authority or
approval agency (governmental or independent)
which that country has established by various laws,
regulations, or codes. See table 1 for an overview of
approvals and approval agencies.
North American Approvals
Of the 15 national testing laboratories (NRTL's) in the
United States, only a few are qualified to approve
products for use in hazardous locations. Two such
agencies are; Factory Mutual (FM) and Underwriters
Laboratories (UL). In Canada, products are approved by
the Canadian Standards Association (CSA).
Hazardous Area Classifications
Product Bulletin
9.2:001
June 2012
D103222X012
European Approvals
International Approvals
Each country belonging to the European Union has
established one or more “Notified Bodies” for product
approval. Notified Bodies not only approve products
for use within their own country, commonly called
national certifications/approvals, but also for any other
country within the union, known as CENELEC
certifications/approvals. CENELEC is the acronym for
European Committee for Electrotechnical
Standardization. A product which has been CENELEC
certified or approved by any of the Notified Bodies is
automatically accepted for use within all of the
participating union countries. In July 2003 a European
Directive, called the ATEX Directive, which pertains to
equipment for explosive atmospheres, was adopted.
All equipment intended for use in explosive
atmospheres must comply with the ATEX Directive in
order to be sold into the European Union.
Countries participating in the IECEx Scheme
(International Electrotechnical Commission on
explosion protected equipment, known as “Ex”) can
issue either an international certification or a national
certification of explosion protected equipment. Each
country within the IECEx scheme establishes an ExCB
(Ex Certification Body) which can approve products.
ExCB's can issue the national certification for their
country based upon the IECEx standards (including any
national deviations) and the international certification.
Currently, Australia is the only country accepting
international certifications for use in their country.
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Product Bulletin
Hazardous Area Classifications
9.2:001
June 2012
D103222X012
Figure 1. Typical I.S Installation
HAZARDOUS AREA
DVC6010
NON-HAZARDOUS AREA
I.S. BARRIER
Vmax = 30 VDC
Imax = 226 mA
Pi = 1.4 W
Ci = 5 nF
Li = 0.55 mH
Voc = ?
Isc = ?
Ca = ?
La = ?
FIELD COMMUNICATOR
Voc = 1.9 VDC
Vmax = 30 VDC
Isc = 32 μA
Imax = 200 mA
Po = 61 μW
Pi = 1 W
Ca = 100 μF
Ci = 0 μF
La = 5600 mH
Li = 0 mH
Guidelines for Selecting
Intrinsic Safety Barriers
Using Entity Ratings
The values Voc, Ioc, Ca, and La are specified by the
barrier manufacturer for any given barrier. The values
of Ccable and Lcable for the signal cable must be
determined for the specific cable used.
Selecting an intrinsic safety barrier with the required
entity ratings depends upon the combined effects of
the instrument, its cabling, and any instrument
accessories such as the 475 Field Communicator.
Determine the barrier entity ratings using the
following guidelines:
A system is comprised of a FIELDVUEr DVC6010 digital
valve controller (FM approved), a Field Communicator
(FM approved), and 1000 feet of cable with 60 pF/ft
capacitance and 0.2 μH/ft inductance. Calculate the
barrier entity ratings.
Voc ≤ Vmax
Isc ≤ Imax
Ca ≥ Ci + Ccable
La ≥ Li + Lcable
where:
Example barrier entity ratings calculation.
Figure 1 shows a typical I.S. installation.
Calculate Ccable and Lcable
Ccable = 60 pF/ft x 1000 ft
= 60 nF
Lcable = 0.2 μH/ft x 1000 ft
Voc = Barrier open circuit voltage
= 0.2 mH
Vmax = Instrument Vmax
Determine Ca and La for the barrier
Isc= Barrier short circuit current
Ca w Ci(DVC6010)+ Ci(475) + Ccable
Imax = Instrument Imax
Ca = Barrier acceptable connected capacitance
Ci = Instrument total unprotected internal capacitance
Ccable = Signal cable total capacitance
w 5 nF + 0 nF + 60 nF
Ca w 65 nF
La = Barrier acceptable connected inductance
La w Li(DVC6010)+Li(475) + Lcable
Li = Instrument total unprotected internal inductance
w 0.55 mH + 0 mH + 0.2 mH
Lcable = Signal cable total inductance
La w 0.75 mH
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Product Bulletin
Hazardous Area Classifications
9.2:001
June 2012
D103222X012
Determine Voc and Isc of the barrier. Note that in this
example the output of the 475 (Voc(475) and Isc(475))
must also be considered because it can also add
energy to the loop besides just the barrier itself. Voc of
the barrier plus any additional voltage that could be
added to the loop from each device must be
subtracted from Vmax for each device. Isc of the barrier
plus any additional current that could be added to the
loop from each device must not exceed Imax for each
device.
Isc of the barrier must meet all of the following
conditional requirements.
Voc of the barrier must meet all of the following
conditional requirements.
3) Isc v Imax(475) 200 mA
1) Voc v Vmax(DVC6010) - Voc(375) 30 VDC - 1.9 VDC
28.1 VDC
Isc v 200 mA
1) Isc v Imax(DVC6010) + Isc(475) 226 mA +
0.032 mA 226.032 mA
2) Isc v Imax(DVC6010) 226 mA
2) Voc v Vmax(DVC6010) 30 VDC
3) Voc v Vmax(475) 30 VDC
Voc v 28.1 VDC
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Product Bulletin
9.2:001
June 2012
Hazardous Area Classifications
D103222X012
Neither Emerson, Emerson Process Management, nor any of their affiliated entities assumes responsibility for the selection, use or maintenance
of any product. Responsibility for proper selection, use, and maintenance of any product remains solely with the purchaser and end user.
Fisher and FIELDVUE are marks owned by one of the companies in the Emerson Process Management business unit of Emerson Electric Co. Emerson Process
Management, Emerson, and the Emerson logo are trademarks and service marks of Emerson Electric Co. All other marks are the property of their respective
owners.
The contents of this publication are presented for informational purposes only, and while every effort has been made to ensure their accuracy, they are not
to be construed as warranties or guarantees, express or implied, regarding the products or services described herein or their use or applicability. All sales are
governed by our terms and conditions, which are available upon request. We reserve the right to modify or improve the designs or specifications of such
products at any time without notice.
Emerson Process Management
Marshalltown, Iowa 50158 USA
Sorocaba, 18087 Brazil
Chatham, Kent ME4 4QZ UK
Dubai, United Arab Emirates
Singapore 128461 Singapore
www.Fisher.com
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8 2006, 2012 Fisher Controls International LLC. All rights reserved.
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