In order to undertake the process of designing a fire system for
a building it is necessary to have a sound understanding of the
relevant design standards, the legal framework surrounding
building safety legislation and a sound working knowledge of
product application theory. The importance of consultation with all
relevant parties cannot be over stressed, neither can the
importance of specialist advice in relevant areas. The following
system design process is intended to give a reasonable overview
of all the areas of knowledge required for the successful design of
a fire alarm system.
It is envisaged that the user will refer to the information contained
within the design section to determine the areas where further
detailed advice will be required and to give guidance as to where
such advice may be contained.
Due to the complex nature of legislation and design standards
relating to fire alarm system design, this design guide is not
intended to be a comprehensive guide to all aspects of fire alarm
design but rather a very useful source of background information
to which further application specific detailed information can be
added from other sources as required.
The standards referred to in this section relate to the UK and
Europe. Although the principles are broadly universal, it is
recommended for readers in other countries that they familiarise
themselves with specific local requirements from their own
standards, only using the British or European standards where
these have been accepted by local fire authorities. Information
relating to equipment facilities and performance apply to Cooper
Lighting and Security equipment and may not necessarily apply to
other manufacturers equipment. The reader should carefully check
whether such comments relate to equipment from other
manufacturers before considering alternative equipment.
Technical - Fire System Design Guide
The following describes a typical fire alarm system design process,
after each item a section number is provided which relates to the
area within the design guide where further information can be
• Understand the reasons for installing the fire alarm system in the
specific property (section 1)
• Conduct a risk assessment to help determine requirements
(section 2)
• Consult with all interested parties (section 3)
• Decide on the relevant design standard (section 4)
• Establish if third party approval is required - for equipment and
/or installation.
• Decide on the type of alarm technology to be used
(see pages 16-20)
• Decide on the appropriate protection category and extent of
coverage where relevant (section 5)
• Discuss and agree the fire strategy (section 6)
• Plan the zoning of the building (section 6)
• Select and position relevant system components (section 7)
- Select the appropriate detectors for each area
- Position the detectors
- Select suitable callpoints and position at appropriate
- Agree on the means of summoning the fire authority
- Plan the alarm signalling arrangements (sounders, beacons,
pagers etc)
• Select a suitable panel (suitably sized and rated with
adequate standby autonomy)
Review the design such as to - minimise the potential for false
alarms (section 8)
Select Contractor
Ensure suitable wiring of the system (section 9)
Make suitable arrangements for commissioning (section 10)
Appoint/Establish responsible person (section 11)
Make suitable arrangements for ongoing maintenance and
monitoring of system performance (section 11)
The following section contains details of European legislation which
relates mainly to legal requirements placed on the manufacturer or
importer of equipment. The description is included here to give the
user/specifier an understanding of the subject.
The EMC directive requires that all electrical and electronic
equipment is able to co-exist without interference. There are two
basic levels, which relate to the type of environment, industrial
and commercial/light industrial. The industrial level allows
equipment to emit more electrical noise taking into account the
problem of containing electrical noise in large electrical machines.
EMC standards are continually evolving as communication
equipment becomes more sophisticated and measurement
techniques improve.
In principle Fire Alarm equipment must emit low levels of noise but
be able to withstand high levels, so that it can be used in all
applications. To that end a product family standard, EN50130-4
has been published to cover alarm equipment susceptibility and the
commercial/light industrial generic standard is used for emissions.
The Low Voltage Directive requires that all electrical equipment
connected to low voltage supplies (up to 1000V) must be safe.
Various standards are published relating to different types of
equipment but the general standard EN60950 is applied to fire
detection and alarm equipment.
Most items in commercial fire detection systems are designed to
work at Extra Low Voltage (24V) and so the LVD does not apply,
the exceptions being fire alarm panels, mains rated relays or
interfaces and other items of equipment connected to the mains
supply such as door closers, smoke vents etc.
The Construction Products Directive relates to building materials
and equipment fixed to the structure of the building. One section
of the directive relates to Safety In Case Of Fire and mandate
109 requires that all fire detection and alarm equipment is
third party certified to the relevant Harmonised European standard.
In most cases this will be a part of the EN54 suite of standards,
e.g. EN54-2 for control equipment or EN54-5 for heat detectors.
Many of these standards are published but are in the process of
harmonisation. Once harmonised there will be a transition period
before compliance becomes mandatory. Therefore at present third
party approval is voluntary but over the next few years it is
expected to become mandatory.
CPD (cont’d)
1.2 Legal Framework
Third party testing to an EN54 standard is very expensive,
this may therefore restrict the level of customisation that can be
offered by manufacturers in the future.
Generally the legal requirement for a fire alarm system relates
to the protection of life. Either of those in the building or those
in adjacent buildings. The primary objective of life protection is
to warn occupants of the risk of fire and get them to a place of
safety as quickly as possible.
Currently CE marking is used to indicate that the equipment meets
the EMC and LV directives. It will also apply to CPD compliance
once mandated standards are in place for the items of equipment
in question. CE marking is not retrospective and generally it will be
clear as to what directive the marking relates to. The mandated
standards will be parts of EN54 for fire alarm and fire detection
The Restriction of Hazardous Substances directive currently does
not apply to fire detection and alarm equipment. However it is
likely that once alternative materials become available and reliable
(particularly in the case of lead solder,) then the scope of the
directive will be enlarged to cover current exceptions and to
incorporate more materials. The objective of the directive is to
require manufacturers to stop using substances that potentially
provide some health risk, in electrical and electronic equipment.
The answer to this question depends on the premises in question
and the legal requirements. In large high-rise buildings, such
systems are essential to warn all occupants that a fire or
emergency situation exists and the system is used to control
evacuation in an orderly way. Large sites with a retained fire
brigade may require the system to call the brigade and direct them
to the area of risk. The property may have considerable intrinsic
value and the insurers either require a fire detection system or may
incentivise its use.
The building may be unoccupied for periods where equipment is
still powered and the owner wishes to ensure that if anything goes
wrong fire fighters are called to the scene in a timely manner.
Fire alarm systems are often used for other purposes as well as fire
detection and alarm, such as bomb alert signalling, monitoring
systems for high risk equipment or places, emergency call systems
and even class change systems for schools.
The UK traditionally had a number of regulations relating to
different types of building and has used the fire brigade to act as
a local enforcement agency either issuing or withholding fire
certificates depending on their view of the level of protection
provided. This has now changed and the government has
devolved the responsibility onto the building owners - with some
exceptions. This means that it will become the building owner (or
occupier) who is responsible to ensure that the building is safe for
those in and around it. The tool to establish the requirement is ‘risk
assessment’. The overall legal framework as it previously was and
is now are detailed in the charts below.
Acts of Parliament
British Standards Institute
Enforced by courts
Produces standards of best engineering
practice by consultation with all
parties. They are called up in guidance
documents as showing legal compliance
Government Departments
e.g. Home office, provide guidance
Fire Authority & Building Control
Implement Legislation, they inspect
premises and decide upon requirements
then issue Fire Certificates to premises
that comply and are responsible for the
fire safest standards of the building
Uses contractor to install products to
meet fire authority requirements who
will then issue a fire certificate
Flowchart of Fire Safety for normal premises since
October 2006
Fire Safety Bill - Act of Parliament
Government Departments
Enforced by courts
e.g. Home office, provide guidance
Fire Authority & Building Control
Sometimes fire detection and alarm systems are used to
compensate for structural fire protection shortcomings or to give
special cover for items of high value. Whatever the reason,
an automatic fire detection and alarm system generally provides
a network of manual callpoints, fire sensors and alarm warning
devices over the area covered. It is, in effect, the eyes and mouth
of the building to constantly monitor the building and warn if a fire
breaks out, or is suspected. In the same way we do if we see
flames or smell burning.
1.1 Insurance Requirements
Insurance requirements normally relate to the protection of property
- rather than life. The objective is therefore to detect fire as early as
possible and instigate measures to put the fire out with the
minimum amount of damage.
Generally a system designed for property protection will also give
protection of life as well but the essential difference is that the
requirements for property protection are driven from the insurance
company’s desires rather than law. BS5839-1 covers both life and
property protection, so is equally useful in both cases.
and their
Fire Risk assessors
They have the total responsibility
for the Fire safety of the premises
Competent Engineers
Specialists in fire alarm and emergency
lighting design installation and
maintenance provide technical assistance
British Standards Institute
Produces standards for equipment and
application that can be used by employers
to demonstrate compliance
If a fire detection or alarm system is required then it is
necessary to establish the specification for the system. In the
UK BS5839-1 is normally the appropriate standard for commercial
and industrial premises. BS5839-6 relates to residential premises
and other standards such as HTM 82 for hospitals relate to
specific building types.
Technical - Fire System Design Guide
Implement Legislation check assessments
The first step in the design process is the risk assessment.
It underpins the whole system strategy and therefore could be
argued as being the most important stage. Risk assessment is the
process of considering each part of a building from the point of
view of what fire hazards exist within an area and what would
happen in the event of fire or if explosion were to occur. This
would normally be done when considering the building from the
point of view of general safety. Clearly very small premises only
require a first level of fire protection, such as safe construction,
clear escape routes and a fire extinguisher. Equally obviously,
large hotels will require a fully automatic fire detection and alarm
system, multiple sets fire protection equipment and adequate
emergency lighting and escape signage. The Risk Assessment
process is to help building owners of buildings between these two
extremes make adequate and appropriate provision.
Building owners or operators will often want to employ the services
of a professional risk assessor to ensure that the building
is considered impartially and in adequate detail. However there
are checklists and technical advice available so that the task can
be done ‘in-house’. The Government web site for communities and
local government provides useful guidance on the subject
( It is recommended that risk assessors
should be fully familiar with the requirements of the latest edition of
BS5839:1 and if in doubt consult a suitably qualified specialist.
BS5839 stresses the need to consult with all interested parties
before embarking on a detailed design. As a minimum the
following need to consult to ensure that the fire detection and
alarm system meets the requirements of all concerned.
- The authority responsible for enforcing health and safety
- The property insurer
- The building user
- The proposed installer
- Fire engineering specialists (where appropriate)
Technical - Fire System Design Guide
Standards are produced for equipment and the application of
equipment, they are generally produced or endorsed by BSI.
They represent recognised best practice either for the design,
manufacture or application of a particular product or product
Often these standards are called up within guidance documents
for pieces of legislation and since they represent best current
practice, can be generally be used by employers to demonstrate
that equipment they have installed is adequate and appropriate.
The following standards relate to the UK and Europe. There are
other standards that relate to specific applications (such as
hospitals or data processing installations) and other countries will
have their own standards covering the same area as those listed.
4.1 BS5839
The BS5839 suite of standards relate to specific areas of
application for fire detection and alarm equipment. Specifically
part 1 relates to public premises and part 6 relates to residential
4.1 BS5839 (cont’d)
BS5839-1 is a comprehensive code of practice for fire detection
and alarm systems, the requirements relate to both life and property
protection and the standard includes much advice and comment
with is very useful in informing the building owner or system
specifier of the background to the requirements. The standard has
been developed through input from the whole fire detection
industry over a period of 30 years and is the distillation of expert
opinion and practical advice. The application notes that follow
relate to the requirements of BS5839:1 2002.
4.2 BS5588
The parts of BS5588 form the technical element of the building
regulations for England and Wales, they should be consulted to
establish the detailed requirements for the building in question.
BS5588 is mainly concerned with the structure and design of the
building but also contains some requirements for fire detection and
alarm systems. The requirements of BS5588 are incorporated
within the building regulations giving it mandatory legal status.
4.3 BS7273, BS EN 60079-14, BS EN 50281-1-2
The parts of BS7273 are codes of practice for different types of
fire protection systems. Generally this is considered separately to
fire alarm systems but there may be occasions where a trade off
can be made between the two systems, or where the two systems
interact and must be interfaced.
BS EN 60079-14 and 50281-1-2 cover areas where there may
be risk of explosive gas/vapour or dust respectively, reference to
them may be required in certain buildings or where there is a
change of use.
4.4 EN54
The EN54 suite of standards relates to the design and
performance of items of equipment that make up a fire detection
and alarm system. Each part relates to a different piece of
equipment, for example part 3 relates to alarm devices, part 11 to
call points, part 4 to power supplies etc.
Some parts of the standards have options with requirements. These
relate to specific features that are required in certain applications
but not all. For example all control and indicating equipment must
be able to detect fire (with the help of appropriate input devices),
must monitor certain functions (such as cables for open and short
circuit faults) and must have a disablement facility so that functions
or areas of cover can be switched off for maintenance or similar
activities. However it is optional to have a test facility or delays to
outputs, but if such features are either provided or required in the
application (e.g. to allow a local search for fire prior to calling the
brigade) then those facilities must meet specified criteria.
It is therefore necessary when specifying compliance to EN54 that
the relevant part is identified and that the application standard
(such as BS5839-1) is consulted to identify specific options. For
example, the UK fire brigade almost always will require zonal light
emitting indicators to be incorporated in control equipment to show
the extent of the fire event at a glance; this is an option in EN54-2
and many countries in Europe do not require such displays.
4.5 BS7671
BS7671 was previously known as the IEE wiring regulations.
The standard is called up in BS5839-1 and covers the installation
of the system.
6.2 Detection Zones
BS5839-1 lists eight categories of cover, depending on what is
required. The category system is a simple short hand method of
informing all parties of the objective of the system.
Fire detection zones are essentially a convenient way of dividing
up a building to assist in quickly locating the position of a fire.
The zone boundaries are not physical features of the building,
although it is normal to make the zone boundary coincide with
walls, floors and specifically fire compartments. The size and
position of the detection zones will therefore tend to be dependant
on the shape of the buildings, but will also depend on what the
building is used for and to some extent the number of people the
building is expected to contain at any one time.
BS 5839-1 has some specific recommendations with respect to
detection zones:
Zones should be restricted to single floors, except where the
total floor area of a building is less than 300m2
Voids above or below the floor area of a room may be
included in the same zone as the room so long as they are
both in the same fire compartment
Zones should not be larger than 2000m2 except for manual
systems in single storey open plan buildings, such as a
warehouse, where up to 10000m2 is allowed
Fire detectors in an enclosed stairwell, lift shaft or the like
should be considered as a separate zone
The search distance within a zone should be less than 60m
(all possible entrance points must be considered). This can be
relaxed when using addressable systems if the information
provided at the control and indicating equipment would allow
fire fighters, unfamiliar with the building, to proceed directly to
the location of the fire. The search distance only relates to the
distance from entering a zone to being able to determine the
location of the fire, it is not necessary to travel to the fire
Zones should not cross fire compartments, a fire compartment
can contain several zones but a zone should not contain more
than one fire compartment
5.1 Life Safety
M - Category M systems are manual systems and rely on the
occupants of the building discovering the fire and acting to
warn others by operating the system. Such systems form the
basic requirement for places of employment with no
sleeping risk. Manual cover should be included in all Life
Safety systems except L5 systems where it may or may not
be provided. In addition to manual means of triggering an
alarm, L category systems will also normally have an
element of coverage using automatic fire detection such as
smoke or heat detectors. The precise classification depends
on the nature of the area(s) provided with automatic
L5 - Category 5 systems are the ‘custom’ category and relate to
some special requirement that cannot be covered by any
other category. Where such systems are specified careful
reference much be made to the objective of the cover.
L4 - Category 4 systems cover escape routes and circulation
areas only. Detectors might be sited in other areas of the
building, but the objective is to protect the escape route.
L3 - Category 3 systems provide more extensive cover than
category 4. The objective is to warn the occupants of the
building early enough to ensure that all are able to exit the
building before escape routes become impassable.
L2 - Category 2 systems relate to automatic fire protection in
defined areas of the building as well as satisfying the
requirements of category 3. The wider cover would relate to
parts of the building considered to have a high level of risk.
L1 - With category 1 systems, the whole of a building is
covered apart from minor exceptions.
Before looking at the details of the alarm system it is necessary to
understand some of the concepts that are used to assist the system
designer. Buildings are divided up into sections in three ways as
far as fire safety engineering is concerned; fire compartments,
detection zones and alarm zones.
6.1 Fire Compartments
A fire compartment is a part of a building that is separated from
the rest of the building by a fire resistant structure so as to limit the
spread of fire within the building. The requirements for designing a
building and hence its fire compartments, are defined in building
regulations and is outside the scope of this document. It is
necessary, however, for the designer of a fire detection and alarm
system to be familiar with the design of the building, in particular
the position and extent of its fire compartments.
Search distance
P2 - Category 2 systems provide fire detection in specified parts
of the building where there is either high risk or where
business disruption must be minimised.
P1 - The system is installed throughout the building - the objective
being to call the fire brigade as early as possible to ensure
that any damage caused by fire is minimised. Small low risk
areas can be excepted, such as toilets and cupboards less
than 1m2.
Technical - Fire System Design Guide
5.2 Property Protection
6.3 Alarm Zones
7.3 Selection of Suitable Equipment Autonomy
Alarm zones are only needed in buildings where operation of the
alarms needs to be different in certain parts of the buildings. If the
only requirement is to activate all the alarm sounders to provide a
single common evacuate signal once a fire is detected, then alarm
zones are not needed, the whole building is one alarm zone.
For more complex buildings where it is necessary to operate alarm
devices differently in parts of the building, then the building should
be divided into alarm zones such that all of the alarm devices in
one alarm zone operate in the same way.
BS5839-1 contains some recommendations for alarm zones:
- The boundaries of all alarm zones should comprise fire-resisting
- Signal overlap between alarm zones should not cause
- The same alarm and alert signals should be used throughout a
- A detection zone must not contain multiple alarm zones, alarm
and detection zone boundaries should coincide. An alarm zone
may contain multiple detection zones
Standby time for life safety systems is normally 24 hrs. For property
protection this may need to be increased to up to 72hrs where the
building is unoccupied over weekends.
7.1 Component Compatibility
Because most conventional systems operate in a similar manner,
there can be a temptation to mix and match detectors, panels and
sounders from different suppliers. Cooper Lighting and Security
strongly recommend that all components be sourced from a single
supplier to ensure that they are fully compatible with each other.
Minor incompatibilities between components may not be
immediately obvious but could cause system malfunction under
particular conditions.
Technical - Fire System Design Guide
Section 11.1 of BS5839 part 1:2002 makes specific mention of
the need to confirm that all system components are fully compatible
with each other.
Note also that section 12.2.2 of BS5839 part 1:2002 requires
that removal of any or all detectors from a circuit should not affect
the operation of any manual callpoint. With Cooper Lighting and
Security conventional systems, this functionality is inherently
provided by the design of the detector base, however with other
systems this requirement may require the purchase of additional
components or place limitations on the wiring order of detectors
and callpoints. Other countries may require that this requirement
is met by the use of separate zones (e.g. France).
7.2 Repeater Panels
Repeater panels are available for most systems and are required
where the fire brigade may enter a building from more than one
entrance, where security staff are located away from the main
panel or where operational staff need the system information in
more than one location, for example in hospital wards.
All control panels including most repeaters, require two power
supplies. The back up supply is built into the panel and is provided
by sealed lead acid batteries, but a secure mains supply is
required for the primary power source. Fuses/isolation switches
should be clearly marked to ensure that the fire alarm system is
not inadvertently powered down.
Conventional panels and most repeater panels generally have
batteries, which are sized to provide a defined level of standby
autonomy based on a fully loaded system. For analogue systems,
batteries are typically custom sized to suit the required
configuration, because the amount and type of connected
equipment can vary considerably.
7.4 Selection of Appropriate Automatic Detectors
Cooper Lighting and Security provide a range of automatic fire
detectors to suit most general risks. Smoke detectors give the
earliest warning of fire, typically responding to a fire 1/10th
of the size as that required to operate a heat detector.
Optical smoke detectors are suitable for most applications giving
the fastest response to slow burning fires - the most common start
to fire events. Ionisation detectors were the first type of detector to
be commercially developed and are also a popular choice.
They have superior response to fast burning fires but an inferior
response to slow smouldering fires, which are typical with modern
construction materials. Ionisation detectors are also less acceptable
from an environmental point of view due to the radioactive material
that they contain. There is increasing restriction on the
transportation and disposal of ionisation detectors so it is
recommended that alternative types are used where possible.
BS5839 section 21.1.8 (d) recommends the use of optical
detectors to provide coverage for escape routes due to their
superior ability to detect optically dense smoke that would easily
obstruct the use of escape routes.
Opto-heat detectors have been developed to mimic the response
of ionisation detectors to fast burning clean fires yet maintain the
advantage of photoelectric detectors when detecting smouldering
fires and allow a higher alarm threshold within the EN54-7
specification under normal conditions thus providing a greater
rejection of false alarms.
Heat detectors should be used in environments where the ambient
conditions might cause false alarms if smoke detection were to be
used, for example where there is a high level of dust, fumes, steam
or smoke under normal conditions.
There are three available types of conventional heat detector,
a fixed high temperature heat detector which has a nominal trigger
temperature of 92°C, a medium fixed temperature heat detector
with a nominal trigger threshold of 77°C and a rate of rise heat
detector which responds to the rate of change in temperature
rather than at a specific temperature. Rate of rise detectors also
have a fixed temperature backstop to ensure that even very slow
increases in temperature will eventually raise an alarm if the
increase continues for a sufficiently long period.
The rate of rise type is the most sensitive type of heat detector,
particularly when used in areas where the ambient temperature
can reach low levels and therefore create a large difference
between the ambient temperature and the trigger temperature
of a fixed temperature detector.
7.4 Selection of Appropriate Automatic Detectors (cont’d)
7.5 Positioning of Smoke and Heat Detectors
In order to avoid false alarms rate of rise detectors should not be
used in areas subject to frequent temperature swings, such as in
kitchens, boiler rooms and warehouses with large doors to open
air. BS5839-1 recommends that the static response temperature of
a heat detector should be a minimum of 29°C above the
maximum ambient temperature likely to be experienced for long
periods of time and 4°C above the maximum temperature likely
to be experienced for short periods of time.
All smoke detectors have similar spacing requirements, heat
detectors also all have similar spacing requirements although these
are different to smoke detectors. According to BS5839 for general
areas the spacing between any point in a protected area and the
detector nearest to that point should not exceed 7.5m for a smoke
detector and 5.3m for a heat detector.
7.5M max
5.3M max
Area of coverage for
a smoke detector
Area of coverage for
a heat detector
The above are the maximum areas that can be covered by an
individual detector. In order to ensure that coverage is provided
into the corners of rooms and to ensure that there is no gap at the
junction point of multiple detectors, spacings have to be reduced.
= Missed coverage in the corners of rooms and intersections
To ensure complete coverage for square layouts, spacings between
detectors and walls should be reduced to 5m for a smoke detector
and 3.5m for a heat detector.
Technical - Fire System Design Guide
Heat detectors must be mounted closer together than smoke
detectors, so whilst the mounting bases are compatible for all
types, care should be taken to ensure that the spacing between
detectors is appropriate for the detector type fitted. With analogue
systems it is possible for the photo thermal detector to act as a
thermally enhanced smoke detector during certain times and as
a pure heat detector at other times. If this mode of operation is
envisaged then spacings must be those appropriate for heat
Each type of conventional heat detector is manufactured to have
specific characteristics, which cannot be altered. Because
analogue systems are more sophisticated, only a single analogue
heat detector is produced, the characteristic of which is
programmable to suit the relevant application requirements at the
time of commissioning and can be altered later if required.
7.5 Positioning of Smoke and Heat Detectors (cont’d)
7.6 Mounting Heights of Detectors
To ensure complete coverage, spacings between detectors should
be reduced to 10.0m between smoke detectors and 7.0m
between heat detectors.
Under all normal circumstances point type fire detectors should be
mounted on the ceiling - this ensures that the height restrictions are
met together with the following table.
Ceiling Heights (m)
General Limits
Rapid Attendance*
Heat detectors - class A1
Heat detectors - other classes
Point type smoke detectors
Spacings between smoke
Rapid attendance values can be used in type P systems providing fire brigade
response time is less than 5 minutes
The above data is based on flat level ceilings; for pitched ceilings
or ceilings with a non-flat surface, spacings will alter. For pitched
ceilings use the data below, for other ceiling types refer to
BS5839 for comprehensive guidance. Where detectors must be
mounted onto a pitched ceiling, a detector should be mounted
near to the apex but spacing can be increased by 1% for each
1° of slope up to 25%. ‘Near’ is defined as within 600mm for
smoke detectors and within 150mm for heat detectors.
Corridor spacing for smoke detectors
7.5M MAX
7.5M MAX
Technical - Fire System Design Guide
Spacings between heat
For corridors less than 2m wide only the centre line need be
considered therefore it is not necessary to reduce detector spacings
in order to provide complete coverage. Therefore for smoke
detectors spacing becomes 7.5m from a wall and 15.0m between
detectors. For heat detectors the spacing becomes 5.3m to a wall
and 10.6m between detectors.
7.5M MAX
Optical beam smoke detectors
7.7 Beams and Other Similar Ceiling Obstructions
Fire detectors should be mounted at least 500mm away from walls
or ceiling obstructions greater than 250mm deep and at least
twice the depth of obstructions less than 250mm deep. They
should also be mounted at least 1m away from any forced air
inlet. Where the obstruction is greater than 10% of the height of an
area it should be considered as a wall. Similarly a floor mounted
obstruction (such as racking) should be considered a wall if it
comes to within 300mm of the height of the detector.
For obstructions of less than 250mm Y should be at
least 2 x Z
7.8 Lift Shafts
Detector at
top of shaft
Where detection is required in vertical shafts, such as stairwells,
a detector should be mounted at the top of the shaft and within
1.5m at each level.
within 1.5m of
penetration of
each floor
Technical - Fire System Design Guide
Typical detector positioning for L2 coverage
7.9 Beam Detectors
7.11 Selection of Manual Callpoints
Beam detectors provide a cost effective method of covering wide
open plan areas, however care should be taken that activities in
the space do not obstruct the beam and that the building structure
is such that the beam does not ‘move’ or false operation may
The selection of manual call points is somewhat simpler. Surface
or flush types are selected depending on the environment and
whether the fire system is being installed into an existing building
(where surface call points are generally easier to install). IP65
types should be specified where there is risk of moisture ingress,
for example in external locations. Standard call points use a
frangible glass element which is designed to break under light
pressure triggering the call point into an alarm condition.
If optical beam detectors are mounted within 600mm of the ceiling
level, they should be positioned such that no point in a protected
space is more than 7.5m from the nearest part of the optical
beam. Should the beam detector be mounted more than 600mm
below ceiling level then spacings should be altered to 12.5% of
the height of the beam detector above the highest likely seat of
any fire.
Other than the part of the beam within 500mm of the beam’s
transmitter or receiver, if any other section of a beam which runs
closer than 500mm to any wall partition or other obstruction to the
flow of hot gasses, that section of the beam should be discounted
from providing protection.
Where optical beam detectors are mounted in the apex of pitched
roofs then the same enhanced spacings can be applied as for
point smoke detectors (see above)
The area covered by a single optical beam detector should not
exceed that of a single detection zone.
7.10 Aspirating Systems
Technical - Fire System Design Guide
Aspirating systems should be specified where protection is required
in areas such as cold stores or areas where a very fast response to
fire is needed, and whilst each sense point can be considered
a smoke detector, special training is needed to design such
systems - particularly as they are normally required to cover special
risks. Other specialist detectors can be connected to Cooper
Lighting and Security systems via interfaces where there is a
specific requirement, such as flame detectors or equipment in areas
requiring an intrinsically safe installation.
The glass element is covered with a thick plastic film to protect the
operator against broken glass, however plastic resettable elements
and protective flaps can be used where there is the risk of
unwanted operation or in food preparation areas. Where hinged
covers are used these should be recorded as a design variation.
Call points can be supplied with LED indicators mounted onto the
front face to simplify the location of an operated call point.
7.12 Positioning of Manual Callpoints
Manual call points should be located on escape routes, at all exits
to free air and at all exits from each level of multi-storey buildings.
The method of operation of call points should be the same
throughout the building - all Cooper Lighting and Security call
points meet this requirement, whether IP65 or standard types.
For general applications, call points should be located such that
nobody need to travel more than 45m to reach the nearest call
point. This distance is based on measuring the actual route that
would be travelled. If at the design stage the actual layout is
unknown then a straight-line distance of 30m should be used as a
design guide and the 45m limit verified after fit out is complete.
Call points should be located near to specific hazards
(e.g. flammable liquid store) and at 1.4m (+/- 0.2m) from the floor
in well lit easily accessible positions. Lower mounting heights might
be needed to accommodate building users in wheel chairs.
The figures of 45m and 30m above should be reduced to 25m
and 16m respectively if either a significant proportion of building
users have limited mobility and it can reasonably be assumed that
one of these occupants will be likely to be the first person to
operate the alarm or if the nature of equipment or activity in an
area gives a high likelihood of rapid fire development.
Typical building layout showing positioning of callpoints
Technical - Fire System Design Guide
Typical building layout showing positioning of callpoints
7.13 Remote indicators
Remote indicators should be used in areas where the detector
mounting position is such that the detector is not easily viewed,
for example in ceiling voids. Remote indicators can also be used
to dramatically reduce search distances where detectors are
mounted inside rooms, such as in hotels, thus simplifying system
zoning and reducing the time taken to locate the source of an
Search Path
Search Path
Technical - Fire System Design Guide
Without remote indication
With remote indication
7.14 Alarm Devices
Alarm devices fall into two types, audible and visual. The audible
types are most common, with a variety of types being available
from bells to all kinds of different electronic sounders including
those containing pre-recorded spoken messages. The choice of
device is dependant on local preference, legal requirement and
the need to have a tone distinct from all other building audible
Generally more low output sounders are better than few high
output sounders in this respect.
In addition to these general requirements the following specific
requirements should also be noted:
- A level of at least 75dBA at the bedhead is required to wake
sleeping occupants
- At least one sounder is required per fire compartment
- All of the sounders utilised in a building should emit a similar
Speech alarms or links to PA systems overcome some of the
complacent responses to warning tones and can be used to good
effect when carrying out regular fire tests in buildings where there
are many people unfamiliar with the regular routines - such as
hotels. Finally visual alarms are to be used where the hard of
hearing may be occupying a building or where the ambient noise
is such (above 90dBA) that audible warning may not be heard,
where hearing protectors are in use or where the sounder levels
would need to be so high that they might impair the hearing of the
building occupant.
BS5839-1 requires that Alarm Circuits should be arranged such
that in the event of a single fault at least one sounder operates
within the vicinity of the control equipment; or in the case of certain
buildings open to large numbers of the general public, a single
fault only partially reduces the alarm level. This is met by looppowered devices or by the use of multiple alarm lines for
conventional systems, interleaved throughout the relevant area or
by use of at least two zones for Bi wire systems (single zone
Bi wire panels have a built-in sounder incorporated within the
control panel).
Sound levels should generally be 65dBA or 5dBA above persistent
background noise levels. This may be reduced to 60dBA in rooms
smaller than 60m2, in stairwells or in specific limited points of the
building. Most sounders have adjustable output levels, which
allows a balance between meeting the requirements of the
standard and providing a sensible level of audible comfort.
Sounder output levels are normally quoted in dB(a) at 1m,
the graph below can be used to calculate effect on sound level
at other distances in free air. In addition allowances have to be
made for obstructions such as doors, the absorption of sound by
furnishings the directional nature of the sounder, mounting position
and location of the sounder etc.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Distance from Source
Effect of distance on sound level
Technical - Fire System Design Guide
Reduction in
Reduction in DB(A)
Distance from
Source (m)
When considering the number and position of sounders the
following should be considered:
- A loss of at least 20 to 30dBA should be allowed for sound
going through doors
- Where two identical sounders are in one location the level
increases by only 3dBA
- The sound pressure level drops with distance according to the
graph below
- It is necessary to consider cable loading requirements when
designing sounder circuits. Volt drop should be limited to less
than 10% of nominal voltage
- It is recommended to always err on the side of caution when
selecting sounders and their locations as it is far simpler to
reduce the volume setting of a sounder where appropriate
than to retrofit additional sounders should the initial levels be
7.15 Fire Protection Equipment
Cooper Lighting and Security provide a range of door holders,
interfaces and relays that can be used to control the operation
of smoke vents, hatches, ventilation systems, lifts etc. It is
recommended that reference is made to the individual product
pages of this catalogue or to our technical sales department who
will be able to advise on the best type for a particular application.
7.16 Alarm Routing Equipment
Alarm output relays are available to connect to alarm routing
equipment. The selection of types of routing equipment will depend
on the requirements of the selected alarm receiving centre.
7.17 Interfaces
Typical sounder positioning based on sounder with 105dB(a)
The product pages of this catalogue list the range of interfaces that
are available, most relate to analogue systems and are designed
for specific applications, such as interfacing an analogue panel to
a conventional zone of detectors, providing an interface to a shop
etc. Conventional systems can interface directly to volt free contacts
by using suitable resistors (for monitoring sprinkler flow switches for
example) and are provided with relay outputs in the panels to
connect to fire and fault routing equipment, fire protection
equipment etc.
By definition an interface bridges the gap between two pieces
of equipment or two systems, consequently it is essential to
consider the requirements of both sides of the interface both from a
loading point of view and with regard to functionality and typical
fault scenarios.
Technical - Fire System Design Guide
The main area of caution is to ensure that the voltage rating of the
equipment and interface are compatible. For example, 24V relay
contacts should not be used to switch mains voltage, even if they
appear to work and it is best to provide isolation between systems
(such as protection and alarm systems) so that there is no risk of
electrical interference causing false alarms.
Typical sounder positioning based on sounder with 105dB(a)
False alarms have the potential to cause substantial disruption to
the smooth running of a business and in addition place a
tremendous burden on fire service resources.
Regular false alarms can cause building users to disregard alarm
signals leading to incorrect actions in the event of a real fire
situation. False alarms can broadly be divided into four categories,
- Unwanted alarms
- Equipment false alarms
- Malicious false alarms
- False alarms with good intent
BS5839-1:2002 introduced more onerous requirements for
the types of cables used in fire detection and alarm systems.
Fireproof cables should now be used for all parts of the system
and enhanced fire resistance cables should be used where there is
a requirement to ensure cable integrity over a longer period of
time. For example when connecting to alarm sounders or where
the connection between sub-panels provides any part of the alarm
signal path.
The following is designed to assist with selection of equipment to
avoid common potential unwanted alarm conditions, BS5839
gives comprehensive guidance on the subject and should be
consulted for in depth guidance.
Areas close to kitchens
Smoke detectors should never be used
Avoid rate of rise heat detectors
Avoid smoke detectors if possible
Do not install Ionisation smoke detectors
Consider photo thermal detector
Rooms in which toasters are used
Avoid smoke detectors if possible
Do not install ionisation smoke detectors
Consider photo thermal detector
Rooms in which people smoke
Avoid smoke detectors if possible
Do not install optical smoke detectors
Consider photo thermal detector
Bathrooms shower rooms and areas
where steam occurs
Avoid smoke detectors if possible
Do not install optical smoke detectors
Consider photo thermal detector
Areas with high dust concentrations
Avoid smoke detectors if possible
Do not install optical smoke detectors
Consider photo thermal detector
Areas where the sensing element is
subject to high air velocity
Do not install ionisation smoke detectors
Areas in which engine exhaust fumes
Avoid smoke detectors if possible
Do not install ionisation smoke detectors
Do not install beam detectors
Consider photo thermal detector
Areas close to openable windows
Avoid smoke detectors if possible
Do not install ionisation smoke detectors
Photo thermal detectors analyse both change in temperature as
well as density of smoke or smoke like phenomena. This can
considerably reduce the potential for false alarms. In addition with
analogue systems it is possible to configure the detector to operate
in heat only mode at specific times when smoke or smoke like
phenomena is likely to be present and then to revert to combined
smoke and heat detection when the presence of smoke is no
longer expected.
Regular testing and inspection of the fire alarm system is essential
to ensure that it is operating correctly. Many of the functions of the
system are monitored but it will still require an inspection of the
panel by the responsible person to see the fault indication and all
such events should be entered into the system log together with the
implementation of an action plan to investigate the reason for the
fault and a repair/correction program.
The Cooper Lighting and Security service division is able to
provide this function. The advantage of making use of this facility
is that the service department will have ready access to all spares
and to information relating to possible design changes or
specification enhancements that invariably happen over time.
BS5839-1 recommends the following minimum regular tests and
Daily - Check to see if the system is indicating fault and that any
corrective actions have taken place.
Weekly - Test the system by operating a manual call point (different
one each week).
Periodic Inspection - Subject to risk assessment, should not exceed
6 months between visits. Check the system log and ensure that
corrective actions have taken place. Visually inspect all items of
equipment, to ensure that the system is not obstructed or rendered
inappropriate by change of use. Check for any false alarms,
compare to nationally accepted levels and take appropriate action
if unacceptable. Test the system on standby power to ensure that
the battery is functioning correctly. Check all outputs for correct
operation. Check all controls and indicators. Check remote
signalling equipment. Additionally any other special checks - for
example beam detectors for correct alignment.
Over 12 month period - Carried out over 2 or more visits.
In addition to the periodic inspection: Test all manual call points
and fire detectors for correct operation. Inspect the analogue
detector levels to ensure that they are within correct levels.
Check all alarm devices for correct operation. Visually inspect all
accessible cable fixings. Confirm the cause and effect
programming is correct and up to date.
An extension to a fire alarm system should be planned and
implemented with the same care and consideration that was given
to the original system. There is always a risk that small extensions
may affect the integrity of the whole system. Special care is
needed if a different manufacturer is chosen for the extension to
ensure that there is compatibility between the old and new
equipment and to ensure that system loading constraints are met.
Technical - Fire System Design Guide
Unwanted alarms are those that are caused by a combination of
factors such as environmental conditions, fire like phenomena such
as steam, aerosol spray or dust triggering smoke detectors or by
inappropriate action by people in the building such as smoking in
areas protected by smoke detectors.
Fire alarm cables should be segregated from the cables of other
systems; they should be clearly marked, preferably coloured red
and should be routed through parts of the building that provide
minimum risk. This latter point is particularly relevant where the
use of the building is being changed - for example if a fuel store
is being moved.
The International Protection code, sometimes called the Ingress Protection code, classifies the protection given by an enclosure against the
touching of live parts, contact with moving parts and protection against the ingress of foreign solid bodies. It additionally specifies protection
against the harmful ingress of moisture or liquids. Two digits are used to describe its protection rating, called the IP code.
First Digit - Protection against solid objects
Technical - IP Ratings
Second Digit - Protection against liquids
No protection
No protection
Protection against large sized bodies e.g. hands
Protection against vertically falling drops of water
Protection against medium sized bodies e.g. fingers
Protection against drops of water up to 15° from the vertical (Drip proof)
Protection against small bodies, 2.5mm dia. or greater e.g. tools, wires
Protection against rain falling up to 60° from the vertical (Rain proof)
Protection against very small bodies, 1mm dia. or greater
Protection against splashed water from any angle (Splash proof)
Protection against harmful deposits of dust (Dust proof)
Protection against jets of water from any angle (Jet proof)
Complete protection against deposits of dust (Dust tight)
Protection against water from heavy seas e.g. water tight for marine deck use
Protected against immersion for a defined period
Protected against immersion for an indefinite period
Example: IP65 is dust tight and jet proof
Addressable system is a system in which signals from detectors and call
points are individually identified at the control panel and often where alarm
devices are individually addressed.
Alarm of fire is a warning of outbreak of fire, originated by a person or by
an automatic device.
Alarm receiving centre is a permanently manned centre, usually provided by
a commercial organisation, the staff of which, upon receipt of a fire signal
notify the fire service.
Analogue system A fire alarm system where the detectors give variable
output signals representing the value of sensed phenomena.
Fire detector is a device which gives a signal in response to a change in the
ambient conditions in the vicinity or within range of the detector, due to a
Fire point is a location where fire-fighting equipment is positioned which may
also comprise a fire alarm call point and fire instruction notices, the whole
being provided and arranged for use by occupants of premises.
Automatic fire alarm system is a fire alarm system comprising components
for automatically detecting a fire, initiating an alarm of fire and initiating
other action as arranged; the system may include manual call points.
Fire procedure is collectively and individually all the actions that need to be
taken, as part of fire precautions by the occupants of a building or other
structure to ensure the avoidance of danger from fire to persons and
Beam detector A type of smoke detector which detects smoke by the
obscuration of a beam of infra red light passing between a transmitter and
Fire protection is design features, systems or equipment in a building,
structure or other fire risk, to reduce danger to persons and property by
detecting, extinguishing or containing fires.
Conventional fire alarm Normally consists of a control panel linked to a
number of circuits of smoke, heat detectors and manual call points, and
having a number of sounder circuits. Consists of a control panel providing
separate circuits per zone for detectors and call points and at least two
circuits for alarm devices.
Fire signal is an alarm of fire originated by an automatic device, given
audibly and/or visibly.
Critical signal path All components and interconnections between every fire
alarm initiation point (callpoints and detectors) and every fire alarm device.
Ionisation smoke detector is a smoke detector that responds when smoke,
having entered the detector, causes a change in ionisation currents within the
Fault warning is an automatic indication given audibly and/or visibly that a
fault exists in a fire alarm system.
Fire alarm control and indicating equipment is the hub of a fire alarm system,
providing controls and normally a power supply for the system.
Fire alarm control equipment is equipment that, on receipt of a fire signal,
controls the giving of a fire alarm by one or more of the following:
(a) Fire alarm sounders
(b) Fire alarm indicating equipment
(c) Transmitting a signal to other fire alarm control equipment
Fire alarm device is a component of a fire alarm system used to give
warning of fire usually a sounder or visual alarm.
Fire alarm indicating equipment is the part of a fire alarm system located at
protected premises which provides indication of any fire alarm or fault
warning received from fire alarm control equipment.
Technical - Glossary of Terms
Fire detection system is a system of fixed apparatus, normally part of an
automatic fire alarm system, in which fire detectors, control equipment and
indicating equipment are employed for automatically detecting fire and
initiating other action as arranged.
Heat detector is a form of fire detector that responds to an increase in
Lantern Light A construction standing above the surface of a roof designed
to provide light to the space below.
Manual fire alarm call point is a device for the manual instigation of a fire
alarm condition.
Manual fire alarm system is a fire alarm system without automatic detectors,
in which the alarm system is initiated manually.
Mimic diagram is a topographic representation of the protected premises
carrying indicators for each sub division so that the indicators of the fire
alarm system can be rapidly related to the layout of the premises.
Phased evacuation System of evacuation in which different parts of the
building are evacuated in a controlled sequence rather than all at once.
Photoelectric smoke detector is a form of fire detector having a photoelectric
cell which responds when light is absorbed or scattered by smoke particles.
Fire alarm remote indicating equipment is the part of an alarm system that
indicates the status of the protected premises from where a fire alarm or fault
warning is being transmitted.
Point fire detector is a form of fire detector which responds to the
phenomenon detected at a fixed point at its location.
Fire alarm sounder is a component of a fire alarm system for giving an
audible warning of fire.
Smoke detector is a form of fire detector that responds to particulate
products of combustion.
Fire alarm system is a system of fixed apparatus for giving an audible
and/or visible and/or other perceptible alarm of fire and which may also
initiate other action. The term normally incorporates the function of fire
detection as well as alarm.
Soft addressing allows the control panel to assign an address to each
device automatically instead of it being done manually.
Fire alarm transmission link is an electrical circuit for transmitting fire signals
and fault warnings from protected premises to a central (fire alarm) station or
to a control room.
Self learn mode allows a totally unprogrammed system to function
immediately power and battery are connected (without the need for device
related text). The control panel will interrogate each device and assign an
address (soft addressing). Manual zone allocation allows the installer to split
the devices into zones.
Fire Authority is the Local Government Authority with a statutory responsibility
for providing the services of a fire brigade and supporting services in a
given geographical area.
Short circuit isolator Component in an addressable system that is able to
isolate a detection loop at both sides of a short circuit, minimising the loss of
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