راهنمای اعلام حریق(لاتین)
SYSTEM DESIGN
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 overstressed, 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.
OVERVIEW OF THE DESIGN PROCESS
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 found.
• 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
•
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 locations
-
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)
BACKGROUND LEGISLATION
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.
EMC
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.
LVD
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.
CPD
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.
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.
CE MARKING
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 systems.
RoHS
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.
1.0 WHY HAVE A FIRE ALARM SYSTEM?
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.
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.
1.2
Legal Framework
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.
The UK has 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 is now changing and the government is
devolving 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 recommended tool to establish the
requirement is ‘risk assessment’. The overall legal framework as it
currently is and is expected to become are detailed in the charts below.
FIRE SAFETY LEGISLATION - Current Situation Flowchart
of Fire Safety as expected for normal premises after Spring 2005
If a fire detection or alarm system is required then it is necessary to
establish the specification for the system. In the UK BS5839-1:2002 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.
2.0 RISK ASSESSMENT
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 web site of the office of the
deputy Prime Minister provides useful guidance on the subject
(www.odpm.gov.uk). Additional information and guidance on the risk
assessment process is available from the Health and Safety executive
(www.hse.gov.uk). It is recommended that risk assessors should be fully
familiar with the requirements of BS5839:1 2002 and if in doubt consult a
suitably qualified specialist.
3.0 CONSULT WITH ALL INTERESTED
PARTIES
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 legislation
- The
property insurer
- The building user
- The proposed installer
-
Fire engineering specialists (where appropriate)
4.0 RELEVANT STANDARDS
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 range.
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 premises. 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.
5.0 SELECTION OF COVER
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.
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 protection |
|
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. |
5.2 Property Protection
|
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. |
6.0 REVIEW OF THE BUILDING
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.
|
6.2 Detection Zones
|
|
6.3 Alarm Zones
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
construction
- Signal overlap between alarm zones should not cause
confusion
- The same alarm and alert signals should be used
throughout a building
- A detection zone must not contain multiple
alarm zones, alarm and detection zone boundaries should coincide. An
alarm zone may contain multiple detection zones
7.0 SELECTION OF EQUIPMENT
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.
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.
7.3
Selection of Suitable Equipment Autonomy
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.
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.
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.
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.
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 detectors.
7.5 Positioning of Smoke and Heat
Detectors
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.
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.
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.
To ensure complete coverage, spacings between detectors should be reduced to 10.0m between smoke detectors and 7.0m between heat detectors.
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.
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.
7.6 Mounting Heights of 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.
|
|
|
|||||
|
Heat detectors - class A1 |
9 |
13.5 |
||||
|
Heat detectors - other classes |
7.5 |
12 |
||||
|
Point type smoke detectors |
10.5 |
15 |
||||
|
Optical beam smoke detectors |
25 |
40 |
||||
|
* Rapid attendance values can be used in type P systems providing fire brigade response time is less than 5 minutes |
||||||
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
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.
Typical detector positioning for L2 coverage
7.9 Beam Detectors
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 result.
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
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.
7.11 Selection of Manual
Callpoints
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.
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.
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. 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.
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 alarm.
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 alarms.
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 loop-powered 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.
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 noise
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 inadequate
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.
|
Typical sounder positioning based on sounder with 105dB(a)
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
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.
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.
8.0 DESIGN REVIEW TO MINIMISE FALSE
ALARM POTENTIAL
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
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.
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.
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.
|
Area |
|
|
Kitchen |
Smoke detectors should never be used |
|
Areas close to kitchens |
Avoid rate of rise heat detectors |
|
Rooms in which toasters are used |
Avoid smoke detectors if possible |
|
Rooms in which people smoke |
Avoid smoke detectors if possible |
|
Bathrooms shower rooms and areas where steam occurs |
Avoid smoke detectors if possible |
|
Areas with high dust concentrations |
Avoid smoke detectors if possible |
|
Areas where the sensing element is subject to high air velocity |
Do not install ionisation smoke detectors |
|
Areas in which engine exhaust fumes occur |
Avoid smoke detectors if possible |
|
Areas close to openable windows |
Avoid smoke detectors if possible |
9.0 CABLES
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.
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.
10.0 MAINTENANCE
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
inspections:
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.
11.0 SYSTEM EXTENSIONS
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.