Fire detection systems · 2011-10-10 · fire detection and alarm zones Most conventional fire...

Fire Detection Systems

contents

intelligent fire alarm systems

conventional fire alarm systems

detector application guide

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Fire detection systems 8/8/06 11:46 Page 3

principle of operationA conventional fire alarm systemnormally consists of a control panellinked to a number of lines of firedetectors and manual call points,normally called detection zones,and a number of sounder or alarmcircuits. A simple system is shownin Figure 1.

control panelThe control panel drives thedetection zones and soundercircuits, provides LED indications of fire, fault or normal conditionsand contains switches to allow thesounders to be activated or silencedand the detectors to reset followingan alarm. The control panel ispowered from the mains (230VAC)and will contain back-up batteriesto allow the system to function for

a minimum of 24 hours, dependanton the application, in case of amains failure.

Note: There are numerous suppliersof fire control equipment and firedetection devices. There is noguarantee that all panels and alldetectors are electricallycompatible. Therefore, to avoidpotential incompatibility issues, it isstrongly recommended to purchaseboth groups of products from thesame source, or to obtainconfirmation of compatibility fromthe panel manufacturer.

fire detectionand alarmzonesMost conventional fire alarm panelshave several detection zonescomprising a mixture of automaticfire detectors and manual callpoints. In order to limit the effect offaults, and to limit the search area inthe case of a fire, the size of a firedetection zone is limited to 2000m2,with a maximum travel distancewithin the zone to locate a fire of60m. In addition, zones should notcover more than one storey, unlessthe total floor area of the building isless than 300m2. As a result unlessthe site is very small, the system willcomprise several detection zones.

A fire alarm (or sounder) circuit maycover more than one detectionzone, but it must follow theboundaries of the relevant detectionzones, and the boundaries shouldbe of fire resisting construction.

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conventional firealarm systems

FIREALARM

CONTROLPANEL

EO

LE

OL

FIREDETECTIONZONE 1

EO

L

FIREDETECTIONZONE 2

FIREALARMCIRCUIT

Zone 1 Alarm

System OK

Zone 2 Alarm

Zone 1 Fault

Zone 2 Fault

Alarm Cct Fault

System Reset

Figure 1: Simple conventional fire alarm system


conventional systemoperationdetection line operationConventional detection systems

normally operate on a 24VDC line.

In the standby condition, the

detectors will draw a low current,

typically less than 100μA. When the

detector senses a fire, it will switch

into the alarm condition with it's

LED illuminated, and will collapse

the line voltage by drawing a larger

current - dependant on the

detectors and control panel, but

typically 50-80mA. The control

panel can sense this, and activate

the appropriate alarms. The

detector will remain latched in the

alarm state with its LEDs

illuminated, even if the smoke or

heat is removed until it has been

reset from the panel by momentarily

removing power from the line.

This allows the fire to be located

even if the signal is intermittent, or

to locate possible sources of

nuisance alarms.

For some control panel - detector

combinations, when a standard

base is used, there is an

incompatibility between the current

specifications of the detector and

panel, leading to incorrect reporting

by the control panel, for example

signalling a fault in place of an

alarm, and in some cases damage

to the detector due to over current

in the alarm state. In these cases it

is necessary to use a base fitted

with a resistor in series with the

detector to limit the current draw

in alarm. Resistors fitted into the

detector base are also used in

some cases to distinguish between

a short circuit fault and an alarm.

The value of the base resistor is

dependant on the control panel,

however a typical value is 470

Ohms. If in any doubt, contact the

control panel manufacturer who

should be able to specify which

detector bases should be used

with different detector brands.

A manual call-point consists of asimple switch with a resistor inseries with it, usually 470 Ohms or680 Ohms. When the call point isactivated, the resistor is switchedacross the line, and a current of 50-80mA, dependant on the control panel, is drawn.

detection line fault monitoringStandard conventional systems areable to monitor the zone for shortcircuit, open circuit and detectorhead removal.

When a short circuit occurs on azone, a high current will be drawn,and the line voltage will be pulledtowards zero volts. The paneldetects the low voltage /highcurrent and a fault is signalled.

In order to detect an open circuit, ordetector head removal, a device isconnected across the end of thezone, which can be monitored. This device can take various formsdependant on the control panel.

5

0V

+24V

Contact Closedwhen detector

inserted in base

Res

isto

r

Figure 2: Resistive end of line operation


The simplest end of line device is a resistor, which will draw a currentdistinct from the quiescent andalarm currents drawn by thedetectors. Installation of detectorsinto their bases closes a contact inthe base supplying the remainder ofthe zone. Thus if the line is broken,or if a detector head is removed, the current drawn by the zone willfall, and a fault will be signalled (See figure 2). Example zone currentand voltage figures are given in figure 3.

The problem with a simple resistiveend of line is that should a detectorhead be removed, the remainder ofthe zone beyond that detector islost and no alarm can be signalledbeyond this point. Should a callpoint be mounted beyond the

removed detector, it will no longerwork, which contravenes therequirements of BS5839 part 1. Toovercome this either all call pointsmust be mounted at the start ofeach zone, or in completelyseparate zones (both of thesesolutions are often impractical andtoo costly), or head removalmonitoring can be employed.

Active monitoring uses bases fittedwith a diode across the contact inthe base (fig 4). Whilst the detector

is mounted in the base, the basecontact connects directly across thediode, and links it out. There isusually provision for manuallylinking the diode out to permitcontinuity testing duringcommissioning. When the detector

head is removed, the diode isconnected across the contact,allowing power to continue to besupplied to the remainder of thezone, whilst still permitting theremoved detector to be monitored.This is achieved in a number of ways.

An active end of line device uses aswitched resistor at the end of lineand can thus be used with astandard control panel. It sends aperiodic signal back along thedetection line, which is normallyquenched by the control panel.When a head is removed, the basediode is switched into the line, andpulse can be seen. The Active endof line then switches the resistor outof the line, and a fault is signalled.

If a capacitive end of line is used,the panel periodically drops the linevoltage for a few milliseconds, andlooks for the line voltage being heldup by the capacitor. When a head isremoved, the panel will see the linevoltage drop immediately as thecapacitor's discharge will beinhibited by the diode, and therebya fault can be signalled.

A third type of end of line device isa diode. With this the panelperiodically reverses the line voltagefor a few milliseconds: If the line isbroken by the diode in the detectorbase, then no current can flow inthe reverse direction.

The type of end of line monitoringused on a system will depend on the control panel. However it is important, particularly when using active end of line monitoring

6

0V

+24V

E.O

.L.

Contact Closeswhen detector

inserted in base

Figure 3: Example resistive conventional system current and voltage figures

Figure 4: Active end of line monitoring circuit

Monitoring of detection line(example only)

Condition Current Voltage

Open Circuit <3mA 24V

Normal 5mA (dependant on EOL device) 18V

Fire 50mA (dependant on control panel) 4 –15V

Short Circuit High (dependant on control panel) 0V


to ensure that the detectors are compatible with the type of monitoring being used. Reference must be made to the panel manufacturer to ensure compatibility.

remote LEDsMost system smoke detectors areequipped with a terminal to allowthe connection of a remote LED.Remote LEDs are often usedoutside bedroom doors in hotels sothat in case of a fire, it is easy forthe fire brigade to identify thelocation of the fire without needingto enter every room in the building.They may also be used where adetector is located in a hiddenposition, such as a floor or roof voidor cable tunnel, for example, toprovide a visual indication that thedetector is in an alarm state.

four-wire system operationIn some cases it is necessary thatthe power to the detectors and thefire detection signal be on separate

wires, see figure 5. In this instance,a base incorporating a change overrelay is used. This configuration isknown as a four-wire system, and isoften seen when a fire zone isintegrated into a security panel.

Figure 5 shows the simplest form offour-wire system, as used with mostsecurity panels. This is used wherethe monitor line is able only toregister an open or closed circuit -there is no distinction between afault and a fire. By using a normallyclosed relay at the end of the powerline, it is possible to monitor for apower failure to the detectors. The

relay contacts are wired in serieswith the normally closed contacts ofthe detector relay base(s). Thus inthe normal state the detectioncircuit is closed; in the case of fireor power failure the relevant relaycontacts will open.

Normally after an alarm, thedetectors are reset by disconnectingthe power to the relevant zone for ashort period by pressing a centralpanel reset button. Fire panels havethis facility built in, however manysecurity panels are unable to do thiswithout turning the entire panel off.Therefore to allow the use of

detectors with security panels, non-latching versions of the relaybases are usually made available,which automatically isolate thedetector from the supply every fewseconds. Thus once the firecondition has passed the detectorwill automatically reset (note thatthe alarm condition should belatched at the control panel.)

Four-wire type systems are also

often used with devices such as

beam detectors where an auxiliary

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C NO NC C NO NC

End of LineMonitoring Relay

FIREALARM

CONTROLPANEL

Detection Line(Open Circuit forAlarm and Fault)

Power Supply(Nominal 12Vor 24V System)

ALA

RM

RE

LAY

(N

/O)

FAU

LTR

ELA

Y (

N/C

)

MA

INT

EN

AN

CE

RE

LAY

(N

/C)

+24

VD

C IN

- 24

VD

C O

UT

+ 24

VD

C O

UT

- 24

VD

C IN

ALA

RM

RE

LAY

(N

/O)

FAU

LTR

ELA

Y (

N/C

)

MA

INT

EN

AN

CE

RE

LAY

(N

/C)

+24

VD

C IN

- 24

VD

C O

UT

+ 24

VD

C O

UT

- 24

VD

C IN

EO

L

BEAM DETECTOR #1 BEAM DETECTOR #2

+ 24VDC

DETECTION CIRCUIT

- 24VDC POWER SUPPLYEND OF LINERELAY COIL

Res

isto

r

Res

isto

r

Figure 5: Typical 4 wire system wiring

Figure 6: 4-wire system with full monitoring


power supply may be required. In

this case if the device is connected

to a fire control panel, able to

distinguish between different

detector states, the circuit can be

routed to provide full monitoring for

alarm and fault. Figure 6 shows

typical wiring for a beam detector,

which includes it's own internal

maintenance and fault monitoring.

With this layout all fault and

maintenance contacts are wired in

series, and all alarm contacts in

parallel with the end of line device.

In the case of a fault or

maintenance signal, the end of line

will be disconnected, and a fault

can be signalled at the panel. To

distinguish between an alarm and

short circuit, a resistor, typically

470 Ohms is placed in series with

each alarm contact as indicated in

order to shunt the detector zone.

Note that a separate reset signal

may be required to reset some

beam detectors

fire alarm (sounder) zone operation Similarly to detection lines, it isimportant to monitor fire alarmzones to ensure that the cable hasnot been broken, disconnected orshorted. However the operation ofalarm zones is different fromdetection lines.

Fire alarm sounders contain apolarising diode, which allows them

to operate when a voltage is applied

in one direction, but not when the

voltage is reversed. When the

system is in standby, the panel

applies a voltage in the 'wrong'

direction, so that the sounders do

not operate and do not draw any

current. An end-of-line resistor

draws a constant monitoring

current, which allows the panel to

verify that the wiring is intact.

Should the panel sense that no

current is being drawn, it signals an

open circuit fault. In the case of a

short circuit, a high current is drawn

from the zone, the voltage drops

towards zero and a fault condition

is shown. To activate the sounders,

the control panel reverses the

polarity of the voltage to the zone.

8

Standby24VDC

Alarm24VDC

EO

L

Figure 7: Conventional fire alarm sounder circuit


introductionConventional fire alarm systemsprovide an adequate and costeffective fire alarm system for manysmall buildings. In larger, morecomplex buildings however, moresophisticated ‘intelligent’ fire alarmsystems tend to be used. Thesesystems offer benefits in speed ofdetection, identification of thelocation of a fire and easiermaintenance. Intelligent systemsalso offer tolerance to faults in thesystem wiring, which allows a single

pair of wires to be used to connecta large number of devices to thesystem, allowing cost savings in thewiring of large systems. In largerinstallations, the benefits ofimproved maintenance and reducedcabling cost are overwhelming.Currently, the point at which anintelligent system becomeseconomical is around 6 zones in the UK.

This guide is intended as an

introduction to the technology used

in intelligent fire alarm systems.

Figure 8 demonstrates an example

of a single loop intelligent fire

system layout. The wiring is looped,

and connects to the control panel at

each end. All detectors, call points,

sounders and interface modules are

wired directly to the loop, each

having its own address.

The control panel communicates

with each device on the loop, and if

an alarm or fault condition is

signalled, or if communications are

lost with one or more detectors, the

appropriate response is triggered.

The loop can be powered from each

end so that if the loop is broken at

any point, no devices are lost. In

addition the use of short circuit

isolators minimises the area of

coverage lost in the case of a

short circuit.

intelligentsystem typesThere are two methods commonly

used for implementing intelligent

fire systems:

The most common type of system is

“Analogue”. In this case the detector

(or sensor) returns a value to the

panel representing the current state

of its sensing element(s).

The control panel compares this

value with the alarm threshold in

order to make the decision as to

whether a fire is present. Note that

the term analogue, used to describe

these systems does not refer to the

communication method (indeed

many “analogue” fire systems use

9

intelligent fire alarm systems

INTELLIGENTFIRE ALARM

CONTROLPANEL

EO

LE

OL

ISOLATOR

CONTROLMODULE

MONITORMODULE

ISOLATOR

ISOLATOR

CONVENTIONALALARM ZONE

CONTACT(E.G. SPRINKLERSWITCH

FIRE ALARM SYSTEM OK

28 January 2004

14:01

SYSTEM OK

SYSTEM RESET

FIRE ALARM

FAULT

Figure 8: Intelligent fire alarm systems


digital communications) but to the

variable nature of the response from

the detector to the control panel.

In “Addressable” type intelligentsystems, mainly used to meet therequirements of the French market,detector sensitivity is programmedto each device by the control panelor is preset in the factory.

The detector compares its currentsensor value with the configuredthreshold to make the alarmdecision, which is then transmittedto the panel when the sensor isinterrogated.

In many systems the featuresoffered by the two detectiontechniques are so similar that it isnot particularly relevant whichtechnique is used to make the alarmdecision. It is better to select asystem based on the featuresoffered by the system as a whole.

communicationprotocolIntelligent systems use the samepair of wires both to supply powerto the loop, and to communicatewith devices on the loop.

The communication language, orprotocol used varies from

manufacturer to manufacturer, butgenerally comprises switching of the24V supply voltage to other voltagelevels to achieve communication.

A typical basic protocol comprisestwo main parts (See Fig 9): A queryor poll of a device by the controlpanel including the device addressand control information, and aresponse from the device giving itsstatus and other information.Precise details of the informationtransferred will depend on themanufacturer, but normally willinclude:

Poll: Control Panel to device:

• Device address

• Control of device LED -blink to indicate polling,switch on when device isin alarm

• Control of device self-test

• Control of module output

• Error detection forexample parity bit orchecksum

Response: Device toControl Panel

• Device type (e.g. opticaldetector, heat detector,multi-sensor detector,module)

• Analogue Signal - i.e. thecurrent sensor value

• Alarm Signal ifappropriate

• Status of module output

• Remote test status

• Manufacturer code

Most commonly, each device on theloop will be polled in turn, howeverto increase speed around a loop,some protocols allow polling ofgroups of devices on a singlecommunication.

Note that since differentmanufacturers have their ownprotocols, it is important toensure compatibility between thedetectors and control panel youintend to use. Some detectormanufacturers produce intelligentdetectors with differentcommunication protocols fordifferent customers, so twodetectors which look virtuallyidentical in appearance may notbe compatible. Always check with the manufacturer of thecontrol panel.

addressingmethodsDifferent manufacturers of intelligentsystems use a number of differentmethods of setting the address of a device, including:

10

Panel to detector Detector Response

Control

Err

or C

heck

DetectorAddress

DeviceType

Test

Sta

tus

SensorValue

Other Infoe.g. driftstatus

+24V

Figure 9: Typical protocol configuration

1 1

2

TENS UNITS

2

3 3

4 45 5

6 6

7 7

8 8

0 09 9

Figure 10: Decade address switchesaddress 03 selected


• 7-bit binary orhexadecimal DIL switch

• Dedicated addressprogrammer

• Automatic, according tophysical position on theloop

• Binary ‘address card’fitted in the detector base

• Decimal address switches

Using the Decimal Address Methoddifferences in the protocol betweendetectors and modules allow themto have the same address withoutinterfering with each other, andnormally address 00 (the factorydefault setting) is not used within a system so that the panel canidentify if a device address has notbeen set: Hence a total of up to 198 devices - 99 detectors and 99modules (including call points,

sounders, input and outputmodules) may be connected to a loop.

system faulttoleranceDue to the looped wiring methodused for analogue systems, they aremore tolerant to open and shortcircuit wiring faults thanconventional systems.

Under normal conditions, the loop

will typically be driven only from one

end. If the loop is broken (See figure

11.), the panel will detect the loss of

communications with the detectors

beyond the break, signal a fault, and

switch to drive the loop from both

ends. The system therefore remains

fully operational, and can possibly

even indicate the area of the break.

In order to give tolerance againstshort circuits on the loop, shortcircuit isolators are placed atintervals on the loop. Should a shortcircuit occur on the loop (Figure 12)the isolators directly on either sideof the fault will isolate that section.The panel will detect the loss of thedevices, signal a fault and drive theloop from both ends, therebyenabling the remainder of the loopto operate correctly and ensuringminimum loss of coverage.

Short circuit isolators are availableas separate modules andincorporated into a detector base.

Some products have isolators builtinto each of the loop devices. Withthis configuration, since only thesection of wiring between the twoadjacent devices is isolated therewill be no loss of coverage should a short circuit occur.

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CONTROL PANEL

24V

24V

Panel detects the loss ofdevices after the break,signals a fault and powersfrom both ends of the loopto retain full coverage.

Line breakSYSTEM FAULT: OPEN CIRCUIT:

Zone 2 Module 01

FIRST FLOOR CANTEEN

SYSTEM OK

SYSTEM RESET

FIRE ALARM

FAULT

IsolatingImpedance

IsolatingImpedance

Short Circuit

Isolators on either side ofthe short circuit switch animpedance onto the lineto isolate it.

Devices between the twoisolators are lost,however the remainder ofthe circuit still operatescorrectly.

Isolators automaticallyreset the line when theshort circuit is removed


CONTROLPANEL

24V

24V

SYSTEM FAULT: SHORT CIRCUIT:

Zone 2 DETECTOR 03

FIRST FLOOR CANTEEN

SYSTEM OK

SYSTEM RESET

FIRE ALARM

FAULT

Figure 11: Open circuit fault Figure 12: Short circuit fault


driftcompensationandmaintenancealarmThe sensitivity of a smoke detectortends to change as it becomescontaminated with dirt or dust (seefigure 13). As contamination buildsup, it usually becomes moresensitive, leading to the risk of afalse alarm, but in some cases can

become less sensitive, so delayingthe alarm if a fire is detected. Tocounter this, if a detector driftsoutside its specification, amaintenance signal may be sent tothe panel warning that the detectorneeds cleaning.

To further increase the maintenanceinterval, many systems incorporate

a “drift compensation” function,included in either the detector or thecontrol panel algorithms. Thesefunctions use algorithms thatmonitor the sensitivity of a detector,and modify its response tocompensate for a build up of dust inthe chamber over time. Once thedetector reaches the “drift limit”when the dirt build up can no longerbe compensated for, a fault can besignalled. Some systems alsoincorporate a warning to signal that a detector is approaching its compensation limit and requires cleaning.

pre-alarmfacilityOne advantage of intelligent typesystems is that since the data sentby a detector to the panel varieswith the local environment, it can beused to detect when the device isapproaching an alarm condition.

This “Pre-Alarm” can be signalled at the panel and can therefore beinvestigated to check if there is areal fire, or if it is caused by othersignals, for example steam or dustfrom building work. This can avoidthe inconvenience and expense ofevacuating a building or calling outthe fire brigade unnecessarilybecause of a nuisance alarm. ThePre-Alarm Threshold is typically set at 80% of the alarm threshold.

fire alarmsWhen a fire is detected, the controlpanel indicates an alarm byactivating the fire indicator for therelevant zone on the control panel,sending a command to the relevantdetector to illuminate its LED andactivate alarm signals to startevacuation. Most intelligent firesystem control panels includealphanumeric displays enablingthem to show information on thesource of the alarm. This maysimply be a zone and detectoraddress, or could be moredescriptive for example “SmokeDetector, Bedroom 234”. Thecontrol panel may also use controlmodules to operate additionalelectrical equipment such as airconditioning units and door releases to prevent the spread ofsmoke and fire.

The alarm signals can either be a

zone of conventional sounders and

strobes activated via control

modules on the loop or directly from

the control panel, or addressable

loop powered devices connected on

the same loop as the detectors and

12

Cha

mbe

r Val

ue

Time

Clean AirValue

UncompensatedAlarm Threshold

UncompensatedChamber Value

CompensatedThreshold

Smoke required toreach alarmthreshold reduces -Detector sensitivityincreases

Thresholdincreased tocompensate forincreased chamberclean air value.

Figure 13: Chamber contamination and drift compensation


activated by direct command fromthe panel. Loop powered sounderstend to have lower wiring costs,however the number permissible on the loop may be restricted bycurrent limitations.

On larger sites, it may be desirableto use zoned alarms. This allows aphased evacuation to be carriedout, with areas at most immediaterisk being evacuated first, then lessendangered areas later.

fire systemzonesConventional fire alarm systemsgroup detectors into ‘zones’ forfaster location of a fire, with all thedetectors in a particular zone being

connected on one circuit. Althoughintelligent systems allow the precisedevice that initiated an alarm to beidentified, zones are still used inorder to make programming thesystem and interpreting the locationof a fire easier. The control panelmay have individual fire indicatorsfor each zone on the system, andthe control panel response to analarm is often programmedaccording to the zone of the device in alarm rather than itsindividual address.

The division of a loop into zones isachieved within the panel software,however, as multiple zones arephysically connected onto the samecable, a short circuit can affect theoperation of a large area ofdetection devices unlike aconventional system. BS5839 part 1

therefore recommends the divisionof the loop as to limit the effect of ashort circuit with the use of shortcircuit isolators. The placement ofthese isolators should typically limitthe loss of coverage to less than2,000 m2 nor more than one floor(figure 14). Allowances are made forthe floor above and below but thisis limited as not to affect more thanfive devices on these floors.

remote LED’sMost system smoke detectors areequipped with a terminal to allowthe connection of a remote LED.Remote LEDs are often used outsidebedroom doors in hotels so that incase of a fire, it is easy for the firebrigade to identify the location ofthe fire without the need to enterevery room in the building. Theymay also be used where a detectoris concealed in loft space, for example,to provide a visual indication thatthe detector is in an alarm state.

interfacemodulesInput and Output modules can beused to provide an interfacebetween a fire loop and a variety oftypes of electrical equipment.Output or control modules can beused to operate sounders or shutdown electrical equipment bycommand from the panel in case ofa fire. Input or monitor modules areused to monitor volt-free switchcontacts, for example from asprinkler supervisory switch or anexisting conventional fire panel.

13

Figure 14: Intelligent system fire zones


Conventional zone monitor modulesare also available, providing aninterface between a zone ofconventional detectors and ananalogue fire detection loop, andare often used when existingconventional systems are upgraded.

programmingof intelligentfire alarmpanelsMost small intelligent systems canbe programmed with ease withoutthe need for any specialisedequipment. The control panel has analphanumeric keypad, which is usedto enter data into the system.Typically a password is required toset the panel to ‘engineering mode’,allowing the panel to beprogrammed. Many control panelshave an ‘auto-learn’ facility,whereby the control panel pollsevery address on the system, anddetects which addresses have beenused, and what type of detector ormodule has been connected to eachaddress. As a default, the panel willusually programme all the deviceson the loop into the same zone.

The user can then customise thesystem by entering how the zonesare configured. The panel may givethe user an option of how modulesare to be configured - for examplewhether an input module shouldtrigger an alarm or a fault whenoperated and whether the wiring is to be monitored for open circuit faults.

Other optional features may also beprogrammed using the keypad. Thesensitivity of each detector on thesystem can be configured for highsensitivity if the detector is installedin a clean smoke-free area, or forlow sensitivity if the area is subjectto cigarette smoke, for example.Complex intelligent systems offermany user-programmable featuresthat can be time-consuming to entermanually using the keypad. In thiscase, many panels have the facilityto connect a portable PC by meansof a serial data link.

The user is supplied with aspecialised piece of software, whichenables the entire configuration ofthe system to be programmed intothe PC, away from site if necessary.It is then a simple matter oftemporarily connecting the PC tothe control panel and downloadingthe system configuration to thepanel. Once the information hasbeen downloaded, it is permanentlystored in the control panel, and thePC can be removed.

advantages ofintelligentsystems• The wiring cost of a

system can be reduced bythe use of a single pair ofwires for many devicesincluding smoke and heatdetectors, call points,beam detectors, input andoutput modules.

• Intelligent Systems allow

the location of a fire to beprecisely located from thecontrol panel

• The use of looped wiringallows the system tofunction normally evenwith an open circuit in theloop wiring

• The use of short circuitisolators allows correctoperation of most, if notall of the system evenwith a short circuit in theloop wiring

• Detectors are constantlymonitored for correctoperation

• The use of a ‘pre-alarm’feature alerts staff tocheck whether a firecondition exists beforethe alarm is raised

• Different detectorsensitivities can be usedfor diverse applications

• The use of addressableloop-powered soundersallows the same wiring tobe used for sensors, callpoints and sounders

• The use of monitormodules allows contactsfrom sprinkler switches,existing fire alarmsystems, fire dampers etc.to be monitored usingdetector loop wiring

• The use of controlmodules allows sounderlines, air conditioningsystems, lifts etc. to becontrolled or shut downusing detector loop wiring

14


detectorapplicationguidefire system categoriesBefore a fire protection system canbe designed, it is necessary todefine the main objectives of thesystem. This is normally determinedby a fire risk assessment, andshould be provided as part of thefire system specification. BS5839Part 1: 2002 defines three basiccategories of fire detection system.

category M systemsCategory M systems rely on humanintervention, and use only manuallyoperated fire detection such asbreak glass call points. A categoryM system should only be employedif no one will be sleeping in thebuilding, and if a fire is likely to bedetected by people before anyescape routes are affected. Anyalarm signals given in a category Msystem must be sufficient to ensurethat every person within the alarmarea is warned of a fire condition.

category L systemsCategory L systems are automaticfire detection systems intended toprotect life. The category is furthersubdivided as follows:

category L5: In a category L5system certain areas within abuilding, defined by the fire systemspecification, are protected byautomatic fire detection in order toreduce the risk to life. This categoryof system may also include manualfire protection.

category L4: Designed to offerprotection to the escape routesfrom a building. The system shouldcomprise Category M plus smokedetectors in corridors and stairways

category L3: Intended to offerearly enough notification of a fire toallow evacuation before escaperoutes become smoke logged.

Protection should be as for categoryL4 with the addition of smoke orheat detectors in rooms openingonto escape routes.

category L2: Objectives are similarto category L3, however additionalprotection is provided for rooms athigher risk. Protection should be asfor category L3 plus smokedetectors in specified rooms at high risk

category L1: The highest categoryfor the protection of life. Intended togive the earliest possible notificationof a fire in order to allow maximumtime for evacuation. Automatic andmanual fire detection installedthroughout all areas of the building.Smoke detectors should beemployed wherever possible toprotect rooms in which people canbe expected to be present.

15

dow

n

Canteen Kitchen Pantry

PaperStore Office Office

dow

n


PaperStore

Office Office

Example L5 System: L4 protection plus areas of high risk

dow

n



dow

n


PaperStore

Office Office

dow

n




Similarly to class M systems, all

alarm signals given in a category L

system must be sufficient to warn

all those people for whom the

alarm is intended to allow for a

timely evacuation.

category P systemsCategory P systems are automatic

fire detection systems whose

primary objective is to protect

property. The category is subdivided

as follows:

category P2: Intended to provide

early warning of fire in areas of high

hazard, or to protect high-risk

property. Automatic fire detection

should be installed in defined areas

of a building.

category P1: The objective of a

category P1 system is to reduce to

a minimum the time from the

ignition of a fire to the arrival of the

fire brigade. In a P1 system, fire

detectors should be installedthroughout a building.

In a category P system, unlesscombined with category M, it maybe adequate for alarm signalssimply to allow fire fighting action tobe taken, for example a signal toalert a responsible person to call thefire brigade.

manual call pointsPeople can often still detect a firelong before automatic fire detectors;hence manual call points areimportant components of firedetection systems in occupiedbuildings to ensure timelyevacuation in the case of fire. Allcall points should be approved toEN54-11, and should be of type A,that is once the frangible element isbroken or displaced the alarmcondition is automatic.

Manual call points should bemounted on all escape routes, andat all exit points from the floors of abuilding and to clear air. It shouldnot be possible to leave the floor ofa building without passing a manualcall point, nor should it benecessary to deviate from anyescape route in order to operate amanual call point. Call pointsmounted at the exits from a floormay be mounted within theaccommodation or on the stairwell.In multiple storey buildings wherephased evacuation is to be usedcall points should be mountedwithin the accommodation to avoid activation of call points onlower levels by people leaving the building.

In order to provide easy access, callpoints should be mounted between1.2 and 1.6m from the floor, andshould be clearly visible andidentifiable. The maximum distanceanyone should have to travel inorder to activate a manual call pointis 45m, unless the building isoccupied by people having limitedmobility, or a rapid fire developmentis likely, in which case the maximumtravel distance should be reducedto 20m. Call points should also be

16

dow

n


PaperStore

Office Officedo

wn

Electrical Plant MaterialsStorage

ComputerEquipment

CanteenKitchen Pantry

Office Office

MAX DISTANCE 45M1.2 to 1.6m

dow

n

Electric Plant MaterialsStorage

ComputerEquipment

Figure 15: Intelligent system fire zones


sited in close proximity to specifichazards, for example kitchens orpaint spray booths.

selection of automatic firedetectorsSmoke detectors are the mostsensitive automatic means ofdetecting a fire and should be used wherever conditions allow.

ionisation smokedetectorsIonisation smoke detectors use aweak radioactive source to ionisethe air between two electrodes,creating positive and negative ionsand so allowing a small current toflow across the chamber. Smokeparticles attract these ionisedparticles, and allow positive andnegative ions to recombine, thusreducing the number of ions andhence the current flow.

Environmental regulationsconcerning the radioactive sourceused in ion detectors means thatthey are now becoming obsolete,and most major manufacturers areno longer including ionisationdetectors in new ranges.

photoelectric smokedetectorsPhotoelectric or optical smokedetectors work by generating pulsesof infra red light and measuring anydiffracted light. If smoke is presentin the sensing chamber, the light isdiffracted by the smoke particlesonto a photodiode, which sensesthe presence of the smoke (see

figure 16). They are now largelyreplacing ionisation detectors as ageneral purpose detector.

Photoelectric smoke detectors aretested across the complete range ofEN54 fires, however they are mostsensitive to smoke containing largeparticles from around 0.4 to 10microns, such as that given off bysmouldering fires. A photoelectricdetector would therefore be a good

choice in an environment where aslow burning fire could be expected,such as a room containing modernfabrics and furnishings.

multi-criteria detectorsMulti-criteria detectors comprise two

or more sensors within the samehousing, integrated by the detectorelectronics or software to give arapid response to a broader range

17

Without smoke: Chamber is designed so that light from the IR-LED does not reach the receiver

Smoke present: Light from the IR-LED is reflected off the smoke particles onto the receiver, triggering an alarm signal

Figure 16: Operation of optical chamber


of fires and greater immunity tonuisance alarms. The most commontype at present is a combination ofoptical and rate of rise heatsensors, which can give a responseto fast flaming fires similar to that ofionisation detectors. Other sensorcombinations are also available.

CO detectorsA recent addition to BS5839 is COdetectors. These generally use anelectro-chemical sensor to detectcarbon monoxide given off byincomplete combustion. Theyprovide reliable detection ofincipient fires whilst giving goodassurance against nuisance alarms.However the chemical cells used inthese detectors have a limited lifespan, and they cannot detect fastburning fires due to the low COlevels produced.

heat detectorsHeat detectors are normally used in

environments where a smokedetector might generate falsealarms, for example kitchens orshower rooms.

Rate of Rise heat detectors willalarm if the temperature rises veryquickly, or if the temperature

reaches a set threshold. This type ofdetector would be the first choice inan environment where a smokedetector could not be used.

In some environments, such asboiler rooms, fast rates of rise oftemperature can be expectednormally, meaning that there wouldbe a risk of false alarms when usinga rate-of-rise device. In this case afixed temperature detector would besuitable. As their name implies,fixed temperature detectors give analarm once the temperature hasreached a preset threshold, mostcommonly 58°C or 78°C for EN54-5Class AS or BS respectively.

optical beam detectorsOptical beam detectors work on theprinciple of projecting a beam oflight across a room, which isattenuated when smoke is presentthus allowing an alarm to be given

18

Time

Cha

mbe

rVal

ue

AlarmThreshold

OpticalAlarm

ChamberResponse

HeatResponse

Multi-CriteriaAlarm

Figure 17: Photo-thermal detector response

Up to 100M

Up

to 2

5m h

eigh

t

CombinedEmitter /Receiver Unit

Reflector

Beamattenuated bysmoke plume

Figure 18: Operation of reflective type optical beam smoke detector


(Figure 18). There are two forms ofbeam detector: emitter and receiverseparate (single path), requiringseparate wiring both to the emitterand receiver, and reflective in whichthe emitter and receiver aremounted in the same box, and thebeam is shone onto a reflectivematerial at the far side of the room(dual path).

Since an optical beam detectorsenses smoke across the entiresmoke plume, it tends to be lessaffected by smoke dilution as theceiling height increases than pointtype smoke detectors. In addition, asingle beam detector can protect alarge area; hence they areparticularly suitable for protectinglarge high rooms such as sports

arenas, warehouses and shopping malls.

Beam detectors are more complexto install than ordinary point smokedetectors and it is advisable toconsult an application guide for theuse of projected beam smokedetectors before considering theuse of these detectors.

19

Figure 19: Selection of fire detectors

Detector type Application Not suitable for

Ionisation smoke General purpose smoke detector Areas subject to smoke, steam,detector – better for fast flaming fires dust or dirt during normal use

Optical smoke General purpose smoke detector Areas subject to smoke, steam,detector – better for smouldering fires dust or dirt during normal use

Photo-thermal multi- General purpose detector – good Areas subject to smoke, steam,criteria detector for smouldering and fast flaming fires dust or dirt during normal use

Optical beam smoke Large and high rooms Areas subject to smoke, steam,dust or dirt during normal use

Rate of rise heat Areas subject to smoke, steam, dust Areas subject to rapid changesdetector of dirt during normal use of temperature or temperature

over 43ºC

Fixed temperature Areas subject to smoke, steam, dust Areas subject to temperaturesdetector (58ºC) or dirt and rapid changes of over 43ºC

temperature during normal use

High temperature Areas subject to smoke, steam, dust Areas subject to temperaturesfixed detector (78ºC) or dirt and temperatures over 43ºC over 70ºC

during normal use


location and spacing ofautomatic fire detectorsIt is important to consult applicablelocal and national standards whenchoosing the spacing and locationof fire detectors. The followinginformation is intended only as aguide to the location and spacing of detectors. There is currently noEuropean standard available; hence this guide is based onBS5839 part 1, 2002.

location and spacing ofpoint fire detectors on flat ceilingsOn a flat ceiling with noobstructions, the radius ofprotection of fire detectors is 7.5mfor a smoke detector and 5.3m for aheat detector, and detectors shouldbe mounted a minimum of 0.5mfrom a wall. Some analogue multi-criteria detectors have a heatsensor only function, switched bythe control panel, typically used toreduce the possibility of falsealarms during daytime when abuilding is occupied, reverting tomulti-sensor operation at night time.If this type of operation isemployed, the radius of protectionfor a heat sensor should be used.Figure 20 gives a simple spacingplan based on these figures,however it should be noted that thismight not be the most efficientlayout for a given site; for examplein larger areas, it is also possible touse a staggered layout, see figure21, which may reduce the numberof detectors required. In practice,the layout of the room must beconsidered to obtain the mostefficient detector layout.

20

Standard Smoke Detector Spacing Standard Heat DetectorSpacing

10.5m5.3m

7.5m

3.7m

5.3m

7.5m

60 °

60 °

11.2

5m

13m

Figure 20: Simple spacing plans for smoke and heat detectors

Figure 21: Alternate smoke detector spacing plan for protecting large areas


ceiling heightSmoke or heat detectors can onlydetect fires once a certain amountof smoke or heat has reached thesensor. As the height of a ceilingincreases, the time taken for smokeor heat to reach a sensor willincrease, and it will become dilutedwith clean, cool air. As a result,maximum ceiling heights are limitedas indicated in figure 22 below.

Often, a boundary layer can formclose to the ceiling, which is free ofsmoke and remains cool. To avoidthis, and maximise the probability ofdetection, smoke detectors shouldnormally be mounted with theirsmoke entry 25mm-600mm belowthe ceiling, and heat detectorsshould be mounted with their heatelement 25mm-150mm below theceiling. Detector design normallyensures that the minimum

requirement is met, but care needsto be taken if the detectors are tobe stood away from the roof, forexample mounting on an openlattice suspended ceiling.

Another problem that should beconsidered is the possibility ofstratification of the air in a room intohot and cold layers, causing thesmoke or heat to stop at theboundaries. This particularly affectshigh rooms or atria, where beamdetectors are often used.Stratification is very difficult topredict, and can vary, even withinthe same room as environmentalconditions change.

ceiling obstructionsCeiling obstructions such as beamsgreater than 10% of the ceiling heightshould be treated as a wall, and willthus divide a room. Detectorsshould not be mounted within500mm of such an obstruction.

If the depth of an obstruction suchas a beam is less than 10% of theheight of the ceiling, but greaterthan 250mm deep, then detectorsshould not be mounted any closerthan 500mm to the obstruction.

Where an obstruction such as abeam or a light fitting is less than250mm in depth, detectors shouldnot be mounted any closer to theobstruction than twice its depth (see figure 23)

Where a ceiling comprises a seriesof small cells, for example ahoneycomb ceiling, or a series ofclosely spaced beams, for examplefloor of ceiling joists, therecommended spacing and siting ofdetectors changes further,dependant on the ceiling height andthe depth and spacing of thebeams. Reference should be madeto relevant standards for details (inthe UK BS5839 Part 1: 2002, 22.3.kfigure 3 and 19).

21

Detector type Maximumceilingheight

Point smokedetectorconforming toEN54–7 10.5m

Heat detectorconforming toEN54–5 Class A1(threshold 58ºC) 9m

High temperatureheat detectorconforming toEn54–5 Class B(threshold 78ºC) 6m

Optical beamdetectors 25m

Figure 22: Maximum ceiling height fordifferent types of detector

Minimum500mm

>10% of Ceiling Height

Treat as separate room

Minimum500mm

>250mm<10% of Ceiling Height

Normal Detector Spacing, eg. 10.5m maxfor “simple” layout.

Minimum 2 xheight

Height < 250mm

Normal Detector Spacing, eg. 10.5m maxfor “simple” layout.

Figure 23: Detector spacing around isolated ceiling obstructions


partitions and rackingWhere the gap between the top of apartition or section of racking andthe ceiling is greater than 300mm, itmay be ignored. If the gap is lessthan 300mm it should be treated as a wall.

To maintain a free flow of smokeand heat to the detector, a clearspace should be maintained for500mm in all directions below the detector.

sloping ceilingsWhere the ceiling is pitched orsloping, the slope of the roof tendsto speed the rise of smoke or heatto the apex, hence reducing thedelay before the detectors aretriggered. For sloped roofs with apitch height greater than 600mm forsmoke detectors, or 150mm for heatdetectors, a row of detectors shouldbe placed within a maximum verticaldistance of 600mm or 150mm forsmoke or heat detectorsrespectively from the roof apex.Sloped roofs rising less than 600mmfor smoke detectors or 150mm forheat detectors may be treated as aflat ceiling.

Since the smoke or heat tends torise faster up the slope, it ispermissible to use a greater spacingfor the row of detectors mounted inthe apex of the roof: For eachdegree of slope of the roof, thespacing may be increased by 1%up to a maximum of 25%. Where,as in figure 24, the roof slopes areunequal the spacing down theslopes can be unequal, howeveralong the roof apex spacing thelesser of the two figures should be

used, in this example 10.5m +18%.Where the slope finishes within theadjusted detection radius, thestandard distance to the next row ofdetectors, 10.5m, should be used.Care must be taken when placingthe next row that no gaps are left indetection coverage.

corridorsIn corridors less than 2m wide,detectors should be spaced at adistance of 15m for smokedetectors and 10.6m for heatdetectors, with the maximumdimension to a wall at the end of the corridor being 7.5m and5.3m respectively.

In narrow rooms and corridorsgreater than 2m wide, due to theway that the coverage radii ofdetectors intersect with the walls ofthe corridor, the spacing betweendetectors will increase. Figure 25shows how, for a room 6m wide, thespacing for smoke detectors can beincreased from the standard 10.5m.

stairwells and lift shaftsInternal stairwells and lift shafts andother vertical service ducts througha building provide a clear path forsmoke to pass between floors of abuilding as if they were chimneys. It is therefore important to protect these, preferably usingsmoke detectors.

All vertical shafts through a buildingmust be protected by a smoke orheat detector at the top of the shaft,and by a detector within 1.5m ofeach opening onto the shaft.

22

18°

15mMax 600mm

10.5

m

12.3

9m=

10.5

+ 1

8%

7.5m

8.85

m

=7.5

+ 1

8%

9.35

m

= 7.

5 +

25%

40°

Figure 24: Spacing of smoke detectorsunder a pitched roof

Note: Detectors are mounted in the centre line of the room

6.88m 13.75m

7.5m

6m

Figure 25: Smoke detector spacing in corridors greater than 2m wide


In internal stairways, a detectorshould be mounted on each mainlanding (Figure 26). In addition, ifthe detectors on the landings areseparated by more than 10.5m,intermediate detectors should bemounted on the underside of the stairs.

Detectors should also be fitted intoany room opening directly onto astairway other than a WC cubicle.

voids and false ceilingsDetectors need not normally beinstalled in voids less than 800mmdeep, unless on the basis of a firerisk assessment it is thought thatfire or smoke could spread

extensively through the voids beforedetection, or unless the fire risk inthe void is such as to warrantprotection. Use of heat and smokedetectors in voids greater than800mm high is dependant on the protection category, and fire risk assessment.

Where they are installed into voids,a detector's sensing element shouldbe mounted either in the top 10% orthe top 125mm of the void spacewhichever is greater. Although it canbe difficult to install detectors thecorrect way up in void spaces, careshould be taken as incorrectorientation of a detector can lead to increased ingress of dirt anddust, leading to reduced

maintenance intervals, and possiblenuisance alarms.

Detectors above a false ceiling maybe used to protect the area below it,if the false ceiling is perforateduniformly across the complete areaof the ceiling, with the holes makingup over 40% of the ceiling surfacearea, having a minimum size of10mm and the false ceiling having athickness of less than three timesthe dimensions of the perforations.

In all other cases, the areas aboveand below a false ceiling should betreated as separate, and thus shouldbe protected separately with detectorsbelow the ceiling, and if necessaryin the void above the ceiling.

23

1.5M1.5M

< 1

0.5M

Figure 27: Protecttion of vertical shaftsFigure 26: Detector in stairwells


lantern lightsA detector should be mounted inany lantern light used for ventilationor having a height exceeding800mm. The temperature in lanternlights can change rapidly owing toheating by sunlight, which meansthat rate-of-rise heat detectorsshould not be used and heatdetectors should be protected fromdirect sunlight.

location and spacing of optical beam detectorsGenerally, for an optical beamdetector mounted within 600mm ofa ceiling, the fire detection coverageis up to 7.5m either side of the beam(Figure 28). The beam of the

detector should not be closer than

500mm to any obstruction. Similar

recommendations to above apply to

the application of beam detectors

with sloped ceilings, voids, false

ceilings, walls and partitions and

ceiling obstructions.

Where it is likely that people will be

present in an area protected by beam

detectors, the detectors must be

mounted at a minimum height of

2.7m, and consideration must also

be given to the possibility of other

temporary obstructions to the beam

such as forklift trucks.

For further information on the use

and mounting of beam detectors,

see Beam Detector Guide.

alarm signalsaudible alarm signalsAudible fire alarm signals must

provide a clear warning of a fire to

all those for whom the signal is

intended. For category M and L

systems this would normally imply

all occupants of a building, however

in some sites this may not apply, for

example in hospitals or rest homes,

residents might need assistance to

evacuate, in which case it may be

sufficient to alert staff.

The general requirement for the

volume of audible alarm signals is

that they should provide a Sound

Pressure Level (SPL) of at least

65dB(A), but not more than

24

Maximum7.5m

Maximum15m

Transmitter orTransmitter/Receiver Receiver or

Reflector

Receiver orReflector

Transmitter orTransmitter/Receiver

Maximum 100m

Minimum500mm

Figure 28: Smoke detector spacing in corridors greater than 2m wide


120dB(A) throughout all accessible

areas of a building. See figure 29.

Exceptions to this general rule are

as follows:

• In stairways the SPL maybe reduced to 60dB(A)

• Enclosures less than 60m2

may be reduced to60dB(A)

• There is no minimum for enclosed areas lessthan 1m2

• At specific points oflimited extent the SPLmay be reduced to60dB(A)

Where a continuous background

noise level greater than 60dB(A) is

present the fire alarm signal should

be 5dB above the ambient, but not

greater than 120dB(A).

Where the alarm is intended to

wake people, an SPL of 75dB(A) is

required at the bed head. Generally

this will require a sounder to be

placed within the room.

Where it is not possible to place a

sounder within a room, there will be

a loss of approximately 20dB(A)

through a standard door, and

30dB(A) through a fire door.

Warning: Volumes greater than120dB(A) will cause damage tohearing.

In open space, as the distance from

a sounder doubles, the sound level

will be reduced by 6dB(A), as

shown.

It is preferable to use multiple

quieter sounders to achieve the

required sound level, rather than a

smaller number of loud devices.

This is to prevent points of

excessive volume, which may lead

to disorientation or damage to

hearing. Two sounders providing

equal sound levels will combine to

add 3dB(A) to the SPL.

25

dow

n

Are

a <

60m

²M

in 6

0dB

(A)

Minimum65dB(A)

Minimum65dB(A)

Minimum65dB(A)

Minimum65dB(A)

Minimum65dB(A)

Minimum65dB(A)

StairwellMin 60dB(A)

Figure 29: General fire alarm sound pressure levels

MachineryGenerating

80dB(A)

SounderMinimum85dB(A)

Volume atBed Head75dB(A)

SounderVolume

115dB(A)

Standard DoorReduces by

20dB(A)

85 - 20 =65dB(A)

Fire DoorReduces by

30dB(A)

115 - 30 =85dB(A)

SOUND REDUCTION AGAINST DISTANCEBased on a sounder rated at 1m

-30

-25

-20

-15

-10

-5

0

0 5 10 15 20Distance (Metres)

Soundreduction(dB(A

) dB(A) Reduction


visual alarm signals

Visual alarms are required in order to

satisfy the Disability Discrimination

Act (DDA) as well as being used in

areas of high background noise

where hearing protection is likely to

be worn. Just as audible alarms

should be placed throughout all

accessible areas of a building,

visual alarms should be placed such

that they can be seen in order to

alert the hearing impaired.

Visual alarms should be clearly

distinguishable from other warning

lights, preferably red and should

flash at a rate of 30 to 130 flashes

per minute. The recommended

mounting height is above 2.1m,

however they should not be

mounted closer than 150mm from

the ceiling. They should be

positioned so that any alarm isclearly visible from all locationswithin the area protected.

maintenanceof firedetectorsCaution: Prior to carrying out anymaintenance or testing on a fire alarmsystem, the relevant authorities andstaff should be notified.

Over time, the sensitivity of a smokedetector can change owing to abuild-up of dirt in the detectorchamber. In most modern detectorsthis effect is slowed by the inclusionof drift compensation functions,

however the build up can still leadto a risk of false alarms or change inthe detector sensitivity.

The frequency of maintenancerequirements on a detector willdepend on site conditions,obviously the dirtier the site themore frequent maintenance will berequired. The optimum frequency fora given site should be determinedover a period of time after thecommissioning of the fire system.

Some detectors (smoke, heat, ormulti-criteria) are designed suchthat they can be easily dismantledfor maintenance. Normally it issufficient to use compressed air or a vacuum cleaner to remove dustfrom the detector chamber.

Once maintenance on a firedetection system has beencompleted, it should be re-tested.

routinefunctionaltesting of firedetectorsBS5839 Part 1: 2002 gives a range of recommendationsregarding routine testing of a fire detection system.

A weekly test should be carried outon a fire detection system byactivating a manual call point toensure that all fire alarm signalsoperate correctly, and that theappropriate alarm signals are clearlyreceived. This test should be carried

26

69dB(A)

69dB(A)

63 + 3= 66dB(A)

62 + 3= 65dB(A)

14m

12.6

m

-16dB -23dB

-16dB

0dB

Note: dB(A) figures are for example only. Left side represents attenuation; right side indicates typical sound pressure level

25m

14m

85dB(A)


out at approximately the same timeeach week, using a different callpoint in rotation.

In order to comply with BS5839 Part1: 2002, periodic inspections,servicing and functional tests of thefire alarm system should be carriedout at intervals determined by anassessment of the site and type ofsystem installed, not normallygreater than six months.

It is recommended to performregular functional tests on all firedetectors annually. These annualtests may be carried out over thecourse of two or more service visitsduring the twelve-month period.

Codes and standards (in the UKBS5839 Part 1:2002, Section 6) nowrequire functional tests to introducesmoke through the smoke detectorvents and into the sensing chamber.It also calls for heat detectors to betested by means of a suitable heatsource, and not by a live flame. COfire detectors now also need to befunctionally tested by a method thatconfirms that carbon monoxide canenter the chamber.

Many installers use a set ofequipment that consists of acomplete range of test tools thatlocate on the end of the pole inorder to aid compliance with codes.Tools exist for testing smoke, heat,and CO fire detectors, whilst alsoenabling them to be accessed andremoved at height.

Using functional test equipment,along with those maintenance toolsshould ensure that the systemremains at its optimum operation formany years.

27


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