Fire Detection and Alarm Systems

Question 1

Need for Fire Alarm Systems in
Buildings

Answer 1

• In event of fire outbreak, any delay in activation of the fire alarm system & notifying of fire service will contribute to danger to life & heavy property losses.

Question 2

Fire detection in small premises

Answer 2

• In small premises like open-air areas & single-storey buildings, all exits
  are visible & escape travel distances are small.

*Therefore, any fire can be quickly detected by occupants present & shouts of ‘fire!’ may be all that is needed.

Question 3

Fire detection in larger premises

Answer 3

• Fire could start & develop to extent that escape routes may become affected before fire is discovered
• Thus need automatic fire warning system

*Hence, an effective means for early detection of any fire outbreak is necessary.

Question 4

Functions of a Fire Detection and
Alarm System

Answer 4

• Active fire protection system for the purpose of early detection & raising an alarm of a fire outbreak within building.
• Consists of detection devices working together to detect & warn people thru visual & audio appliances when smoke, fire or other emergencies are present.
• Alarms may be activated automatically from detection devices such as smoke detectors & heat detectors or manual call points or pull stations.
• Alarms can come from either electrically operated alarm bells or visual strobes.

Question 5

Provision of Fire Alarm Systems in
Buildings

Answer 5

• Most Purpose Groups buildings must be provided with a fire detection & alarm system.
• Provision of automatic fire detection and alarm systems & type of fire alarm system is dependent on height of building & total floor area per storey.
• Home fire alarm device (HFAD) must be installed for individual residential units under PG I or II.
• Operation of HFAD must be based on smoke detection technology, with indicator lights to inform occupants

Question 6

Manual Fire Detection System

Answer 6

• Consists of manual call points, that is wired together with alarm system with normally open contacts.
• Usually of the break-glass type & bright red in colour.
• In event of fire, breaking of glass will close electrical contacts and activate alarm system.
• Only effective in premises when people are present to raise alarm in event of a fire.

Question 7

Code Requirements for Manual Call Points

Answer 7

• Provided on every storey of building or part of building and located so that no person need travel more than 30m from any position within building to activate alarm.
• Located on exit routes preferably next to hose reels & on floor landings of exit staircases and at exits to street.
• Located between 0.8m and 1.2m above floor level & should be located at easily accessible and noticeable positions free from obstructions.

Question 8

Audible Alarm Sounders or Alarm Bells

Answer 8

• Should generate a continuous tone.
• Sound should be readily distinguishable from other forms of alarm systems.
• In places of entertainment / areas where sound & special effects lighting systems are installed such as karaoke booths, sound systems must be electronically interlocked with fire alarm system such that these systems will be automatically cut-off when fire alarm system is activated.

Question 9

Visual Alarm Devices

Answer 9

• Signals should be provided to alert people who are hearing-impaired
  or where hearing protection is likely to be worn.
• Signals should not be used in place of audible alarm signals.
• Intensity of light must be sufficient to draw attention of people in vicinity.
• Should be mounted at height of 2m to 2.5m above floor level, such that it is visible from all corners of floor.
• Visual alarms can be in form of a flashing beacon or strobe light.
• Visual alarms must be located tgth with manual alarm call points.

Question 10

Automatic Fire Detection Systems consist of…

Answer 10

• smoke detectors
• heat detectors
• flame detectors
• video imaging fire detector
• maybe manual call points
• maybe fire suppression systems like automatic fire sprinkler system

Question 11

Components of Automatic Fire Detection Systems are wired together for…

Answer 11

Providing continuous surveillance & early detection of any fire outbreak.

Question 12

Automatic Fire Detection Systems are useful where?

Answer 12

• Particularly useful in places where few people will ever visit such as storage areas / at night where people are not around.

Question 13

Why are Automatic Fire Detection Systems effective?

Answer 13

do not rely on people to raise an alarm.

Question 14

Functions of Main Alarm Panel

Answer 14

• Main alarm panel (MAP) is ‘brains’ of fire alarm system.
• Responsible for monitoring various alarm ‘input’ devices like signals from manual call points & automatic detection devices & then activating alarm ‘output’ devices like sounding of audible alarm sounders / alarm bells, visual alarm devices to notify occupants that there is a fire outbreak so that evacuation procedures can begin.

Question 15

DECAM stands for…

Answer 15

Decentralised Alarm Monitoring Station

Question 16

what is DECAM?

Answer 16

• private organisation certified by SCDF to provide Central Alarm Monitoring service to monitor fire alarm signals linked to SCDF Operations Centre.
• acts as an intermediary between building and SCDF Operations Centre.

Question 17

Function of Decentralised Alarm
Monitoring Station (DECAM)

Answer 17

• MAP transmit alarm signal to DECAM and thence to SCDF/Fire service
• Fire alarm system will automatically be placed in alert state.
• After alarm signal has been transmitted, FSM will verify if alarm signal comes from a fire outbreak.
• FSM need affirm w DECAM if got fire or is false alarm
• If is false, DECAM will communicate w Fire Service & signal will be cancelled
• If got fire, DECAM will convey to Fire Service, Fire service send ppl.
• If no reply to DECAM within 2 min, Fire Service still send ppl.
• If Fire Service go and is false alarm, got penalty on building owner

Question 18

Activation of secondary systems:

Answer 18

• Homing of lifts to designated floors, usually first floor so can use to transport firefighters to fight fire & conduct rescue.
• Shut down air-handling units to prevent smoke spread.
• Activate smoke exhaust systems to remove smoke from fire.
• Activate air pressurisation systems to keep smoke out of evacuation routes such as lobbies & staircases.
• Lowering of smoke curtains to keep smoke out of occupied areas.
• Deactivating doors held open by electromagnetic devices to prevent smoke travelling afar.
• Others

Question 19

Precautions against Failure: Fire Detection

Answer 19

• Main Alarm Panel must have means to ensure that automatic detection system is in working order.
• Must be capable of detecting failures, such as loss of power supply to system
  or faulty detectors.
• Such failures will normally be registered visually by the lighting up of an amber fault lamp and audibly by the sounding of the fault buzzer.
• Battery system has to be used for backing-up for 24 hours when the main
  power supply fails.
• Regular inspection, testing & maintenance of the system on daily, weekly and monthly basis.

Question 20

Siting of Main Alarm Panel

Answer 20

(a) Fire command centre
or
(b) Main entrance of building if a Fire Command Centre is not available.

Question 21

Use of Sub-Alarm Panel

Answer 21

• Located remotely from the Main Alarm Panel.
• Has alarm zone facilities or alarms to show the location of the alarm signal and transmits such alarm signal to the Main Alarm Panel.
• Normally located on every floor at fire lift lobbies, smoke stop lobbies, or at the main point of entry to the alarm zone.

Question 22

Zoning for Fire Detection and
Alarm Systems: Consideration

Answer 22

• Area & accessibility
• By ensuring that each zone is accessible from main corridors leading from where the Sub-Alarm Panel is sited.

Question 23

Zoning for Fire Detection and
Alarm Systems is carried out as follows:

Answer 23

• allocate one zone for each floor & each fire compartment.
• divide large floor areas into smaller ones, each not exceeding 2000 m2.
• provide separate protection zones for concealed areas, areas with difficult
  access & high hazard areas such as fuel storage rooms.

Question 24

Weekly Checks and Tests on Fire
Detection and Alarm System

Answer 24

• Carry out simulation & transmission of fire alarm signal & fault signal
  to monitoring station & confirm that it is functioning correctly.
• Necessary to contact decentralised monitoring station & inform them of test before transmitting simulated fire alarm & fault signal
• Necessary to check w monitoring station after completion of test to ensure fire alarm & fault signal were received and to advise them when
  system has been placed back to normal.
• Check the battery voltage and battery condition.
• On completion of the test, take corrective action immediately on any
  abnormality or faults encountered within the system.
• Enter the test results and follow-up actions, if any, in the log.

Question 25

Description of Heat Detectors

Answer 25

• Respond to convective heat transfer due to smoke flow from fire.
• Generally less sensitive than smoke detectors & should not be used to protect places where a small fire will cause unacceptable losses, such as in
  computer rooms.
• But may give a more rapid detection than smoke detector in a situation
  where fire gives out heat rapidly with little smoke.
• It gives off an alarm when local temp. exceeds fixed temperature & are
  used in spaces such as kitchens, laundries and boiler rooms.

Question 26

Principle of Operation of Heat Detector: Bimetallic Strip Type

Answer 26

• Bimetallic strip heat detector consists of two metals of different expansion rate bonded together.
• When heated, bimetallic strip expands & tilts upwards closing electrical contact & triggers off an alarm.

Question 27

Description of Smoke Detectors

Answer 27

• Detect fires by sensing smoke particles in air given off by fire.
• Enables smoke detectors to detect a fire while it is still in early stage, giving occupants ample time to respond & control developing fire before severe damage occurs.
• Preferred detection method concerning life safety & high content value applications compared to heat detectors.

Question 28

Disadvantage of Smoke Detectors

Answer 28

• More expensive to install compared to heat detectors and are more prone to false alarms.

Question 29

Advantage of Smoke Detectors

Answer 29

When properly selected & designed, can be highly reliable with very low probability of false alarm.

Question 30

two main types of smoke detectors

Answer 30

• ionisation type and optical type.

Question 31

type of smoke detector used will depend on…

Answer 31

type of fire risk to be protected
against

Question 32

How is smoke detected?

Answer 32

• Smoke includes both solid & liquid particulates.
• Range of most smoke particulates is between 0.1 μm &1.0 μm.
• Size of smoke particulate plays important role in choice of detection systems.
• If light scattering principle is used as means of detection, particles w diameter greater than 0.3 μm would be detected since these particulates are able to scatter light whereas smaller particles are usually referred to as invisible because of their inability to scatter light.

Question 33

Ionisation Type Smoke Detector

Answer 33

• Electric current flow between two electrodes in chamber & this current is reduced by the presence of smoke,
• Particularly sensitive to small smoke particles such as those produced in clean burning and flaming fires, but respond slowly to optically dense smoke containing large particles, such as those from smouldering fires.
• More prone to false alarms from
  cooking, & non-visible products of combustion.

Question 34

Examples of situations where ionisation type detectors are used:

Answer 34

libraries, telephone exchange rooms, spirit fuel stores.

Question 35

Optical Type Smoke Detector

Answer 35

• More sensitive to large particles found in optically dense smoke, such as in smouldering fires, but are less sensitive to small particle smoke such as flaming fires.
• More widely used than ionisation types due to growing use of flame retardant materials in building construction, decoration & furnishings.

Question 36

Principle of Operation of Ionisation Type Smoke Detector

Answer 36

• A radioactive source (Americium-241) emits alpha particles, which ionise surrounding air molecules in chamber inside the detector.
• Ionisation process creates a stable electric current within chamber.
• When smoke particles enter detector due to fire, they interfere w electric current.
• Presence of smoke disrupts flow of ions, causing fluctuations in electric current.
• This disruption triggers alarm, indicating presence of a fire.

Question 37

Operation of Optical Type Smoke
Detector: Light Obscuration

Answer 37

• A source of light is directed at a receiving photocell causing an electric current flow.
• When smoke particles enter chamber, light path is disturbed.
• Obscures light, reducing electric current flow and triggering off alarm.

Question 38

Operation of Optical Type Smoke Detector: Light Scattering

Answer 38

• Contains a beam of light directed into a chamber.
• When fire breaks out, smoke will enter chamber scattering beam of light.
• Once scattered beam of light hits photocell, a circuit is made & an alarm will be triggered.

Question 39

Beam Smoke Detectors works on what principle

Answer 39

principle of obscuration.

Question 40

Beam Smoke Detectors

Answer 40

• Sends out an invisible infra-red (IR) beam of light that receiver measures.
• If smoke in air obscures/ blocks light transmitted from transmitter, amount of light received at receiver will be reduced.
• When enough smoke is in air, infra-red light level will drop below a set level, triggering an alarm signal.
• Can detect smoke from fires that might occur over a large area.
• Must be sufficient amount of smoke to cause obscuration before it can trigger.

Question 41

Beam Smoke Detectors use

Answer 41

protect buildings that that are open & have high ceilings such as auditoriums, warehouses, airports & historical buildings.

Question 42

Distance of Beam Smoke Detection

Answer 42

100m

Question 43

Conventional Fire Detection & Alarm Systems

Answer 43

• Physical cabling is used to interconnect several detection devices, the signals from which are wired back to main alarm panel.
• Detection devices are arranged in zones for fire safety personnel to identify where the fire alarm is coming from.
• Each zone where emergency happens is indicated at main alarm panel by an
  indicator light.

Question 44

Advantages of an Addressable
System

Answer 44

• Enables faster response times allowing for unambiguous identification of fire location by first wardens.
• New detectors can also be added easily to system over time as needs arise.

Question 45

Disadvantages of an Addressable
System

Answer 45

• Price is generally higher than conventional systems due to added equipment, installation & maintenance costs.
• Requires specialist design & installation & initial configuration
  will take longer than with a conventional system.
• More complex & requires additional electrical infrastructure.
• Programming can take longer & be more challenging to master.