Fire Detection and Alarm System

Prompt detection of an out-break of fire in its incipient stage and generation of alarm for quick and correct application of fire fighting media minimizes the loss from fire to a great extent. The purpose of a fire detection and alarm system is to detect a fire or its likelihood and generate audible and visual alarm to alert the building occupants.

The entire system shall confirm to IS 2189 as amended upto date. Where IS standards are not available BS 5839 shall be applicable. The wiring work shall be carried out confirming to specifications for electrical works.

The fire detection and alarm system is classified into manual fire alarm and automatic fire detection system. All building with heights of more than 15 m shall be equipped with manually operated electrical fire alarm (MOEFA) system and automatic fire alarm system. However, apartment and office building between l5 m and 24 m in height may be exempted from the installation of automatic fire alarm system provided the local fire brigade is suitably equipped for dealing with fire above 15 m in height and in the opinion of the authority, such building does not constitute a hazard to the safety of the adjacent property or occupants of the building itself.

Table of Contents

Manual Fire Alarm

Small and medium capacity exchanges not exceeding 1 K lines shall have Manual Fire Alarm System. For the purpose of alarm system, the building shall be divided into a number of zones. In a multi storeyed buildings each floor shall constitute one or more zones depending upon the area of the floor.

The manual fire alarm system consists of manual call points or pill boxes, hooters and a control panel and necessary wiring.

Manual Call Point or Pill Box

The call boxes shall confirm to the following:

  1. The manual call point shall be rectangular or circular, made of aluminum or MS and painted with fire red. The box shall have front glass (minimum 30 cm²) and gasket to make it completely vermin and dust proof, along with hammer and chain.
  2. The glass front cover shall have a write up “ BREAK GLASS IN CASE OF FIRE”.
  3. The box shall be suitable for wall mounting and shall be mounted at 1.2 meter above floor level.
  4. The location of call boxes shall be decided after taking into consideration the floor plan with a view to ensuring that one or the other call box shall be readily accessible to all occupants of the floor without having to travel more than 22.5 m.
  5. The call boxes shall be of the break-glass type where the call is transmitted automatically to the control room without any other action on the part of the person operating the call box. The mechanism of operation of the call boxes shall preferably be without any moving part. However, where any moving part is incorporated in the design of the call box, it shall be of an approved type so that there shall be no malfunctioning of the call box.
  6. All call boxes shall be wired in a closed circuit to a control panel in the control room in accordance with good pratice so that the number/zone where the call box is actuated is clearly indicated on the control panel.
  7. The call boxes shall be arranged to sound one more sounders so as to ensure that all appropriate occupants of the desired floor(s) shall be warned whenever any call box is actuated.
  8. The call boxes shall be so installed that they do not obstruct the exit ways and yet their location can easily be noticed from either direction.
  9. Manual call point may be provided with neon lamps to indicate healthy condition.

Hooters

  1. The hooters shall be suitable for wall mounting and shall incorporate hooter card and speaker inside a metallic box. The hooter shall be mounted at 2.4 m above the floor level.
  2. The hooter shall be actuated by control panel; PA system will have separate speakers. These should preferably be provided in corridors, exit routes, lobbies, staircase landings and other places such that the alarm is heard distinctly above all the ambient sound prevailing in the area. The hooters shall have 4 W / 8 W output with 80 dB sound level and shall be capable of giving sound upto 100 m
  3. A minimum of two speakers for audible alarm and/or public announcement shall be provided on each floor and at least one speaker shall be provided on the terrace.

Control Panel

The panel shall include one or more batteries with a capactiy of 48 hour normal working at full load. The battery shall be arranged to be continuously trickle charged from the electric mains. The circuit may be connected to alternative source of electric supply.

Automatic Fire Detection System

It is to be provided as per local bylaws and in absence of bylaws, all buildings whose height is more than 15 m. For telecom, all digital exchanges of more than 1 K capacity in addition to manual alarm system.

Selection Criterion:

  1. Importance.
  2. Proneness to fire.
  3. Cost of equipment.
  4. Type of fire expected.

Components:

  1. Detectors.
  2. Response Indicators.
  3. Control Panel.
  4. Power Supply.
  5. Batteries.
  6. PA System.
  7. Manual Call Points.
  8. Hooters.
  9. Cabling.

Detectors

Detectors which are normally used are broadly covered in two categories viz. Heat and Smoke Detector. Smoke Detector is of two types viz Photo Electric & Ionisation. Heat Detector also is divided into Fixed Temperature Type, Rate of Rise of Temperature (RoR) Type, and Fixed Temperature cum RoR Type, the last one being the heat detector which is normally used in exchanges. The principle of operation of detectors is given below:

Ionisation Type

This detector contains small quantity of radioactive material such as americium-241, which emits α particle into two chambers (dual chamber): an ionization chamber (which is open to air) and a sealed reference chamber. These alpha particles ionizes the air. The chamber has two plates, one acting as radiation source and other as delection plate, separated by about 1 cm. The voltage applied across the plates causes positive and negative ions to be attracted towards opposite plates, causing small current to flow within the chamber.

Under normal condition, same current flows in ionization and reference chamber and currents are balanced in the bridge. When smoke enters into ionization chamber, ions gets attached to smoke particles, causing them to slow down and thus reducing the current in ionization chamber. When the current drops below a predetermined level, alram is activated. Reference chamber cancels the effect due to change in pressure, temperature and ageing.

It detects both visible or invisible products of combustion and responds quickly to both fast burning fires and slow smouldering smoke. But ionization detectors are more sensitive to flammable fires, while optical is more sensitibe to fires in early smouldering stage.

Photo Electric Type

This detector operates on the principle of light scattering. It comprises of solid state LED, a lens to collimate the light into a beam, and a high speed light sensing photodiode at an angle to light beam, enclosed in a chamber. In the absence of smoke, beam is straight and nolight reaches sensor. When smoke enters into the chamber, some light is scattered by smoke particles, reching the sensor and activating the alarm.

Heat Detector

Bimettalic strip is used for fixed temperature rise. They operate when temperature crosses a predetermind level. These have the problem of 'thermal lag' i.e. the delay for accumulation of heat at the sensing element compared to surroundings.

The RoR type operate on rapid rise in temperature, irrespective of starting temperature. It has two heat sensitive thermocouple/thermistor. One partially sealed thermistor senses heat transferred by convection and radiation, while other senses ambient temperature. In the case of difference in temperature, diaphragm gets distorted and alarm is raised. The selection of RoR heat detector is based on the air velocity, for less velocity a detector with a sensitivity of 5 °C/min and for higher velocity a detector with a sensitivity of 15 °C/min is used.

RoR type may not respond to low energy release of slowly developing fires. To detect slowly developing fires, Fixed cum RoR detector adds a fixed temperature element.

A typical specification of smoke detector is given below:

  • Sensitivity Range: 1.2 + 0.6 % OBS/FT (nominal), adjustable from 0.8 to 1.3 OBS/FT
  • Air Velocity: 300 FPM (Max.)
  • Remote Lamp: 2 mA at 24 V DC.
  • Temperature Range: 0 to 38 °C.
  • Humidity Range: 0 to 93 % RH.
  • Input Voltage (Standby): 16 – 29 V DC.
  • Input Volts (Alarm) (Max.): 8 V DC.
  • Start-up Current (Max.): 65 mA.
  • Start-up Time (Max.): 15 s.
  • Standby Current (Max.): 50 mA.
  • Alarm Current: 36 – 80 mA.
  • Alarm Impedance: 365 – 447 W.

Comparison of detectors

Comparison of detectors
Sl.No.PropertyHeat DetectorSmoke Detector
Fixed cum RoRIonisationPhoto Electric
1CostLessMoreHighest
2ResponseSlowFastFast
3SuitabilitySmall SpaceLarge SpaceSmall and Large
4Heat/Smoke DissipationFastSlowSlow
5SuitabilityFlammable fireFlammable fireSmouldering fire
6Fire Alarm RateLeastHigherHigher

Design and Selection of Detectors:

  1. Ionisation or Photo-electric detectors shall be provided in areas which are normally free from smoke. Heat detectors shall be provided in areas like kitchen, battery room etc. which are prone to smoke.
  2. Each detector shall be numbered zonal wise such as Z09/N10, wherein Z09 indicaties zone number 9 and N10 indicates detector number 10 in that zone.
  3. In case of exchanges having false floor plenum and false ceiling (attic space), such areas shall be treated as separate zones.
  4. When depth of beam is 450 mm or more, all grids formed by such beams shall be considered as separate enclosure.
  5. There should be at least one detector in each enclosed area.
  6. In one zone no of detectors should not exceed 15.

  7. Each Heat detector shall cover an area not exceeding 40 m².

  8. The area to be protected by smoke detectors shall generally be in accordance with the following table:

    Recommended Floor Coverage / Detector
    Sl. No.LocationCoverage per DetectorRemarks
    1Electronic Exchange:  
    a)Equipment Room15 m².AC Room with air change per hour less than or equal to 3.
    b)Computer Room (upto 3m ceiling height) 20 m²- do -
    c)Below False Flooring/ Above False Ceiling10 m².- do -
    2Equipment Protection25 m².Non-AC
    3General Area40 – 60 m².Non-AC

    High density of detectors (more than IS specifications) is used in in exchanges because of high value consideration, more proneness to fire and because of dissipation of smoke by AC.

  9. In technical areas, both ionization type and optical type should be used in equal ratio in equal ratio adjacent to other for mixed monitoring purpose. The smoke detectors shall be interchangeable.

    In AC plant room also only smoke detector need be used, but cross-zonic is not required. An administrative areas, only ionisation type smoke detector be used. In EA room or conventional battery rooms, where fumes are there, only heat detector should be used.

  10. Spacing between detectors at various heights will be as under:

    Spacing between Detectors atvVarious heights
    Height (m)3.54.55.56.57.5
    Spacing (m)8764.53

    However in electronic exchanges, smoke detectors shall be installed above the racks (light fittings shall be provided in between racks) and the spacing between detectors shall not exceed 4 m. Also Maximum horizontal distance between center to center of heat detector and smoke detector when provided in corridor shall not exceed 10 m.

  11. Each return air opening in the weather maker room shall be provided with one duct detector. The detector shall be of ionisation type smoke detector fitted inside the sampler box (as air flow is strong) which is closed from all sides except the front.
  12. Detectors placed in ducts or plenums shall not be used as a substitute for open fire protection.
  13. Each room including electrical rising main room shall necessarily be provided with at least one detector irrespective of its area.
  14. Detector should be placed where maximum density of smoke is expected. At certain places dead zones are created due to ceiling, structure & AC ducts. Such places shall be avoided for locating detectors i.e. no detector in aerodynamically dead zones.
  15. In a room or building where forced ventilation is present, detectors should not be placed near supply diffusers where smoke can be diluted before it reaches the detector. Detector should be at least 1.5 m away from inlet ducts.
  16. Detectors should be placed in a systematic manner and should be rigidly fixed. They should be located to favour the air flow towards the return openings.
  17. For perforated ceiling, perforations upto a distance of 0.5 m from detector should be closed.
  18. In equipment area (switch room, OFC room), detectors should be provided in cross zonic fashion i.e. detectors should be placed in 2 zones.
  19. The distance between first detector and wall should not exceed 1.5 m.

Response Indicators

  1. Signals from detectors which are not visible shall be extended in the shape of Response Indicators to a suitable location which is easily visible.
  2. The RI shall be lit by means of twin LEDs in red colour and shall be housed in a MS box.
  3. The RI for the detector below the false floor shall be installed with top at 300 mm above false floor at nearby column/wall or directly on false floor by making suitable cutout and covered with thick glass. For detectors above gfalse ceiling, it will be installed either right below on the false ceiling or on the nearby wall/column with bottom 300 mm below false ceiling. Alternatively all the RIs can be located at convenient places. The cover plate of the RI shall boldly display the detector numbber to which it corresponds.

Control Panels

General: 

  1. Main Control Panel shall be installed preferrably at the ground floor in the control room or main entrance lobby. It shall be provided at conspiocuous location, prefferably attended 24 hours. It has power pack which supplies power to itself as well as to LCPs. It will tell the zone of fire which has operated. In MCP, there is one zone for each LCP. Standby batteries for power supply to the panel shallbe provided near the panel.
  2. At least one local control panel is provided on each floor and preferably there should be at least one LCP for each switch room. Is shall be located at easily accessible areas like corridors where the same can be properly monitored.
  3. The various controls and indicating panels shall be totally enclosed, dust and vermin proof and shall be suitable for environmental condition at the site of the installation.
  4. The main control shall be designed such that the equipment for power supply, battery charging and PA system are housed in independent compartments. Batteries shall however not be accomodated inside the panel to avoid problems due to corrosion.
  5. All components and their wiring shall be arranged so as to be conveniently attended to from the front of the panels.
  6. All indicating lamps, control switches, buttons and fuses shall be located in the front of the panels. These shall be suitably and unambiguosly labelled.
  7. The indicating lamps shall be LED type of the following colours. The fire condition shall be indicated by twin lamps.

    1. RED to indicate FIRE condition.
    2. AMBER to indicate FAULT condition.
    3. GREEN to indicate HEALTHY condition.
  8. Test buttons to test the indicating lamps shall be provided.
  9. All controls and indicating panels shall be of solid state type.
  10. The panel shall confirm to IS 2189 : 1988.
  11. The panel shall be suitable for operation on AC supply with DC as power backup.

MAIN CONTROL PANEL: 

  1. Audio visual indications for:

    1. Fire Condition in any LCP.
    2. Any fault in LCP (SC, OC, removal of detector).
    3. Fire/Fault in MCP itself.
    4. Battery low voltage / battery disconnection.
    5. AC fuse blow.
    6. DC fuse blow.
  2. Only visual indication for:

    1. AC Power ON/OFF.
    2. Standby Battery ON/OFF.
    3. Battery Charger ON/OFF.
    4. Isolation of Zone (For testing etc.).
    5. Operation of Alarm Silencing switch.
    6. Public Address System ON/OFF.
  3. Other features:

    1. Test button to check healthy condition of lamps.
    2. Silencing switch to stop the hooter after fault has been attended to.
    3. Test switch for each zone.
    4. PA system.
    5. Auto resetting of alarm system after clearance of fault/fire.
    6. Separate card for each zone (so that in case of fault in any zone that card can be raplaced.)
    7. Enough capacity of battery suitable for at least 24 hours back up during supervisory condition and 1 hour during fault condition.
    8. Maintenance free battery.
    9. Power pack with battery charger.

LOCAL CONTROL PANEL: 

  1. Audio visual indications for:

    1. Fire Condition in any zone.
    2. Fault Condition in any zone.
  2. Only visual indication for:

    1. Isolation of Zone (For testing etc.).
  3. Other features:

    1. Test button to check healthy condition of lamps.
    2. Silencing switch to stop the hooter after fault has been attended to.
    3. Test switch for each zone.
    4. Auto resetting of alarm system after clearance of fault/fire.
    5. Separate card for each zone (so that in case of fault in any zone that card can be raplaced.).

Note

The panel shall give different tones for fire and fault conditions.

Typical connections are shown in figs.

P.A. System:

  1. The main control panel shall incorporate PA system with microphones and amplifier of adequate capacity with selector switches for alert and evacuation alarm and public address to all the floors.
  2. The amplifier shall work on AC/DC supply derived fron the MCP. Automatic changeover facility for uninterrupted service shall be provided. Protection against overload, short circuit and wrong polarity shall be provided.
  3. A minimum of two speakers for audible alarm and/or public announcement shall be provided on each floor and at least one speaker shall be provided on the terrace.
  4. TALK BACK SYSTEM: The main control system shall be provided with the electronic circuitory so as to operate talk back system using telephone handsets between main control panel and local control panel and vice-versa.

Power Supply

The entire system shall be suitable for operation on AC supply with DC battery as secondary source.

BATTERIES: 

  1. Enough capacity of battery suitable for at least 24 hours back up during supervisory condition and 1 hour during fault condition.

  2. Calculation of Battery capacity:

    Typical Power Specifications are:
          Zone Card: 84 mA Standby & 514 mA during Alarm with five detectors working.
          Control Card: 84 mA Standby & 120 mA during Alarm.
          Power Supply: 216 mA (Standby/Alarm).
          Hooter: 450 mA. (For 24 V DC)
          PA (30 W): 1250 mA. (For 24 V DC)

    Now as per IS 2189 : 1988, only 2.5% zones at alrm or a  minimum of 2 zones with all sounder load is considered  for calculation of battery capacity, so
          For a 8 Zone MCP with 4 hooters:
          Zone Card: (Standby) = 504 mA (6 Nos)
          (Alarm) = 1028 mA (2 Nos)
          Control card: = 120 mA
          Power supply: = 216 mA
          Hooters: = 1800 mA (4 Nos)
          PA (30 W) = 1250 mA

          TOTAL = 4950 mA ~ 5 A.

    So a 5 A⋅h battery will be required to drive all hooters for one hour.

Mimic Diagram

A mimic diagram with clear indication of location of all the zones and the topographical representation of the premises shall be provided near the control panel. Floor wise mimic diagram shall also be provided. The construction of mimic diagram shall be in metal framework suitable for wall mounting, with a fascia of acrylic sheet with lighted and labelled (or engraved) indications.

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