Prevent • Make sure it do not start • Control fuel sources Communicate • Ensure if fire happens, occupants know what to do Escape • Provide a route for escape for occupant to move safely before threatened by smoke Containment • Ensure fire can be contained to smallest possible area Extinguishment • Ensure fire can be extinguished quickly with minimum damage FIRE DETECTION SYSTEM SMOKE DETECTORS HEAT DETECTOR FLAME DETECTOR GAS SENSING DETECTOR Ionisation Dectectors Fixed Temperature Detector Infrared Flame Detector Infrared Flame Detector Photolectic Detector Rate Compensation Detector Ultra Violet DetectorUltraviolet detector Rate of Rise Dectector SMOKE DETECTOR IONISATION TYPE -flaming fire PHOTOLECTIC TYPE – smouldering fire Ionise air with small amount of radioactive material Projected beam type Spot type Cloud chamber Produces small amt of electrical currect that flows thru air in chamber light projected across protected area light scattering principles Use air sampling system consist of a tube network Spot type, mounted on ceiling smoke particles that obscure the light beam reduces light intensity thus initiate signal smoke enter unit causes reflected light to strike photoelectic cell air draws into humidity chamberMore responsive to combustion particles than large particles detector should be enclosed so movement of object would not cause false alarm more smoke / large particles = reflect more light moisture in chamber condeneses smoke particles forming a cloud can be located several fts below ceiling if there is hgiht ceiling cloud density measured by photoelectic principle denser than predetermined level = alarm initiated. allow smaller smoke particles to be detected. cumbersome, need to maintain and pump. HEAT DETECTOR Respond to abnormally high temperature FIXED TEMPERATURE DETECTOR RATE CONDENSATION DETECTORRATE OF RISE DETECTOR actuate when temperature reaches predetermined temp Used where high ambient temperatures exist /sudden changes in temperature can occur Types of design Bimetallic sensing element High expansion aluminum tube encase 2 insulation struts with opposing open contact points. Operate when temp ^at a rate exceeding predetermined amount (Threshold btwn 15 – 25 deg) e.
g. kitchens, boiler rooms etc. Electric conductivity type Fusible alloy type Expansion struts and expansion shell have different coefficient of expansion Sealed chamber with air contains diaphragm switch and small vent. Heat sensitivity cable type Slow rate of temp ^ – Rapid rate of temp ^ – Expand > touch > Actuate – Contract > no touch > reset Temp ^, air expand, some escape out of vent. If air expand too quickly for excess air to escape, pressure will trigger the switch (balloon touch contact point), actuate alarm. Liquid exppansion sensing element type Flame detector • • • Sensitive to infrared, visible or UV radiation produced by a fire designed to respond to a fire within the detector’s cone of vision typically within one second Flame detector applications – aircraft hanger, yard storage, chemical processes and flammableliquid storageA. • • Infrared Flame Detectors Contain photocell that is responsive to radiant energy at wavelengths below human vision range A light filter allows only a narrow band of infrared radiation, which is unique in a fire to reach the photocell.
Ultraviolet Detectors • Contain a Geiger-Muller tube responsive to radiant energy in the 0. 1- to 0. 35 micron wavelength range The tube produces a pulse of current directly proportional to the level of uv light reaching the tube An alarm is initiated when the number of pulses per second is greater than the predetermined threshold B. • Note: To reduce false alarms caused by non-fire sources, combination of UV/ infrared detectors are used. Flame detector should be shielded so that they are not actuated by radiant energy sources that could produce false alarm Infrared lamps, matches, cigarette lighters and sunlight may trigger an unwanted alarm from an infrared detector Gas Sensing Detector ? ? ? ? ? Device which detects the presence of various gases within an area.
This type of equipment is used to detect a gas leak and interface with a control system so a process can be automatically shut down.A gas detector can also sound an alarm to operators in the area where the leak is occurring, giving them the opportunity to leave the area. Two types of gas-sensing fire detectors: semiconductor and catalytic-element Should not be installed where, under normal conditions, concentrations of detectable gases are present.
E. g. Aerosol sprays A. • Infrared Flame Detectors Create electrical charges in the semiconductor, as a result of certain combustion products from a fire Ultraviolet Detectors • Contain a material that accelerates oxidation of combustible gases in a fire’s presence.This results in temperature rise of the element, which initiates the alarm B.
Functions of Fire Alarm System Arrangement of detectors, sounders and manual call-points as indication of fire alarm ESSENTIAL FEATURES FUNCTIONS Reliable power supply Supervision of signalling system Testing and maintainence Notify occupants for evacuation primary supply for transmission and reception of alarm short circuit in system should not initiate alarm regular inspection and testing Summoning organised assistance secondary supply in event of failure battery ounded only when required, indicate of location and type of trouble signals when there is a fault, shld be easily restored to full op condition Supervision of extinguishing systems availability of replacement parts Supervision of Process Supervision of Personnel Actuation of fire control equipment Dry pipe automatic sprinkler system Deluge automatic sprinkler system Types Preaction automatic sprinkler system Combination of the above system Water supply Installation of control valve Sprinkler system Flow switch Water proofing facility FeaturesFire department Breeching inlet Water distribution Pressure switch Spinkler head Sprinkler point Breeching inlets Glass bulb Orifice Size Spray Pattern Fusible Link Temperature Ratings Inspection, Testing and Maintainence Sprinkler control valve Main sprinkler tank Main fire pumps Test criteria 4 types Wet pipe automatic sprinkler system • • a piping system containing water under pressure at all times Individual sprinklers are actuated by the heat from the fire and water flows through the sprinklers immediately used whenever there is no danger of freezing of the water in the pipes Majority of the systems used in Singapore are wet type • Dry pipe automatic sprinkler system • • a piping system which contains air or nitrogen under pressure When fire occurs, the heat actuates the sprinkler head and air/nitrogen flows through the opened sprinkler causing the pressure in the pipe to drop. The pressure is reduced to a point such that the water pressure on the supply side of the dry pipe force open the valve. Water flows into the system and out through the sprinkler Used in environment where there is a possibility of water frozen in the pipe • • • Pre-action sprinkler system • piping system containing air/nitrogen that may or may not be under pressure Supplementary fire-detecting devices (smoke detectors) are actuated and open the water control valve of which permits water to flow into the piping system before the heat of the fire could actuate the sprinkler head When the heat of fire subsequently opens the sprinklers, water flows through immediately. Used to protect properties where there is danger of serious water damage due to accidental damager of sprinkler heads or broken piping • • Deluge sprinkler system • • Sprinklers are open all the time to let water flow out quickly Supplementary fire-fighting device (smoke detector) is actuated when there is a fire. This opens the deluge valve and water flow and is discharged from the sprinklers on the piping system attached to a piping system This system is able to apply water to a fire more quickly and with wider distribution than with system whose operation depends on opening of sprinkler heads only as fire spreads Use for extra high hazard occupancies in which flammable and hazardous materials are handled or stored. Fire may flash ahead of operation of ordinary sprinkler heads • FEATURES A.
WATER SUPPLY • Four types of acceptable water supply for sprinkler system: • • water storage tank, elevated reservoir with/without pumps and river Normal water supply is provided by means of automatic pumps drawing from water storage tanks of adequate capacity. The tanks are automatically replenished • B. INSTALLATION CONTROL VALVE —– 2 types: 1. MAIN CONTROL VALVE ? Normally locked open o to isolate the system to permit maintenance or modification work to be done and to shut down the sprinklers after the fire is extinguished in order to minimize water damage 2. ? ? ? ALARM VALVE Located above the main control valve Separates sprinkler system from water supply when the system is operational but not operating. Valve is kept closed by the trapped pressure of water above it Operation of a sprinkler will cause this closing pressure to fall so that the valve opens under excessive pressure beneath it, this allowing it to flow into the system to feed the sprinkler discharge Some water also flows to an alarm gong of the alarm valve assembly thus raising an alarm ? B. WATER DISTRIBUTION ?Water passing through the alarm valve flows up a vertical riser and hence to the main distribution pipes of each ceiling level of the protected premises ? From the main distribution pipes, water flows to range pipes, to which sprinklers are attached C.
FLOW SWITCH ? Flow switch is installed at each main distribution pipe at ceiling level ? Triggered when water flow ? Permits ready location of fire by fighting personnel. Extremely important for multi-storey or large building D. WATER PROOFING FACILITY ? Located at the control valve and comprised basically of ? ? test pipe arrangement, a suitable flow meter and pressure gaugesTo allow water to be drain so as to test whether the design water flow rate and pressure can be achieved without breaking the sprinkler heads to obtain the flow of water E. FIRE DEPARTMENT BREECHING INLET ? It is to permit firemen to provide secondary supply to the sprinklers F. PRESSURE SWITCH ? Water flowing through the sprinkler head will cause a pressure drop in the system.
? When the pressure drops to a set level, the pump will start to supply water from the sprinkler water tank to the activated sprinkler. ? The assigned pressure level for starting the jockey, duty and stand-by pump is different. G.
SPRINKLER HEAD ?It is a heat sensitive valve which is designed to open by the heat from the fire and discharge water as a spray over a specific area ? The head comprises of a discharge opening normally sealed by a valve assembly held in position by the thermally sensitive element, which is a glass bulb or a fusible link. The other end of the bulb or link is supported by the yoke arms, which also carry the deflection. ? The design water flow rate and pressure can be achieved without breaking the sprinkler heads to obtain the flow of water ? Temperature Ratings: Design to operate at normal temperature ranges from 57 to 260 deg C ?Size of opening 10, 15 and 20mm o determined by the occupancy hazard class to be protected o 10mm size for extra light hazard; o 15mm for ordinary hazard and extra-high hazard classes; o 20mm for extra-high hazard risks only Type 1: Glass Bulb • Glass element consists of a small glass bulb containing a liquid with a small gas bulb • • • to accommodate changes in the volume of the liquid due to normal temperature changes Excessive temp from the fire causes the liquid to expand causing the glass bulb to break thus opening the valve to discharge water from the orifice on to the deflector to produce a spray over the area belowType 2: Fusible Link • • Solder is used to hold levers or struts in position in the valve assembly Solder melts when heated and separates the levers, thus ejecting the water from the orifice Spray Pattern ? 3 main types: Conventional type: Produces a water distribution both above and below the sprinkler, and hence some degree of ceiling wetting Spray type: A wider deflector is used to produce a distribution practically below the sprinkler with little or no water reaching the ceiling Side wall type: Gives a skew distribution below the sprinkler throwing much of its discharge back to the roomFire Extinguisher Rising Main and Hosereel System Dry Riser – provided in building with a height between 24 and 60m where water can charged from the fire pumper Wet riser – for building exceeding 60m, the riser (stand pipe) shall be constantly charged with pressurized water Agents A.
Agent: Water Advantages Heavy High specific heat capacity – remove heat apidly Good latent heat of vapourization – become steam Conversion to steam increases its volume to about 1600 times Cheap and easily available Disadvantages Water is conductive because of impurities Do not apply to LIVE electrical equipment and appliances Not recommended for fire involving combustible metals and radioactive items Too much water causes damages B.Agent: Carbon Dioxide Known agent for fires involving electrical, flammable liquid, gas fires Effective as it reduces oxygen content by dilution of atmosphere A minimum concentration is needed for extinguishments Disadvantages Use is generally limited by low cooling capacity and enclosure incapable of retaining extinguishing atmosphere – won’t help for big areas High concentration and longer holding time for deep seated fires Gas not visible – leakage causes suffocating atmosphere / leak wont knowAdvantages Non-combustible (igniting) Non-conductive of electricity Does not react with most substances Non-toxic (within tolerable limits) No residue – diluted with normal air Gaseous and penetrate to all parts of fire area Easily liquefied and bottled under pressure C.Agent: Dry Powder Powders are composed essentially of very small particles of chemical(s) Usually extinguish AB (wood, liquid) or ABC (wood, liquid, electrical) Forms barrier to exclude oxygen content to block fire Forms a crust to cool and retards burning Disadvantages Very messy, not suitable for delicate electronic equipment Inhaling of chemical may be detrimental to one’s health Advantages Effective for plastics, burning metal fires Gives a quick knock-down to fires Forms a radiant heat barrier
