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Fire Detectors
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Automatic Fire Detectors
Do we really need a detector?
Kerosene Kerosene
Speed & Aftermath of Fire
YesFire Detectors detect fires at their earliest stages and sound a loud warning to help you get out safely
Detection
Typical room
Typical roomAlarm bellFire AlarmPanelBellStair pressurisation fanCorridorFire escape stair
Typical room in hotelDetectorSprinklerAlarm bellFire AlarmPanelBellStair pressurisation fanCorridorFire escape stair
Fire starts in room
Smoke detector activates alarmSmoke fills guest roomAlarm sounds in rooms and at lobbyStairway fan pressurisation begins
Occupants make way to stairwellSmoke slowly spills into corridorStairwell provides SAFE egress path to outside of building
Sprinklers in room operate, discharging water, controlling and extinguishing fireOccupants exit from building
Occupants leave building to safe areaSmoke is discharged from building
DetectionDetectors sense the existence of a fireFire Panels acknowledge the detectors,test the system, check for faults operate the alarmsAlarms inform the occupants of a fire and assist the evacuation
1. Concentration of energy2. Source of oxygen3. Spontaneous oxidation at surface of combustible material4. Release of particles into atmosphere5. Exponential propagation of chain reaction6. Release of energy in the form of light and heat
Ignition and fire growth
Fire GrowthSTAGE 4STAGE 1STAGE 2STAGE 3VISIBLE SMOKEINTENSE HEATFLAMING FIREINCIPIENT STAGE - NO VISIBLE SMOKETIMESMOKE DENSITY AND HEAT OUTPUT
DetectorsSmokeFlame HeatCO
Detects the presence of smoke particlesInexpensive, early detection for smouldering firesNo need for line of sightIndoor applications onlySubject to occassional false alarmsSmoke Detector
Ionisation OpticalBeamSamplingInstalled every 10mSmoke Detector
Ionisation
ION-CHAMBER SMOKEChamber coverCollectorAlpha sourceBatterySmoke Detector
Working of Ionisation Detector
Smoke DetectorDouble Chamber Ionization Detector
OPTICAL SMOKEInsect ScreenFinsInsect ScreenSmoke PathSamplingVolume
Optical DetectorLight Scatter Type
Optical DetectorObscuration Type
Sampling Detector
What is an Air Sampling System?
Air sample ismoved throughthe laser chamber via the aspiratorand filterInlet manifoldAspirator Air enters detectorLaserChamberDual Stage FilterUltra pure air is used to keep optical surfaces cleanDust is filtered outThe signal is then passed to the processor card for and onto the Display ModuleDisplayOperation of the VESDA Detector
Very Early Smoke Detection ApparatusVESDA
Radiation / Flame Detectors
Forms of radiant energy produced by a fire
Detects radiation from flameAnalyses one or more UV or IR frequenciesExtremely fast on flaming firesLong range, line of sightSophisticated and expensiveSuitable for high risk, liquid and gas hazardsFlame Detector
Infra-red (IR) Radiation Detector
Scanning Infra-red (IR) Radiation Detector
Ultra-violet (UV) Radiation Detector
Ultra VioletWeldingX-rayLens contaminationHigh power consumptionInfra RedsunlightFALSE ALARMS
Senses temperature or temperature change Immune to false alarms in most casesReliable, fairly slow detection Fire must be near detectorLow maintenanceInexpensive
Heat Detector
Fixed temperatureRate-of-riseHeat Detector
Heat DetectorExpansion of single metal strip
Heat DetectorExpansion of single metal strip
Heat DetectorExpansion of bi-metallic strip
Heat DetectorExpansion of gases
Heat DetectorExpansion of gases
Heat DetectorLinear Heat Detecting Cables
Technology provides continuous profiles of temperature using a single optical fibre as the sensing elementAn instrument containing an Optical Time Domain Reflectometer and signal processing softwareMonitors hundreds of points in seconds Sensor is insensitive to EMISensor is Intrinsically safe
Optical Fibre Distributed Temperature Sensing
Beam DetectorsEffects of Flame on IR BeamEffects of Smoke on IR Beam
CO is a toxic gasCO is the major cause of death in firesCO detectors sense slow smouldering fires before smoke detectorsBest option for hotels, hospitals, nursing homes
Carbon Monoxide Detector
CARBON MONOXIDE SOMETHING NEW IN FIRE DETECTION?
Carbon Monoxide GasProduced in firesOdourlessColourlessTravels more freely than smokeMakes victims lethargic, disorientedBrain damage, death at high ppmFACTS
Slow Smouldering Fires
Vast quantities of CO before flamingCause of many deathsDifficult to detect using traditional Ion- or Optical based detectorsCause of backdraft?FACTS
Fire GrowthSTAGE 4STAGE 1STAGE 2STAGE 3VISIBLE SMOKEINTENSE HEATFLAMING FIREINCIPIENT STAGE - NO VISIBLE SMOKETIMESMOKE DENSITY AND HEAT OUTPUTFLAMESPRINKLERPHOTOIONBEAMHEATVESDA
Allow manual alarm of fireDifferent types include:BreakglassPush buttonLeverLocated at exits and throughout risk
Call Points
PanelsPanels are the Brains that receive the detector inputs and decide the action or output responseThe panels and detectors are configured into SYSTEMSThere are two types of system configurations:CONVENTIONAL and ADDRESSABLE
Conventional systemsSimple installationDetectors and inputs are grouped into ZONES
Addressable SystemsEach detector and input is individually identifiedOne wire connects different types of inputs
OutputsAlarmsBellsSirensLightsEVAC systemsVoice commands for regulated evacuationDrivers for controlSuppression systemShutdown of air handlingControl of doors
SelectingDetectorsPrevention issuesLife safety, Business interruption, Asset protection, Explosion preventionTolerable damage levelsFire issuesSlow or rapid developmentSmouldering or flamingSolids or liquids?
Selecting DetectorsAnalyse relative importance of:Speed of responseRange of responseSensitivity and discriminationReliabilityGeneral immunity to false alarm sourcesImmunity to specific radiation sourcesElectronic interfaceCost
Early Detectionleads toLife Safety