• Make sure it do not start • Control fuel sources
• Ensure if fire happens, occupants know what to do
• Provide a route for escape for occupant to move safely before threatened by smoke
• Ensure fire can be contained to smallest possible area
• Ensure fire can be extinguished quickly with minimum damage
FIRE DETECTION SYSTEM
GAS SENSING DETECTOR
Fixed Temperature Detector
Infrared Flame Detector
Infrared Flame Detector
Rate Compensation Detector
Ultra Violet Detector
Rate of Rise Dectector
- smouldering fire
Ionise air with small amount of radioactive material
Projected beam type
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 chamber
More 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.
Respond to abnormally high temperature
FIXED TEMPERATURE DETECTOR
RATE CONDENSATION DETECTOR
RATE 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
• • • 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 storage
A. • •
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
Note: To reduce false alarms caused by non-fire sources, combination of UV/ infrared detectors are used. Flame...