Type of Detector

Type of Detector  

 

Smoke detectors (general)

 

 

      

Merits

Slow burning fires, smoldering fires, for most of the areas where principal tire hazard is not from the presence of flammable liquids. Fires involving wood, paper, textile, etc, in earlier stages         

Demerits

Not sensitive for clean burning fires which does not produce smoke particles; areas in which the principal fire hazard is the presence of tlammable liquids or gases that produce little smoke during a fire

Ionization smoke detector      

 

Merits

General purpose smoke detector-better for smoke containing small particles, such as rapidly burning fast flaming fires         

Demerits

Less sensitive to the larger particles found’in optically dense smoke of similar mass, such as can result from smoldering fires including those involving polyurethane foam, or overheated PVC. Areas subject to smoke, steam, dust or dirt during normal use. Usage of these detectors are on way to phase out due to radiation problems

Optical smoke detector 

 

Merits

General purpose smoke detector -better for smoldering fires      

Demerits

Areas subject to smoke, steam, dust or dirt during normal use

Light scattering type (smoke detector)  

    

 

Merits

Sensitive to light coloured smoke      

Demerits

Less sensitive to very dark smoke which absorbs light rather than scattering it

Light obscuration type (smoke) detector   

 

Merits

Sensitive to very dark smoke which absorbs light rather than scattering it     

Demerits

Areas subject to smoke, steam, dust or dirt during normal use

Photo-thermal multi-criteria detector       

Merits

General purpose detector - good for smoldering and fast flaming fires, optically dense smoke          

Demerits

Areas subject to smoke, steam, dust or dirt during normal use, less sensitive to small particles found in clean burning fires that produce little visible smoke

 

Optical beam smoke detector 

Merits

Large and high rooms, open plan spaces with relatively high ceilings (for example warehouses), fires not involving production of smoke (with built in thermal turbulence detection). Suited for applications where anticipated fire would produce black smoke. Sensitive to cumulative obscuration presented by a smoke field

Demerits

Areas subject to smoke, steam, dust or dirt during normal use. Less sensitive to colour of smoke. Cannot detect clean colourless smoke

 

Aspirating (air-sampling) type smoke detector

  

Merits

They are suitable for use where usage of other types of smoke detectors present difficulties, such as aesthetics, height and temperature of the enclosure. Sampling points can be located almost anywhere unlike detectors which cannot be installed on walls, storage racks, machinery space, floor voids, etc. Each sampling point is a detector itself. Suitable for cold storage. Higher sensitivity levels, ease of installation and most suitable for protection of high value and critical equipment

Demerits

Air-sampling detectors are not suitable if the air movement due to HVAC requirements is outside the range specified by the manufacturers 20

 

 

Heat detectors (general)   

      

Merits

Clean burning fires, such as those involving certain flammable liquids. Areas subject to smoke, steam, dust or dirt during normal use, fires that evolve heat and flame rapidly, suitable for rooms where heat producing equipment like kitchen, pantry, boilers, DC sets, etc, are installed/used

Demerits

Unlikely to respond to smoldering and slow burning fires, unsuitable for high value areas where a small fire can cause major damage. Areas in which presence of smoke can pose a potential threat to the occupants

Rate-of-rise heat detector 

     

Merits

Areas subject to smoke, steam, dust or dirt during normal use   

Demerits

Areas subject to rapid changes of temperature or temperatures over 43 DC

Fixed temperature heat detector     

Merits

Areas subject to smoke, steam, dust or dirt and rapid changes of temperature during normal use      

Multi-sensor fire detector      

Merits

Combines the characters of two types of detectors, each of which responds to different physical and/or chemical characteristics of fire. The purpose of combining sensors in this way is to enhance the performance of the system in detection of fire or its resistance to at least certain categories of false alarms or both. There is significant potential for reduction of many types of false alarm. It is also possible to disable an individual sensor depending on the circumstances at the place of installation       

Flame detectors (general)   

OUT DOOR

INDOOR

 

   

Merits

High ceiling, open spaced buildings like warehouses/aircraft hangers, outdoor/semi-outdoor areas, areas where rapidly developing flames occur like petrochemical/refinery/gas installations/paint shops, etc     

Demerits

Not sensitive to smoldering/slow burning fires and hence cannot be called general purpose detectors. Not suitable for the type of fires where, flaming can occur only after substantial release of smoke

 

Infra-red flame detector        

Merits

Same as above, these detectors penetrate through smoke well. High speed, moderate sensitivity. Suitable for indoor/outdoor applications        

Demerits

Affected by temperature range in the vicinity, subject to false alarms caused by blackbody radiation like heaters, incandescent lamps, halogen lamps, flickering sunlight, etc and hence usage 21in such areas to be avoided. Sensitive to IR radiation from sources like any hot surface, ovens, furnaces, lamps, etc. also and due care shall be taken while installation

Ultraviolet flame detector      

Merits

Highest speed, highest sensitivity. Suitable for indoor applications     

Demerits

Not sensitive for high ceiling, etc, as the radiation from fire is attenuated by smoke. Random UV radiation from sources, such as lightning, arc welding, etc, can cause false alarms and hence usage in such areas to be avoided. Blinded by thick smoke and oil vapours on optics

 

IRfIR flame detector    

Merits

High speed, moderate sensitivity, low false alarm rate, most suitable for chemical and hydrocarbon flames in particular as signal received is processed at two sensors. Suitable for indoor/outdoor applications     

Demerits

Somewhat affected by temperature range in the vicinity, suffer from atmospheric attenuations, especially on long range detection applications

UVfIR detector   

Merits

Highest speed, highest sensitivity and low false alarm rate        

Demerits

Blinded by thick smoke and oil vapours on optics. Suitable for indoor/outdoor applications

 

IRfIR/IR (IR3) detector         

Merits

Highest speed, highest sensitivity, lowest false alarm rate. Most suitable for chemical and hydrocarbon flames in particular as signal received is processed at three sensors    

Demerits

No significant disadvantages. Suitable for indoor/outdoor applications

Spark detector    

Merits

Spark detectors are suitable for detection of sparks some types of duct or conveyor, monitoring the fuel, etc, as it passes by. Usually, it is necessary to enclose the portion of the conveyor where the detectors are located, as these devices generally require a dark environment         

 

 

Demerits

Extraneous sources of radiant emissions that have been identified as interfering with the stability of spark detectors include: (a) ambient light (b) electromagnetic interference (EMI, RFI), and (c) electrostatic discharge in the fuel stream

 

Ember detector    

 

Merits

Same as above except that ember detectors can also detect fires in lit environment like coal conveyors, etc      

Demerits

Detector window clarity shall always be ensured

 

Linear heat sensing cables

 

Merits

Cables tunnels, trays and vaults, material conveyors, bulk storage multi-racked areas, rim seals of floating roof tanks storing hazardous chemicals, and a few other special occupancies   

Demerits

Not suitable at all applications other than what is specified