Alertness and Warning systems –fire Safety


Whenever we are using any type of equipment or devices, its proper placement and installation should be given top priority. Whatever the efficiency of the devices or equipment, if they are not properly placed at the required place or if the specified norms are followed, they will not function properly. This will result in simply wasting of funds on the equipment without any end result. Therefore mounting of the beam detectors plays important role.
Before installing the transmitter/receiver unit or reflector in these types of applications(Specially used for detection of fire) special consideration should be given to insure proper operation of the beam detector. The beam detector should not be installed in environments where there is no temperature control and condensation or icing is likely. Condensation or icing of the reflector surface or the outer surface of the transmitter/receiver unit will obscure the light beam resulting in a false alarm. If elevated humidity levels and rapidly changing temperatures can be expected then condensation will likely form and the application should not be considered acceptable for the beam detector. The beam detector should not be installed in locations where the transmitter/receiver unit, the reflector, or the optical pathway between them may be exposed to outdoor conditions such as rain, snow, sleet, or fog. These conditions will impair the proper operation of the detector and must be avoided.
Many factors affect the performance of smoke detectors of all types. The type and amount of combustibles, the rate of fire growth, the proximity of the detector to the fire, and ventilation factors are all important considerations. UL Listed beam smoke detectors are tested using the UL 268 Standard, “Smoke Detectors for Fire Protective Signalling Systems” and should be installed and maintained in accordance with NFPA 72, The National Fire Alarm Code and the manufacturer’s instruction.
Each manufacturer requires that the detector’s sensitivity be set with reference to the length of the beam used on a given application. The detector should be installed within the minimum and maximum beam length allowed by the manufacturer’s instructions which are limited by the UL listing. Location and Spacing NFPA 72 is the standard for location and spacing of detectors. The following design criteria are quoted or summarized from NFPA 72, The National Fire Alarm Code: “Projected beam-type smoke detectors shall be located in accordance with the manufacturer’s documented instructions.” NFPA 72-2002, “The effects of stratification shall be evaluated when locating the detectors.” NFPA 72-2002, Mounting Consideration for Reflective Beam Detectors Beam detectors require a stable mounting surface for proper operation. A surface that moves, shifts, vibrates, or warps over time will cause false alarm or trouble conditions. Initial selection of a proper mounting surface will eliminate false alarms and nuisance trouble signals. Mount the detector on a stable mounting surface, such as brick, concrete, a sturdy load-bearing wall, support column, structural beam, or other surface that is not expected to experience vibration or movement over time. DO NOT MOUNT the beam detector on corrugated metal walls, sheet metal walls, external building sheathing, external siding, suspended ceilings, steel web trusses, rafters, non-structural beam, joists, or other such surfaces. In cases where only one stable mounting surface as defined above can be used, the transmitter/receiver unit should be mounted to the stable surface and the reflector should be mounted to the less stable surface. The reflector has a much greater tolerance for the unstable mounting locations defined above. Smooth Ceiling Beam smoke detectors must be mounted on stable stationary surfaces to prevent movement and subsequent
Note: During our discussion of the topic we will be coming across with the words like NFPA and UL standards. These are some standards accepted globally. We will discuss the same in our future topics separately
Will be continued
G K Bhat
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