A beam smoke detector is a device that consists of transmitter/receiver unit and a reflector. It transmits beam of light in order to detect smoke across large areas, wherein smoke is naturally a sign of fire. Beam smoke detector works on the principle of light obscuration, where there is a transmitter that emits beam and a beam receiver. If the presence of the smoke disrupts a certain percentage of beam light of the transmitted light, it will send signal to the panel that there is a fire. Beam smoke detectors area commonly used in area wherein standard point smoke detectors are not economical or efficient to use.
Beam smoke detectors are commonly used in warehouses as a cost-effective way of fire detection and protecting large open areas and inappropriate for outdoor applications. Environmental conditions such as temperature extremes, rain, snow, sleet, fog, and dew can affect with the proper operation of the detector and might cause false alarms. In addition, outdoor conditions make smoke behavior impossible to predict and will affect the detector’s response to fire.
1.Consisting of receiver and transmitter unit. In normal state, light beams sent from transmitter reach the receiver unit. If the receiver did not receive enough light beams, it will trigger a general alarm. The distance between two units can be between 5-100 meters.
2.Second type consists of reflector and a unit that works as both receiver and transmitter. In normal state, IR light beams sent from receiver-transmitter unit reflect from reflector and reaches the unit. In case of fire, smoke obstruct the IR light beams and some of light rays did not reach receiver-transmitter unit. If there are 4 reflectors, the distance between reflector and the unit can be between 40-100 meters. If there is 1 reflector, the distance between reflector and the unit can be between 8-40 meters.
Many factors may affect the performance of smoke detectors of all types. The type and number of combustibles, the rate of fire growth, proximity of the detector to the fire, ventilation and environmental factors are all important that needs to be considered.
a.Detector’s sensitivity should be set within the parameters of the beam used on a given application, combined with the environmental conditions of the area.
2.Location and Spacing
a.On a flat, clear or unobstructed ceiling, the maximum range/distance covered by a beam detector should be 100m, or as per manufacturers recommendations. No point in the protected area should be more than 7.5m from the center line of the beam detector. This gives a maximum spacing between two beam detectors of 15m, and a maximum distance from a wall to a beam detector of 7.5m.
a.Obstructions on or near the ceiling or on the walls of a protected area will affect smoke distribution, and thus need to be taken into consideration. If there are number of joist or structural beams in the protected area, the detector should be placed in parallel in the joists. It is a good practice to ensure that the spacing from the beam center line is applied to all objects.
a.Beam smoke detectors rely on a clear path between transmitter, receiver and/or reflector. If the beam of light is blocked, the detector will not be able to detect a fire on early stage. Care must be taken that the beam is not installed where it could be blocked on a normal condition of the area protected. If people are likely to be present in the protected area, the detector should be mounted to a minimum of 2.7m above floor level. This is to prevent a nuisance or false alarms.
The normal means of testing beam detectors is to place an obstruction in the path of the beam to reduce the amount of received light below the detector threshold and will trigger a general alarm.
As dust builds upon a beam detector’s optical components, it will affect its sensitivity and will increase susceptibility of false alarms. It is advisable to periodically clean the detector transmitter/receiver lenses and reflector. The maintenance interval will be dependent on the protected area conditions: the dirtier the area the more frequent required in cleaning the devices.