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Aspirating smoke detection

An aspirating smoke detection device today is largely understood to be one which comprises of a housing containing a smoke detector, an aspirating device (such as a fan), and some output controls. Rather than applying the device such that air is forced through the detector, the aspirating device provides the negative pressure required to draw air through a network of connected pipe extending over the application hazards with sampling points at appropriate locations along the network.

Application

The first application of high sensitivity, aspirating smoke detection, was in areas which contained high value capital equipment, such as computer rooms, or where business downtime as a result of a fire incident would be extremely damaging or expensive (telecommunication and clean rooms). The idea was that the devices were of such high sensitivity that a fire could be detected long before it began.

Because of the high sensitivity of these devices, computer rooms and telecommunication suites, with their high airflow environments, are often protected with aspirating smoke detectors installed so as to sample the inlet air of an air-handling unit or from a central duct system. As aspirating smoke detectors are designed to work in forced airflow there is never a problem with high air flow in the application-effecting operation of the device, nor with the dilution of smoke.

The first major benefit of these devices is in their ability to detect smoke at the earliest stages of fire. Another feature is the ability to cover large areas, either by using the forced ventilation available in the application or, alternatively, by extensive layout of sampling pipe. The latter limit is governed by air transport time along the pipe which is not to exceed 12 s.

Aspirating detection can be used for multilevel detection, samples of application being in atria and warehouses. The major benefit is to be able to sample at various levels overcoming the effects of stratification of smoke, the level of which will vary dependent on temperature and humidity. Additionally, particularly in the case of warehouses, the maintenance is reduced as the sampling points are connected to a single aspirating detector.

The ability to remotely sample air for smoke means that aspirating detection can be an almost invisible form of detection (only a 3 mm sampling point is required), either for aesthetic purposes or for functionality purposes. Many hundreds of aspirating detectors have been installed in heritage properties and the like.

For further details contact the FDIA on tel: (011) 397 1618.

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