Radiation detector requirements, fire

The use of two separate electrical or mechanical zones of detectors, both of which must be actuated before the confirmation of a fire or gas detection. For example, the detectors in one zone could all be placed on the north side of a protected area, and positioned to view the protected area looking south, while the detectors in the second zone would be located on the south side and positioned to view the northern area. Requiring both zones to be actuated reduces the probability of a false alarm activated by a false alarm source such as welding operations, from either the north or the south outside the protected area. However this method is not effective if the zone facing away from the source, sees the radiation. Another method of cross zoning is to have one set of detectors cover the area to be protected and another set located to face away from the protected area to intercept external sources of nuisance UV. If welding or lighting should occur outside the protected area, activation of the alarm for the protected area would be inhibited by second... 

The principle of lidar is that a laser pulse is fired into the atmosphere and as it proceeds along its path, radiation that is scattered by aerosol and other particles is directed back toward the laser where it is collected with a telescope and measured with a detector. The lidar system can be operated either in single- or multi-wavelength mode (by using a tuneable laser) so as to detect a number of different species according to the attenuation they cause at specific wavelengths. Several practical systems have been developed to monitor species such as SO2 and O3 but the instrumentation required is complex and very expensive. Analysis of the signal also requires considerable expertise. 

A fire eye or flame detector detects the radiation from a flame. It requires line-of-sight capability. There must be no blockages between the instrument and the potential fire locations. A fire eye s field-of-vision usually covers a larger area than that of a heat detector, but it will not detect a smoldering fire as quickly as some smoke detectors. 

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