Fire Safety Science Digital Archive

Previous studies of the thermal response of heat-sensitive fire detectors, and methods of testing them, have been restricted to the "point" or spot type in which the sensitive element is relatively small and is only affected by the temperature conditions existing in the small area around it. There are however a number of detectors in which the sensitive element is extended linearly ("line" detectors), and these will be affected by the temperature conditions existing over a fairly large area of the ceiling on which the detector is mounted. TYPical designs of such detectors include those in which a fluid in a thinwalled tube expands on heating and produces a pressure at a sensitive capsule, and others in which the electrical resistance or capacity of a filar conductor or dielectric changes as its temperature increases. It has been shown that the response of a line detector of this type will depend on the length of detector subjected to the hot gases, and also upon the temperature distribution of the gases over the length of the detector. This note desoribes some experiments in which various lengths of a line detector have been subjected to an airflow of uniformly-rising temperature. The response times obtained have been analysed and possible methods of testing this type of detector have been deduced from the results.