An Experimental Study on the Photoelectric Optical Smoke Detector Response

This study investigates the fire safety problem of a smoke detection system in terms of the probable response of light scattering photoelectric smoke detectors. In particular, response characteristics of the smoke detectors were studied experimentally in a test chamber described in UL268, with cotton wick generated fire smoke flowing at a velocity between of 0.5 ms and 3 ms. Measurements of a ‘base case’ detector, i.e. a detector installed with a sensing chamber, a sensor screen and an outer casing, were compared with those of three other casing configurations: (1) a detector with the sensing element freely exposed; (2) a detector with a sensing chamber; and (3) a detector with a sensing chamber and a sensor screen. It was reported that the amount of fuel burnt, the smoke movement velocity and the detector configuration would have significant influences on the detector response. A detector response constant k for a photoelectric smoke detector in the smoke movement velocities was proposed to correlate the optical density attenuation and the changes of detector output signal. This response constant would be useful in development of design parameters for specifying response characteristics of a photoelectric smoke detector in fire detection system.