A Calculation Method for Predicting Heat and Smoke Detector's Response

Abstract

Utilizing a zone model and a ceiling-jet model, a simple calculation method for predicting fire detector's response time is presented. The parameters are the floor area and the ceiling height of the room, the radial distance of the detector from the fire axis, time history of the heat and smoke release rates of the fire, and the response characteristics of the detector. For the heat detector, application of RTI-C model (a modified Response Time Index model) is discussed and a method utilizing two RTI's, one for the sensor element and the other for the detector body, is introduced. The method using two RTI's shows better results than the original RTI-C model, which was derived for predicting the response of sprinkler heads. In addition, a calculation method for predicting the response of rate-of-rise heat detector is presented. For the response of photoelectric smoke detector, a method utilizing a response threshold in the optical smoke concentration and a response threshold in the air velocity is introduced. It is shown that different response thresholds in the smoke concentration are needed for the smoke released from flaming sources and for the smoke released from smoldering sources respectively.