Prediction of Ceiling Jet Smoke Concentration under Two Layer Environment

Abstract

For predicting the response of a fire detector in an actual fire, it is important to evaluate the transient properties of the ceiling jet, to which the fire detector is exposed. In this study, a relatively simple and yet accurate enough calculation method was developed by combining a two-layer zone model and an unconfined ceiling jet model to predict the optical smoke density in a ceiling jet.
The method mutually compensates the weakness of the two-layer zone model, which can only predict the average temperature of the interior upper layer, and the weakness of the ceiling jet model, which is not suited for a closed space surrounded by walls. The prediction formula is validated by the fire experiments conducted using the test fire procedure as prescribed in an ISO/TC21/SC3's standard (draft) for fire detection and fire alarm systems.