Fire Safety Science Digital Archive

The means for predicting ceiling jet temperature under an unconfined ceiling has been well established by the previous work under an unconfined ceiling. However, a room ceiling is usually enclosed by walls so a fire plume rises in a stratified environment in the event of room fire. Previous work under an unconfined ceiling will not be sufficient to predict the ceiling jet temperature in such a configuration. On the other hand, a two layer zone model is often used for predicting fire temperature in a stratified configuration but it only gives average condition in the upper layer, which is too crude to predict the near ceiling temperature to assess the actuation of ceiling mounted detectors and sprinklers. In this study, a formula for ceiling jet temperature in a two layer configuration was derived by combining previous work under an unconfined ceiling, upper layer temperature and layer interface height. The validity of the formula was examined by comparing the results of prediction and the experiments using the test fires prescribed in an ISO/TC21/SC3 draft standard. The predicted ceiling temperatures generally exhibit satisfactory agreement with the measured temperatures