Modelling the response of sprinklers in compartment fires

Abstract

AbstractAlpert's expressions are used extensively to calculate the maximum temperature and velocity in the ceiling‐jet at any distance, r, from the fire axis. These expressions are valid for unconfined ceilings insofar as the environment outside the ceiling‐jet is uniform in temperature and is atmospheric ambient. In compartments the outward flow of hot gases is checked by the presence of bounding walls and so a layer of hot gases is formed in the upper portion of the compartment. The environment outside the ceiling‐jet is no longer ambient atmospheric. Expressions due to Alpert becomes unsuitable, unless the effects of the accumulated hot layer are included in these expressions.The effect of the upper layer temperature has been taken by assuming that since the ceiling‐jet is completely submerged in the upper hot gas layer, the entrained gases are drawn from this layer only instead of the ambient atmospheric air at T∞. Thus T∞ has been replaced by TL in the Alpert's empirical expression for ceiling‐jet temperatures. The proposed equation is then used to calculate the response time of sprinklers fitted in compartments of varying sizes. Calculations have been done for identical conditions to those employed by Evans and compared. Comparison has also been made with Cooper's LAVENT model predictions. The study shows that the present model is capable of predicting the maximum, as well as average, temperatures in the ceiling‐jets submerged in the hot gas layer. Copyright © 2001 John Wiley & Sons, Ltd.