Smoke filling and extraction in atria: Time constant

Abstract

Whether a smoke extraction system has to be installed for an atrium building in Hong Kong is currendy determined by its volume. This is not a satisfactory criterion, since the smoke filling times in atria of the same volume but different shapes are very different. A time constant is proposed as an appropriate parameter to replace the atrium volume. This paper reports an evaluation of this quantity using the zone model FIRST developed at the Building and Fire Research Laboratory, NIST, USA. Simulation by this model of smoke extraction effects in different types of atria is studied, and the results are compared with experimental results on smoke filling from the literature. In addition, a crude analysis without thermal effects was carried out. Closed-form expressions on the time required to fill 80% of the atrium height with smoke were derived. Lastly, a'design fire' is proposed to calculate the time constant of the atrium.