Review on using the 'time constant' for studying the atrium smoke-filling processes

A time constant has been proposed to characterize the time it takes to fill an atrium space with smoke for design purposes. This was defined through the use of the empirical equation expressing the mass entrainment rate to the 3/2 power of the clear height. However, the equation holds only when the flame tip touches the smoke layer, and the flame temperature was taken to be 1100 K (827°C 1521°F). Another time constant using the plume equation proposed by Zukoski is used and the concept is further evaluated in this paper using zone models developed at NIST and another model developed at the Building Research Institute, Ministry of Construction, Japan. A design fire of thermal power and area related to the volume at the atrium space is proposed in order to evaluate the time constant. Results of the zone modeling simulation supported the fact that the time required to fill 80% of the atrium space with smoke is related to its time constant. Full-scale experimental results on smoke-filling processes in atria available in the literature are compared. This quantity is recommended to specify the smoke-filling time for an atrium space for design purposes, and its use for smoke control design is also discussed.