Mass flow rates across layer interface in a two-layer zone model in an atrium with mechanical exhaust system

Two-layer zone models are commonly used for studying smoke filling in enclosures. There, a clear distinct layer of hot smoke lies above a cool air layer. No mixing of air mass is assumed across the layer interface plane. Based on that, empirical equations are derived in designing atrium smoke management system guides such as NFPA-92B. As observed physically, there might be mass flow across the layer interface of the two layers in the atrium when a mechanical smoke exhaust system is operating. Such a two-layer picture might not be resulted in a big hall. In this paper, exchange mass flow rate across the two layers will be studied based on earlier experimental data on atrium hot smoke tests. It is found that for most of the tests, the mass flow rate across the smoke layer interface can be 30% of the mass exhaust rate of the smoke exhaust system.