Shortcomings of engineering design based calculations for smoke control systems in atriums; an investigation of critical parameters using comparative CFD simulations

Correct design of smoke ventilation in large building atriums protects the means of escape during the occupants’ evacuation phase and helps the fire and rescue crews by clearing the building from smoke and heat. In this study we evaluate the importance of common practical deviations from explicit and implicit assumptions in the engineering-correlations based design of such systems, by testing the performance of an atrium smoke control system using CFD simulations with the Fire Dynamics Simulator (FDS). The simulations showed that even in the ideal scenario of fairly uniform inlet fresh air supply, instabilities are generated in the fire plume which ultimately result in mixing between the layers. This mixing becomes more severe if the inlet air distribution is not uniform. In this scenario, the soot yield of the burning material becomes very important and we showed that when the soot yield is increased the previously safe design becomes unsafe and this can’t be anticipated by the engineering correlations themselves