A Comparison of Driving Forces for Smoke Movement in Buildings

Abstract

It has been suggested that automatic shutdown of mechanical ventilation systems upon smoke detection may be superfluous and unnecessary because other driving forces will continue to transport smoke throughout buildings after the ventilation systems have been shut down. To evaluate this hypothesis, an analysis is presented that considers the relative smoke concentrations throughout a building arising from the driving forces of stack effect, wind effect, and buoyancy of combustion gases as well as those arising from mechanical ventilation. This analysis considers a representative 10-story building, but the approach presented can be extended to buildings of different heights and areas. The results of this study indicate that the shutdown of mechanical ventilation may not prevent the smoke contamination of nonfire floors, but it may still be preferable to leaving ventilation systems running unless the systems are specifically designed for smoke management.