Effectiveness of High-Capacity Smoke Exhaust in Large Spaces

Abstract

Current codes in many countries require that the smoke layer in an atrium or other large space be maintained above the highest means of egress in the space. The smoke exhaust capacity needed to maintain the smoke layer above the highest level of the means of egress can be substantial if that level is near the top of a tall atrium. However, the air entrained along the clear height of the plume that creates the vast quantity of smoke also acts to dilute the smoke. As such, a cost-effective design for an atrium smoke management system may be suggested that causes people to be exposed to the dilute smoke. The adequacy of such a design requires that the qualities of the remaining smoke layer be estimated. A first order analysis to estimate the properties of the smoke layer is described in this paper. Properties of interest include the concentration of gas species, visibility reduction and temperature. In some cases, the visibility may be reduced below 1 m even though the temperature rise and generation of toxic gases are relatively modest. However, with a smoke exhaust rate of 200 kg/s in an atrium, the hazard associated with the smoke layer temperature and CO concentration is modest for a wide range of fuels.

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