The influence of a perforated false ceiling on the performance of smoke ventilation systems

Abstract Perforated false ceilings ougth not to interfere appreciably with the flows of hot smoky gases from a fire to smoke ventilation openings above the false ceiling. The Fire Research Station currently recommends that such false ceilings should have a minimum free area of 25 percent. An experiment using a 1/10th scale model of a single-level enclosed shopping mall has examined the performance of five perforated false ceilings having different percentages of free area. For both powered and natural venting, it was found that minimum free areas of between 30 and 10 percent could be used depending on the depths of the shop fascia below the false ceiling, and on whether the shops were open- or glass-fronted. The previously recommended minimum of 25 percent has been confirmed as a generally useful ‘rule of thumb’ value for allowing safe escape, even though cool smoke can be expected to affect some nearby shops under some circumstances.