Toxic product yields and hazard assessment for fully enclosed design fires

Abstract

Fires in multi-compartment buildings often occur in enclosed spaces or in enclosures opening into other rooms or corridors. Where such fires occur in relatively small enclosures, with limited external venting, the growth of the fire itself remains restricted. If large vents are present opening into large enclosed spaces or to the outside, flashover may occur. In either case these fires are likely to become oxygen vitiated, producing large amounts of smoke and toxic products. Fire-retarded (FR) and non-FR materials behave differently in these situations from the well-ventilated conditions in most standard tests, with smaller differences in toxic product yields. The main hazard to building occupants is the rapid contamination of building spaces by toxic smoke. Visual obscuration and irritancy of smoke impedes escape efficiency, affecting escape behaviour and slowing travel speeds. This may be followed by incapacitation, primarily due to exposure to asphyxiant gases (mainly CO and HCN), and death. A series of full-scale fire tests conducted in enclosed test rigs and buildings is reported, in which detailed measurements of smoke, heat, toxic gases and time to detection were made, enabling assessment of time to incapacitation using Fractional Effective Dose methodology. Also described are hazard analyses for fires in which an active suppression was used. These include fires in two-storey maisonettes with and without domestic sprinklers. Results are presented on the relationship between plume oxygen and CO concentrations, and between CO and HCN yields. The effects of interactions between fuel type and load, ventilation and building enclosures are discussed and their implications for choice of design fires appropriate to different fire scenarios. © 2000 Society of Chemical Industry