Fire Safety Science Digital Archive

ISO 13571:2007 describes the calculation of safe escape time using yields of asphyxiant and irritant gases for performance based design. Hydrogen chloride (HCl) gas is an incapacitating irritant, reported to be intolerable at concentrations above 100 ppm, but lethal to rats only at concentrations around 5000ppm for a 30 minute exposure. It is evolved from burning PVC, and other chlorine containing plastics. The experimental evidence of the concentration/dose effects on a range of animal species has been reviewed, and concludes that the HCl concentration leading to incapacitation of 1000 ppm, used in ISO 13571, is rather too high to ensure safe escape. Experimental data is presented from burning unplasticised PVC, plasticized PVC cable, and LDPE to show that HCl interferes with the flame chemistry, particularly the conversion of CO to CO2, further increasing the hazard from the fire effluent. The product yields are used to estimate the fire effluent toxicity, comparing the standard based on rat lethality, ISO 13344 with the newer standard, which also takes the effect of incapacitating irritants into account, showing the large contribution of HCl to the fire hazard. Finally, the relationship between the toxicity and a simple analysis of effluent acidity (EN 50297-2-3) is discussed.