The effect of gas phase flame retardants on fire effluent toxicity

Standard industry formulations of flame retarded aliphatic polyamides, meeting UL 94 V-0, have been burned under controlled conditions, and the yields of the major asphyxiants, carbon monoxide (CO) and hydrogen cyanide (HCN) have been quantified. Although both the combination of aluminium phosphinate and melamine polyphosphate, and the combination of brominated polystyrene and antimony oxide, inhibit combustion reactions in the gas phase, this study shows that the phosphorus causes a much smaller increase in the CO and HCN yields than antimony-bromine. The mechanisms of CO and HCN generation and destruction are related to the flame inhibition reactions. Both CO and HCN form early in the flame, and the OH radical is critical for their destruction. Crucial, in the context of the flame inhibition mechanism, is the observation that the phosphorus system reduces the H and O radical concentrations without a corresponding decrease in the OH radical concentration; conversely, the bromine system reduces all three of the key radical concentrations, H, O and OH, and thus increases the fire toxicity, by inhibiting decomposition of CO and HCN. Moreover, while the phosphorus flame retardant is effective as an ignition suppressant at lower temperatures (corresponding to early flaming), this is effect “switches off” at high temperatures, minimising the potential increase in fire toxicity, once the fire develops. Since flame retardants are most effective as ignition suppressants, and at the early stages of flaming combustion, while most fire deaths and injuries result from toxic gas inhalation from more developed fires, it is clearly advantageous to have an effective gas phase flame retardant which only causes a small increase in the toxic product yield