Behavioural impairment in smoke environments

When aircraft cabin occupants are exposed to fire effluent, the first hazard encountered is usually smoke, containing particulates and toxic gases, which cause immediate visual obscuration and painful irritation of the eyes and respiratory tract. This may be followed by incapacitation due to pain or asphyxia, if exposure continues. In smouldering or small, confined, in-flight fires, where the yields of organic irritants and acid gases are likely to be high and exposure times long, then the distressing effects of irritants, lung inflammation, and asphyxia induced by carbon monoxide (CO) are likely to be the main hazards. For post-crash fires, which tend to develop rapidly to flashover, the time available for escape is often limited to a few minutes before conditions become lethal due to the effects of toxic smoke and heat, so that survival depends upon a rapid egress. Visual obscuration and smoke irritancy are important during the early stages in that they may reduce the speed and efficiency of escape. People have been shown to be reluctant to enter smoke-logged areas if these are between them and an exit, and movement speeds are greatly reduced at optical densities above OD/m 0.5, and even more when the smoke is irritant. Once cabin lining and seating materials become heavily involved in the area opposite a cabin breach, then the concentrations of toxic gases, especially CO and hydrogen cyanide, can increase rapidly further down the cabin causing rapid incapacitation of any remaining cabin occupants. This is followed or accompanied by extreme heat, so that deaths result from asphyxia and/or heat shock. For in-flight fires, it is recommended that consideration should be given to reducing the hazard from irritants. For post-crash fires, measures aimed at delaying the involvement of cabin contents (such as spray mist systems) should be considered.