Fractional effective dose model for post-crash aircraft survivability.

The development of a survival model for post-crash aircraft cabin fires is described in this paper. Its development is based on an extensive review of the literature on the toxicity of combustion gases and on thermal hazards. This model is to be used as a predictive tool to gauge human survivability in full scale aircraft cabin fire tests. The extensive literature search was conducted for carbon monoxide (CO), carbon dioxide (CO2), hydrogen cyanide (HCN), low oxygen, hydrogen fluoride (HF), hydrogen chloride (HCl), hydrogen bromide (HBr), nitrogen dioxide (NO2), sulfur dioxide (SO2), acrolein (CH2CHCHO), and heat exposures. Those studies by various investigators of exposures to single and mixed gases on humans, primates, rats, and mice at different physical activity levels were compared. Regression equations were derived from those studies to give the best fit to the gas exposure concentration and duration data. The equation judged to best model the human escaping from an aircraft cabin was selected for each gas. This survival model uses incapacitation data to obtain a fractional effective dose (FED) for incapacitation (FED(I)) and lethality data, inclusive of post exposure deaths, to obtain a FED for lethality (FED(L)). The exposure time required for either FED(I) or FED(L) to reach unity, using a projected set of gas concentrations, represents the exposure time available to escape from the specified fire environment or to survive post exposure, respectively. The effect of CO2 in increasing the uptake of other gases was factored into the concentration term in the FED equation for all gases with the exception of CO2 and oxygen. Higher respiratory minute volumes due to CO2 exposure were found to be an important factor in predicting the time available to escape. This FED-based model can be applied to the evaluation of the toxicity of smoke in computer modeling of aircraft fire situations.