Carboxyhemoglobin and blood cyanide concentrations in relation to aviation accidents

It is important in aviation accident investigations to determine if a fire occurred during flight or after the crash and to establish the source(s) of the toxic gases.

Bio-specimens from aviation accident fatalities are submitted to CAMI for analyses. In blood, CO is analyzed as carboxyhemoglobin (COHb) and hydrogen cyanide as cyanide (CN-). Analytical data were stored in a database, and this database was searched for the period of 1990-2002 for the presence of COHb and CN in the submitted cases.

Out of 5945 cases, there were 223 (4%) cases wherein COHb was > or = 10%. Of the 223 cases, fire was reported with 201, no fire with 21, and undetermined fire status with 1. CN concentrations were at or above 0.25 microg x ml(-1) in 103 of the 201 fire-related cases. None of the 21 non-fire cases had CN-, but nicotine was detected in 9 of the cases. All non-fire cases with COHb > 30% (four cases) were associated with exhaust leaks. Of the 223 cases, COHb-CN- fractional toxic concentration (FTC) was lethal only in 31 cases with elevated CN levels.

The presence of COHb and CN in elevated concentrations in the blood of victims found by autopsy to have died on impact would indicate an in-flight fire. In the absence of fire and CN-, the elevated COHb concentrations would suggest an exhaust leak, particularly at COHb > 30%. The findings of this study also suggest that, in addition to COHb, CN plays a detrimental role in fire-associated aviation accident fatalities.