Blood carbon monoxide and hydrogen cyanide concentrations in the fatalities of fire and non-fire associated civil aviation accidents, 1991–1998

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Blood samples submitted to the Civil Aeromedical Institute (CAMI) from aviation accident fatalities are analyzed for carbon monoxide (CO), as carboxyhemoglobin (COHb), and hydrogen cyanide, as cyanide (CN −). These analyses are performed to establish possible exposure of victims to smoke from in-flight/post-crash fires or to CO from faulty exhaust/heating systems. The presence of both gases in blood would suggest that the victim was alive and inhaled smoke. If only COHb is elevated, the accident (or a death) could be the result of CO contamination of the interior. Information pertaining to blood levels of these gases in aviation fatalities, in relation to the associated accidents, is scattered or not available, particularly with regard to toxicity. Therefore, considering that COHb≥10% and CN −≥0.25 μg/ml are sufficient to produce some degree of toxicological effects, the necessary information was extracted from the CAMI database. Samples from 3857 fatalities of 2837 aviation accidents, occurring during 1991–1998, were received; 1012 accidents, encompassing 1571 (41%) fatalities, were fire associated, whereas 1820 accidents were non-fire related. The remaining five accidents were of unknown fire status. There were fewer fire related fatalities and associated accidents in the (COHb≥10% and CN −≥0.25 μg/ml) category than that in the (COHb<10% and CN −<0.25 μg/ml) category. No in-flight fire was documented in the former category, but in-flight fires were reported in 14 accidents (18 fatalities) in the latter category. No non-fire accident fatality was found wherein levels of both gases were determined to be at or above the stated levels. There were 15 non-fire accidents with 17 fatalities wherein only COHb (10–69%) was elevated. The present study suggests that aviation fire accidents/fatalities were fewer than aviation non-fire accidents/fatalities and confirms that aviation accidents related to in-flight fires and CO-contaminated interiors are rare.