Report No: DOT/FAA/AM-94/7

Title and Subtitle: Toxicity of Carbon Monoxide Hydrogen Cyanize Gas Mixtures: Exposure Concentration, Time to Incapacitation, Carboxyhemoglobin, and blood Cyanize Parameters, N94-29919

Report Date: April 1994

Authors: Sanders, D.C., Chaturvedi, A.K., Endecott, B.R., Ritter, R.M., and Vu, N.

Abstract: During aircraft interior fires, carbon monoxide (CO) and hydrogen cyanide (HCN) are produced in sufficient amounts to cause incapacitation and death. Time-to-incapacitation (ti) is a practical parameter for estimating escape time in fire environments. Exposures to CO-HCN mixtures have demonstrated that these gases have additive effects (producing shorter times to incapacitation), but the resulting concentrations of carboxyhemoglobin (COHb) and blood cyanide (CN-) at incapacitation are not well defined.

These undefined relationships between COHb and blood CN- levels and the onset of incapacitation make the interpretation of postmortem levels difficult for medical accident investigators. To explore these relationships, ti was determined in laboratory rats exposed to 2 CO-HCN mixtures consisting of CO and HCN concentrations that produce 5- and 35- min ti in individual gas exposures; COHb and blood CN- concentrations were determined at incapacitation. In the high concentration CO HCN mixture, the resultant ti was shortened from 5 min to 2.6 min; COHb dropped from 81% to 55% and CN from 2.3 μg/mL to 1.1 μg/mL. At the lower concentration COHCN mixture, where the resultant ti as reduced from 35 min to 11.1 min, COHb dropped from 71% to 61% and blood CN- decreased from 4.2 μg/mL to 1.1 μg/mL.

Comparison of the COHb and blood CN- values with the values from our single gas exposure studies indicated that any alteration of the uptake of either gas in blood by the presence of the other was minimal. These findings suggest that changes in COHb and blood CN- may not be directly correlated with the onset of incapacitation and that postmortem blood levels should be carefully evaluated, particularly when both gases are present in fire victims.

Key Words: Inhalation toxicology; combustion gases; carbon monoxide hydrogen cyanide gas mixtures; time to incapacitation; carboxyhemoglobin; blood cyanide

No. of Pages: 13