title: Exposures to carbon monoxide, hydrogen cyanide and their mixtures: interrelationship between gas exposure concentration, time to incapacitation, carboxyhemoglobin and blood cyanide in rats.
abstract: Carbon monoxide (CO) and hydrogen cyanide (HCN) are generated during aircraft interior fires in sufficient amounts to incapacitate cabin occupants. For typical post-crash and in-flight fires, minimum protection periods of 5 and 35 min, respectively, have been suggested for breathing devices to protect the occupants from smoke. Relationships of blood carboxyhemoglobin (COHb) and cyanide (CN-) levels to incapacitation have not been well defined for these gases. Therefore, time to incapacitation (ti) and blood COHb and CN- at incapacitation were examined in rats exposed to CO (5706 ppm for 5-min ti; 1902 ppm for 35-min ti), HCN (184 ppm for 5-min ti; 64 ppm for 35-min ti) and their mixtures (equipotent concentrations of each gas that produced 5- and 35-min ti). Blood CO and HCN uptakes were evaluated at the two concentrations of each gas. With either gas, variation in ti was higher for the 35-min ti than the 5-min ti The COHb level reached a plateau prior to incapacitation at both CO concentrations, and COHb levels at the 5- and 35-min ti were different from each other. Blood CN- increased as a function of both HCN concentration and exposure time, but CN- at the 5-min ti was half of the 35-min ti CN- level. The HCN uptake at the high concentration was about three times that at the low concentration. In the high concentration CO-HCN mixture, ti was shortened from 5 to 2.6 min; COHb dropped from 81 to 55% and blood CN- from 2.3 to 1.1 microgram ml(-1). At the low-concentration CO-HCN mixture, where ti was reduced from 35 to 11.1 min, COHb decreased from 71 to 61% and blood CN- from 4.2 to 1.1 microgram ml(-1). Any alteration in the uptake of either gas by the presence of the other was minimal. Our findings suggest that specific levels of blood COHb and CN- cannot be correlated directly with the incapacitation onset and that postmortem blood COHb and CN- levels should be evaluated carefully in fire victims.
authors.affiliation: Toxicology and Accident Research Laboratory (AAM 610), Federal Aviation Administration, US Department of Transportation, Oklahoma City, OK 73125-5066, USA.
authors.forename: A K
authors.initials: AK
authors.lastname: Chaturvedi
authors.forename: D C
authors.initials: DC
authors.lastname: Sanders
authors.forename: B R
authors.initials: BR
authors.lastname: Endecott
authors.forename: R M
authors.initials: RM
authors.lastname: Ritter
mesh_terms: D000401:Aircraft; D000818:Animals; D002248:Carbon Monoxide / Q000008:administration & dosage / Q000378:metabolism / Q000633:toxicity*; D002249:Carbon Monoxide Poisoning; D002263:Carboxyhemoglobin / Q000187:drug effects* / Q000378:metabolism; D003486:Cyanides / Q000097:blood*; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D005390:Fires; D006856:Hydrogen Cyanide / Q000008:administration & dosage / Q000378:metabolism / Q000633:toxicity*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D012044:Regression Analysis
chemical_list: D003486:Cyanides; D006856:Hydrogen Cyanide; D002248:Carbon Monoxide; D002263:Carboxyhemoglobin