Toxicity of Fire Smoke

This review is an attempt to present and describe the major immediate toxic threats in fire situations. These are carbon monoxide, a multitude of irritating organic chemicals in the smoke, oxygen depletion, and heat. During the past 50 years, synthetic polymers have been introduced in buildings in very large quantities. Many contain nitrogen or halogens, resulting in the release of hydrogen cyanide and inorganic acids in fire smoke as additional toxic threats. An analysis of toxicological findings in fire and nonfire deaths and the results of animal exposures to smoke from a variety of burning materials indicate that carbon monoxide is still likely to be the major toxicant in modern fires. However, the additional toxic threats mentioned above can sometimes be the principal cause of death or their addition can result in much lower than expected carboxyhemoglobin levels in fire victims. This analysis also revealed that hydrogen cyanide is likely to be present in appreciable amounts in the blood of fire victims in modern fires. The mechanisms of action of acute carbon monoxide and hydrogen cyanide poisonings are reviewed, with cases presented to illustrate how each chemical can be a major contributor or how they may interact. Also, lethal levels of carboxyhemoglobin and cyanide in blood are suggested from an analysis of the results of a large number of fire victims from different fire scenarios. The contribution of oxygen depletion and heat stress are more difficult to establish. From the analysis of several fire scenarios, they may play a major role in the room of origin at the beginning of a fire. The results in animal studies indicate that when major oxygen depletion (<10%) is added to lethal or sublethal levels of carbon monoxide or hydrogen cyanide its major role is to substantially reduce the time to death. In these experiments the carboxyhemoglobin level at death was slightly reduced from the expected level with exposure to carbon monoxide alone. However, blood cyanide was reduced by a factor of ten from the expected level with exposure to hydrogen cyanide alone. This is another factor (among many other presented) complicating the task of establishing the contribution of cyanide in the death of fire victims, from its analysis in their blood. Finally the role of ethanol intoxication, as it may influence carboxyhemoglobin levels at death, is reviewed. Its role is minor, if any, but the data available on ethanol in brain tissue and blood of fire victims confirmed that brain ethanol level is an excellent predictor of blood ethanol.