Research shows that smoke contains agent more lethal than carbon monoxide
Firefighters who remove their self-contained breathing apparatus (SCBA) during or shortly after the extinguishment of a fire increase the likelihood of contracting cardiovascular diseases, tumor, and cancers, warns William T. Lowry, Ph.D., a toxicologist with the Institute of Forensic Sciences in Dallas, TX.
Taking smoke/air samples from both actual fire incidents and controlled burnings, Lowry conducted studies on the gaseous products to determine if there were any lethal agents other than carbon monoxide present. According to Lowry, a substantial carbon monoxide level was present only after flashover. However, Lowry found that both before and after flashover conditions, free radicals became trapped in amounts that would be considered toxic and incapacitating to humans within 10 seconds.
These newly detected free radicals are fragmented molecules of a carbon substance that can be more dangerous than carbon monoxide, says Lowry, since they will cause faster incapacitation than will carbon monoxide.
Free radicals are produced by the incomplete combustion of organic materials (materials commonly having carbon, hydrogen, oxygen, and nitrogen in their makeup). Inhaling these free radicals causes interference with the lungs’ ability to absorb oxygen.
In a structural fire test involving rats, it was shown that carbon monoxide levels were minimum until flashover occurred, but that free radicals became trapped during all fire phases. An autopsy of the rats showed that free radical reaction (a rapid rise in lung surface tension which decreases oxygen uptake) took place. According to Lowry, there is no other element more toxic than the lack of oxygen to the human body.
Studies and blood tests conducted on victims hospitalized from smoke inhalation showed that free radical reactions continued even after the incident. Two weeks was the shortest time it took for a human body to return to normal, and 60 days was the longest time.
Lowry cautions that, depending on the material burning, free radicals can be produced at temperatures as low as boiling water (212°F) and that their concentration can be as much as three times that of carbon monoxide. The concentration of free radicals can remain high for 10 minutes or more after a fire is extinguished, depending on the recovery time of the environment.
Lowry also discovered that the physical conditions of a fire, such as burning rate and temperature, can be as important as the kind of material burning in determining the composition of smoke. For example, Lowry learned that a fire in an old wood building with wood furnishings and a fire in a chemical company producing paint additives generated a similar mixture of gases. This can be accounted for by the fact that synthetics decompose and increase in toxicity at low temperatures.
One positive note for free radicals is that because they are so reactive, they readily combine with solid materials on contact. This would help account for the fact that all the survivors of the Air Canada incident had filtered their breathing through tissue or cloth.
For firefighters, this research further strengthens the arguments for proper use of SCBA during both firefighting and overhaul operations.
The study of free radicals in smoke environments and their effects is still going on. Lowry is also looking into the various materials of combustion to determine their relative toxicity and their effects in a fire situation.