SMOKE TOXICITY

Th e specter of fi re in the air is a pilot’s recurrent nightmare... IRE is an integral part of our everyday life, and smoke is one of its products. There Fhave always been efforts to control fi re and use it for constructive purposes, but even then, accidental fi res do occur and fi re contin- ues to cause loss of lives and property. Uncontrolled fi res threaten homes, facto- ries, and transportation systems. The specter of fi re in the air is a pilot’s recurrent night- mare, carried over from the early days of fab- ric covered aircraft, when the time between ignition and loss of the aircraft could be mea- sured in relatively few minutes. Modern aircraft benefi t from fl ame retardant materials and improved fi re extinguishing sys- tems to such an extent that in-fl ight fi res are rare occurrences. However, survivable crashes followed by fi re happen, primarily from fuel spills around the downed aircraft. In the confi ned environ- ment of an aircraft cabin, the presence of smoke automatically indicates the existence of an emergency situation. Extinguishment of fi res obviously has fi rst priority, but smoke inhalation should be recognized as a very real danger while this is being accomplished. Inhalation of toxic gases in smoke is the primary cause of fatalities in most fi res—this is true whether the fi re is in an aircraft cabin, a residential bedroom, or a high-rise building. Smoke gases do not need to reach lethal levels to seriously impair pilot performance. Sublethal exposures can cause even experienced pilots to make potentially fatal mistakes.

1 In view of the seriousness of any aircraft nitrogen- containing synthetics will produce the fi re, let us examine the various aspects of fi re more toxic hydrogen cyanide gas. Irritant gases, and smoke. such as hydrogen chloride and acrolein, are generated from burning wiring insulation and FIRE some other cabin materials. Generally, carbon dioxide levels increase and oxygen concentra- Each fi re is diff erent... tions decrease during fi res. ire is a complex, dynamic, physico- SMOKE EFFECTS chemical event and is the result of a rapid Fchemical reaction generating smoke, heat, fl ame, and light. Each fi re is different. Smoke At high altitude, the effects are greatly composition and heat generated in a fi re de- enhanced... pend on types of burning materials and envi- isual smoke can delay escape from a ronmental conditions. fi re, while the irritant gases can induce tears, pain, and disorientation. The visu- SMOKE V al obscuration is obvious, but the subtle effects of carbon monoxide and hydrogen cyanide Its gases could be toxic... inhalation, although less readily detected, can moke is a complex of particulate matter, cause physical incapacitation and subsequent as well as a variety of invisible combus- death. Toxicologically, carbon monoxide com- tion gases and vapors suspended in the bines with the hemoglobin in blood and inter- S feres with the oxygen supply to tissues, while fi re atmosphere. Smoke may diminish light and obscure vision, and its gases could be toxic. hydrogen cyanide inhibits oxygen utilization at the cellular level. Carbon dioxide, a relatively innocuous fi re gas, increases the respiration SMOKE GASES rate causing an increase in the uptake of the other combustion gases. The decreased oxygen Carbon dioxide levels increase and oxygen level found in most fi re scenarios further en- concentrations decrease... hances the problem of getting enough oxygen arbon monoxide and hydrogen cyanide to the biological sites to maintain normal func- are the two principal toxic combustion tion. Continued inhalation of these gases can gases. Most cabin furnishings contain result in severe hypoxia. At high altitude where C oxygen levels are lower, the effects of carbon carbon and will generate both carbon monox- ide and carbon dioxide when burned; carbon monoxide and hydrogen cyanide are greatly monoxide can also be released from faulty enhanced. cabin heaters. Burning wool, silk, and many

2 SIGNS AND SYMPTOMS chances for survival in an aircraft fi re. A small, hand-held fi re extinguisher can be used to put Not all symptoms will necessarily be out small onboard fi res. Careful inspection and maintenance of cabin heaters will mini- experienced... mize the chance of carbon monoxide leakage arbon monoxide poisoning produces into the cabin air system. A carbon monoxide headache, weakness, nausea, dizzi- detector could also be installed in the cock- Cness, confusion, dimness of vision, pit to detect the presence of this colorless, disturbance of judgment, and unconsciousness odorless gas. As always, planning your prob- followed by coma and death. Although carbon able actions before an emergency arises will monoxide causes deleterious effects on the increase your chances for acting quickly and central nervous system, death usually occurs correctly. from cardiotoxicity. Not all symptoms will necessarily be expe- Remember... rienced by every individual exposed to this • Fires are the main hazard for the occu- gas. Some have succumbed from inhaling low pants of a survivable crash carbon monoxide levels, while others have • A fi re generates smoke, heat, fl ame, and survived breathing higher concentrations. light • Inhalation of toxic gases in smoke Hydrogen cyanide poisoning signs and symp- is the primary cause of death in most toms are weakness, dizziness, headache, nau- fi res sea, vomiting, coma, convulsions, and death. • Carbon monoxide and hydrogen cyanide Death results from respiratory arrest. Hydro- are the main toxic gases in smoke gen cyanide gas acts very rapidly—symptoms • Exposure to carbon monoxide can also be and death can both occur quickly. the result of faulty heaters • A wet cloth held over the nose and SURVIVAL mouth provides some protection from smoke inhalation Knowledge of the less obvious hazards and a few • A small, hand-held fi re extinguisher simple preparations can increase one’s chances... should always be carried aboard general here is no universal best procedure to fol- aviation aircraft low in the event of an aircraft fi re because • Install a carbon monoxide detector in the Tno two fi res are likely to be the same. Ex- cockpit tinguishing the fi re, if possible, is the immediate priority. An equally obvious second priority is MEDICAL FACTS FOR PILOTS to breathe as little smoke for as short a duration Publication AM–400–95/1 as possible. Written by: Some larger aircraft are supplied with por- Arvind K. Chaturvedi, Ph.D. table, self-contained breathing masks for the Prepared by: crew, but small private aircraft usually are not. FAA Civil Aerospace Medical Institute Any cloth held over the nose and mouth will Aerospace Medical Education Division provide protection from smoke particulates; if the cloth is wet, it will also absorb most of the To order copies of this brochure, write: water-soluble gases (i.e., hydrogen cyanide Federal Aviation Administration and hydrogen chloride). Civil Aerospace Medical Institute Cabin venting will reduce the concentra- Shipping Clerk, AAM-400 tions of combustion gases, but is not usually a P.O. Box 25082 viable option while actually fi ghting the fi re. Oklahoma City, OK 73125 Knowledge of the less obvious hazards and a few simple preparations can increase one’s

3