### SMOKE TOXICITY

### *The Specter of fire in the air is a pilot'srecurrent nightmare...*

Fire is an integral part of our everyday life, and smoke is one of its products.There have always been efforts to control fire and use it for constructivepurposes, but even then, accidental fires do occur and fire continues to causeloss of lives and property.
Uncontrolled fires threaten homes, factories, and transportation systems. Thespecter of fire in the air is a pilot's recurrent nightmare, carried over fromthe early days of fabric covered aircraft, when the time between ignition andloss of the aircraft could be measured in relatively few minutes.
Modern aircraft benefit from flame retardant materials and improved fireextinguishing systems to such an extent that in-flight fires are rareoccurrences. However, survivable crashes followed by fire happen, primarily fromfuel spills around the downed aircraft. In the confined environment of anaircraft cabin, the presence of smoke automatically indicates the existence ofan emergency situation. Extinguishment of fires obviously has first priority,but smoke inhalation should be recognized as a very real danger while this isbeing accomplished.
Inhalation of toxic gases in smoke is the primary cause of fatalities in mostfires - this is true whether the fire is in an aircraft cabin, a residentialbedroom, or a high-rise building. Smoke gases do not need to reach lethal levelsto seriously impair pilot performance. Sublethal exposures can cause evenexperienced pilots to make potentially fatal mistakes.
In view of the seriousness of any aircraft fire, let us examine the variousaspects of fire and smoke.
**FIRE**
***Each fire is different...***
Fire is a complex, dynamic, physicochemical phenomenon and is a result of arapid chemical reaction generating smoke, heat, flame, and light. Each fire isdifferent. Smoke composition and heat generated in a fire depend on types ofburning materials and environmental conditions.
**SMOKE**
***Its gases could be toxic...***
Smoke is a complex of particulate matter, as well as a variety of invisiblecombustion gases and vapors suspended in the fire atmosphere. Smoke may diminishlight and obscure vision, and its gases could be toxic.
**SMOKE GASES**
***Carbon dioxide levels increase and oxygen concentrations decrease...***
Carbon monoxide and hydrogen cyanide are the two principal toxic combustiongases. Most cabin furnishings contain carbon and will generate both carbonmonoxide and carbon dioxide when burned; carbon monoxide can also be releasedfrom faulty cabin heaters. Burning wool, silk, and many nitrogen- containingsynthetics will produce the more toxic hydrogen cyanide gas. Irritant gases,such as hydrogen chloride and acrolein, are generated from burning wiringinsulation and some other cabin materials. Generally, carbon dioxide levelsincrease and oxygen concentrations decrease during fires.
**SMOKE EFFECTS**
***At high altitude, the effects are greatly enhanced...***
Visual smoke can delay escape from a fire, while the irritant gases caninduce tears, pain, and disorientation. The visual obscuration is obvious, butthe subtle effects of carbon monoxide and hydrogen cyanide inhalation, althoughless readily detected, can cause physical incapacitation and subsequent death.Toxicologically, carbon monoxide combines with the hemoglobin in**bloodand interferes with the oxygen supply to tissues, while hydrogen cyanideinhibits oxygen utilization at the cellular level. Carbon dioxide, a relativelyinnocuous**fire gas, increases the respiration rate causing an increase inthe uptake of the other combustion gases.
The decreased oxygen level found in most fire scenarios further enhances theproblem of getting enough oxygen to the biological sites to maintain normalfunction. Continued inhalation of these gases can result in severe hypoxia. Athigh altitude where oxygen levels are lower, the effects of carbon monoxide andhydrogen cyanide are greatly enhanced.
**SIGNS AND SYMPTOMS**
***Not all symptoms will necessarily be experienced...***
Carbonmonoxide poisoning produces headache, weakness, nausea, dizziness, confusion,dimness of vision, disturbance of judgment, and unconsciousness followed by comaand death. Although carbon monoxide causes deleterious effects on the centralnervous system, death usually occurs from cardiotoxicity. Not all symptoms willnecessarily be experienced by every individual exposed to this gas. Some havesuccumbed from inhaling low carbon monoxide levels, while others have survivedbreathing higher concentrations.
Hydrogen cyanide poisoning signs and symptoms are weakness, dizziness,headache, nausea, vomiting, coma, convulsions, and death. Death results fromrespiratory arrest. Hydrogen cyanide gas acts very rapidly-symptoms and deathcan both occur quickly.
**SURVIVAL**

***Knowledge of the less obvious hazards and a fewsimple preparations can increase one's chances...***
There is no universal *best* procedure to follow in the event of anaircraft fire because no two fires are likely to be the same. Extinguishing thefire, if possible, is the immediate priority. An equally obvious second priorityis to breathe as little smoke for as short a duration as possible. Some largeraircraft are supplied with portable, self-contained breathing masks for thecrew, but small private aircraft usually are not. Any cloth held over the noseand mouth will provide protection from smoke particulates; if the cloth is wet,it will also absorb most of the water-soluble gases (i.e., hydrogen cyanide andhydrogen chloride). Cabin venting will reduce the concentrations of combustiongases, but is not usually a viable option while actually fighting the fire.
Knowledge of the less obvious hazards and a few simple preparations canincrease one's chances for survival in an aircraft fire. A small, hand-held fireextinguisher can frequently prevent small electrical fires in the instrumentpanel or cockpit from becoming a major problem. Careful inspection andmaintenance of cabin heaters will minimize the chance of carbon monoxide leakageinto the cabin air system. As always, planning your probable actions before anemergency arises will increase your chances for acting quickly and correctly.
***Remember...***- Fires are the main hazard for the occupants of a survivable crash   A fire generates smoke, heat, flame, and light  Inhalation of toxic gases in smoke is the primary cause of death in most    fires  
- Carbon monoxide and hydrogen cyanide are the main toxic gases in smoke   Exposure to carbon monoxide can also be the result of faulty heaters  A wet cloth held over the nose and mouth provides some protection from    smoke inhalation  
- A small hand-held fire extinguisher should always be carried aboard    general aviation aircraft                   **Medical Facts for Pilots**Publication AM-400-95/1
-   Written by: Arvin K. Chaturvedi, Ph.D.                                    
  Prepared by
  :                                
  - Aeromedical Education Division                                          FAA Civil Aerospace Medical Institute                                          AAM-400, P.O. Box 25082                                          Oklahoma City, OK 73125                                         
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Last modified 12/3/01