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Technical Article

Smoke the silent killer

There are basically three common poisons that kill smoke inhalation victims, carbon monoxide, hydrogen sulphide and hydrogen cyanide and by far the most significant is carbon monoxide.


Most fire deaths occur from carbon monoxide inhalation which is generated in every fire situation and the less complete the combustion the greater the level of carbon monoxide produced. As a general rule the darker the smoke the higher the carbon monoxide level simply because black smoke contains a high level of carbon as a direct result of incomplete combustion 


Carbon monoxide is lighter than air and has an attraction for blood cells that is over 200 times greater than that of oxygen. It tends to displace oxygen at a greater rate and if enough oxygen carrying blood cells are displaced the victim will die from anoxia which is simply a term for oxygen depletion. The usual concentration of carbon monoxide in air is less than 0.03% and any concentrations higher than 0.5% is dangerous and lethal within 30 minutes. 

Hydrogen sulphide is also a significant contributor and is distinguished by its noticeable “rotten egg” smell. It is heavier than air and is present at floor level in smoky rooms. In high concentrations it is thought to actually paralyse the respiratory process resulting in suffocation. It can also be produced by organic decomposition, can be found in sewers, drains and wells and any concentration above 0.1% is dangerous and can prove fatal in a very short time frame. 

Hydrogen Cyanide is another by product of combustion and interferes with respiration at a cellular level preventing the usual exchange of oxygen, carbon monoxide and carbon dioxide within the lungs. It also increases the respiration rate increasing the amount of carbon monoxide inhaled as well as producing gasping respiration and muscle spasms. 

The actual term smoke inhalation is somewhat confusing because in fact we have identified three constituents of smoke that readily attack the respiratory system in different ways through hypoxia, systemic poisoning and irritation. Each in itself can be fatal but when we combine the effects of two or more the result is more pronounced.

Combine these toxic vapours with the heat produced in a fire situation and it quickly becomes understandable how vulnerable the human body is to the effects of fire. 


There have been considerable medical advances in treating burns victims and the number of people that die from burns alone has been considerably reduced in recent years. However changes to the composition of modern furnishings, fittings and construction materials has added to the toxicity of smoke therefore any reduction in fire deaths must come from a reduction in deaths due to smoke inhalation. 


Without question it now becomes clear why the New Zealand Fire Service places so much importance and encourages us to work within our communities to promote the installation of smoke alarms in every sleeping area and on every level of all residential occupancies. If occupants receive early warning of a fire situation, have a prepared and practised home escape plan the risk of becoming a victim of smoke inhalation is considerably reduced 


For all operational firefighters the importance of wearing breathing apparatus in fire and smoke situations cannot be over stressed. The use of BA is paramount in many situations including toxic atmospheres inside and outside buildings. BA provides the needed level of protection in varied situations and must be considered a vital tool in the health and safety and staff welfare toolbox. At no time should any firefighter be criticised for continuing to wear BA on the fire ground even long after the fire has been controlled and nor should officers expect personnel to carry out any salvage or overhaul roles without the protection of breathing apparatus. 

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