Ministry of Forests, Lands and Natural Resource Operations - Wildfire Management Branch
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A fire retardant is any substance that by chemical or physical action, reduces flammability of combustibles. They can be dropped from an aircraft to cool a fire and slow its progress long enough for fire fighters to take action.
Water soluble retardants are most commonly used because of their long-lasting effect on fires. They contain ammonium salts which char on contact with flame. This reaction releases a water and carbon dioxide combination that cools and suffocates the fire. Fire retardants are essentially an industrial strength fertilizer with colouring.
Because the active ingredients in retardants don't evaporate, they are particularly useful in fighting high-intensity fires requiring a distant and indirect attack. In these situations, long-term retardant mixtures are usually applied ahead of the advancing fire by air tankers and helicopters.
Water is a suppressant used to suppress or extinguish wildfires. Water is applied by ground crews using water bags, tanks, pumps and hoses, or by helicopters equipped with buckets or belly tanks.
In British Columbia, aerial water bombers are usually limited to coastal areas because of adverse landing and loading conditions in many interior areas.
Foam is a suppressant (which is similar to dish soap) that is applied to fires to suppress or extinguish them.
Fire control foam is created by mechanically aerating a water-diluted concentrate, injecting the concentrate into ground or air-borne water tanks, or by simply dropping the mixture from an air tanker or helicopter.
Once dispersed on a fire, foams absorb heat from combustion while the bubble structure slowly releases water, which is absorbed by wood fuels.
A mixture can produce dry or wet foams, depending on the ratio of water and concentrate. Dry foams produce smaller high-insulation bubbles while wet foams develop larger bubbles that provide better water penetration.
Although fire-control foams are a better suppressant than water, their usefulness is limited, particularly against high-intensity fires, where long-term retardants have proven more successful.