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A fire retardant is any substance that reduces the flammability of combustibles. Retardants can be dropped from an aircraft to cool a fire and slow its progress long enough for fire fighters on the ground to take action. Retardants are applied to various forest ecosystems during seasonal fire suppression operations to assist in wildland fire suppression efforts, support ground crews, and to protect values across the NWT.
There are two primary types of retardants used in the Northwest Territories (NWT).
Short-term retardants increase water efficiency, cooling the fire by direct application onto the flame front or just ahead of the perimeter of the fire. The short-term retardant product used is FireFoam WD881-C, in the CL-215 (Skimmer) Air Tankers.
Long-term retardants create a barrier between the wildland fire and available fuels, and are applied just outside the perimeter of a fire. The long-term retardant product used is Liquid Concentrate 95-AMV (LC95-AMV), in the Lockheed Electra L-188 Land Based Air Tanker aircraft.
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.
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.
Foam is a suppressant (which is similar to dish soap) that is applied to fires to slow their growth.
When dropped from the air, the foam covers a wide area and helps limit the spread of the fire. Once dispersed on a fire, foams absorb heat from combustion while the bubble structure slowly releases water, which is absorbed by wood fuels.
Foam improves the effectiveness of water by:
- helping water soak deeper and more quickly into forest fuels--wood, brush, wood debris
- slowing the evaporation of water held within the foam
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.