A fire can be stopped by breaking the fire triangle through the removal of one or more of its components -- heat, air or fuel (see Fire Behaviour). With water or mineral soil as the suppression agent, fire can be extinguished by cooling the fuel below the point of ignition, or by smothering or robbing the fire of air. Fire can also be stopped by removing the supply of available fuel by making it temporarily unburnable through the application of a water/foam suppressant mixture.
When fire crews reach the scene of a fire, power pumps are set up at nearby water sources and hose lines laid out to the fire. Depending on fire size and intensity, it may be extinguished by direct attack, where action is taken at the burning edge of the fire with hand tools and or water supplied by the power pumps, tankers and heli-buckets. MNR fire crews also have the option of pumping straight water or fire suppressing foam.
If the fire is to hot to approach or moving too quickly, the other method of suppression is the indirect attack. This may be accomplished by constructing a fire line away from but in the path of the fire, using hand tools and heavy equipment, and tying in natural fire barriers such as lakes, rivers, or rocky outcrops. The fuel in front of the approaching fire can then be removed by burning out from the fire line towards the fire.
Burn out ignition is accomplished along the ground using a hand held drip torch, or may be ignited from the air using a heli-torch slung beneath a helicopter.
Various control measures can be applied to a fire. One side or flank might be attacked directly, while another side is controlled by burning out. Fire crews often lay hose lines to take advantage of natural barriers such as roads, lakes, rivers, swamps, rocky outcrops or stands of hardwood timber.
Aerial and Ground-Based Foam Applications
Ontario is fortunate to have many thousands of suitable lakes and rivers from which its fire fighting aircraft can scoop loads of water to bomb fires. There are times though when fire managers want to use more than just water to suppress fires or to protect high cost values such as buildings, equipment or cut timber.
The OMNR uses both aerial and ground applications of fire suppressant foams to enhance the effectiveness of their fire suppression and values protection efforts. Foam systems work by reducing the surface tension of water so that air can be mixed with the water molecules to form a bubble structure. This blanket of foam acts as a barrier to fire spread and insulates unburned fuels from the flame front. The bubble structure also provides for a controlled drainage of water out of the foam, increasing the effective life of the water application, and increasing the penetration of the water into woody fuels.
In addition to the foam injection systems found on Ontario's water bombing fleet, fire crews can utilize foam mixers which draw foam concentrate from a container, injecting it into the hose line at the power pump. An application of foam has proved effective under actual fire conditions. A wood building, for instance, coated with foam may be able to withstand ignition from a fire passing close by.
