Study

Other Factors Influencing Fire Behaviour

 

Fires require three elements: Fuel, oxygen and heat. If one of these elements is missing or removed the fire is no more.

Weather is a dominant factor in firefighting safety. Hot, dry and windy conditions are far more dangerous than cool, moist conditions with little or no wind. Exercise caution as weather conditions change for the worse. If a wind event is predicted, the fire dispatcher will issue a weather advisory to all crews in the field. Be prepared to abandon firefighting efforts if high wind conditions occur. Always be aware of weather conditions and plan operations with them in mind. Fire behaviour will normally be more aggressive as the day progresses into the afternoon.

Slope can have a dramatic effect on fire behaviour. Fire will move up a slope at a far greater speed than fire on the flat. Be aware of daily afternoon up slope winds and evening down slope winds. Working on a steep slope requires a lot of extra personal energy and the firefighter will move much slower making entrapment a greater risk.

Aspect will affect the quantity, type and moisture content of the forest fuels. A southern exposure will have drier fuels whereas the northern exposure will be cooler and have a higher moisture content. Never let the aspect distract the firefighter for exercising caution at all times.

Topography will affect how hard it is to access the fire. Exercise extra caution when crossing steep side slopes or areas of loose rocks. Never work directly below anyone else on a steep slope. If you knock a rock or log loose and it starts to roll down the hill, yell “rock”.

If you feel you are in the path of a rolling object, do not look up, but immediately protect yourself by staying low to the ground or behind a tree or large rock. In mountainous country, fire fighters should be aware of the chimney effect. This is where a fire will rush up a gully or valley with great speed potentially trapping anyone working above.


Fire Ranking System

 

In order for the firefighter to better understand the fire conditions they will encounter, this general ranking system will give them a picture of what the fire looks like, depending on fuel types.

Rank 1: Little or no flames. Smoldering ground fire or slow moving surface fire.

Rank 2: Visible open flames, surface fire only. Low vigor surface fire in grass and brush.

Rank 3: Flames at 1-2 meters. More aggressive ground fire in brush and lower limbs.

Rank 4: Flames over 2 meters. High vigor fire burning on surface and into some tree tops.

Rank 5: Flames in tree tops. Extreme surface fire and running from crown to crown.

Rank 6: All trees on fire. Fire above tree tops. Moderate to long range spotting.

Fire fighters will not attempt to control fires greater than a rank 3 blaze unless otherwise directed by the supervisor.