Common wildfire terms

Person-caused fires are believed to be started by human activity like campfires, cigarettes disposed without care, or trees fallen by individuals or companies which may land on powerlines.

Lightning-caused fires are fires believed to be started by lightning. 

Most wildfires in the Northwest Territories start because of lightning.

In wildfire management, fuel means organic material that is available to burn.

Most commonly, that is natural features like plants, leaves, and trees.

Ignition is when fuel is lit by a spark or heat source causing it to burn. All wildfires begin with ignition.

Embers are small pieces of burning fuel which can often fly into the air, travel far away from the main location of a fire, and potentially ignite other fuel on the land. They play a big role in wildfire spreading and growing.

Fire suppression is when wildfire fighters, air tankers, and/or helicopters are actively trying to stop a wildfire from growing and spreading.

Learn more about fire suppression and responding to a wildfire here.

A fire line is an area where natural or person-made breaks in fuel exist and where wildfire fighters use them to contain wildfires and base their operations.

This is often created by wildfire fighters by removing potential fuel, like trees or bushes, or by air tankers by dropping fire retardant.

To Control a fire is to complete a fire line around a fire, any smaller fires which have started because of it, and any interior island(s) to be saved; cooling down all hot spots that are immediate threats to the control line until the lines can be expected to hold under foreseeable conditions.

Values-at-risk are anything on the land that is of value to people. This could include:

• Communities
• Cabins
• Critical infrastructure
• Camps
• Critical wildlife habitat
• Cultural values such as grave sites

When wildfire managers make decisions on whether to fight a fire or to let the burn naturally, values-at-risk are the most important consideration.

When wildfire management personnel search the landscape for signs of wildfire the most obvious sign to look for is usually the smoke.

A wildfire where a fire perimeter has not yet been established and perimeter spread is not being contained is described as Out-of-Control (OC).

It is important to note that a wildfire can be out-of-control, but still not pose danger to anyone.

A wildfire that is described as Being Held indicates that with currently committed resources, sufficient suppression action has been taken that the wildfire is not likely to spread beyond existent or predetermined boundaries under prevailing and forecasting conditions. 

A wildfire having received sufficient suppression action to ensure no further spread of the fire is described as Under Control (UC).

Mopping up means the wildfire area is being patrolled to checked for hot spots to prevent further flare-ups.

When the wildfire has been completely extinguished it will be described as Out (DO).

Low wildfire danger means fires may start easily but there will be minimal involvement of deeper fuel layers or larger fuels. 

People can have campfires and burn with regular caution.

Moderate wildfire danger means forest fuels are drying and there is an increased risk of surface fires starting.

Use extra caution with any campfires or other burning.

High wildfire danger means forest fuels are very dry and the fire risk is serious. New fires may start easily, burn vigorously, and challenge fire suppression efforts. 

Extreme caution must be used in any forest activities. Open burning and industrial activities may be restricted.

If the danger is high, it is not a good idea to have a campfire or take on other burning activities unless it is necessary for food or warmth. 

Extreme wildfire danger means extremely dry forest fuels and the fire risk is very serious. New fires will start easily, spread rapidly, and likely challenge fire suppression efforts. 

General forest activities may be restricted, including open burning, industrial activities, target shooting, and campfires.

When the danger is extreme, avoid all campfires or burning activities unless there is no other choice for food or warmth. 

Everything that could burn below the litter layer, which is where you would find compacted organic material (duff), which could support smouldering fires and can significantly add to fire intensity if very dry.

Includes everything that could burn on and above the forest floor between the ground and ladder fuels. This is where surface fires happen. 

In the surface fuel layer, you could likely find dead leaves and twigs, low and medium shrubs, tree seedlings, stumps, or dead logs.

Fuels that provide vertical continuity between the surface fuels and crown fuels in a forest stand, thus contributing to the ease of torching and crowning (e.g. tall shrubs, small-sized trees, bark flakes, tree lichens).

The ladder fuel layer plays an important role in wildfires growing larger and more intense.

This is the layer of fuel made up of the branches, leaves or needles on tall trees. 

The crown fuel layer is most likely to be involved in the most severe wildfires and rapid fire growth and spotting.

A fire that burns in the ground fuel layer.

A fire that burns in the surface fuel layer, excluding the crowns of trees, as either a head fire, flank fire, or backfire.

A fire that advances through the crown fuel layer, usually alongside a surface fire. 

Crown fires can be classified according to the degree of dependence on the surface fire phase, as follows:

• Intermittent: A fire which torches some trees, but the rate of spread is controlled by the surface layer.
• Active Crown Fire: A fire that advances with a well-defined wall of flame extending from the ground surface to above the crown fuel layer. Probably most crown fires are of this class. Development of an active crown fire requires a substantial surface fire, and thereafter the surface and crown phases spread as a linked unit.
• Independent Crown Fire: A fire that advances in the crown fuel layer only.

A smaller fire started outside the main perimeter of a larger one by flying sparks or embers.

A common situation where several smaller fires come together in a particular area. 

Some of the largest, most challenging wildfires in the Northwest Territories are caused by wildfire complexes.

A wildfire of such size, complexity and/or priority that requires a big team, lots of investment, and a long period of firefighting time to bring the wildfire under control or put it out.

A fire burning without flame and barely spreading.

A fire spreading slowly over the ground, generally with a low flame.

A fire rapidly spreading and with a well-defined head.

A single tree or a small clump of trees is said to "torch" when its foliage ignites and flares up, usually from bottom to top. 

Sometimes also called Candle or Candling.

A fire producing embers carried by the surface wind, a fire whirl, and/or convection column that fall beyond the main fire area and causes a new fire that may or may not burn into the original fire.

A fire ascending into the crowns of trees – the part where the branches, leaves or needles are -- and spreading from crown to crown. 

A wildfire, or part of a wildfire, which has experienced sudden and unexpected major increase in rate of spread and intensity. 

A Blow up can upset overall fire suppression actions or plans. They can happen both in very intense and moderately intense wildfires.

The action taken to halt the spread or potential spread of a wildfire by the first firefighting force to arrive at the wildfire.

This would include forming the lines of control, also known as fire lines, and setting the stage for how a wildfire will be fought.

When firefighters and those assisting from the air take actions close to the fire itself to stop the fire from spreading.

This could include spraying water or applying chemicals directly to the area where the wildfire is burning, or working to put space between burned and unburned fuel to act as a control line.

Direct attack is used most in lower-intensity fires with lower flames where it is safe for firefighters to be close to the fire.

When firefighters and those assisting from the air take action far away from a fire itself to influence where the fire goes to take advantage of areas where there is less fuel naturally, and create fire lines through their own actions to stop fire from spreading further.

A form of indirect attack where extensive fire is set along the inner edge of a control line or natural barrier, usually some distance from the wildfire and taking advantage of indrafts, to consume fuels in the path of the fire, and thereby slow down or stop fire spread. 

Fire deliberately utilized in a predetermined area in accordance with a specified and approved burning prescription to achieve set objectives.

Prescribed fires is often used to prevent damage to communities, cabin areas, and critical infrastructure – or as part of establishing a fire line when fighting wildfires.