Suppressing wildland fires
In this section
Many people wonder, "How do you put out a wildland fire?"
It’s important to note that not all wildland fires in the Northwest Territories (NWT) are fought, or “suppressed”. Fires are first assessed, to determine if they should be monitored, addressed to protect values at risk, or suppressed (fought).
When fighting wildland fire, firefighter and public safety are the first priority.
Knowing how a wildfire might behave is critical for fire managers. Many factors affect how a wildfire burns and how difficult it may be to control. The three sides of the fire behaviour triangle are weather, topography and fuels.
To put out a fire, heat, fuel or oxygen must be removed. Putting dirt and water or retardant on fire removes the oxygen from the fuel. This allows a firefighter using a hand tool such as shovel, axe, rake or Pulaski to extinguish small fires.
Larger fires require more people and equipment, such as engines, pumps, bulldozers, helicopters and air tankers dropping water or retardant.
Air tankers do not put out fires. This is done by firefighting crews on the ground.
A good wildland firefighter fights fire in many dimensions simultaneously, and is continually aware of changes in these dimensions. This is called Situational Awareness, and is extremely important as fire occurs on the ground, in the trees, and even in the air when embers are carried on the wind. The fire environment is more of a dome than a flat tabletop or chessboard.
Fire suppression starts with the detection of the fire. Next, fire crews, engines, helicopters or other suppression resources are delivered to the fire. Upon arrival, the leader, known as the Incident Commander (IC) sizes up the fire. Fuels, terrain, weather, fire size and other fire behaviours are noted and used to determine strategy and tactics.
The IC then reports to the regional duty officer and orders resources applicable to the current and expected fire situation. Depending on the fire size, the IC may decide to begin indirect and/or direct initial attack, or use firefighters to establish a helispot or drop point to facilitate logistics.
All fires are managed using the Incident Command System (ICS). Management positions are added and taken away depending on the fire situation.
Often, preparatory suppression tactics are used a distance away from the oncoming fire. This is called an indirect attack.
Indirect attack can include the use of firelines, backburning and wetting unburned fuels. It can also include the creation of control lines, which are boundaries that contain no combustible material. Control lines can be constructed by physically removing combustible material with tools and equipment, or portions may be naturally occurring.
Lines may also be created by backfiring–that is, creating small, low-intensity fires using driptorches or flares. The resulting fires are extinguished by firefighters or, ideally, directed in such a way that they meet the main fire front, at which point both fires run out of flammable material and are thus extinguished. Additionally, the use of long-term retardants may be used. Such compounds reduce the flammability of materials by either blocking the fire physically or by initiating a chemical reaction that stops the fire.
Unfortunately, any method can fail in the face of erratic or high-intensity winds and changing weather. Changing winds may cause fires to change direction and miss control lines. High-intensity winds may cause jumping or spotting as burning embers are carried through the air over a fireline. Burning trees may fall and burning materials may roll across the line, effectively negating the barrier.
The IC determines an anchor point, generally located near the origin of the wildland fire or another point such as a road, stream, or trail where firefighters can begin to safely the fire.
The IC designates an escape route and a safety zone where firefighters can go if fire conditions worsen, making it too dangerous to continue working. The safety zone is an area the fire has already completely burned, or an area that will not burn, like rocks or dirt.
Lookouts may be posted to protect firefighters from unexpected fire behaviour, and weather reports are communicated to crews so that there are no surprises with wind shifts or other weather factors.
While firefighters work up the sides or flanks of the fire from the anchor point, a variety of other activities can be occurring at the same time. Helicopters and/or air tankers can make drops of water or retardant on the edge of the fire to cool it enough for firefighters to get next to it to remove fuels with hand tools.
If water is available, it can be accessed with portable pumps and hoses as another cooling agent. Chainsaw operators may begin falling trees to enhance firefighter safety. Roads, if present, will be assessed to determine their value as future access points to the fire ground. Water sources may be established to support the helicopter bucket operations and, if required, a helibase and fire camp established.
The threat of wildfires does not cease after the flames have passed, as smoldering heavy fuels may continue to burn unnoticed for days after flames are no longer visible.
Mopping up occurs after a fire, or any part of a fire, is controlled. Mopping up makes a fire safe by extinguishing or removing burning and hazardous material.
Mopping up includes:
- extinguishing all smouldering material along the fire's edge
- ensuring logs/debris cannot roll across the fire line
- making sure all burning fuel is burnt out or is spread or buried to stop sparks travelling
- clearing both sides of the fire line of snags, rotten logs, stumps, singed brush and low hanging limbs of trees
- searching for underground burning roots near the line
Cold trailing is a method of determining whether or not a fire is still burning, involving careful inspection and feeling with the hands to detect any heat source.
Infrared scanners detect heat and hot-spots invisible to the naked eye. They can be hand-held or mounted on planes and helicopters. Scanners are effective in locating hot-spots and thus reduce mop-up time.