Trainer’s Corner: Wildland fire behaviour for structural fire fighters (2nd of a 2-part series)
Wildland fire behaviour for structural fire fighters (2nd of a 2-part series)
December 10, 2007 By Ed Brouwer
Most fire fighter training includes a simple explanation of the fire triangle as it relates to combustion. The parts of the fire triangle are: fuel to burn; a heat source to start and continue the combustion process; and a supply of oxygen to sustain the flame. Stop the fire by controlling any part of the fire triangle. In an open wildland setting, controlling oxygen often means covering the flames with dirt (this won’t work for long flame lengths). Once the fire starts (by human or natural means) a major control factor will be through the fuels.
Sizing up a small fire is often done by quickly walking around the outside edge of the fire or by viewing the fire area from a vantage point. Assessing the fire is an ongoing process. Changes in wind speed or direction and slope or fuel types will all affect fire behaviour and rate of spread (ROS). The Incident Commander must constantly re-assess the fire situation, adapting suppression strategies to deal with new complications and keeping crews briefed.
At least two escape routes leading to adequate safety zones must always be noted in case fire fighters and equipment are threatened by sudden changes in fire behaviour.
The basic approach to successful fire suppression is to attack where the fire is most likely to escape. Take prompt action on all vital areas. Do not become bogged down at one location and allow the fire to escape elsewhere.
The fire fighter’s primary job is to construct the fireline. The fire fighter digs below the surface of the ground to the mineral layer of soil. This procedure clears fuels (dry leaves and duff, including roots) and prevents the fire from spreading. On average, the fireline built with hand tools (Pulaski, shovel, hoe) is not more than 30 to 60 cm (12 to 24") wide. The depth of the line is always to the mineral layer of the soil.
A control line is necessary at every fire. The control line may be a combination of man-made firelines or natural fire barriers (e.g. rivers).
There are three attack methods (fire departments use the first two):
This attack method is normally used to suppress a slow-moving fire. The fireline is constructed adjacent to burning fuel. The fire is attacked and suppressed immediately.
This method is applied in situations where a fire is spreading rapidly. The fireline is constructed as close to the fire as heat and flames permit. This technique helps to control the fire as opposed to immediately stopping it (direct method); igniting unburned fuel between the fireline and the fire reinforces the line and speeds up the control effort by consuming or “burning off” fuel between the fireline and the fire perimeter.
You must get rid of the “put the wet stuff on the red stuff” mentality. In wildland fire fighting the best thing is to let the fire burn up the fuel. Contain the fire and let it burn itself out. What is burned will not likely burn again.
A method whereby the fireline is strategically located to take advantage of favourable terrain and natural barriers or breaks well in advance of the fire perimeter. Used under the direction of a Forestry Fire Boss, a “backfire” is set to stop the advancing fire.
Burning off vs. backfiring
“Burning off” and “backfiring” are two terms often confused.
Burning off is a suppression technique, an attack method wherein a fire is set by the fire crew along the inside edge of the control line or natural barrier to consume unburned fuels between the line and the fire perimeter. Burning off is a limited, small scale routine operation as opposed to “backfiring.”
Backfiring is a form of “indirect attack” where extensive fire is set along the inner edge of a control line or natural barrier. Used in more extreme situations, the line is situated some distance from the fire and, with the assistance of wind, consumes fuel in its path. As a result, this procedure halts or retards the progress of the fire.
Mop-up is the act of making a fire area safe. It begins after the fire or any part of it is brought under control and before suppression work is reduced to patrol. It is an important component to successful fire suppression and should be taken seriously. Fires have re-spread through failure to properly mop-up and patrol, This is considered unacceptable by forest protection personnel.
Techniques for mop-up: The following tasks must be accomplished:
• Extinguish all smouldering material along the fire edge after the spread has been stopped.
• Place all rolling fuel so it cannot roll across the line or trench below it.
• Make sure that all burning fuel either burns itself out or is spread or buried to stop spark travel.
• Clear the line on both sides of all special threats such as snags, rotten logs, stumps, singed brush and low-hanging tree limbs.
• Search for underground burning roots near the line.
• Mop up all material adjacent to the line on large fires to make sure the fire cannot blow, spot or roll over the control line.
• Watch out for smouldering spot fires across the line in front of the main head of the fire. (In the Okanagan Mountain Park fire of 2003, the fire produced spot fires 2.4 kilometres ahead of the main fire.)
Cold trailing and patrolling
Cold trailing is a method of determining whether a fire is still burning. It involves careful and methodical inspection of burned material and the surrounding area by carefully feeling with the bare hand. Once a fire is controlled and mopped up, the fire boss will declare the fire to be on a “patrol” basis. The job of the fire patrol is to walk the control line to prevent escapes, discover and control spot fires and mop-up whenever necessary. If there is no forestry personnel to do this a couple of fire fighters may have to take turns.
A fire patroller will also keep a sharp lookout for “sleepers.” Sleepers should be spotted before they have a chance to ignite the adjacent fuel and cause the fire to escape.
A sleeper is a hidden fire, deep inside the duff layer or in a root tip. As well, there is no glowing stage. The “sleeper” is aptly named – it may take weeks before an adjacent patch of fuel is brought up to ignition temperature. Until then, it normally defies detection.
Patrolling may be long-term
Patrol and inspection may continue for days or weeks. The importance of adequate patrol and inspection cannot be over-emphasized. To have a fire that has been controlled and apparently mopped up start again – hours, days or weeks later – can only be classed as an inexcusable failure. In California over 800 homes were lost the morning after a fire department called the fire as “out.”
There are three basic rules in fire suppression:
• Fast initial attack: be organized, move crews to the fire as quickly as possible and stop the fire from spreading.
• Aggressive action: deploy adequate resources, work hard and work quickly to bring the fire under control.
• Prompt and complete mop-up: if the fire is contained, a thorough mop-up must begin immediately.
Wildland fire suppression is a hazardous occupation. Most injuries and fatalities on the fireline are the result of fire fighters not following safe work procedures. As always, stay safe out there and remember to train like their lives depend on it, because it does.
Ed Brouwer is the Fire Chief/Training Officer for Canwest Fire and a member of the Osoyoos (B.C.) Fire Dept. The 18-year veteran of the fire service is also a Fire Warden with Ministry of Forests, a First Responder III instructor/evaluator, Local Assistant to the Fire Commissioner and a fire service motivational speaker and chaplain. E-mail firstname.lastname@example.org .
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