Weather, topography and type fuel can determine plan of attack
Wildfire is the word used by the fire service to denote the various types of grass, brush and forest fires that occur. A wildfire can be a raging conflagration in the hills of Los Angeles, covering thousands of acres and causing millions of dollars in damage. It can also be a swamp grass fire of two or three acres that stops all rush-hour traffic on the Beltway, with no real damage except to the drivers’ nerves.
In any wildfire, two of the necessary elements for combustion are always present: fuel and oxygen (air). The third element, heat, is most often supplied by man, wittingly or unwittingly, but frequently nature takes a hand with lightning.
Weather a factor
Weather is an important factor in wildfire. Prolonged dry weather makes for a dry fuel that burns hot and fast. The moisture content of the air is responsible for this and it is measured as relative humidity. Forest fire fighters find that it is easy to handle a fire when relative humidity is above 70 percent.
As the humidity level drops, fire becomes proportionately more difficult to control. A reading below 30 percent is considered highly dangerous. Add high winds and high temperatures and you have a potential for catastrophe. The sun preheats the fuel and the wind supplies more oxygen.
The contour of the land must be considered (preplanned if possible) in all wildfire operations. Fire naturally burns faster uphill than down, and a chief or fire boss can use this natural phenomenon to advantage in safeguarding his men and attacking a fire.
Roads, streams, cliffs, bare rock or other nonflammable areas provide natural fire breaks. These can reduce the burden on manpower and equipment if properly used. It is better to let a few acres burn up to a natural barrier reinforced by a fire line than to have men go in and possibly have the fire pass them.
Fire fighters forming lines at cliffs, however, should see to it that a line of retreat is left open.
Light fuels such as dry grass, leaves and twigs have a large surface area exposed in relation to weight. With ample air, they burn extremely fast.
Conversely, heavy fuels—logs, stumps, brushes, peat—burn more slowly because of their heavier weight relative to surface area. Their moisture content will have to be dried by the advancing fire before they burn freely.
The quantity of fuel can vary on the same fireground from patchy to continuous. Patchy fuels consist of clusters of grass, bushes, logs, etc., that are separated by roads, streams, base rock or other natural barriers.
Continuous fuel, as the name indicates, is a large mass of grass, brush forest etc., unbroken by any barriers.
Surface fires are the most frequent type of wildfires encountered. They feed on the top layer of dry, loose fuel, spread rapidly and are quickly accelerated by winds and topography (hilly). Because of fast spread, these fires call for fast extinguishment.
Ground fires frequently develop from surface fires, and attack soils of highly organic content, of which peat is an example. This type of fire is a smoldering one that spreads slowly and is difficult to extinguish. It is highly destructive and consumes soil to bedrock. Control and extinguishment requires unlimited water or possibly a trench dug completely around the burning area.
Ground fires must be continuously patrolled else they will break out anew at the surface.
Crown fires are raging conflagrations that can consume entire forests. They usually start in advance of the main body of a fire in trees that are ignited by flying branches and embers carried by the wind. Crown fires occur in areas of heavy fuels (softwood trees) and during periods of low humidity and high winds. They are extremely dangerous to fight. Fire line crews must maintain close contact with the command and each other.
Fighting the wildfire
Few fire departments in this country and Canada are ever called upon to fight the vast, raging conflagrations that occur on the Western Ranges and a few other areas. But all departments are regularly called upon to fight small and perhaps medium-size wildfires. (Even densely populated New York City has had a wildfire—on Staten Island—that caused millions of dollars in damage.) It is to these smaller wildfires, the everyday ones, that the following is directed.
As with all fires, wildfire operations begin with a size-up which includes:
- The site of the fire and the area involved,
- The type of fuel burning and the type exposed,
- The type of fire—surface, ground or crown,
- The general weather conditions: wet, damp, humid, dry and wind velocity and directions,
- The speed with which fire is moving,
- The direction in which fire is moving,
- Possible life hazards,
- Exposure to buildings, equipment, crops and large wood or brush area,
- Communications needed,
- Natural fire barriers,
- The time of day. Daylight hours may be limited. Wind shifts may be expected after sundown.
Once the chief makes his size-up, he must then decide on the best method to combat the fire.
The parts of a forest fire are referred to by a series of standard terms:
The main body of the fire is the center area of the whole fire where burning continues to consume any combustible materials.
The heel of the fire is the upwind, slow-burning part of the fire.
The heat of the fire is the downwind, fast-burning part of the fire.
The flanks are the edges of the fire where the flames are burning at right angles to the wind direction.
The fingers are narrow, fast-moving parts of the fire at the downwind side, usually where the spread of flame has been accelerated by concentrations of fast-burning ground cover.
Spot fires are small fires on the downwind side of the fire caused by falling sparks or brands carried aloft by the wind and convection currents.
Attacking the fire
Wildfire can be attacked directly (head-on) or indirectly (from the flanks). Use the direct attack to suppress slow-spreading fires or those with low heat intensity. They can be knocked down by water spray or by beating them out. All embers or burning materials should then be shoveled back into the burned-out area. Patrols are always necessary until the fire is declared out.
Hot, fast-moving fires call for an indirect attack. Operating from the flanks is safer and affords the fire fighter time to build adequate fire lines. There are several variations of the indirect attack that can be used.
The indirect frontal attack can be used on a fast-moving fire that has assumed a long, narrow shape and has a head confined to a narrow width. In this method, you construct the fire line across the path that the head is taking. Start at the center, work toward the flanks and then continue along the flanks toward the heel.
There is also an indirect cut-off method that can be used on wildfires that have several small heads in the form of fingers. In this method, fire fighters first construct lines across the front of the heads and then connect them.
A third method, called the parallel or oblique, is used on fires that are moving downwind and sideward over a wide front. The fire fighters can line across the head of the fire at a safe working distance while permitting the fire to reach the fire line progressively.
Backfiring offers another way to indirectly attack a wildfire. In this method, areas well in front of the main fire are deliberately burned. Theoretically, when the main fire reaches the burned-out area, there will be no fuel for it to feed on and it will die. But in practice, backfiring is a highly chancy operation that can spread fire if not performed properly. Backfiring should be used only as a last resort. And it should be done only under the supervision of a skilled forest fire fighter.
Fire line construction
Simply stated, a fire line is a non-combustible swath constructed across the path that a wildfire is taking. The swath must be wide enough to prevent fire from crossing the line. How wide depends upon the size and intensity of the fire and prevailing conditions, such as wind and weather. It is a matter of judgment for the fire boss.
Ideally, the fire line should be scraped or dug down to mineral soil. It should be as close to the fire as the heat will permit and should be constructed simply—on a long curve that avoids sharp angles.
Fire fighters should take advantage of the terrain. Whenever possible, construct the fire line on open and level areas that have a minimum of ground cover. Avoid fire line construction on slopes that might permit logs or other debris to roll across the line. In most cases, constructing a fire line ahead of a fire that is traveling uphill is a waste of time. Better to construct it on the other side of the hill just below the crown since fire travels much more slowly downhill.
Water is best
One volume of water, if properly applied, can extinguish 300 volumes of class A fuel. It should be used on wildfires whenever available. Water for this purpose should be projected as a spray to permit it to cover more area. But occasionally straight streams are called for to hit fire in trees or snags, to hit dangerous hot spots and to dig out ground fire.
The nozzleman should move in fast (the spray will act as a shield) and always work along the edge of the fire until it is extinguished. A good water line does not have to drown the fire.
Fire spreading through dried grass and weeds is no doubt the most frequently occurring wildfire and the easiest to subdue. But grass fires should not be taken lightly since they have great capacity for inflicting damage.
One man with a pump tank or broom can often control a small fire. For the larger fires, three-man crews are called for, and the number of crews is determined by the size of the job. The first man carries the pump tank and deadens the fire. His objective is to cover the greatest area with the least amount of water. The second man carries a broom and follows closely behind the first, beating out the flames, if any, that remain. The third man, also with a broom or shovel, acts as the mopup, making certain that all fires are out.
Makeshift equipment, such as wet burlap sacks, can also be used effectively. If necessary, soil thrown on the fire by shovels can be used instead of water.
Basically, the same strategy and tactics used on a small grass fire can be applied to large fires. Portable pump tanks are replaced, but not completely, by portable pumps, skid pumps, pumpers and tankers. Manpower needs increase and earth-moving equipment takes the place of shovels and picks.
Dry line operations
Wildfires often strike in remote areas in which water supply is either insufficient or nonexistent. When this occurs, dry line operations are called for. Fire fighters establish a line around the fire by baring mineral soil. The fire is then permitted, even encouraged, to burn itself out inside the line. Such dry lines are also used for large ground fires that make it impractical to use long hose stretches.
Dry line operations also call for fire fighters to operate in crews, each with a specific mission such as locating the fire, constructing the fire line, line burning (where necessary), patrolling and mopping up.
Wildfire fighting can be extremely hazardous, with varied hazards that come under three main groupings:
Hazards connected with the actual fire:
- Flying embers and sparks
- Improper fire line construction
- Improper fire line burning
- Shifting of fire path due to wind shift
Hazards connected with terrain:
- Falling trees, heavy brush
- Rough ground, steep slopes
- Poor visibility (smoke, darkness)
- Getting lost.
Hazards connected with work:
- Sharp tools
- Lack of adequate working room
- Improper use of tools, manual and powered
- Use of vehicles and machinery under emergency conditions.
To minimize these hazards, the United States Forest Service offers the following ten standard fire fighting rules:
- Keep informed on fire weather conditions and forecasts.
- Know what your fire is doing at all times.
- Base all actions on current and expected behavior of fire.
- Have escape routes for everyone and make them known.
- Post lookouts when there is possible danger.
- Be alert, keep calm, think clearly, act decisively.
- Maintain prompt communication with your men, your boss and adjoining forces.
- Give clear instructions and be sure they are understood.
- Maintain control of your men at all times.
- Fight fire aggressively, but provide for safety first.
Adapted from the Grass, Brush, and Forest Firefighting Course Workbook published by the New York State Division of Fire Safety, courtesy of George H. Proper, Jr., Director.