BY DAN REESE
Firefighters on the ground are ultimately the ones who extinguish fires. But they can only fight fire as fast as they can walk, at best, and usually engage flames that are only three to four feet high. Firefighters with equipment such as bulldozers may be able to handle flames of six to eight feet, and they travel only as fast as the fire’s fuels and the terrain in which they are working will allow. The fastest these machines can travel is no more than 885 yards per hour—barely a half mile—on a single pass. Most fire lines may need up to three passes to create a fire break, depending on the fuel type.
This is where aircraft come into the picture. Aircraft drop water and retardant to support the firefighters on the ground.
Many years ago, the California Department of Forestry and Fire Protection (Cal Fire) strategically placed air attack bases so that flight times would allow each base’s aircraft to reach its assigned area within 20 minutes or less. This 20-minute area is commonly referred to as the initial attack area. Documents dating back to 1958 corroborate the whole concept of rapidly deploying aerial resources to catch fires when they are small and just getting started. This is when aerial firefighting resources are most efficient and cost effective.
Often, barring extreme fuel loading, fuel conditions, topography, and weather, aircraft are able to hold fires in check until ground resources can get in to extinguish them. Once the fire grows in size beyond the initial attack, depending on the number of resources at the scene, the fire’s rate of spread may often be greater than firefighters can handle.
Fire agencies use two types of firefighting aircraft, helicopters and airplanes. The planes are called air tankers; when attacking an established fire, they are often used to flank the fire (fight the sides of the fire). Helicopters may be used in the same fashion and, in addition, have the advantage that they can fly more easily in smoke. Hence, they can protect structures at the fire’s head, that frontal area that usually has the most active and rapidly advancing flames.
Fixed-wing aircraft carry water that can be mixed with foam, water-enhancing gel, or long-term fire retardant chemicals. Water enhancers are relatively new to aerial firefighting, and more research and testing must be done to determine the capabilities of these chemicals and compare them to long-term retardants when used as directly as possible on the flaming front or flanks. Nevertheless, gels seem to be most effective during the initial attack when they are used as an extinguishing and holding agent. This is how Cal Fire uses them.
During an extended attack, when a firefighting force is significantly augmented with staffing or equipment and a major attack employed against the greatest fires, air tankers often carry long-term retardant. If applied full strength on the fuel, this chemical may retard the fire’s spread. The word “may” is significant because only in rare cases will retardant completely stop a fire, so ground crews must be able to follow up the air resources. Long-term retardants, unlike water enhancers, may be applied days or weeks ahead of an approaching fire; moreover, these chemicals retain their retarding capabilities until washed away by water.
Aerial firefighters know their job is to support the firefighters on the ground. When the fire’s rate of spread is greater than the firefighters on the ground can manage, it is important to slow the fire until ground crews can go in and catch the fire. The air space, fire intensity, topography, and wind around a fire are contributing factors to the numbers of aircraft that can be effectively and safely used.
Wind is the most important factor affecting the spread of a fire and the use of aircraft to control it. Here, the best analogy is that of a bellows stoking a fire. Fire is a chemical reaction in which rapid oxidation takes place, so the more oxygen-rich air introduced to a fire, the more intensely it will burn. The wind at a fire may be produced by weather or a result of the fire burning so intensely that it actually changes the wind and weather. Wind affects a fire in four ways.
1 The stronger the wind, the more intensely the fire will burn and the faster it will travel.
2 The stronger the wind, the more potential there is for spotting, in which the rising heat of a fire picks up firebrands or embers and blows them far ahead of the fire—sometimes miles ahead—and drops them on a fuel bed that is quickly ignited, causing the fire to hopscotch. The sizes of these embers vary; they may be as small as a little piece of leaf or as large as a pine cone, a sheet of plywood, or even a whole tree.
3 This factor relates to the use of aircraft. Simply, the harder the wind blows, the more difficult it is to control the plane or helicopter. Thus, it has long been established that aircraft are most effective on fires when winds are blowing at less than 30 miles per hour.
A firefighting aircraft flies very close to the ground, and its payload is a fluid. As the wind increases, the drops become more difficult to place precisely, and often the wind disperses the fluid so that it is too thin and ineffective. What is more, for these chemicals to be most effective, they must rain straight down on the vegetation that fuels the fire. If the chemicals enter the fuel bed with forward momentum, only one side of the fuel will be treated and leave a shadow on the ground. This shadow and the effect of only one side of the fuel being treated increase the likelihood that the fire will continue to burn at a fast rate.
Often, as the buffeting winds increase, it becomes difficult for pilots to compensate laterally to hit their target. And at times, the desire of pilots to hit the target and to support the ground crews forces them to drop lower. This can put pilots and their planes at great risk. The widest line that a very large air tanker such as a DC-10 can lay parallel to a fire is about 50 feet (photo 1). However, to put this in perspective, fires often jump two- to 10-lane freeways, which are hundreds of feet wide.
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| (1) Photo courtesy of Cal Fire/Wes Schultz. |
4 This factor relates to the smoke the fire generates, which is referred to as the smoke column. As the column rises, the wind pushes it over. The stronger the wind, the more the column leans. Very high winds will lean the column to the ground, which makes it impossible to fly anywhere near the optimum target zone because the air crews cannot see, and the smoke and embers could damage the aircraft enough to make it crash.
Perhaps you now can imagine how difficult it is to control a well-established, wind-driven wildfire. At that point, firefighters are often at the mercy of Mother Nature.
Because placing numerous high-speed aircraft into a confined airspace in a very smoky atmosphere creates a dangerous situation, only a certain number of aircraft may be safely flown over a fire at any one time. Nevertheless, once a fire escalates into a major incident, the chances of rapid control without nature’s cooperation are minimal, regardless of the number of tankers or helicopters deployed.
Fire commanders know this and are often under extreme pressure from the public, politicians, and the media to fly aircraft on these fires. This can increase the risk to firefighters to a point where it outweighs any gain. It takes professional aviators flying these fires years to become proficient at their trade. Most fire pilots have flown thousands of hours and have usually flown as a co-pilot for a year or more prior to flying fires as the pilot in command. The professional goal of fire pilots is to contain and keep fires as small as possible, prevent destruction, maintain the safest operations, and help ensure everyone goes home. It is neither appropriate nor fiscally responsible to substitute the judgment of armchair quarterbacks for the seasoned skills of experienced aviators in engaging these fires.
DAN REESE is an air operations battalion chief supporting the California Department of Forestry and Fire Protection’s (Cal Fire’s) aviation program statewide from Sacramento; he manages its wildland fire chemical program. He is an air operations branch director, managing aerial firefighting operations on large fires, and has served on a Type I incident command team for the past eight years. He began his firefighting career in 1985 with the Nevada Division of Forestry and joined Cal Fire in 1987.
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