USING STRUCTURAL APPARATUS AT WILDLAND FIRES, PART 1
THE ENGINE COMPANY
Conventional wisdom has it that structural firefighting apparatus are not wellsuited to wildland firefighting. However, structural firefighting equipment and firefighters can be used to fight many wildland fires effectively and in some situations have the potential to be even more effective than their wildland counterparts. It’s a matter of using their strengths optimally in the appropriate situations.
The first problem of wildland firefighting is that of access. Obviously, structural firefighting equipment is not going to be of much use at fires where it cannot gain access. Off-road maneuverability is not one of the strengths of structural equipment. However, the wildland-urban interface is growing: Many wildland fires originate alongside roads and near habitations, and structural apparatus can get to these fires quickly, while the fires are still relatively small, in an early stage of growth. Their main strength—their ability to apply large volumes of water to a fire and to the surrounding environment in a minimum amount of time—can be used to great effect.
Let’s look at how structural equipment can be utilized in wildland firefighting with respect to three strategic functions: direct attack, indirect attack, and support.
DIRECT ATTACK
Fires that originate alongside roads are accessible to structural firefighting apparatus. Often, the engine and aerial apparatus companies sent to respond to these fires by suburban and rural fire departments are assigned almost automatically the same tactical functions as wildland vehicle units—attack tlanks with smalldiameter handlines and booster lines, backfire along roads, resupply four-wheeldrive vehicles, and so forth. This may, in the end. prove effective, but it fails to take advantage of the chief firefighting characteristic of structural apparatus: the ability to provide high-volume fire flows.
Compare the knockdown capability of a 1,500-gpm pumper equipped with a deluge gun with adjustable-pattern nozzle and a 1,000-gallon tank with that of a wildland truck with a 250-gpm pump, 300-gallon tank, and two booster lines. The high-volume pumper at a moderate flow rate of 600 gpm can deluge a rectangular area approximately 400 feet long and 200 feet deep—approximately two acres—with 1,000 gallons of water in less than two minutes. A light-attack wildland truck flowing a typical 35 gpm through each of its 300-foot booster lines would take five minutes to put less than one-third as much water on about the same area. To get 1,000 gallons on the same area, assuming a fast refill time of five minutes for the smaller apparatus, it would take more than 25 minutes— more than 10 times as long as the highcapacity pumper. In short, the structural apparatus using a deck gun and a twomember crew can put 1.000 gallons on the fire in the same time that a wildland truck can get out about 140 gallons.
Using such high flows with proper nozzle selection to obtain optimum water droplet size produces rapid cooling of the deluged area as the droplets absorb heat and convert to steam, darkening the fire. This raises the relative humidity tremendously. and the cool, moist air flows from the deluged area into any still-burning areas. It retards the combustion process, reducing the rate of heat production and slowing the fire spread.
Smaller-diameter lines do the same thing, of course, but at a much slower rate. The problem with using low-flow equipment is that the fire is generating more heat while extinguishment efforts are taking place—that is, it is more difficult to surpass the critical flow rate, the point at which water cools the fire faster than the fire generates heat. If a fire flow of 300 gpm is required to control a fire, lower flows will do little good, while higher initial rates—600 gpm, for example—will in most cases speed up extinguishment. But attacking a small wildland fire with large-caliber streams not only will quicken knockdown, it also will not expose personnel to the main body of fire—this is the primary benefit of the tactic.
An immediate follow-up attack with handlines is usually desirable following a “blitz” with a deluge gun. Since wet-down, burned-over ground frequently provides the most direct and easiest access to the remaining fire, the follow-up attack often can be made through the center of the wetted burned area. The incident commander and firefighters conducting such an attack must be aware of the potentially life-threatening conditions that may be present in the deluged area and must take appropriate safety measures. Firefighters entering such an area immediately following a deluge attack should be equipped with full protective gear, including SCBAs, since oxygen levels in the ambient air may be insufficient to sustain consciousness. The atmosphere in this area is especially dangerous if winds are light. Pockets of such hazardous conditions can linger for some time in low-lying terrain or when there is insufficient wind to move the oxygen-depleted air away from the fire scene. If the ground and fuel have been sufficiently wetted and cooled and are unlikely to rekindle, you can use hose streams to ventilate the area, if necessary.
A good blitz attack 1 have employed on small (oneto two-acre) fires with relatively light fuel (grass, brush, and scattered trees) uses a 1,500-gpm pumper quipped with a 1,000-gallon tank, responding with a slower-moving 750-gpm, 1,250-gallon tanker (called tenders in some districts). The pumper usually arrives before the tanker (tender) and deluges first the perimeter of the fire and then the interior, working from the pumper’s position on the road to the head of the fire and out.
A 60-second blitz with a 500-gpm flow rate through a variable pattern nozzle is used while attack crews don SCBA and prepare a 1 3/4-inch line, sometimes connecting two 200-foot attack lines together to get the necessary length, and a booster line for the follow-up attack. For fires with heads at greater distance from the road, the monitor attack employs a 1 ¼-inch solid-stream nozzle with a nozzle pressure designed to produce a 500-gpm flow, which can be changed to a variable pattern nozzle to hit areas closer to the apparatus. The initial blitz uses about half the available tank water.
If knockdown is achieved, the handlines are advanced, usually through the fire area, with the objective of hitting the head of the fire with the 1 ¾-inch line. The booster line is used to secure the attack route and protect the attack crew. The handline, flowing about 100 gpm, is operated for two or three minutes, then shut down until the tanker arrives. Stream duration and flow rate are interdependent; we are operating with a limited water supply and must use extreme caution so that there is enough water to protect firefighters and ensure a safe retreat from the area if necessary. The 35gpm booster line is used to secure the attack route or, after shutdown of the heavier stream, to continue the attack at a minimum flow until the tanker can be employed. On arrival of the tanker, flow rates can be increased as needed.
This sequence of fire flows provides the maximum initial extinguishment/control and sustained attack flows with the available water supply. The speed of knockdown is often dramatic. Many fires that would take 10 to 15 minutes to control with handlines can be extinguished or contained with the one-minute initial monitor attack. The deluged area usually is left smothered in steam, and the overall fire temperature drops tremendously as the fire is knocked down. It does take some training to become proficient in providing the proper volume, patterns, and timing of the various fire flows described here, but the payback is well worth the investment. Obviously, with more water available from additional units, the initial high-volume flow can be sustained for longer periods of time, if necessary.
Water pipe-equipped ladder apparatus, articulating booms, aerial platforms, and so on can perform similarly; although they may take longer to put into action and may require tanker support, the reach and power of their fire streams can be well worth the setup time.
Aerial apparatus are great firefighting tools. Equipped with large-diameter solidstream nozzles, they can place effective high-volume streams on fires hundreds of feet away. Equipped with variable pattern nozzles, they can create a gentle 400to 1,000-gpm + rain or mist and place it on a fire, exposure, or unburned fuel with great reach and accuracy. Teamed with a suitably sized tanker group, a single piece of aerial apparatus can perform herculean feats of suppression and control in wildland firefighting.
Part 2 will discuss indirect attack and support roles.
Endnotes
1 .Fire Stream Practices, seventh edition (IFSTA, 1989, p. 26).
