Aerial firefighting
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Aerial firefighting (or water bombing) is a method to combat wildfires using aircraft. The types of aircraft used may be either fixed-wing or helicopters. Agents used to fight fires may be either water or specially-formulated fire retardants. Smokejumpers and Rappellers are also classified as aerial firefighters; being delivered by parachute from a variety of fixed-wing aircraft, or rappelling from various helicopters.
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[edit] Equipment
A wide variety of helicopters and fixed-wing aircraft are used for aerial fighting.
Helicopters may be fitted with tanks or carry buckets. Buckets are usually filled by submerging in lakes, rivers, reservoirs, or portable tanks. The most popular of the buckets is the flexible Bambi Bucket. Tanks may be filled on the ground or water may be siphoned from lakes or reservoirs through a hanging snorkel. The Erickson Aircrane helitanker also has a sea snorkel for filling while in flight. Popular firefighting helicopters include variants of the Bell 204 and the Erickson S-64 Helitanker.
Fixed-wing aircraft are fitted with tanks that can be filled on the ground at an air tanker base or, in the case of flying boats and amphibians, by skimming water from lakes, reservoirs, or large rivers.
Various aircraft have been used over the years for firefighting. Though World War II era bombers were for a long time the mainstay of the aerial firefighting fleet, newer purpose-built tankers are coming online. The smallest are the Single Engine Air Tankers (SEATs). These are agricultural sprayers that generally drop about 800 gallons of water or retardant. Medium aircraft include the S-2 Tracker (retrofitted with turboprop engines as the S-2T) as used by the California Department of Forestry & Fire Protection (CDF), as well as Conair Group Inc. of Abbotsford, British Columbia, while the Douglas DC-4, the DC-7, C-130 Hercules, Neptune P-2V, P-3 Orion and others have been used as heavy tankers. The largest aerial firefighters currently in use include two converted Martin Mars flying boats in British Columbia, carrying 7,200 U.S. gallons of water or fire retardant each, and Tanker 910, a converted McDonnell Douglas DC-10 that can carry 12,000 gallons of water or retardant. The Russian government operates convertible-to-cargo IL-76 aerial firefighters that can carry up to 15,000 gallons but have been operating with 11,000 gallon tanking systems and Evergreen International Aviation is developing a Boeing 747 aerial firefighter that can carry 24,000 gallons.
Similar in configuration to the World War II-era PBY Catalina – also a common firefighting aircraft – the Canadair CL-215, CL-217, and Bombardier CL-415 are designed and built specifically for firefighting. The Canadian "Super Scoopers" are not common in the United States because of a lack of suitable water sources in wildfire-prone states, but Los Angeles County leases two CL-415s from the Province of Québec during the fire season and the states of Minnesota and North Carolina own CL-215s. A company in Arizona owns several that work on contract in the U.S.
Similarly amphibian is the new Beriev Be-200. It can carry a maximum payload of about 3,170 gallons (12,000 litres) of water, making "scoops" in any stretch of water in 14 seconds.
The O-2 Skymaster and OV-10 Bronco are used as spotters. The Beechcraft Baron was long used as a lead plane or air attack ship; more common now is the Beech King Air, used as an air attack ship and lead plane.
In the United States, most of these aircraft are privately owned and contracted to government agencies, and the National Guard and the U.S. Marines also maintain fleets of firefighting aircraft. On May 10, 2004, The U.S. Forest Service (USFS) and the Bureau of Land Management (BLM) suddenly announced that they were cancelling contracts with operators of 33 heavy airtankers. They cited liability concerns and an inability to safely manage the fleet after the crashes of a C-130 in California and a PB4Y-2 in Colorado during the summer of 2002. Both aged aircraft broke up in flight due to catastrophic fatigue cracks at the wing roots.
Bombardier's Dash 8 Q Series aircraft are the basis for two new ventures. Cascade Aerospace has converted two pre-owned Q400s to act as part-time water bomber and part-time transport for France's Sécurité Civile, one of which is registered F-ZBMC, while Neptune Aviation is converting a pre-owned Q300 as a prototype to augment their P2V aircraft.
[edit] Fire retardant
Borate salts were used in the past to fight wildfires but were found to sterilize the soil and were toxic to animals. Newer retardants use ammonium sulfate or ammonium polyphosphate with attapulgite clay thickener or diammonium phosphate with a guar gum derivative thickener. These are not only less toxic but act as fertilizers to help the regrowth of plants after the fire (however, the retardants can be toxic to fish if accidentally dropped in water and then exposed to sunlight). Fire retardants contain wetting agents, preservatives and rust inhibitors and are colored red with ferric oxide to mark where they have been dropped. Brand names of fire retardants for aerial application are Fire-Trol and Phos-Chek.
Some water-dropping aircraft carry tanks of a guar gum derivative to thicken the water and reduce runoff.
[edit] Tactics
Helicopters can hover over the fire and accurately drop water or retardant. The S-64 Helitanker has microprocessor-controlled doors on its tank. The doors are controlled based on the area to be covered and wind conditions. Fixed-wing aircraft must make a pass and drop water or retardant like a bomber. Spotter aircraft often orbit the fire at a higher altitude to coordinate the efforts of the retardant-dropping aircraft. Lead planes fly ahead of larger airtankers to mark the trajectory for the drop.
Water is often dropped directly on flames because its effect is short-lived. Fire retardants are often dropped ahead of the moving fire or along its edge and may remain effective for two or more days. This can create an artificial firebreaks where the terrain is too rugged or remote for ground crews to cut fireline.
Helicopters are also used to deliver firefighters or ignite backburns and controlled burns. A driptorch slung beneath the helicopter (helitorch) can be used for this purpose. Another device called a Delayed Aerial Ignition Device (DAID) can be used, which shoots a stream of flaming "ping-pong balls" into the forest. The small plastic spheres which contain potassium permanganate are individually injected with ethylene glycol or glycerine just before they are ejected from the aircraft. This method's delayed oxidation reaction (which results in vigorous fire in just minutes after mixing the chemicals [1]) poses less of a danger to the helicopter than carrying along materials which are already burning. The ping-pong ball system works best in continuous fuels or in areas where a mosaic burn pattern is desired.
Aerial firefighting is almost always used in conjunction with ground-based efforts, as aircraft are only one weapon in the firefighting arsenal. However, there have been cases of aircraft extinguishing fires long before ground crews were able to reach them.
