page_title: Aerial firefighting and forestry in southern Australia
section_title: Water/ Foam/ Retardant
hierarchical_section_title: Aerial firefighting and forestry in southern Australia / Firebombing / Water/ Foam/ Retardant
caption_attribution_description: English: Firebombing at Mt Buggery- Terrible Hollow on the edge of a wilderness area in the Victorian Alpine National Park. Lightening strike overnight on 19 December started fire. Phoscheck retardant line below fire to contain fire. Firebombing base at nearby Mt Buller.
context_page_description: The development of aerial firefighting and forestry in southern Australia ran in parallel with the rapid improvements in aircraft technology over the last century. As more advanced and capable aircraft became available firefighters and foresters quickly sought opportunities to utilise and adapt them.
  Aircraft have three main advantages over ground resources: speed, access, and observation.
  Aircraft have been used for a wide range of tasks including reconnaissance, firebombing, crew transport, aerial ignition, back burning, gathering infrared imagery as well as operational forestry tasks like aerial photography, surveys, spraying, fertilising and seeding.
  Much of the early pioneering work in Australia was led by the Forests Commission Victoria in collaboration with other State forestry and fire authorities including the Western Australia Forests Department, Forestry Commission of NSW, Woods and Forest Department of South Australia and Forestry Tasmania. Federal agencies including the CSIRO also contributed significantly.
context_section_description: Class A Foam and Retardant are some of the various chemicals mixed with water to improve their fire suppression efficacy.
  Water is efficient at extinguishing fire, and usually has the advantage of being available at little cost, but when dropped from an aircraft has big disadvantages because it breaks up in the air-stream and a significant proportion erodes into mist and either evaporates before it hits the target or falls in concentrations too light to be effective against a fire, so its extinguishing properties do not last very long. Water is only effective if dropped directly on flames.
  Trials showed that only about one-third of a 420-litre load of water dropped from a Piper Pawnee reached the target in concentrations high enough to be effective. The percentage lost from bigger loads appeared to be less, probably because erosion occurs at the surface of the load and the surface area/volume ratio of the mass dropped is less for bigger loads. Early trials also demonstrated that the poor drop characteristics of water could be improved significantly by additives which increase the viscosity and hold it together as it falls from the aircraft.
  Most firefighting aircraft can drop either salt or fresh water. However, for helicopters equipped with bellytanks and use hover-fill pumps, or those with buckets on ‘short’ lines, pilots prefer to use fresh water to avoid ingesting salt into the turbine engines which are susceptible to corrosion.
  Class A Foam is akin to detergent. It is added or injected into the load of water in a helicopter or fixed-wing aircraft and when its dropped the shearing action as it falls through the air causes bubbles to form which improves the smothering or “knock down” effect on the flames, allowing it to be more effective and to remain on the ground for a longer period. Class A Foam is often applied directly to the fire in close support of ground crews.
  Retardants are generally a slurry that contains a mixture of water and ammonium phosphate or ammonium sulphate. Sodium calcium borate was one of the earlier chemicals used in North America and then trialled in Australia. Since the mid 1950s most of the chemical retardants used for firebombing throughout the world rely on either of these chemicals to provide the fire-retardant ingredient. They also contain a thickening agent to increase viscosity and other agents to inhibit corrosion and provide colour. Unlike foam or water, retardant is laid ahead of the fire and coats the fuel and as the fire burns into the line of retardant a chemical reaction occurs that effectively slows the fire. The main advantage of retardant is that it remains effective for some time after it has been dropped. Firebreaks can be constructed using lines of retardant.
caption: Line of phoschek retardant (shaded red) to control a fire started by lightning on the summit of Mt Buggery in the Victorian Alpine National Park. A firebombing base was established at nearby Mt Buller. Dec 2013. Source: Peter McHugh.
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