Fire and Other Emergencies

See also Retardant

'Class A' Foam

Class A foam, or ‘bushfire fighting foam”, is used by the Department of Sustainability and Environment to assist in the control of bushfires in Victoria. Foam is applied from fire tankers and from aircraft - both fixed and rotary wing.

The concentrate used to make foam is very similar to household detergent. In conjunction with tanker use, it is normally injected into the water by an accurate proportioner as the water is pumped towards the nozzle. The foam concentrate\water mixture is then pumped out through an aspirating nozzle, which adds air, and results in the development of a frothy, bubbly mixture. In aircraft, the foam concentrate is mixed with water by injecting the concentrate into the aircraft tank as it is filled. Most firebombing aircraft carry a foam concentrate storage reservoir for this purpose. The mixture is then aspirated by the air passing through the load as it is dropped.

The bubbles in the resulting foam effectively make the water more useful, by increasing the surface area, allowing the water to coat the fuel more evenly, and by delaying the water from running off the fuel and soaking into the ground. Foam is normally used to assist ground crews, by knocking down flames to enable the crews to work closer to the fire edge. It is also particularly useful in ‘mopping up’ operations, allowing scarce water to be used as effectively as possible, when ‘blacking out’ the fire area to prevent re-ignition. The time that foam bubbles for depends on humidity, temperature, wind and sunlight, but is usually between 20 and 40 minutes.

"Mopping up" with foam from a 400 litre 4WD tanker

All foam concentrates used by DSE are rigorously tested for potential environmental effects and health effects by the United States Department of Agriculture (USDA). Only foams approved by the USDA are used in Victorian park and forest fire suppression.

Foam concentrate is mixed with water at very low proportions - generally less than 1% for application from ground based tankers and less than 0.5% for application from aircraft. Even though this very dilute mixture is unlikely to have any adverse effects on the environment, the Department implements standard practices which minimise any possibility of effects on vegetation or wildlife, and which minimise the possibility of foam entering water courses.

Class A Foam notes (PDF - 412 Kb)