Fire retardants are chemicals that slow the spread or intensity of a fire. They help firefighters on the ground and are sometimes dropped from aircraft.
Short-term fire retardants are detergent chemicals mixed into foam. Long-term fire retardants are chemicals that are mixed with water to form a slurry.
Fire retardants have been used in Victoria for the past 30 years.
Fire retardants – how they work
Long-term fire retardants are mixed with water before they are dispersed across the target area.
When the water is completely evaporated, the remaining chemical residue helps prevent vegetation or other materials from igniting. The vegetation is protected until the fire retardant is removed by rain or erosion. Fire retardants also work by binding to the plant material (cellulose) and preventing combustion.
Gels and foams are used to fight fires by preventing the water they are mixed with from evaporating easily. They coat the fuel (grass, trees and shrubs), and prevent or slow combustion. A slurry of gel can be pumped over the fire, and it immediately cools down the intense heat and helps put out the fire.
Fire retardants – composition
Long-term fire retardants are essentially fertilisers (ammonium and diammonium sulfate, and ammonium phosphate) with thickeners (guar gum) and corrosion inhibitors (for aircraft safety).
Sometimes a red-coloured pigment, made from iron oxide, is added so that those spraying can see where they have released the fire retardant.
Long-term fire retardants include:
- Phos-Chek D75-F
- Phos-Chek D75-R.
Short-term fire retardant foams are made from a combination of wetting agents and foaming chemicals, mixed with water. These allow the water to penetrate surfaces more easily. Their usefulness is limited against high-intensity fires, where long-term retardants have proven more successful.
Short-term fire retardants include:
- Ansul Silv-Ex
- Angus Forexpan S
- Phos-Chek WD-881.
Fire retardants – aqua gels
Super absorbent polymers (SAPs) can absorb high volumes of water relative to their own weight. In their concentrated powder form, SAPs can irritate eyes, airways and the skin. This does not occur after they have been mixed with water.
When SAPs are mixed with water, they produce a gel-like substance that acts as a barrier against evaporation resulting from heat. Gel fire retardants can be applied via aircraft or trucks as a firebreak, for direct suppression or for structure protection.
Polybrominated flame retardants
Polybrominated flame retardants (PBFRs) are a category of chemicals that are widely used in household and industrial items, including:
- computers, electronics, electrical equipment and televisions
- foam furniture
- insulating foams and other building materials.
They are sometimes also called fire retardants, but are quite different from the fire retardants described here and are not used in fighting bushfires.
Fire retardants – environmental effects
Although little research has been done in this area, the current evidence does not suggest any significant effects of fire retardants on birds or mammals.
However, in Australia, long-term fire retardants have been observed to cause effects on some species of native plants (leading to low-level damage to new growth). Water plants and animals are more sensitive to the effects of fire retardants than terrestrial flora and fauna. Foams, in particular, can be moderately toxic to aquatic life. For this reason, pilots try not to apply fire retardants close to waterways.
Fire retardants – human health effects
Testing shows that the chemicals used in fire retardants can produce minor irritant effects. The concentrated powder may cause minor respiratory irritation to workers who are handling it. Once it is mixed into slurry, this irritation does not occur. Workers must wear gloves, goggles and dust masks when handling the powder.
Risk assessments carried out in the United States and Victoria have demonstrated that the risk of health effects is very low, even to people who are accidentally exposed to fire retardants during their application.
Fire retardants around water tanks
If you live in a fire-prone area and have a water tank, you should:
- disconnect your water tank to prevent contaminated water from entering it
- install a first-flush diverter or make sure the first part of run-off after rain cannot go into your tank.
This will prevent any water run-off from your roof containing fire retardant from entering your tank. It will also prevent embers, ash and other contaminants from entering your drinking water.
If the fire retardant does enter your water tank, do not drink the water. High levels of ammonia and sulfate in water will make it smell terrible and taste salty. It will not be suitable as drinking water for humans or animals (pets or livestock).
Keep in mind that contaminated water can still be used for irrigation and firefighting purposes.
Cleaning up fire retardant residue
If aerial fire retardant or firefighting foam residue is present on your house and/or cars, use a mild detergent with water and brushes to scrub and dilute the dried residue, and flush it from the surfaces. Rinse with clean water. A follow-up with pressure washing may help, but should not replace scrubbing to remove the residue. Gloves and nonslip shoes should be worn, as it may be slippery.