During forest fires, a bright red cloud often catches the eye. This liquid, dropped by Dash 8 aircraft or used on the ground by firefighters, is a key tool in fighting fires. Known as a ‘retardant’, it helps to slow the spread of fire by creating a protective barrier around vegetation.
A water-based fertiliser mixture
The flame retardant used in France, the Fire-Trol-931, is manufactured by the American company Perimeter Solutions. Its distinctive red colour comes from iron oxide, a natural pigment that helps firefighters identify areas that have already been treated. Comprising 80–90 per cent water, it also contains ammonium polyphosphate, a compound similar to agricultural fertilisers. Once applied, it forms a layer that reduces the flammability of vegetation and slows down combustion.
Firefighters use it from aircraft such as the Dash and the A400M, but also on the ground, to protect areas at risk. Its effectiveness makes it a valuable ally in tackling increasingly intense fires, particularly during episodes of heatwave alert or drought.
An environmental impact that needs to be put into perspective
Whilst the flame retardant is effective, its use raises environmental concerns. Maude Jimenez, a lecturer and researcher in chemistry at the University of Lille, explains to TFI that “too much nitrogen and phosphorus in the water can lead to eutrophication, which encourages the proliferation of algae and threatens certain aquatic species”.
However, given the damage caused by the fires, its impact remains limited. “Compared with the problems caused by forest fires, such as pollution or the destruction of ecosystems, the fire retardant is very low in pollution,” explains the specialist. Firefighters use it with caution, targeting strategic areas to minimise risks.