It stands out against a backdrop of charred landscapes. Above forests, houses and cars, this bright red or neon pink material is everywhere in Los Angeles, devastated by fires. Spilled by plane, it is a flame retardant, essentially a product called Phos-Chek.
It has been used in the United States by the Forest Service since the 1960s. This type of retardant is also an integral part of the range of French firefighters fighting forest fires. It is often dropped by Dash, in association with other aircraft, such as Canadair (used mainly for water drops, thanks to their ability to resupply in flight) or Beechcraft (an aircraft specialized in intelligence ).
A cocktail of phosphate, iron, and various additives
The use of flame retardants is well known. But its use above residential neighborhoods in Los Angeles has been on a “never before seen” scale, notes Daniel McCurry, associate professor of civil and environmental engineering at the University of Southern California. Phos-Chek is a mixture of ammonium phosphate, a common fertilizer, and various additives, including iron oxide (from rust), which gives it its neon color.
“This bright tint helps pilots ensure they don’t leave uncovered areas above fires,” says Jason Colquhoun, a helicopter pilot with a company specializing in firefighting. The flame retardant substance continues to work even after the water with which it is mixed has evaporated. While thickeners provide “a viscosity to the product which prevents it from drifting from the targeted area”, adds Daniel McCurry.
What impact on the environment?
A former firefighter, however, explained to him that the product “wasn’t of much use” in the case of high-intensity fires, like those which have killed at least 25 people over the past week in Los Angeles and are still out of control.
-The Forest Service explains that it only uses flame retardants “that meet the criteria of the Environmental Protection Agency” ensuring that they are “virtually non-toxic to humans, mammals and aquatic species” .
An old formula was withdrawn across the United States on December 31. The one used now would be less toxic. It does not contain eternal pollutants, nor substances “known to cause cancer or other ailments”, prohibited by Californian law, assures Perimeter Solutions, the company which markets Phos-Chek. But it can cause skin irritation and, if ingested, cause nausea and vomiting.
Our file on the Los Angeles fires
McCurry says the Forest Service has lost lawsuits in the past on environmental cases. Now Phos-Chek is “probably harmless to the environment”. “At the same time, the impact on human health is not yet entirely clear,” he concedes.
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