Fires: What is this fluorescent pink liquid dropped on the Los Angeles fires?

This red or pink material, which stands out starkly against this backdrop of grayish plumes and charred landscapes, is a flame retardant, essentially a product called Phos-Chek, used by the Forest Service since the 1960s.

“It’s an incredible thing… you can see it so easily,” said Jason Colquhoun, a 53-year-old pilot with HeliQwest, a helicopter company specializing in firefighting. But since last week, the substance has been dropped over residential neighborhoods on a scale “never seen before,” notes Daniel McCurry, associate professor of civil and environmental engineering at the University of Southern California. And so this disturbing question: is it dangerous or not?

Phos-Chek is marketed by Perimeter Solutions, a fire protection company. It’s a mixture of ammonium phosphate, a common fertilizer, and various additives, including iron oxide (from rust), which gives this fluorescent color.

This bright tint helps pilots ensure they don’t leave uncovered areas above fires, says Jason Colquhoun. Normally, when pilots drop water, they have to spot “the bright and the dark” to know where to make their next drop. But with this substance, “it’s so much easier to see,” he explains.

Another advantage over water: the flame retardant continues to work even after the water it is mixed with evaporates, says Daniel McCurry. Thickeners provide a viscosity to the product that prevents it from drifting away from the targeted area, adds Daniel McCurry, who has conducted research on heavy metals in this type of flame retardant. The product, which comes in the form of a powder, is most often mixed in large basins before being loaded onto planes and helicopters for coordinated drops, explains Jason Colquhoun.

Daniel McCurry explains having seen images where “a bushfire stopped its progression exactly on the line up to which Phos-Chek had been spread”. But he has mixed opinions about the product. A former firefighter explained to him that the product “wasn’t of much use” in the case of high-intensity fires, like those which have killed 25 people over the past week in Los Angeles and are still out of control.

The Forest Service explains that it only uses flame retardant “that meets Environmental Protection Agency criteria, ensuring that it is “virtually non-toxic” to humans, mammals and aquatic species. It prohibits releases onto bodies of water and areas harboring threatened or endangered species – the exception being when “human life or public safety is threatened” and it is “reasonable to believe” that the retardant could put out the fire. But accidents can happen, with a change in wind direction or an involuntary release.

An old Phos-Chek formula, LC95, which Daniel McCurry’s research showed had high levels of heavy metals that could contaminate drinking water, was withdrawn across the United States on December 31. The one used now, MVP-Fx, is less toxic. But it can cause skin irritation and, if ingested, cause nausea and vomiting.

McCurry says the Forest Service has lost lawsuits in the past on environmental cases, but now Phos-Chek is “probably environmentally safe.” “At the same time, the impact on human health is not yet entirely clear,” he concedes.

“Over the past week, there have been drops on a scale never seen before,” he continues, adding that the product is most often dumped away from inhabited areas. “But who knows?” he concludes.

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