Fanned by strong Santa Ana winds, wildfires in Southern California have killed at least 25 people and burned about 100 square miles in the greater Los Angeles area.
More than a week after it broke out, the largest fire in the area, the Palisades, was 19% contained as of January 15. Los Angeles County has declared a public health emergency due to the smoke.
The powder sprayed on wildfires is called Phos-Chek. It can be dropped from the air or spread on the ground by truck.
The substance is primarily water, ammonium phosphate — a common ingredient in fertilizers — and pink food coloring, although it is thickened with gum to increase the precision of aerial drops.
It is a fertilizer-based fire retardant product that has the same ingredients used in lawn care fertilizers, said Shannon Horn, chief operating officer at Perimeter Solutions, the maker of Phos-Chek.
When used in flame retardants, ammonium phosphate can change the way cellulose in plants reacts to heat.
Normally, wood exposed to the heat of a fire would begin to decompose and become fuel, but Phos-Chek acts as a mulch, creating a barrier that consumes the heat energy. The reaction creates a non-combustible carbon material, slowing the fire down, giving firefighters more time.
The main purpose of the pink dye is simply to help firefighters and pilots create and accurately identify fire retardant lines.
“It basically allows the pilot to see where the lines are,” said Horn. “If it was transparent, they wouldn’t know where the fire retardant line was.”
Phos-Chek can fade over time in sunlight and is washable with water, so it does not permanently stain where it covers.
The main environmental concern with flame retardants is the presence of heavy metals. A study last year found that one version of Phos-Chek contained higher levels of metals like cadmium and chromium than are considered safe under regulatory thresholds. The heavy metals are not added directly to the product, but can come from naturally occurring impurities.
However, the version of Phos-Chek released in California is “a different product than it was many years ago,” Mr Horn said.
The benefits of using flame retardants outweigh the risks, said Yifang Zhu, professor of environmental health sciences at the Fielding School of Public Health at the University of California, Los Angeles.
There is little evidence that it has serious long-term health effects in humans, Ms Zhu said.
She added that the immediate health risks from wildfire smoke, which contains high levels of particulate matter, outweigh potential concerns related to flame retardants.
According to the Environmental Protection Agency, exposure to smoke pollution can cause a variety of respiratory and cardiovascular problems, such as shortness of breath, bronchitis or heart attacks.
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