Some of the visuals coming out of Los Angeles County over the past week are what we’ve come to expect with wildfires: dramatic flames, orange skies and damaged structures.
But what about the pink dust covering some neighborhoods?
The eye-popping substance that coats streets, cars and surfaces is actually fire-resistant, released by aerial fire tankers in massive red or pink plumes.
Unlike water droplets, which target an active flame, fire retardant is dropped by aircraft ahead of a fire’s path to slow fire progress and allow crews to build fire lines.
Thousands of gallons of fire retardant have been dumped in Los Angeles County since the fires broke out last week, officials say. The deadly fires have so far killed at least 25 people, destroyed more than 12,000 buildings and displaced tens of thousands of residents.
What exactly is fireproof?
Fire retardants consist of fertilizer chemicals such as ammonium phosphates. They often include bright pigments to help pilots accurately drop the retardant.
They work to slow the rate of fires by cooling and coating plants that serve as fire fuel, depleting the fire’s oxygen and slowing the burning process “because the inorganic salt retardants change the way the fuel burns,” according to the US Forest Service.
Phos-Chek, manufactured by Perimeter Solutions, is the retardant used in Los Angeles County and is the most common in Canada. It is also the most widely used fire retardant in the world, according to a 2022 report by The Associated Press.
Although there are several formulations, it usually comes in the form of a powdered concentrate that is mixed with water before being discharged from the tanker.
Is it safe?
In general, approved flame retardants are not considered toxic to humans — although direct inhalation, eye contact or consumption can cause irritation, and scientists say more research on long-term exposure is needed.
But fire retardants can be toxic to fish or other aquatic life if they get into waterways. For this reason, the US Forest Service prohibits the release of fire retardant within 300 feet of waterways or specially designated avoidance areas, “except when human life or public safety is threatened.”
Study published last year in the journal Environmental Science & Technology Letters found that some fire retardants, including Phos-Chek LC-95W, contain toxic metals, including lead and arsenic.
A representative of the US Forest Service he told NPR that LC-95 was phased out in 2025 in favor of the newer formulation MVP-Fx. According to Perimeter, Phos-Chek is MVP-Fx much less toxic for fishing from older LC-95 formulations.
Perimeter previously said residents should try to remove the retardant with water and mild soap as soon as safety allows.
“The longer the retardant dries, the more difficult it is to completely remove it,” the company said in a short text. High-pressure washers can be used on larger surfaces, it added.
The bright color will slowly fade with exposure to sunlight.
Wayne Coulson, CEO of Vancouver-based Coulson Aviation, said most of the flights his company made to help Los Angeles fire crews were at night.
Forest fires are linked to a number of health problems, and studies show that long-term smoke inhalation can seriously affect the lungs and heart, and even increases the risk of dementia more than other forms of air pollution.
The U.S. Forest Service has used aerial fire retardants since the 1950s, according to their website, but their use has undergone many transformations over the years as older formulations have been phased out and regulations changed.
In 2005, the U.S. District Court for the District of Montana ruled that the Forest Service violated the National Environmental Policy Act by failing to conduct an adequate analysis of the airborne fire retardant’s effects on the environment and endangered animals. After years of back-and-forth, the US Forest Service evaluated and implemented the requirement to ban dumping in waterways and avoidance zones in a 2011 decision.
Last year, the U.S. Forest Service announced it had decided not to award a contract to Compass Minerals for magnesium chloride-based airborne fire retardants after inspections found corrosion in the air tankers used to deploy the company’s retardants.
