Some of the images that have come out of Los Angeles County over the past week are reminiscent of those we've come to expect from wildfires: dramatic flames, orange skies and damaged structures.
But what about the pink powder covering some neighborhoods?
The eye-catching substance covering streets, cars and surfaces is actually fireproof and dropped by firefighting air tankers in massive red or pink plumes.
Unlike water droplets, which target active flames, flame retardants are dropped from aircraft in front of a fire's path to slow the fire's progress and allow crews to build a fire line.
Officials say thousands of gallons of flame retardant have been dumped since wildfires broke out in Los Angeles County last week. The deadly fires have so far killed at least 25 people, destroyed more than 12,000 buildings and forced tens of thousands of residents from their homes.
What exactly is fireproof?
Flame retardants consist of chemical fertilizers such as ammonium phosphates. They often contain bright pigments that help pilots accurately drop the retardant.
Their purpose is to slow the rate of fires by cooling and coating the facilities that serve as fire fuel, depleting the fire's oxygen and slowing the combustion process “because inorganic retardant salts change the way fuels burn,” according to the U.S. Forest Service.
Phos-Chek, manufactured by Perimeter Solutions, is the retarder used in Los Angeles County and the most commonly used in Canada. It is also the most widely used flame retardant in the world, according to a 2022 report by The Associated Press.
While several formulas exist, it typically comes as a powder concentrate that is mixed with water before being dropped from tankers.
Is it safe?
Generally, flame retardants approved for use are not considered toxic to humans, although direct inhalation, eye contact or ingestion may cause irritation, and scientists say more research is needed on long-term exposure.
However, flame retardants can be toxic to fish and other aquatic animals if they enter waterways. For this reason, the U.S. Forest Service prohibits the discharge of flame retardant within 300 feet of waterways or specially designated areas to be avoided “except when human life or public safety is threatened.”
Test released last year in the journal Environmental Science & Technology Letters found that some flame retardants, including Phos-Chek LC-95W, contain toxic metals including lead and arsenic.
Representative of the United States Forest Service he told NPR that LC-95 was discontinued in 2025 in favor of the newer MVP-Fx formula. According to Perimeter data, Phos-Chek MVP-Fx is much less toxic for fishing than the older LC-95 preparations.
Perimeter previously said residents should try to remove the retardant with water and mild soap as soon as safety allows.
“The longer the retarder takes to dry, the more difficult it is to completely remove,” the company said in a briefing. He added that pressure washers can be used on larger surfaces.
The light color will slowly fade in sunlight.
Wayne Coulson, CEO of Vancouver-based Coulson Aviation, says most of the flights his company did to support Los Angeles fire crews were at night.
Wildfires have been linked to a number of health problems, and research shows 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.
According to their website, the U.S. Forest Service has been using airborne flame retardants since the 1950s, but their use has undergone many changes over the years as older formulations are phased out and regulations change.
In 2005, the U.S. District Court for the District of Montana ruled that the Forest Service violated the National Environmental Protection Policy Act by failing to adequately analyze the effects of airborne flame retardant on the environment and endangered animals. After years of ongoing discussions, the U.S. Forest Service conducted an assessment and, in a 2011 decision, implemented a requirement to prohibit discharges in waterways and avoidance zones.
Last year, the U.S. Forest Service announced it had abandoned a contract with Compass Minerals to supply magnesium chloride-based aircraft flame retardants after inspections found corrosion in tankers used to transport the company's retardant.