Crews battling the deadly Los Angeles wildfires have been dropping a bright pink fire retardant across the city ahead of the advancing flames – leaving some wondering what the substance is, and how safe it is for the public and environment.
The eye-catching substance — seen coating homes, cars and yards in photographs from the evacuation zones — is called Phos-Chek, and has been used to fight fires for more than 50 years.
Made by the company Perimeter Solutions, Phos-Chek is dropped on still standing plants and structures to make them flame-proof, and so prevent fires from spreading to new locations.
Firefighters say the chemical is a vital tool for battling wildfires, and officials say it is safe – but others have said it could be damaging to wildlife.
A plane drops fire retardant as smoke billows from the Palisades Fire at the Mandeville Canyon neighborhood of Los Angeles, California, on January 11, 2025. REUTERS
Pink fire retardant covering a car in the Mandeville Canyon neighborhood of Los Angeles on Jan. 11, 2025. Photo by AGUSTIN PAULLIER/AFP via Getty Images
A house in Mandeville Canyon covered in the flame retardant. AFP via Getty ImagesBelow is everything you need to know:
What is the fire suppressant, and what is it made from?
Phos-Chek is made from ammonium phosphate – a salty compound similar to many common fertilizers – which is mixed with iron oxide to create its bright pink color.
Manufactured as a powder, the Phos-Chek is mixed with water prior to use to give it more substance, and is generally dumped across landscapes from planes or helicopters.
Backyard furniture covered on flame retardant dropped on the Pacific Palisades neighborhood. Photo by Justin Sullivan/Getty Images
Flowers on a tree in Mandeville Canyon colored pink after flame retardant landed on them. REUTERS/Ringo ChiuHow do they work?
The phosphate in the fire suppressant alters the decomposition process of cellulose in plants, making that plant non-flammable when it becomes coated in the powder.
When dumped directly on to flames, the Phos-Chek helps starve oxygen from the area, and slows burn rates by cooling whatever it covers.
Phos-Chek is generally dropped on places ahead of advancing flames to prevent fires from spreading to fresh ground.
Firefighters working on a hillside covered in fire retardant in Mandeville Canyon near the Palisades Fire. REUTERS/Ringo ChiuIt is helpful for quickly fireproofing vast tracts of land, and places that are difficult for firefighters to reach on foot.
The vibrant pink color is used to help firefighters see where they have dumped suppressant and where they still need to.
Risks of using Phos-Chek
The fire suppressant is generally considered safe for humans, but some have cautioned that it could be harmful to wildlife and water.
The front steps and mailbox of an house in Mandeville Canyon after fire retardant was dropped on the neighborhood. AFP via Getty ImagesUse of fire suppressant is banned around waterways and in the habitats of endangered species – and only allowed in those areas “when human life or public safety are threatened,” according to the US Forest Service.
Researchers from the University of Southern California have said it is “plausible” that fire suppressants have contributed to high levels of heavy metals found in California waterways.
But Perimeter Solutions says it does not add any metals to Pho-Chek – and that its products “are exhaustively tested by the USDA Forest Service and meet or exceed all health and safety standards.”
How to remove Pho-Chek
Pho-Chek’s bright color will fade in sunlight, according to the USDA, and can be wiped clean without residue.
The substance is also designed to be cleaned away by weather over time.
With Post wires.
