Phos-Chek Applied at Local Fires: What Is It?

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Phos-Chek (red) is a fire retardant and was used in the Palisades Fire along Palisades Drive.

DC9 airplanes dropped Phos-Chek at the Palisades Highland fire, and today a DC10 dropped the fire retardant (at the Easy Fire) by the Ronald Reagan Presidential Library.

Phos-Chek’s bright red color is easily spotted, but what is it and how does it work?

The retardant, which became available in 1962 (the brand originally belonged to Monsanto) consists of ammonium phosphate, monoammonium phosphate and diammonium phosphate, clay, guar gum, a color pigment and corrosion inhibitors, according to United States Department of Agriculture.  (Phos-Chek is a registered trademark of ICL Performance Products.)

The solution is dropped on vegetation and the red retardant coats brush, trees and other possible plant fuel. The retardant  reacts with the cellulose in the plant. When the fire approaches, the grass/plant decomposes giving off water vapor that cools the fire, and leaves behind a black, graphite-like, non-flammable carbon coating, according to George Roby, a retired fire chief and incident commander for the United States Forest Service

The USDA has evaluated and approved ICL’s wildland fire retardant products.

According to a USDA report, Phos-Chek retardants that are not removed from vegetation, may dehydrate the plant and cause the foliage to turn brown and the plant to wither. But the report added, “After rain, most plants will return to normal and growth may be enhanced due to the added nutrients.”(visit: › Internet › FSE_DOCUMENTS › stelprd3851594)

“There are no known adverse effects to domestic or farm animals that consume small amounts of foliage covered with the Phos-Chek retardant,” USDA writes.

“Various Phos-Chek retardants have been tested both by ICL and by U.S. government agencies for possible acute toxicity effects on small terrestrial wildlife (birds, rodents, earthworms),” the document notes. “Reports emanating from these studies indicate that the Phos-Chek retardants pose a comparatively low order of acute toxicity.”

Phos-Chek does contain ammonia and that is toxic to aquatic life.

The USDA writes “Care is recommended and is exercised to as great an extent as possible, by the using agencies, to minimize application into streams, ponds, and other bodies of water.

“It should be recognized, also, that fish are quite sensitive to even minor changes in water temperature (such as may result from a fire) and to runoff of decomposition products from burning vegetation and other debris resulting from the denuded burned area. Thus, mortality of aquatic life is common in areas where large wildland fires have occurred, even when retardants have not been used.”

A San Gabriel Valley Tribune July 2016 story “Is That Red Fire Retardant Dropped from Planes during Wildfires Safe for Humans and the Environment?” notes “Most agree that the chemical is not harmful — at least not to humans and other mammals — even though it can cause quite a mess. However, studies show it may be lethal to aquatic life in lakes, creeks or rivers and scientists more recently are concerned about lingering effects of retardant on trees and chaparral during the current drought, which has made scarce the cleansing rains that can wash the chemicals away.

“‘With these drought conditions, with vegetation already stressed and now, with retardant staying on these plants and waiting six months before it rains, we don’t know if that changes the equation,’ said Marti Witter, a fire ecologist with the National Park Service in the Santa Monica Mountains National Recreation Area.

“‘Having salt sitting on your leaves — that would interfere with the leaf surface. Salts are not that great,’ she said.”

In the Tribune story, it said the US Forest Service reported that Phos-chek should never be used within 300 feet of lakes, creeks, streams or any body of water.

In a Ventura County Star March 2019 Opinion piece “Are Firefighters Using All the Right Stuff?” columnist Tom Elias writes “CalFire pays just under $3 per gallon for Phos-Check, about $47,000 per full load for a Boeing 747 tanker, a total of $28.4 million last year.

“But backers of the less toxic competitor Pyrocool maintain their product is better, partly because it actually extinguishes fires, partly because it is cheaper at about 17 cents per gallon and partly because of its lower toxicity. It won a major federal Environmental Protection Agency safety award in 1998.

“‘We’ve been trying for at least 10 years to get CalFire to use our product,’ says Pyrocool CEO Robert Tinsley. ‘With these devastating fires, you’d think they’d take a look at something else that has credentials.”

The suppliers of Phos-Chek  have an exclusive contract with the state Department of Forestry and Fire Protection (CalFire).

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3 Responses to Phos-Chek Applied at Local Fires: What Is It?

  1. Ron Midwin says:

    Thanks for the info. I was wondering what the effect of getting the red stuff on my tires and the underside of my car?

  2. Sue says:


    From the articles I read, it sounds like it can be easily washed off–let me know.


  3. CHRIS VAN HOOK says:

    I have often wondered about the fire retardant they use. Millions of gallons of it. I would like to understand why Phos-Check has an exclusive contract with the Dept. of Forestry and Fire Protection. Thanks

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