'Orange Slime' use in fighting fires debated (photos)

Fire Retardant

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The retardant is colored bright orange so that fire crews know where each discharge starts and leaves off.

Fire Retardant

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Cal Fire's Kevin Reed is one of more than 20 technicians, engineers, pilots and firefighters that are stationed at the Air Attack Base in Hemet, Calif.

Fire Retardant

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Fire retardant is mixed on site in Hemet, Calif. Each tank can hold up to 10,000 gallons of Phos-Chek, the commercial name for the retardant.

Fire Retardant

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Cal Fire air technician Kevin Reed starts the pumps that mix the powder retardant with water. During wildfires, Reed will mix retardant continuously to keep up with the need.

Fire Retardant

Maya Sugarman/KPCC

Water pours into 10,000-gallon tanks where the retardant is mixed. So far this year, the Hemet base has used 800 thousand gallons of retardant, twice the amount from last year.

Fire Retardant

Maya Sugarman/KPCC

Cal Fire air technician Kevin Reed demonstrates how fire retardant is put in an air tanker at the Cal Fire Air Attack Base in Hemet, Calif. – one of 12 bases of its kind in California. This S-2T air tanker holds 1,200 gallons of retardant.

Fire Retardant

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Battalion chief Travis Alexander stands outside an air tactical aircraft. Alexander and other commanders can spend hours in the cockpit during a fire.

Fire Retardant

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With the push of a button from the cockpit, doors at the bottom of an S-2T air tanker open and release all 1,200 gallons of fire retardant.

Fire Retardant

Maya Sugarman/KPCC

Doors at the bottom of an S-2T air tanker open and release all 1,200 gallons of fire retardant. Timing is key, as all the retardant drops at once.

Fire Retardant

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Firefighters Adan Castro, left, and Anthony Pappani work in the control tower. Castro coordinates aircraft coming and going at the base.

Fire Retardant

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Deen Oehl, left, has been a tanker pilot for more than 30 years. Travis Bailey, right, is a base mechanic for Cal Fire in Hemet, Calif.

Fire Retardant

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Hearing protection muffs hang everywhere in Cal Fire's Air Attack Base in Hemet, Calif.

Fire Retardant

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Underneath an S-2T air tanker, which holds 1,200 gallons of fire retardant. This S-2T is one of 23 former military tankers that have been converted for Cal Fire's use during wildfires.


During wildfire season, the nightly news often shows images of tanker planes dropping orange liquid near the infernos.

That's fire retardant, a substance designed to slow and in some cases halt a blaze.

On average, California uses more retardant than any other state, but some forest service employees argue the substance doesn't work when it matters most.

PHOTOS: Check out images of Cal Fire's Air Attack Base on KPCC's AudioVision.

Orange slime

Up close retardant looks like carrot juice and feels like slime.

It's totally safe for people to touch, says Kevin Reed. He works for CalFire at Hemet Ryan Air Attack Base and is in charge of preparing the retardant.

He says it's orange so firefighters can see it from the air when it's dumped.

Retardant is mostly ammonium phosphate, a substance often used as fertilizer, says George Matousek with the company Phos-Chek, the only supplier of retardant in the U.S.

Phosphate does the magic

When ammonium phosphate-covered wood feels the heat of an oncoming flame a reaction occurs, Matousek explains.

The phosphate converts the woody material into an almost pure form of carbon. Think  of diamond or graphite. Pure carbon does not burn.

RELATED: Follow and research California's wildfires with KPCC's Fire Tracker

When this reaction happens on a tree, he says, "it would be black on the outside, but alive on the inside."

Worth the risk?

The ammonium in retardant is poisonous to fish, says Andy Stahl with the watchdog group Forest Service Employees for Environmental Ethics.

"Dump a load of retardant in a creek, you can kill the fish for miles downstream," he said.

That happened in 2009 when retardant was accidentally dropped in a sensitive area of Santa Barbara County, despite a rule saying firefighters can't drop within 300 feet of a waterway.

Dozens of endangered steelhead trout died as a result.

The fertilizer-like quality of the substance can also help aggressive invasive plants grow, sometimes choking out sensitive local species.

But Stahl says his biggest issue is that there is no statistical evidence the stuff reliably helps contain fires.

"We can find individual anecdotal examples where yes, it appears that in this one place we dropped the retardant and the fire stopped," he said. But he adds there are also plenty of examples where the retardant appears to have done nothing.

One tactic of many

Glen Stein studies retardant for the US Forest Service.

He says the reason there are no studies showing the effectiveness of retardant in the field is because each fire happens amid a unique set of circumstances making it hard to compare cases.

"There are so many variables," he said.

But Stein points out that there are hundreds of lab tests showing that retardant slows fires in controlled settings.

RELATED: 10 largest wildfires in California history

And he adds that the Forest Service is continually refining its rules on using the substance safely.

He says retardant isn't meant to stop a fire on its own. It's only one tactict firefighters use to protect forests and homes.

Correction: An earlier version of this story incorrectly spelled the name of Phos-Chek. KPCC regrets the error.

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