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"All of the retardants as concentrates are practically nontoxic. They’re even less toxic by the time they’re diluted," Johnson said.
So who’s right? The finer points of the debate get complicated.
Fire retardant doesn’t attempt to put out wildfires or even necessarily halt flames in their advance. Consisting primarily of ammonium phosphate — fertilizer, basically — fire retardant is formulated to slow down the combustion of trees, brush and grass.
The idea is to give firefighters time to mount a ground attack. The ground forces clear away flammable material in a wide line around the edges of the fire. They hem in the flames and eventually a soaking rain falls or the fire just burns itself out.
Often, even a fully contained high Rockies wildfire will smolder, sputter and flare for weeks or months, into autumn and the first significant snows.
The U.S. Forest Service spent $19 million on 23 million gallons of retardant last year, which was unusually busy for wildfires.
"We’ve observed streams for miles be sterilized of all their fish life. Tens of thousands of fish can be killed in one dump," Stahl said.
Meanwhile, very few fish poisonings have been documented. Even Montana U.S. District Judge Donald Molloy, in siding with Forest Service Employees for Environmental Ethics in its second lawsuit over fire retardant, pointed out in his 2010 ruling that only 14 of 128,000 retardant drops over eight years killed protected fish or plants.
Ammonia in watersheds from fire retardant is not a human health risk.
Many endangered Rocky Mountain plants are adapted to thrive in very limited habitats with poor soils. Fire retardant can encourage the growth of invasive weeds that can crowd out native plants that otherwise would have a competitive advantage, said Glen Stein, a Forest Service fire ecologist who led the effort to write the new rules for fire retardant.
Stahl said the Forest Service hasn’t proven with field studies that fire retardant helps.
"We throw it on for the air show," Stahl said.
There’s a reason why fire retardant isn’t tested in the field, said Stein.
"The problem that I have with what Andy wants us to do, is out there in the wild, you have so many variables that are constantly changing. You’ve got slope, you’ve got aspect, you’ve got wind, you’ve got temperatures. It’s hard to know what the result of the retardant is versus some of the other variables," he said.
Anyway, he’s seen fire retardant work in the field, such as when a DC10 tanker plane dumped thousands of gallons at a California fire a few years ago.
"Five miles long, I drove that whole road where we dropped it. There were two little spots where it went into the retardant and stopped. And the rest of it just stopped at the retardant. So I know it’s effective," Stein said.
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