What Are They Dumping on Wildfires?

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Justin Sullivan / Getty

An air tanker drops fire retardant on brush, August 31, 2009, near Acton, California.

It's practically a rite of the season: as dependably as long sleeves come out of the closet and candy corn appears on store shelves, parts of the west go up in flames this time of year. Thousands of firefighters are battling a major blaze in southern California that has charred more than 130,000 acres, filling TV news reports with footage of hulking airplanes showering a bright red powder onto smoking forests below.

What the air tankers are dumping is a fire retardant known as slurry, a mixture of mostly water and fertilizer designed to protect trees and other flammable material from flames. The coating clings to vegeation and insulates it from the approaching inferno; the fertilizer helps the damaged areas regrow in the wake of the blaze. The powdery concoction is a key ingredient of a multi-pronged firefighting strategy; after the air drop, bulldozers and ground crews move in to cut a fire break designed to halt the advancing flames.

Slurry is dyed bright red to aid in visibility and help tanker pilots drop a seamless line of retardant. "Basically, they're trying to box in the fire," says Janet Upton of the California Department of Forestry and Fire Protection (Cal Fire), which is helping to battle the giant Station fire near Los Angeles. Another advantage of slurry is that unlike water, fertilizer doesn't evaporate. (It offers still another bonus for farmers, who have requested that unused slurry be dropped onto their fields as aircraft make their way home.)

Though aerial firefighting is effective, especially in rugged areas, it's also extremely expensive. The U.S. Forest Service spent nearly $300 million battling blazes from the sky in 2007. According to a report by the Los Angeles Times, it cost $368,645 to operate a single heavy-lift helicopter for one week during a recent fire (though choppers have a smaller capacity than large tanker planes, they're more maneuverable and can also ferry personnel and equipment). The cost of the retardant itself adds up as well; the Phos-Chek slurry used by Cal Fire costs about $2 per gallon, Upton says. Tankers can dump 1,200 gallons during each pass.

Aerial firefighting is also risky, as it often requires flying at low altitude through poor visibility. Nine people died in a helicopter crash during the Buckhorn fire in northern California last year, and last month a pilot died in the crash of a single-engine tanker near Reno, Nevada. (The Station fire has so far claimed the lives of two ground-based firefighters after their fire truck fell down a hillside.) Yet, as we're again reminded this year, tanker flights are favorite action shot of television news shows — California fire officials have dubbed them "CNN drops" — and that makes them a favorite among politicians, as well. As the Times reported, U.S. Rep. Duncan Hunter ignored the wishes of local officials and called Washington to demand aerial support during a 2003 fire in San Diego County. Six C-130's were dispatched over the next two days.

Though slurry doesn't look particularly eco-friendly, aerial firefighting is not environmentally harmful, Upton says — though planes avoid dumps near lakes, streams and other waterways (in especially sensitive areas, tankers drop plain water instead). The Forest Service also advises against allowing pets to swallow the stuff, as with other fertilizers. Still, the retardant poses another, less-publicized hazard, Upton says: to fashion. She's been on the ground as a rain of colored fertilizer falls from the sky: "I've had plenty of pink t-shirts."