Fire Retardants: Preservation at a Price

Fire Retardants: Preservation at a Price

There's something in the water -- the water fire fighters use to suppress wildfires. It's a mixture of chemicals that make the water denser and ground fuels less flammable. But few studies have been conducted to determine the effect of the chemicals on the environment.

Nonetheless, fire retardants continue to be an essential part of fire-fighting strategy.

Research on the environmental effect of fire retardants shows they harm fish if they seep into waterways. Their effect on vegetation and invertebrates appears to be minimal, but data is scarce.

Do the effects outweigh the benefits?

"I think it depends on the severity of the fire," said Susan Finger of the USGS Environmental and Contaminants Research Center. "I would say that with appropriate caution and proper attention to application, all chemicals provide a valuable tool, and when you look at in context of fire ecology, they are an important resource to fire fighters."

Fire fighters are educated about fire retardants and trained in how to use them. "I've seen an environmental ethic at work along with fighting fire," said Finger. "That was not the case a decade ago."

Several types of chemicals, grouped into two categories (retardants and foams), are used to suppress wildfires. The Forest Service stocks about 30 such chemicals, and one or several are usually used to extinquish a blaze.

The retardants are combinations of several ingredients: water, fertilizer salts, thickeners that provide stability to the solution and make it cling to fuels (dry organic matter), corrosion inhibitors which minimize damage to equipment, viscosity stabilizers and bactericide to improve stability, and coloring agents.

A retardant is applied in front of an advancing fire or along its flanks to reduce its intensity and ability to spread, said Bob Pfouts of the Wildland Fire Chemical Systems division of the Forest Service.

Foam suppressants are similar to soap. They make water denser and help take oxygen out of the fire. They are applied directly to a fire to suppress flames or used in areas already burned to cool and dampen hot surfaces. Foams are applied via aerial drops or by vehicles on the ground.

Recent research published in a report titled "The Effects of UVB Radiation on the Toxicity of Fire-Fighting Chemicals," also shows that exposure to sunlight can affect sodium ferrocyanide, which is used in some retardants as a corrosion inhibitor. Exposure to sunlight makes retardants containing sodium ferrocyanide more toxic, said Finger.

The Forest Service plans to test the soil at sites where retardants containing sodium ferrocyanide were dropped over the past two years. The service has contracted with the USGS to perform field studies of currently approved chemicals containing sodium ferrocyanide.

Already, the Forest Service has decided to phase out retardants containing sodium ferrocyanide by 2004.

Over the past five years, 409,721 fires in the United States have burned 18,382,397 acres. An annnual average of 15 million gallons of retardant have been used to contain the blazes in the past 20 years.

It is estimated that in this fire season, a record year in which more than 4.3 million acres have already burned, nearly 40 million gallons of retardant and an unknown quantity of foam will be used.