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Aerial fire retardants: It’s raining red

By Avery Lindeman | October 24, 2017

A wet winter followed by record heat this summer have contributed to one of California’s worst-ever fire seasons. In the month of October alone, thousands of structures have been destroyed in fires in Northern California as more than ten separate wildfires have burned across the state. Firefighters have literally worked around the clock; and over the course of just five days, more than two million gallons of fire retardant were dropped in California in an effort to control the blazes.

So what exactly is that bright red slurry dropped by planes during wildfires?

Several different types of fire retardant may be used in fighting wild fires, including:

  • Long-Term Retardants: these water-based mixtures often contain ammonium phosphate salts and other additives, and they are typically dropped on wood fuel in advance of a fire. The salts promote charring of wood materials, so the mixture continues to provide fire retardancy after the water has evaporated. The distinctive bright red coloring is an added dye that makes it easier for responders to keep track of treated areas.
  • Class A Foams and Water Enhancers: these water-based mixtures are applied directly to flames and are often used for the protection of structures. They contain solvents and surfactants that help the water “stick to” and soak into materials so that it can work more effectively. Foams may be aerially dropped; but these products are also used in ground operations.

These flame retardant mixtures are different from the flame retardant chemicals historically used in furniture:

  • Flame retardants used in furniture have been associated with chronic adverse human health impacts, such as learning deficits, reduced fertility, and cancer. In contrast, fire retardants used in wildland fire fighting may cause some skin irritation on direct contact, but they are not considered a chronic health risk.
  • Flame retardant chemicals used in home furniture to comply with standards like the outdated Technical Bulletin 117 generally provide no meaningful improvement in fire safety. In contrast, aerial fire retardant, Class A foams, and water enhancers can facilitate protection of firefighters and the public beyond the use of plain water in the right conditions.

While they are generally not considered harmful to humans, these wildland fire fighting products can cause unintended harm to ecosystems if they are not used carefully. Components of these mixtures can be toxic to aquatic life (for example, if they are accidentally dropped into streams or bodies of water); for this reason, the US Forest Service has a policy of not dropping retardant within 300 or more feet of waterways. In addition, use of these fire retardant mixtures may contribute to reduced plant diversity in areas of re-growth after a fire.

Protection of people, structures, and property are priorities for fire management, an especially difficult challenge in the so-called “wildland urban interface”. Sometimes, fire retardant solutions may be invaluable for managing wildland fires; other times, they may not be as effective. Since fire seasons are expected to worsen, it is increasingly important for experts and regulators to employ strategies beyond fire suppression, such as strategic forest restoration and reduced development in fire-prone landscapes.