Chemical agents have been used to combat forest fires since at least the 1950s, but increasing fire occurrence has caused a rapid expansion in their use over the past decade. The increasing incidence of forest fires affecting a growing number of acres and communities has also resulted in public sightings of mass quantities of red liquid dropped from low-flying planes and helicopters, often near or on residential areas. Such sightings often have left a trail of media coverage and questions concerning the possible human and environmental impacts of the chemicals used in fire retardants and suppressants.
These developments have raised important questions from citizens, public interest groups, and local regulatory agencies alike. Forest fires are a part of the natural regeneration and turnover of a healthy ecosystem, but how can their inevitable occurrence be safely limited to avoid or mitigate impacts to surrounding communities? How do the chemical agents used in fire retardants and suppressants impact plant, aquatic, and wildlife species, and do they present any risks to humans? While these questions seem to arise anew with every fire season, over the last decade various federal agencies involved in fighting fires have considered and answered most of them. This has resulted in improvements to chemical application practices to minimize any potential adverse environmental impacts, as well as a heightened awareness of the safety of the chemicals to human populations.
The U.S. Forest Service (USFS) is responsible for wildfire management and response across 193 million acres of the National Forest System, while the Department of the Interior manages wildfire response for more than 400 million acres of national parks, wildlife refuges, and other public lands. Since 2000, wildfires have burned an average of 6.9 million acres of forest annually—more than double the 3.3-million-acre average reported in the 1990s. In response, the USFS has increased its use of chemical retardants and suppressants by an average of 8.1% annually between 2014 (when just over 13.6 million gallons were applied) and 2018 (during which more than 27 million gallons were used). 2018 Aviation Annual Report, Aviation Aircraft Use Summary, U.S. Forest Serv. (2018). USFS spending on fire suppression has also increased from 15% of the agency’s annual budget to more than 55% of the budget in 2017, when such costs exceeded $2 billion. As a result of this increased spending, the USFS has been unable to use money intended for forest management and fire prevention—including prescribed burning and harvesting—out of fear that those resources will be needed to actually fight fires. Forest Service Fire Suppression Costs, U.S. Dep’t of Agric. (Sept. 14, 2017).
The USFS chemical fire-fighting agents—fire retardants used to prevent fire ignition and suppressants used to extinguish fires—are a water-based mixture containing a commercial fertilizer, ammonium polyphosphate, in addition to various thickeners and dyes. The agents typically are applied by helicopter or air tanker to a target area just ahead of the fire line. Due to their speed, range, and delivery capacity, air tankers—which can hold up to 3,000 gallons and typically make their drops from an altitude of 150 to 200 feet—are most commonly used to halt the spread of fire, while helicopters are used on areas further away from the fire to delay spread or reduce fire intensity. Biological and Conference Opinion, Nat’l Marine Fisheries Serv. (Nov. 7, 2011); Aerial Firefighting Use and Effectiveness Report, U.S. Forest Serv. (Mar. 2020). Once applied, the retardant solution coats threatened vegetation and, as the fire draws near, water content in the mixed product evaporates and the fertilizer salt reacts with cellulose in the vegetation and decomposes, giving off water vapor that cools the fire. A residue of black, nonflammable carbon coating both insulates and restricts airflow to any remaining vegetation. As a result, the intensity of the fuel-starved fire decreases and control is much easier to achieve. Any residual material that is not consumed in the fire will continue to be effective in preventing ignition and flame spread until removed, typically by wind or rainfall.
Before the early 2000s, there was little transparency concerning the environmental and human impacts of fire retardants and suppressants. This led to a series of National Environmental Policy Act (NEPA) lawsuits against federal fire-fighting agencies, seeking greater scientific and public understanding of the chemical agents. In 2003, a group of USFS employees filed a NEPA lawsuit against the USFS, alleging that NEPA required the USFS to analyze the effects of aerial application of fire retardants on endangered species, and that the Endangered Species Act (ESA) required the USFS to consult with the U.S. Fish and Wildlife Service (FWS) on the same issue. In 2005, the court held that USFS had violated NEPA and the ESA by failing to analyze the effects of fire retardants and ordered “the USFS to engage in formal consultation with FWS regarding the use of fire retardant in national forests.” Forest Serv. Emps. for Env’t Ethics v. U.S. Forest Serv., 397 F. Supp. 2d 1241, 1257 (D. Mont. 2005).
Working in conjunction with the FWS and the National Marine Fisheries Service (NMFS), the USFS issued an environmental assessment (EA) in October 2007 and then a Decision Notice/Finding of No Significant Impact in February 2008 for the aerial application of fire retardants. On April 2, 2008, USFS employees filed another NEPA lawsuit, against the USFS, FWS, and NMFS, challenging the adequacy of the EA as well as the consultation between the three agencies. In 2010, the court again held that the USFS decision-making process violated NEPA and ordered the USFS, FWS, and NMFS to cure NEPA and ESA violations. Forest Serv. Emps. for Env’t Ethics v. U.S. Forest Serv., 726 F. Supp. 2d 1195 (D. Mont. 2010). In response, the USFS completed an ESA section 7 consultation with the FWS and NMFS, which each issued a biological opinion in late 2011, and prepared, circulated, and responded to public comment on a draft environmental impact statement (EIS).
The December 2011 biological opinion by the USFS reports that the inadvertent delivery of retardant—by accidental application, drift, or surface runoff—into a waterway occupied by threatened and endangered fish species can cause mortality due to ammonia exposure. A medium to heavy drop, accounting for greater than 800 gallons of retardant per second being released from an aircraft, may cause mortality in fish at the initial drop site, while certain fish downstream may be able to detect and avoid treated waters. But the opinion reports that the intentional delivery of retardant outside a 300-foot avoidance zone will not cause adverse effects to fish other than potential surface runoff impacts during a rainfall event. Similarly, the November 2011 NMFS biological opinion concluded that any incidental effects of fire retardant runoff into waterways are not likely to jeopardize the continued existence of threatened or endangered species. (Subsequently, a USFS ecological risk assessment (ERA) issued in December 2013 concluded that no acute toxic effects to aquatic wildlife would occur in streams receiving runoff from land where retardant was applied.)
The culmination of this work resulted in USFS issuing a Record of Decision in December 2011 that approved the use of aerially applied fire retardants while implementing an adaptive management approach to protect natural resources and that provided for improved documentation of retardant effects through reporting, monitoring, and application coordination efforts. Under this approach, aerial drops are not allowed in mapped avoidance areas for threatened, endangered, proposed, candidate, or sensitive species, or within 300 feet of any mapped water feature. However, the USFS implementation guidelines allow drops to occur within areas included in the avoidance mapping where human life or public safety is threatened and if retardant use within the area could be reasonably expected to alleviate that threat. Pilots are required to report any such application, and the area must then be assessed for impacts, and monitored and remediated as necessary, according to USFS regulations. Implementation Guide for Aerial Application of Fire Retardant, U.S. Forest Serv. (May 2019).
Chemical retardants and suppressants can also affect plant communities by facilitating the invasion of nonnative species and by attracting more herbivores to an application site due to the increased quality of forage, despite a decrease in plant diversity. The fertilizer in the agents may encourage growth of some plant species, giving them a competitive advantage over others. However, according to the 2011 USFS biological opinion, these effects may last up to one year, and the invasion of nonnative weeds is likely more threatening to the viability of threatened or endangered plants, while widely distributed native species are unlikely to be jeopardized. For example, the December 2013 ERA reports that species richness was reduced in the North Dakota prairie ecosystem after exposure to retardants, regardless of whether the plot was burned or unburned. After exposure, all plots were dominated by nonnative Poa pratensis, which gained a competitive advantage from retardant application and crowded out other species.
All of the retardants used by the USFS have been classified by the U.S. Environmental Protection Agency as “practically non-toxic” for humans, wild animals, and aquatic species. The Role Retardant Plays in Fire Suppression, U.S. Forest Serv. (accessed Nov. 17, 2020). Recent risk assessments also generally conclude that the chemical agents are largely nonthreatening to human health. The September 2017 USFS health risk assessment for long-term retardants reports that, for typical to maximum exposures, all products evaluated were predicted to pose a negligible risk to fire-fighting personnel, while no risks were reported for members of the public in an accidental “drench” scenario (a primary subject of local news reports).
Media images of retardant and suppressant use continue to raise public concerns, especially in areas not historically subject to forest fires. However, the information and studies from federal agencies’ review over the past decade indicate that fire retardants and suppressants pose a negligible risk to animal, plant, and human receptors when used in accordance with USFS guidelines and procedures.