In a 2022 report, the UN Environment Programme (UNEP) and GRID-Arendal noted that the intensity and range of wildfires was increasing, with climate change, land-use change and poor land and forest management fueling destructive fires that pose a growing risk to people and the environment. The far-reaching environmental impacts include polluted water resources, soil erosion, loss of vegetation that has knock-on effects on ecosystems and habitats, endangering wildlife, and air pollution. Indeed, according to estimates, studies have shown that smoke from wildfires is “an important contributor to global mortality” in the hundreds of thousands every year and rising. “Uncontrolled wildfire produces negative effects which can include increased water temperature, altered water chemistry, increased sedimentation, changes in nutrient cycling and food availability, and increased erosion potential, among others. These effects can impact aquatic organisms and populations,” underlined John Winn, National Press Officer for the US Forest Service. The UNEP report forecasted a global increase in extreme fires of up to 14% by 2030, 30% by the end of 2050, and 50% by the end of the century. The report stated that it is “practically impossible to entirely remove the risk posed by wildfires”. Therefore, the onus is on management and risk reduction.

Aerial firefighting plays a vital role in wildfire management and control and, with accelerating incidence and severity, the importance of increasingly effective and innovative aerial firefighting strategies cannot be overstated. “Aerial application of fire retardant is part of an integrated firefighting strategy and is applied in a wide range of situations,” confirmed Winn. “High-intensity fire, rapid rates of fire spread and other factors make it difficult for ground-based firefighters to access and fight wildland fires safely. Aerially applied fire retardant slows the rate of spread by cooling and coating fuels, depleting the fire of oxygen, and slowing the rate of fuel combustion as the retardant’s inorganic salts change how fuels burn. This can decrease fire intensity and give firefighters time to construct fire lines that are more likely to hold. It also increases firefighter safety and minimizes fire impacts to the environment. Aerially delivered fire retardant formulations currently in use are primarily inorganic fertilizers (ammonium phosphates) or other inorganic salts (magnesium chloride).”

Indeed, among the types of fire retardant used to fight wildfires are water-based long-term retardants containing ammonia phosphate salts and other additives, and class A foams and water enhancers. Unfortunately, the ammonium phosphate base traditionally found in aerial firefighting products is toxic to certain habitats. Firefighting water additives are only intended to be applied to terrestrial habitats but there is potential for aquatic exposure, which can cause adverse effects on aquatic species. Traditionally, perfluorinated chemicals (PFCs) were used in firefighting water additives; they are not only toxic to many species but also persistent, leading to global environmental distribution. In a 2023 study, researchers assessed the toxicity and risk of firefighting water additives to aquatic invertebrates. The impacts of nine of the firefighting water additive products were tested on three aquatic invertebrate freshwater species and the researchers found that the majority of the additives they assessed could be hazardous to biota. Restrictions have been placed on conventional foams due to the environmental hazards they pose; for example, in the European Union (EU), restrictions on perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) are in place. A key consideration for the industry is therefore the environmental impacts of aerial firefighting tools, and the challenge is the development of fire retardants and suppressants that are not only effective but also sustainable.

The Forest Service continually works to improve formulations to minimize potential adverse impacts while maintaining or improving fire retardant effectiveness

Enhancing safety and effectiveness

At the US Forest Service, which is an agency within the US Department of Agriculture (USDA), research is underway to explore the toxicity of foams and foam suppressant chemicals to plants and animals and there is a keen eye on ensuring environmental sustainability. Winn shared with AirMed&Rescue a snapshot of the agency’s work and priorities in this area. “The Forest Service continually works to improve formulations to minimize potential adverse impacts while maintaining or improving fire retardant effectiveness. The agency tests all types of qualified wildland fire chemicals for toxicity,” he stated. “All fire retardants used by the Forest Service fall into the Environmental Protection Agency’s practically non-toxic category for mammals, aquatic species and humans. Risks of negative effects to aquatic species depend on the type and amount of retardant applied, stream size and flow, behavior of the species (i.e. they may move to other areas), time of year, duration of exposure and other factors.”

In its investigations, the US Forest Service used models developed by the US Geological Survey (USGS) to gain insight on exposure. “We found that retardant intrusion exposure times are usually short, lasting between 0.17 and 2.73 hours. Based on the modeled duration of exposure, lethal intrusions are expected to be extremely rare, and most effects, if any occur, are assumed to be sub-lethal or indirect,” Winn revealed.

The United Aerial Firefighters Association (UAFA) is also concerned with enhancing the safety and effectiveness of aerial firefighting operations. AirMed&Rescue spoke with Paul Petersen, the association’s Executive Director, who said that members provide fire suppressants/retardants today that are environmentally friendly. “They meet the USDA Forest Service functional and chemical requirements and undergo strict testing procedures performed by federal agencies,” he asserted. “Our members are constantly working on new products to improve the performance desired by the government and reduce impacts on the environment.”

Our members are constantly working on new products to improve the performance desired by the government and reduce impacts on the environment

In addition to this work on firefighting products, UAFA members are also striving to improve the environmental impact of aircraft. “Our members are maximizing the carrying and drop capabilities of the aircraft to reduce the number of takeoffs/landings needed,” Petersen stated. “They are also implementing new technology that better defines the location and accuracy of the retardant or water drops to improve its effectiveness in slowing down the fire. Also, continued aviation fuel improvements/formulations will advance engine efficiency, reducing costs and emissions.”

It’s true that, looking at the wider picture, sustainability in aerial firefighting contains multiple components and opportunities – for example, reducing the carbon footprint of aircraft operations and exploring electric and hybrid-electric propulsion systems.

Exploring eco-friendly alternatives

Research in this arena is advancing the current and future potential for eco-friendly firefighting agents. “The Forest Service has conducted and continues to conduct studies on the environmental impacts of retardant use,” said Winn. “These studies go beyond the toxicity and risk assessment required by the agency.”

Another example of research in this area is a 2022 study in which researchers conducted fire prevention and firefighting experiments to investigate the effectiveness of an environmentally friendly hydrogel and noted the hydrogel’s short extinguishing time and low consumption volume. Researchers at Stanford University in the USA developed a preventative gel that can be applied to ignition-prone areas and maintains its fire prevention properties through peak fire season. “This has the potential to make wildland firefighting much more proactive, rather than reactive,” said Eric Appel, senior author on the study and an Associate Professor of materials science and engineering.

The increasing use of satellites to provide reconnaissance information and drones to perform new roles in protecting the wildland firefighters on the ground will open up many opportunities for new ways of managing wildfires

The researchers worked with the California Department of Forestry and Fire Protection (CAL FIRE) to test the gel and Alan Peters, a CAL FIRE division chief, stated: “We don’t have a tool that’s comparable to this. It has the potential to definitely reduce the number of fires.”

There is also the potential provided by firefighting drones, which have the ability to quickly survey vast areas affected by fire, reducing risk to ground crews. Their size and maneuverability mean that they have excellent precision and can access places that aircraft can’t. They could even play a role in putting out fires: a Portuguese drone called SAP has the potential to help control early- or late-stage fires. “The increasing use of satellites to provide reconnaissance information and drones to perform new roles in protecting the wildland firefighters on the ground will open up many opportunities for new ways of managing wildfires,” said Petersen.

The use of drones could also help mitigate the environmental impacts of conventional aircraft, as well as eliminating risk to firefighters and crewmembers. In a 2023 paper, NASA explored the use of Autonomous Biodegradable Self-sacrificing Drones (ABS) which, as the name suggests, ‘self-sacrifice’, releasing fire retardant when they fall. As such, they enable the safe deployment of fire retardants without the danger to firefighters.

Ongoing innovation in aerial firefighting tools mean that suppressants are increasingly environmentally friendly. “Over the past more than 10 years, approved products have reduced ammonia content by 33% compared with formulations approved prior to 2011,” underlined Winn. “Fish toxicity requirements were increased in the 2020 revision of the specification in order to encourage a trend toward less toxic products.”

It can be expected that continued innovation in this area will mean the firefighting products of tomorrow are even more effective and sustainable. Winn confirmed that the Forest Service will continue to develop specifications that will provide more environmentally friendly fire retardants: “For example, over the years and through rigorous testing and review, the Forest Service has worked to reduce the amount of ammonia in qualified retardant to reduce toxicity.”

Petersen pointed out that the future of aerial firefighting is largely dependent on what the governments who manage wildfires decide it will be. “There are many research and development projects funded by our members, private equity and venture capital, but until decisions are made by governments on what they will use, it’s an unfortunate guessing game,” he said.

Reducing the acres burned, especially near the wildland urban interface, will be critical in reducing the amount of ecological and economical damage from the property that does burn

Indeed, as the challenges presented by climate change continue to grow and forest fires become increasingly frequent and severe, firefighting additives will be used more and more, and investment, research and global collaboration between stakeholders in the aerial firefighting community and beyond is vital. The development of eco-friendly fire retardants and foam is crucial for the planet, wildlife and human health, and incumbent for a safe and resilient future. “Aerial firefighting will be a standard in wildfire management and suppression for the foreseeable future. Reducing the acres burned, especially near the wildland urban interface, will be critical in reducing the amount of ecological and economical damage from the property that does burn,” Petersen concluded. “For the foreseeable future, the gold standard for the ecological wellbeing of the earth’s ecosystem is to suppress all unplanned wildland fires as quickly as possible. Aerial firefighting will continue to play a critical role in that effort.”