Types of Retardants

601.0 Understanding the Major Types of Fire Retardants

601.1 Why Different Fire Retardants Exist

No single fire retardant or suppressant is suitable for every wildfire situation. Fire behavior varies dramatically depending on fuel type, weather conditions, terrain, fire intensity, and suppression objectives. As a result, wildfire agencies use several specialized products that have been engineered to perform specific tasks. Some products are designed to create long-lasting fire barriers, while others provide immediate cooling, fuel wetting, or moisture retention to slow fire growth and support firefighting operations.

Understanding the differences between these products helps explain why incident commanders select one retardant over another during wildfire suppression. Each formulation offers unique advantages and limitations, making product selection an important part of developing an effective suppression strategy.

• Specialized Formulations: Fire retardants, foams, gels, and water enhancers are designed for different fire conditions, operational objectives, and methods of application.

• Different Methods of Fire Control: Some products chemically inhibit combustion, while others cool fuels, increase water retention, improve surface coverage, or reduce surface tension to slow fire spread.

• Operational Flexibility: Fire managers select suppression products based on fire behavior, available aircraft and equipment, fuel conditions, weather forecasts, environmental considerations, and overall incident objectives.

601.2 The Two Primary Categories

Wildfire suppression products are generally classified into two broad categories: Long-Term Fire Retardants and Short-Term Fire Suppressants. Long-term retardants remain effective after the water carrier has evaporated because their active chemical ingredients continue inhibiting combustion. In contrast, short-term suppressants rely primarily on water, cooling, moisture retention, and improved fuel coverage to reduce fire intensity for shorter periods.

• Long-Term Retardants: Typically phosphate-based formulations that remain on vegetation and continue helping prevent ignition after drying.

• Short-Term Suppressants: Include firefighting foams, gels, and water enhancers that provide rapid suppression through cooling and improved water performance.

601.3 Choosing the Right Product for the Job

Selecting the most effective suppression product requires balancing multiple operational factors rather than relying on a single solution. Firefighters and incident commanders evaluate fuel characteristics, expected fire behavior, weather conditions, accessibility, available suppression resources, and environmental constraints before determining which product will provide the greatest operational benefit. In many incidents, multiple suppression products may be used together as conditions evolve throughout the firefighting operation.

• Fuel and Fire Behavior: Grass fires, brush fires, timber fires, and wildland-urban interface incidents may each require different suppression strategies and product types.

• Application Method: Products may be delivered by large airtankers, helicopters, ground engines, portable pumps, or hand crews depending on the tactical situation.

• Integrated Fire Management: Fire retardants are most effective when combined with firelines, burnout operations, water application, heavy equipment, and coordinated ground and aerial suppression efforts.

602.0 Long-Term Fire Retardants

602.1 What Are Long-Term Fire Retardants?

Long-term fire retardants are specialized chemical formulations designed to reduce the flammability of vegetation and slow the spread of wildfires. Unlike water alone, which provides only temporary cooling, long-term retardants continue protecting treated fuels even after the water carrier has evaporated. Their active ingredients chemically interfere with the combustion process, allowing retardant lines to remain effective for hours or even days under suitable environmental conditions.

These products are most commonly delivered by large fixed-wing airtankers and helicopters during initial attack and extended wildfire operations. By creating continuous retardant lines ahead of advancing flames, firefighters gain valuable time to establish containment lines, conduct burnout operations, and protect threatened communities and critical infrastructure.

602.2 How Long-Term Retardants Prevent Combustion

Most modern long-term fire retardants contain ammonium phosphate or related compounds that alter the way vegetation burns. When exposed to heat, these chemicals encourage plant materials to form a stable layer of carbon-rich char rather than releasing highly flammable gases. This process reduces flame intensity, slows fire spread, and makes treated fuels more resistant to ignition. Because the chemical remains on the vegetation after the water evaporates, its protective effect can continue until it is removed by rainfall, weathering, or mechanical disturbance.

• Chemical Fire Inhibition: Active phosphate compounds promote char formation while reducing the production of combustible gases that sustain wildfire combustion.

• Persistent Protection: Unlike water-based suppression alone, long-term retardants continue providing fire resistance after drying, making them highly effective for building defensive firelines.

602.3 Common Applications and Operational Advantages

Long-term fire retardants are used primarily to slow wildfire progression rather than extinguish active flames directly. Airtankers frequently apply retardant ahead of advancing fire fronts, around communities within the Wildland-Urban Interface (WUI), and along natural or constructed control lines where firefighters intend to stop fire spread. Their ability to remain effective after drying makes them particularly valuable during fast-moving wildfires where ground crews require additional time to strengthen containment efforts.

• Building Containment Lines: Retardant lines reinforce natural barriers and constructed firelines, helping firefighters establish and maintain control of wildfire perimeters.

• Supporting Ground Crews: By reducing fire intensity before firefighters arrive, long-term retardants improve operational safety and increase the effectiveness of hand crews, engines, bulldozers, and burnout operations.

603.0 Short-Term Fire Suppressants

603.1 What Are Short-Term Fire Suppressants?

Short-term fire suppressants are products designed to reduce fire intensity immediately through cooling, wetting, and moisture retention rather than long-lasting chemical inhibition. Unlike long-term fire retardants, these products lose their effectiveness once the water component evaporates. They are commonly used during direct firefighting operations where rapid suppression is needed to knock down flames, cool burning fuels, or protect structures and firefighters working close to the fire’s edge.

Short-term suppressants include firefighting foams, fire suppression gels, and water enhancers. Although each product functions differently, they all improve the effectiveness of water by increasing its ability to adhere to fuels, penetrate vegetation, or remain in place longer than water alone.

• Immediate Fire Suppression: Short-term suppressants provide rapid cooling and fuel wetting to quickly reduce flame intensity during active firefighting operations.

  • Water-Based Performance: Their effectiveness depends on retaining moisture within vegetation and combustible materials.

  • Temporary Protection: Once the water evaporates, these products no longer provide significant fire suppression benefits.

• Multiple Product Types: Firefighting foams, gels, and water enhancers each offer unique performance characteristics for different wildfire conditions.

  • Operational Flexibility: Agencies select products based on fire behavior, available equipment, fuel conditions, and tactical objectives.

  • Wide Compatibility: Most short-term suppressants can be delivered using engines, helicopters, portable pumps, or structural firefighting equipment.

603.2 How Short-Term Suppressants Control Fire

Rather than chemically preventing combustion, short-term suppressants improve the physical performance of water. Many reduce water’s surface tension, allowing it to spread more evenly across vegetation and penetrate deeper into fuels. Others increase water retention, helping treated materials remain wet for longer periods despite high temperatures and low humidity. These characteristics improve cooling efficiency while reducing the amount of water required to achieve effective suppression.

• Improved Water Coverage: Enhanced wetting allows water to coat vegetation more uniformly and reach combustible materials that untreated water may miss.

• Extended Moisture Retention: Some formulations slow evaporation, allowing fuels to remain cooler and less likely to ignite during suppression operations.

603.3 Common Applications and Operational Advantages

Short-term suppressants are widely used during initial attack, structure protection, mop-up operations, and direct suppression of active fire fronts. Because they work immediately, they are especially valuable where firefighters need rapid results or where continuous water application is practical. They are also frequently used by helicopters performing bucket operations and by ground crews working in the Wildland-Urban Interface (WUI) to protect homes and critical infrastructure.

• Rapid Initial Attack: Immediate cooling and flame knockdown help firefighters contain small fires before they grow into larger incidents.

• Versatile Operations: Short-term suppressants support direct attack, hotspot extinguishment, structure defense, and mop-up activities across a wide range of wildfire environments.