Fire Chemicals are just tools in the toolbox when it comes to Aerial Firefighting, but this toolbox seems to be the one that sits in the garage with hardened cans of Bondo and Harbor Freight Tools leftovers in it. Fire Chemicals used in Wildland Fire Aviation provide a specific capability, for a multitude of reasons, but we continually seem to default to “Slurry for Indirect Attack, water for Direct Attack,” lather, rinse, and repeat. Especially as the lines continue to blur between the Wildland Urban Interface (WUI) and we seek to be more aggressive in Initial Attack, why not “stack all the tactical cards in our favor?” This paper seeks to inform, reorient, and spur discussion at all levels around Wildland Suppression activities and using more than just Retardants and water.
Fire Chemicals for Wildland are broken into two major categories: Long Term Retardants (LTR) and Suppressants. Retardants, or “the red stuff” are intended for Indirect Attacks, and they actually modify fuels they touch chemically, reducing the fire’s ability to generate heat. LTRs, as the name implies, are intended to continue to retard the fire growth after the water mixed in the LTR has evaporated.
Suppressants are different and meant for a different tactic. Suppressant materials are added to water to change the properties of the water itself, or “enhance” it for a specific use. The key difference is that Suppressants are dependent on the water they use and unlike all Retardants, when the water is evaporated, so is the Suppressant. Suppressants are intended for specific missions such as Direct Attack operations or structure protection and are capable of fuel penetration (foams) or coating (gels or air induced foams) depending on the need.
Suppressants are categorized on the Forest Service’s Qualified Products List (QPL) by their intent: Class A Foams and Water Enhancers. Foams are intended to reduce the surface tension of water and allow water to penetrate fuels. Foams are hard to deliver by air because of its properties, so most of the effectiveness of the water modified by the foam is lost in the drop. Water Enhancers keep the surface tension of the water molecules intact, and have polymers or other “thickeners” in them that, from an Aerial Firefighting perspective, help “hold” the water together through heat and wind and hopefully deliver it in a more effective payload directly on fire. Water Enhancers work to modify behavior or extinguish the fire by absorbing the energy being released (heat). It does this by thickening the water into a film (of various viscosity) and “sticks” to fuels in a form that is slower than water to evaporate. Although not a retardant, which chemically alters the fuel when heat is applied, water enhancers can hold fire like a retardant, though for a much shorter period of time; usually around 30-45 minutes. The water evaporates as heat energy is absorbed and the and the enhancer loses effectiveness, which is why it shouldn’t be compared or used as LTR.
