Aerial Fire Retardants: It’s Time for a Meaningful Change

Aerial Fire Retardants: It’s Time for a Meaningful Change

A sponsored post by Fortress

Long-term fire retardants have become an essential tool in the fight against wildfires, serving as a primary line of defense against fast moving fires and allowing ground crews to move into position to fortify fire defenses. Despite their importance, long-term retardants have seen very little innovation over the past 60 years. The exact recipe has seen some modifications, but the primary active ingredient from 60 years ago, ammonium phosphate, is still the same chemical that’s used in the vast majority of aerial drops today.

The 1954 Operation Firestop study and the 1970 Blakely study are often credited for establishing ammonium phosphate as the preferred fire retardant. Based on the formulations and standards used over five decades ago, it was shown to outperform its contemporaries on the basis of burn reduction. Until recently, the qualifications of ammonium phosphate were seldom debated and rarely challenged. However, chemical engineering has advanced significantly in the last 50 years. Solutions disregarded by Operation FireStop and Blakely, including magnesium chloride, can now be made exceptionally effective with modern material processing techniques and careful formulation.

Meaningful Change

Fortress is the first commercial long-term fire retardant to move away from ammonium phosphate. We chose magnesium chloride as our primary active ingredient because of its superior fire suppression capabilities, its exceptional durability, its natural abundance all around the world, and because it can be produced on an industrial scale and deployed in the field with minimal environmental impact.

The unique chemistry of magnesium chloride provides a thermally responsive, staged reaction scheme that hydrates fuels, cools the flame front, delays ignition, and disrupts combustion [1,2]. Together, these reactions make for stronger fire lines and superior fire control.

Due to their hygroscopic properties, magnesium chloride based fire retardants have greater rain resistance and remain effective for longer after they’re dropped. Magnesium chloride chemically binds and retains moisture, and has the unique advantage of re-hydrating every evening when humidity exceeds 33%. While magnesium chloride is highly effective when dry, the additional water that is adsorbed from the environment adds to its effectiveness and durability in the field.

Unlike ammonium phosphate, magnesium chloride is not a fertilizer; it does not contribute to invasive vegetation growth or eutrophication [3,4,5]. And to top it off, the magnesium chloride in Fortress products is sourced domestically and processed with natural sun and wind, drastically lowering the carbon footprint of retardant manufacturing [6,7].

Proven Performance

The Forest Service’s product qualification protocol is designed to test and establish confidence in new products, and is required to qualify new fire retardants for aerial use. Tests are either performed directly by the Forest Service at their Missoula Fire Sciences Lab or by third party contractors to eliminate the potential for any biases. Official testing has demonstrated the exceptional performance of Fortress fire retardants. In fact, our magnesium chloride formulations have outperformed their fertilizer-based counterparts on nearly every dimension. Fortress offers best-in-class burn reduction, best-in-class corrosion protection, and best-in-class aquatic toxicity.

Fortress now has four different retardant formulations that are fully qualified or interim qualified by the US Forest Service. Magnesium chloride is here to stay, and we urge industry leaders to seriously consider which chemicals we should be dropping from the skies. It’s time for a meaningful change in the technology that we use to fight wildfires.

Thank you for reading this article. If you would like to learn more about the environmental effects of long-term fire retardants, how Fortress achieved best-in-class corrosion protection, or what makes for an effective fire retardant, you can check out our scientific White Paper series at

[1] Huang, Q., Lu, G., Wang, J. (2011). Thermal decomposition mechanisms of MgCl2·6H2O and MgCl2·H2O. Journal of Analytical and Applied Pyrolysis.

[2] Wu, Y.; Yao, C.; Hu, Y. (2014). Comparative Performance of Three Magnesium Compounds on Thermal Degradation Behavior of Red Gum Wood. Materials.

[3] Besaw, L. M., Thelen, G. C., Sutherland, S. (2011). Disturbance, resource pulses and invasion: Short-term shifts in competitive effects, not growth responses, favour exotic annuals. Journal of Applied Ecology.

[4] Marshall, A., Waller, L., & Lekberg, Y. (2016). Cascading effects of fire retardant on plant-microbe interactions, community composition, and invasion. Ecological Applications.

[5] Angeler, D. G., & Moreno, J. M. (2006). Impact-recovery patterns of water quality in temporary wetlands after fire retardant pollution. Canadian Journal of Fisheries and Aquatic Sciences.

[6] Tripp, T. G. (2009). Production of magnesium from Great Salt Lake, Utah USA. Natural Resources and Environmental Issues.

[7] Jaber D., Climate Positive Consulting. (2022). Verification and issuance of opinion on carbon footprint analysis conducted by Fortress North America LLC, following the guidance of ISO 14064.