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Proc Natl Acad Sci U S A. 2019 Oct 15;116(42):20820-20827. doi: 10.1073/pnas.1907855116. Epub 2019 Sep 30.

Wildfire prevention through prophylactic treatment of high-risk landscapes using viscoelastic retardant fluids.

Author information

Department of Materials Science & Engineering, Stanford University, Stanford, CA 94305.
Department of Civil & Environmental Engineering, Stanford University, Stanford, CA 94305.
Department of Bioengineering, Stanford University, Stanford, CA 94305.
Department of Natural Resource Management & Environmental Sciences, California Polytechnic State University, San Luis Obispo, CA 93407.
Desert Research Institute, Reno, NV 89512.
Department of Chemistry, Stanford University, Stanford, CA 94305.
Stanford Woods Institute for the Environment, Stanford University, Stanford, CA 94305.
Department of Materials Science & Engineering, Stanford University, Stanford, CA 94305;


Polyphosphate fire retardants are a critical tactical resource for fighting fires in the wildland and in the wildland-urban interface. Yet, application of these retardants is limited to emergency suppression strategies because current formulations cannot retain fire retardants on target vegetation for extended periods of time through environmental exposure and weathering. New retardant formulations with persistent retention to target vegetation throughout the peak fire season would enable methodical, prophylactic treatment strategies of landscapes at high risk of wildfires through prolonged prevention of ignition and continual impediment to active flaming fronts. Here we develop a sprayable, environmentally benign viscoelastic fluid comprising biopolymers and colloidal silica to enhance adherence and retention of polyphosphate retardants on common wildfire-prone vegetation. These viscoelastic fluids exhibit appropriate wetting and rheological responses to enable robust retardant adherence to vegetation following spray application. Further, laboratory and pilot-scale burn studies establish that these materials drastically reduce ignition probability before and after simulated weathering events. Overall, these studies demonstrate how these materials actualize opportunities to shift the approach of retardant-based wildfire management from reactive suppression to proactive prevention at the source of ignitions.


hydrogels; polymers; retardant; viscoelastic; wildfire

Conflict of interest statement

Conflict of interest statement: A.C.Y. and E.A.A. are listed as inventors on a patent describing the technology reported in this manuscript.

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