A long-lasting gel-like fluid developed by Stanford University researchers could keep wildfires from starting and spreading when it's combined with a common fire retardant. The substance extends the retardant's ability to extinguish fire, researchers said.
The treatment contains nontoxic substances widely used in food, drug, cosmetic and agricultural products, according to the team headed by Eric Appel, an assistant professor of materials science and engineering at Stanford's School of Engineering. The study was published in September in the Proceedings of the National Academy of Sciences.
The finding is significant because retardant treatments are currently used after fires have started and are ineffective as a protection on grasses and shrubs, the authors said.
The combined gel and retardant could profoundly impact the peak fire season, they said. The substances can protect treated areas against fire for months, even after rain falls, and are easy to manufacture and inexpensive to produce, the researchers wrote.
The new fluid is made of biopolymers, silica and cellulose derivatives and can be used with polyphosphate fire retardants. The combined substances resist degradation due to the weather and environmental factors.
The need for such fire-prevention technologies is growing. Humans cause 85% of fires in the United States, accounting for 44% of the area burned, and have tripled the length of the fire season, according to a 2017 study published in the Proceedings, the authors noted.
This is especially true in California. Many wildfires begin in "high risk" locations such as roadsides and power lines, the latter having ignited some of the state's biggest conflagrations in recent years, they noted.
"California exhibits one of the most severe wildfires seasons worldwide and has the highest population living in the wildland-urban interface, where wildfires pose the greatest threat to human life. Approximately 84% of the 300,624 wildfires occurring in California over the past 10 years were initiated at these high-risk areas," the authors said.
Applying the new substances along roadsides and power lines could keep fires from starting in these areas. To test their theory, the researchers sprayed two vegetation types most responsible for igniting and carrying fire: dry grass and chamise shrubs.
For the grass, they tested both unmowed, standing grass and mowed grass, the latter commonly thought of as less likely to spread fire. Spraying mowed grass with the new substances lightly -- at what's known as a standard coverage level for fire retardation -- immediately stopped fire ignition in the researchers' test plots. In contrast, in untreated plots, more than 90% of the grass burned within one minute.
• VIDEO: See mowed grass burning
When the treated mowed grass was "weathered" with 0.5 inches of rain, the light level of coverage by the substances was not effective. A medium coverage level didn't completely stop fires from starting, but it dramatically decreased the rate at which fire ignited. The researchers boosted the coverage level again and found it prevented fire ignition, even after weathering.
• VIDEO: See mowed grass burning only momentarily after its been treated with the gel/retardant
The researchers also established coverage levels that were effective in preventing standing, unmowed grass from igniting after weathering, the researchers said.
They also tested the substances on chamise, a common California dense shrubland notorious for carrying fire. Untreated piles of chamise rapidly ignited after about two minutes; a light treatment of the piles delayed ignition and slowed flame growth until nearly seven minutes elapsed, a nearly four-fold decrease in the rate of spread, which could buy firefighters time to control a wildland fire.
The impact of the fire retardants on the chamise occurred during the burns' early phases. Once the fires reached their peak, however, the heat released overcame the effects of the retardants and the piles proceeded to burn normally, resulting in similar flame sizes and average temperatures regardless of coverage level, they noted.
The study and accompanying videos can be viewed at pnas.org/content/116/42/20820.