New gel could fireproof forests

A spray-on sticky gel might soon provide long-term protection against wildfires, researchers suggest. 

In a paper published in the journal PNAS, scientists led by Anthony C. Yu of Stanford University in the US report the prototype and lab-level deployment of what they term an “environmentally benign cellulose-based viscoelastic fluid” that can effectively fireproof large areas of vegetation throughout the peak fire season.

The gel is used as a carrier for ammonium polyphosphate (APP), the most common fire retardant used against forest blazes in the US.

In its current formulation, AAP is delivered encased in a fluid designed to form a wet and viscous barrier on plants. The medium is usually derived from guar gum or clay particles, which quickly deteriorate when exposed wind or rain.

For this reason, about 380 million litres of APP are dumped on vegetation in California alone every year, but only in the path of fires already well and truly alight. Its retardant properties work just for a day or two, making it unsuitable for use in planned prevention strategies. 

190930 fire gel

The researchers performed test burns on a grassy roadside area near San Luis Obispo, California, to gauge the effect of a fire-retarding hydrogel. The images above show untreated (left) and treated (right) plots shortly after fire ignition.

Eric Appel

The new carrying medium devised by Yu and colleagues, experimentally at least, overcomes this problem and fireproofs plants for up to a month – arguably long enough to prevent it bursting into flame across the highest risk weeks of a fire season.

The key, the researchers write, is a gel constructed from cellulose derivatives, including hydroxyethylcellulose and methylcellulose, with microscopic particles of silica bonded to its surface.

“Manufacturing of these materials is straightforward and inexpensive at large scales as they contain solely nontoxic starting materials widely used in food, drug, cosmetic, and agricultural formulations,” the researchers write.

Tests in the laboratory and on three-metre-square test plots – filled with grass at various lengths and densities – returned some impressive results. Where untreated grass plots burned almost completely inside 60 seconds, those treated with the gel did not burn at all.

Significant fire protection remained even after a simulated 12 millimetres of rain.

Yu and colleagues report that in laboratory scale tests the gel proved to be environmentally benign, leaving plant respiration and microbial activity unchanged. 

The gels degraded completely over about 30 days – long enough to provide protection against ignition during the danger period.

The next task for the researchers is to seek ways to scale up to commercial production levels and test the effectiveness of the gel on a wider range of wild environments.

However, there will never be a need for blanket spaying across forests, the researchers note. In California, at least, about 70% of wildfires break out near known ignition hazards, such as roads. Concentrating exposure only on such types of high-risk areas will thus drop fire outbreak probability by a very large amount.

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