(Image Credits: Cal Fire)

California is weathering the worst fire season many of us have seen out here and responders are still inundated with heavy work. One question I keep seeing, besides “remember Volcano?”, is “why are the firefighting planes dropping red water?” Well, there is a reason. And that’s not just water.

The simple answer is: that red liquid is a fire-retardant chemical that’s color dyed so that it’s easy to see from the ground and from the air. That helps firefighters see where it’s going, and makes it easier to see where it’s been dumped already.

Water is an excellent firefighting tool as it is abundantly available, relatively inexpensive and generally effective at cooling fires and rendering fire fuel non-flammable. But when a conflagration spreads to an area as large as the tracts of scrubland currently ablaze in Southern California, you need a harder-hitting delivery system than a hose and you want to mitigate future burning as much as suppress the flames that are already raging.

That’s why Cal Fire has a sizable fleet of aircraft capable of carrying and dropping fire retardant over a big area at high speed.

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Seriously, check out Cal Fire’s plane brochure. The agency has everything from Cobra attack helicopters for watching and reporting on incidents to 747 jets for dumping up to 24,000 gallons of the fire-dousing cocktail you may be wondering about.

As Cal Fire’s own literature explains, that red stuff you’ve seen spraying from the bellies of planes and onto burning forests is “a slurry mix consisting of a chemical salt compound, water, clay or a gum- thickening agent, and a coloring agent.”

More specifically, that juice is called Phos-Chek or Fire-Trol. And while there are many variants of it optimized for different situations, the stuff is largely a better fire-mitigator than water because it lingers. A firefighting outfit like Cal Fire might dump a strip of the stuff at the edge of a fire, and it would coat unburned “fuel” like trees and houses to render them, ideally, non-flammable. Whereas water would just evaporate.

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These chemicals are of course just one tool in a wildland firefighter’s arsenal. But in serious cases like California’s current fires, the red “slurry” can be instrumental in containing major burns.