PLACERVILLE, Calif. (KTXL) — Firefighting helicopters are now working from early morning to midnight on the Caldor Fire, filling up with retardant from a mobile base along Pleasant Valley Road in Placerville.

The term Phos-Chek 259-Fx may mean nothing to the average person, but to the firefighters trying to keep California from burning, it is a major weapon against the stubborn flames.

Phos-Chek is the brand name of the red retardant used by both Cal Fire and the U.S. Forest Service.

“You’re coating the vegetation with the Phos-Chek product. And it helps to render that non-flammable,” said Wes Bolsen, the director of wildfire prevention and protection for Perimeter Solutions, the company that makes Phos-Chek. “From being called, we can be set up in about six hours.”

All throughout Wednesday afternoon, three firefighting helicopters were dropping in, filling up and heading out to the western flanks of the Caldor Fire, working to protect communities like Somerset and Pollock Pines.

“About every 90 seconds there’s a helicopter coming in,” Bolsen said. “These guys are keeping up with that and working super hard.”

“A huge effort between Cal Fire, the United States Forest Service,” Bolsen continued.

And a welcome sight to evacuees like Rachel Heath, who pulled over with her children to watch.

“I think these guys are amazing; they’re doing a great job. They’re up against the dry and the weather,” Heath said.

Phos-Chek is delivered to the base in one-ton sacks of red powder and then piped into a tank where the powder is mixed with water from a hydrant.

“We mix one gallon of water to every one pound. So that’ll make about 2,100 gallons. Each of those sacks will make 2,100 gallons,” Bolsen said. “Takes them about 60 to 90 seconds to fill up and get back in the air.”

The liquid mix is then piped constantly into the 5,000-gallon dip tank the helicopters draw from.

They may look small from a distance, but the nozzles beneath these helicopters are about a foot in diameter, and every time they dip into the tank they’re able to draw up 1,000 gallons of retardant for the front lines of the Caldor Fire.

At the current pace, Bolsen says they can drop more than 100,000 thousand gallons of retardant from this base by the end of the day.

“So, really what we’re trying to do is give the heroes at Cal Fire some time to make additional fire breaks to help flank a fire and help save a community,” Bolsen said.

Phosphate is the fire-suppressing ingredient in Phos-Chek. According to Perimeter Solutions, it meets environmental safety standards for people, pets, water and fish.

As for why fires sometimes spread beyond the retardant lines, Bolsen says that’s often because the wind carries embers ahead of those lines.