Fire retardant

Water puts out fire that is already burning. Retardant does something different. It coats the surface and makes it much harder to ignite in the first place, so crews use it to draw lines ahead of a fire.

The best-known product is Phos-Chek, the bright red material you see trailing from aircraft. Testing by University of Southern California researchers for the outlet LAist found heavy metals such as lead and cadmium in samples from recent fires. The manufacturer says the levels are far below federal limits.

Some suppliers now sell gentler formulas. FireDome says its capsules can carry an eco-friendly retardant or simply water.