As fire crews and air tankers work to block the wildfires' explosive growth, images of red clouds of fire retardant falling onto trees are common. What is it — and what's in it?

Its design pulls in oxygen from the surrounding air when it explodes, giving it a stronger blast wave than conventional weapons that carry an oxygen mixture in their explosive payloads.

"It's basically a mixture of water ... For anyone who's heard of fertilizer being used in explosives: That's ammonium nitrate. Phos-Chek commonly contains two types of salt: diammonium phosphate ...