B.S.
Unburnt powder from tens of thousands of rounds and hundreds of shooters collects in astroturf. Enough that something hot touches and lights it off.
Range needs to wash down their filthy range with water once in awhile and lift the idiotic ban, but good luck explaining to the FUDDs that poor maintenance caused it.
Ours was washed down every sunday morning. But 14-20 of unburnt AR powder cases, years of buildup in the sound baffling on the wall equals poof. Unburnt powder got caught up in the sound baffling as well over 12 years. Just like in the astroturf did.