we have dry conditions here and i have set it off in a dry lake bed, 20#s at a time, strapped to a old water heater, 99% of the time it shouldn't start a fire because the rate of burn and expansion is such that the ball of fire blows it's self out. (meaning that its so fast that it doesn't have the heat to finish the three legged stool for fire.. Fuel, air, heat)
But 20# in a ammo can will break down an old water heater like a champ.. There is little left, and decient crator.