Blasting powder

Frequently used for mining and other responsible things... until adventurers get their hands on it.
  A fine grey powder with large grains and the faint smell of sulfur and charcoal that comes in small packets weighing 1/2 pound. When ignited by 1 or more fire or lightning damage, it explodes violently. All creatures within 10 feet of it must make a DC 14 Dexterity saving throw. On failure, they take 1d4 fire + 1d4 thunder damage, or half as much on a success.   The amount of damage increases by 1d4 (both the fire and thunder) and the radius increases by 5 feet for each additional packet of Blasting Powder detonated in the same spot, up to a maximum of five packets.   Deals double damage to buildings and structures. Creatures in range of more than one stack of upto 5 explosives at the same time take damage only from the highest damage effect.