I mixed up a five lb. bag of saltpeter and sugar and was burning small piles of it in the backyard. The bag was sitting too close and a spark jumped and ignited the whole thing into a mini Mt. Vesuvius.
I had the same result with a newly-mixed batch of black powder. Hadn’t ground the charcoal well enough, and a spark jumped from the test pile to the batch pile. Did it in the feed room of our chicken house; I exited quickly through the window...