Years ago, I was a member of the BRPC here in Seattle. The range was located in the basement of an old downtown building fronting 1st St. & accessed from a back alley on the waterfront side. (needless to say it wasn't the best of neighborhoods) I had a chance to trade my Ruger 10-22 for a MAC-10 (open bolt 9mm) & I wanted to try it out before I made the trade. I loaded a couple of 30 round mags up & proceeded to blast away... half-way thru the first mag, the un-burned powder residue coating the steel deflection plate at the end of the range began burning furiously. Lots of smoke, but the fire didn't blow up like as shown in the video, just sort of sputtering in an ever-widening circle & spewing lots of smoke. I ran down to the end of the range (since I was the only one down there at the time) and shuffled a line around the fire with my foot. The fire burned to the line & went out, leaving me choking on the fumes and wondering why I would ever consider such a trade. I passed on that trade, but my point is that the video blows up way too fast for powder residue IMHO. I would guess some gaseous accelerate like natural gas or propane, or whatever that flooring is made of would be out-gassing. From my perspective as a one-time fire chief who has seen a few chemically-enhanced fires, and personal experience with burning powder residue, dust in the air usually explodes in a more violet manner - you can actually see the flame path following left to right before flaring up into the atmosphere. If you slow the film down or step thru, it appears the fire starting under the flooring as you can see it thru the floor joints just before flaring up. From there it might be feeding on dust or fumes not sufficiently present to ignite spontaneously, but with help from the flames below.
