This is a video of the Civil Guard of Belém, Brazil doing some 12-gauge shotgun training at an indoor firing range with incendiary ammo. Personally, even I would have thought that was a bad idea, and I'm the undisputed king of thinking bad ideas are actually good ideas. Suck it, Florida Man. Some more info:
The incident happened in Belém, Brazil during training of the Civil Guard with 12-guage shotguns firing incendiary-effect type ammunition. The fire started on the left under the floor.
This may be a result of unburnt powder and dust on the range igniting.
Clean your range!!! Also, the range design is important.
Thankfully, nobody was injured in the incident despite that looking like a pretty serious blast. Maybe not the most serious blast I've ever seen, but I did just mention I'm the king of thinking bad ideas are actually good ideas. "Are you referencing the time you shot mortar fireworks up the chimney with the flue closed?" No, but that was also a doozie.
Keep going for the whole video, actual fire and explosion begins around 1:20.
Thanks to Greg C, who agrees that, like swinging a shower curtain rod around like a bo staff, some things are best practiced outside.