Smokeless powder can explode, under the right conditions, as will some grain products, it needs to be airborne and have a lot of o2, in the proper or if you will improper mix. I have seen flash fires on 2 instances, one a good friend who was sweeping his garage while smoking, and he reloaded in his garage, the other was at the indoor range, which had recently been swept and all the refuse was piled in the corners, it was my buddies time to shoot and he threw his smoke into the corner, whoosh, just a very big flash fire, but in Australia ( which used to make the best long range .22rf ammo, the WW Powerpoint ) had a powder silo explode, air/fuel ratio complete, it did explode and I cherish 2 bricks of the stuff, only used for matches that have prizes or money involved. The powerpoint is being made again, but the bullet design is not the same. The Australian version was a 42grn, semi wadcutter with 4 driving bands and a healthy charge of powder, best all around 10/22 ammo for the Chevy Challenge I ever used.