"Beware" is literally the conjunction of "be aware" and I use it in both senses. This may not be a real issue but is certainly worth some thought.
What one is worried about is a dust fire/explosion. As we all know, gunpowder in a pile or cartridge burns, it doesn't explode.
Gunpowder as an aerosol (fine particles suspended in air) can explode if the density of the aerosol is high enough. If you've every heard of grain silo explosions, that's what's happening - the dust from filling a silo finds a spark and kaboom. When I was a kid I once put flour in a syringe and squirted it out at a lit match - Woof!
The ignition source can be an arcing/sparking device or static electricity. For a wall switch, you're not likely to have a problem unless a room is full of gunpowder dust or gasoline fumes.
For vacuums, have you ever forgotten to put in a bag / filter or had a bad hose connection and generally made a mess of things? That's a scenario where powder could get into the motor.
Static is the the hidden hazard. The air flowing along a plastic hose will build up a static charge, especially in dry air. Plastic is notoriously hard to ground, so if the hose (which will be full of powder dust in air) builds up a static discharge & then is suddenly grounded (I dunno, maybe by touching a metal reloading press?) you can spark.
We don't use fiberglass tanks much in the oil industry because you have to put a good ground system on the inside because of the static that builds up from filling/emptying.
Sometimes in winter weather you can get out of your car and shock yourself on the outside of your car because it's built up a static charge. That's been a cause of fires at gasoline stations.
If you're aware of the hazards you can take precautions. For example if I dropped some powder on the floor & wanted to dispose of it, I would sweep it up - don't vacuum up a big pile.
Don't keep your fire extinguisher right next to a source of potential fire. For example, don't keep an extinguisher right next to the oven or a deep fat fryer.
Experienced reloaders - if there's something I'm missing please chime in.