I know that the survivor doesn’t smoke at all. I think the other smoked occasionally, less than one smoke per day, but knowing how careful he was I can’t imagine that he would have been smoking. But no, I can’t be sure. The deceased was operating a four stage press, the other watching and chatting. No other equipment in use, e.g. bench grinder.
That’s possible. I’m not certain but I think the property owner (the deceased friend) had several four-stage loaders.
The explosion was BIG and was heard up to 15 miles away. I don’t know how much powder would have had to ignite for an explosion that size.
Progressive loaders, if that is the four stage you mention, with primer feeds, especially the tube type, can be hazardous in this regard, as I said above primer "dust" can accumulate or a primer can get cocked in the feed and detonate or both. They have been identified for a while as culprits.
As far as the explosion, smokeless if not contained is just going to burn, real fast, but just burn. If in a container sealed it will cause an explosion, but it is going to have to get hot enough to start it burning first so it would be a secondary thing, and commercial containers are designed to "come apart" before reaching a high pressure.
Black on the other hand as was stated above, has one speed, boom. but if in closed containers protected from flame and spark it would too, have to get hot enough (less hot than smokeless) to go off.
As far as being heard a long ways off, I would think a single 1# can of black could easily manage that, depending on physical and atmospheric conditions. Of course, if it was the primer feed on the press, the first things to go would be the rest of the primers in the feed tube, and the powder reservoir on the press.
Smoking, while hazardous is probably not going to cause an immediate boom (unless dropped in an open container of black) while reloading, but an ensuing fire could. A primer detonating though surely would create an instant boom, even if no more than the rest of the primers went up in the feed device. One primer is loud. Fifty or a hundred would be, well, 50x or 100x louder or more.