Primer mixing plant- Usually these are automated processes. I had the misfortune of investigating a similar incident back in the 1980's. The primer mixing plant was putting out primers that were not meeting specs instead of doing the process by computer. The worker, a young lady, decided it took too long for the computer to adjust the right pressure on the primer mix into the primer case and decided to do it manually. Unfortunately she put too much pressure on the primer and it detonated along with the shot glass size container of primer mix. The explosion blew the roof off of the building (which it was designed to do). By the time I got at the site of the explosion there was still pieces of her rib bones imbedded in the cider block walls. It was not pretty. The plant manufactured 40mm Grenade rounds for Uncle Sam.
--fjruple