Sorry for your loss. I hope your friend fully recovers.
Powder storage, properly done is really only an issue immediately after an incident when a fire is started. If it is stored properly, away from the loading bench itself in a steel cabinet designed not to hold pressure (so as to forestall an explosion) it will be protected from sparks and will not ignite until a fire reaches it and heats it sufficiently.
You should always only keep what powder you are actually using on the bench at any given time. Remember storing powder in a non-temperature-controlled area (like outdoors in a shed) can lead to its premature degradation and also cause it to spontaneously combust. Heat is the enemy of modern smokeless.
Most accidents of this type are caused by primer dust accumulated in progressive presses or a cocked, misaligned or mishandled primer, exacerbated by excess powder laying around. Entire tubes of primers in a progressive press have been known to detonate like mini pipe bombs.
Loading black powder cartridges with drop tubes not designed for black is also hazardous, as with plastic, static electricity can build up and you could get a spark with steel, so a purpose-built drop tube made from brass is a must
Of course, smoking and or any open flame is an absolute no-no which should go without saying.
Handloading is an exacting and demanding hobby, it is somewhat miraculous that more are not injured, and it is sad that the rest of us need this kind of reminder to remain vigilant.
