This is probably worth following:

Idaho lawmaker's wife hurt in gun room explosion
Associated Press
Sep. 30 4:48 PM EDT
http://bigstory.ap.org/article/idaho-lawmakers-wife-hurt-gun-room-explosion

BURLEY, Idaho (AP) — Fire officials say the wife of an Idaho lawmaker was injured when a room that they had converted into a gun safe exploded.

The Times-News (http://bit.ly/SdMY0q ) reports that Amy Wood, the wife of state Rep. Fred Wood, was taken by air ambulance to a Utah hospital with second-degree burns on her face and hands after the explosion Saturday night in southern Idaho.

Idaho House Assistant Majority Leader Scott Bedke said Fred Wood, R-Burley, received minor injuries.

Burley Fire Chief Keith Martin said the couple was eating dinner when the explosion occurred. Amy Wood was on the back patio — which is directly over the gun room — and the blast apparently caused the slab to collapse into the room below.

The cause of the explosion is not yet known.

WoW

Did he store primers & reloading powder next to each other

Do primers and powder just go off when stirred next to each other?

propellent ignited by an exploding flashlight battery?
 

This is why you never store explosives in any hardened structure (safes included).  

Tell that to people who have proper powder/explosive magazines.

Say what?????

Explosives should be stored in a container designed to vent itself.  Safes and vaults are usually not designed to do that.

Not true.  It varies a little by class of explosive but for the most part explosives are required by law to be stored in hardened, lockable magazines.

Yes, I am licensed in the proper storage and use of explosives.

Yes.  Hardened, lockable magazines (and here's the important part) designed for explosive storage.

Bank vaults, gun safes, and under patio gun rooms do not fit this description.  You should not store explosives in anything not designed to store explosives.  When you do, you run the risk of blowing your wife through the roof over the patio, which is exactly what happened in this story.

Since you deal with explosives, you're well aware of what happens when an explosion takes place, and there are no measures in place to control it.  For those not familiar, they should pay close attention to this story.  Even a gun safe could be turned into a bomb by storing too much powder inside of it.

Yes, I am fully aware of what happens when explosives detonate.  

The ironic part is that magazines “designed” to store or transport explosives can be their own “bombs” if contained within a fire.  The only thing that they are “designed” to do is prevent theft and sparking.  Small stationary or transportable magazines are to be hardened (metal), watertight and lockable.  They don’t “vent” anything (well, until the top, bottom or sides blow off).  Toss one of these in a fire and you have a bomb.  The force of the blast might not be exactly to the level of a safe blowing up but I’d not want to be anywhere near it neither.

A permanent magazine (i.e. storage unit dedicated for explosives) is hardened even more (concrete, timbers, earthen bunker).  If one of those things goes off it would make the OP's story pale by comparison.

The regs approach the problem of a magazine detonating by preventing it in the first place.  Metal magazines must be lined with a non-sparking material along with a host of other procedures that must be followed.

So what are the procedures if my storage unit catches on fire?  I am to remove all personnel from the area and intercept the fire department to advise them of the exact location of the magazine.  If it is determined that they can fight the fire “safely” then they proceed.  However, if the fire is in the vicinity of the magazine we all vacate the area and watch the show.  

This is why we cannot store explosives in a structure used as a dwelling.

The sentence above is key.  We KNOW that magazines holding explosives are going to blow if they become involved in a fire.  In the event of a fire, we deal with that by removing the threat to human life as much as possible.

I also have a walk-in gun vault that holds both firearms and ammunition.  If our house ever catches on fire we will be quite a distance away sadly watching it burn.

Yup and smokeless powder is NOT an explosive, it is classified as a flamable solid according to the DOT.  I am sure it could be figured as to how much powder would have to be stored in a gun safe to contain/build pressuers high enough to 'explode.'  But I am fairly certain that you would need a decent percentage of the safe to be powder.  What powder desity rates are common amongst our reloading?  Would even 25# of powder be enough to make a room 'explode?'

I would look more towards a gas (natural/LP) leak as to the cause of this event.

So how should one store their powders and ammo at home to avoid such bomb like events from occurring in the case of a fire?

This please....


I put them in ammo cans and those are All locked in a metal gun cabinet. Not the safe/ fire proof type, just the cheap sheat metal lockable gun cabinet.

I don't think this was meant to be funny...but I spit coffee all over the place when I read this.

Ahem...

Actually the wooden or cardboard boxes that ammo is shipped from the factory in are about the best.  If these are involved in a fire the container itself does little to contain the expansion of gasses thereby lessening the force of the power generated.  All bets are off when it comes to black powder but even that is shipped in similar containers that will lessen the force of the blast.

It’d be interesting to see a test of ammo storage in a fire resistant gun safe involved in a fire.  I can’t remember at what temps ammo cooks off (surely it varies with caliber) but I wouldn’t be surprised to see it survive in an “average” fire if stored in a safe designed to insulate heat.

All of that being written, I have ammo stored in my fireproof (I hope it is anyway) walk-in vault with overflow simply stored in factory cartons or ammo cans on shelves in the general area of the basement.  Powder is stored in their factory jugs in wooden cabinets.  The only thing that I would be a bit worried about “blowing” would be the ammo cans . . . but I wouldn’t expect the blast to be significant.  Even so, in the event of a fire I would be directing firefighters to avoid placing themselves in that general area.

Gas leak perhaps? Unless there were real explosives stored in that gun room, a gas leak that filled the space with a sufficient gas/air mix before ignition is the only thing I can think of that could produce the force to destroy a concrete slab ceiling.

It's well known and tested that ammunition not in a chamber presents little hazard in a fire. Yes, they pop and toss a bit of shrapnel around, but that shrapnel is at BB level velocities and shown to be unable to penetrate standard fire dept turnout gear. Bottles of smokeless powder will also pop, but since it's a propellent, not an explosive and the bottles offer minimal containment it again isn't a real explosion.