At some point will you be doing a 'How to get everyone there' post, something along the lines of CASMEET, or the mnemonic I was supposed to use and have since forgotten since I stopped working in emergency medicine?

(It 's been along time since I was SILVER MEDIC, or more often, BRONZE PARKING)

You don't need to know that the explosion is about to happen: you need to see it.

The visuals will get to you at the speed of light (as will the radiant heat). Fortunately, that heat usually produces only superficial injuries. You want to get to the ground (preferably with your feet or head oriented directly toward the blast to minimize your exposed surface area) before the pressure wave gets to you. That pressure wave is traveling at supersonic speed, but still significantly slower than light. The pressure wave will arrive before the sound. Stay on the ground until after any projectiles (subsonic) and the blast wind (subsonic) pass over you. Note the time difference between the sight of the explosion and the arrival of the pressure wave here.

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A pipe | is an "or" switch for the things inside the parentheses. Thus (XXX|YYY) will match either XXX or YYY. The character group period-question mark .? is a wildcard which matches anything or nothing. The reason all spaces have a wildcard associated is to catch those spams which add extra spaces between words to defeat filters like this. (Any group of three or more spaces in a row is trapped by a different filter.) A forward slash / means "everything between these marks is part of this filter." The i switch at the end means that both upper and lower case letters will match, to trap those spams which attempt to evade filters by use of random capitalization.

The three spams that arrived (and were trapped by the Gnomes) during the time I was composing the above reply were, in full:

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All three of these spams appear, verbatim, in thousands of other blogs all over the 'net. They are very common patterns.

Typing as a chemist (albeit with a varied work history and no special study made of things that go bang), I still like your general presentation on the matter of explosives and what they do.

The thing that gets you is the velocity with which the compression/decompression of your bodily tissues happens.

And since tires were mentioned, I've had to transport a gentleman who was injured when a truck tire he was inflating exploded. This would have been a mechanical explosion. A pressure wave is a pressure wave.

If you know there's about to be an explosion, drop. The difference between sight and sound getting to you will mostly be small for values where dropping makes a difference. You might look silly if you drop too quickly; and you might look seriously damaged if you drop too slowly. Don't wait. Drop. You get to laugh if you were wrong, and be really grateful if you were right.

Jim, that's a nitpick on my part. Your posts of this sort are totally awesome, and an amazing community service. I look forward to seeing each one, read it carefully, and stick the bits of it in my backbrain for when I find myself in a difficult situation. You rock, dude.

Dropping flat minimises your exposed cross-section. One source of blast projectiles is the material excavated when a crater is formed, and a lot of that will be going slightly upwards. Gravity will bring it down again, but air-drag will also be slowing it.

The "pineapple" grenade, typified by the British Mills bomb, broke up into a few large fragments, which could travel a long way: the ribbed or grooved casings are there to make it a bit easier to hold reliably with muddy hands, not to produce smaller fragments. The German stick grenades had a lightweight casing and relied more on blast. Modern grenades try to produce a lot of fragments, big enough to injure, which don't travel too far.

Everyone calls the fragments "shrapnel", which was something quite different a hundred years ago. Words change their meanings sometimes.

My Grandfather was telling a bunch of raw replacements not to worry about the shells when a blast projectile hit him. He was lucky, and supremely unlucky to be injured at all.

With all that in mind, duck and cover is a good idea. You can be far enough to have the time, and near enough to be shredded by that window glass you are looking through.

As for later explosions, if you can smell gas, things are shortly going to be bad. I'm not talking WW1 here, I'm talking not becoming a casualty.

If you know there's about to be an explosion, drop.

Well, of course if you know there's going to be an explosion, drop. (Assuming that you don't have time to put yourself a couple of miles away.) But you don't need to know that there's going to be an explosion. Many explosions are entirely unexpected.

Too close and you won't have reaction time between the flash and the shock wave.

If the shock wave is faster than the speed of sound, I would think that anything much under half a mile is too close -- especially if it's *entirely* unexpected and not something you were already watching, like a fire that suddenly triggers an explosion (as in the linked video from #7).

But maybe I'm underestimating reflexes.

On the other hand, projectiles and the blast wind are slower, so you'd have more time to take cover from them.

Speaking of cover, how useful is it? What kinds of objects make you safer when sheltering behind them vs. objects that become an additional danger? (Glass is the latter, obviously, but aside from that.) Will pressure waves be blocked or weakened by solid objects?

@18: You never know. There could be military personnel (of any of several nations) on active duty reading this site in their free time. (Although, if they're in any sort of armed forces, I hope they would've received equivalent information already as part of their training.)

Cover will mostly help with projectiles. Glass won't help -- glass will become a projectile itself with the shock (see the Chelyabinsk meteor earlier this year, with around fifteen-hundred people injured, mostly by flying or falling glass) -- but pretty much anything else solid will help. Solid masonry walls, trees, that sort of thing should be good. If you have the time to dig a foxhole....

I would've thought it'd be obvious that you shouldn't store millions of pounds of rocket fuel oxidizer on top of a gas pipeline, but there you go.

Shock waves are tricky beasts. They will pass through most anything, but rapid transitions in density can do strange things to their directions.

You can get (small) shadows behind fairly solid objects, with the wavefront wrapping around corners. You can also get serious amplification during the same circumstances.

Personally, I would avoid hiding behind a building, but have less hesitation about dropping into a trench. Instinctively, it feels like the trench won't make it worse (no second path for compounded pressure). I don't know how well-informed this is (although I have had some training in handling (some) HE compounds, under a variety of conditions).

As a general comment, feeling a supersonic pressure wave go through your body is a very strange sensation.

It's more about protection from blast projectiles, I reckon. And a lot of stuff might be knocked over by the blast. You don't have time to think, but I suppose it might be a little like the effect of a hurricane on structures.

I've read enough eyewitness accounts in military history to color my judgment, and I'd be thinking of cover that would stop bullets. Ordinary brick walls, the commonplace of UK housing, aren't quite enough.

(As for repeated explosions there's the fire in Florida, at a plant where they refill portable propane cylinders. A big fire, repeated explosions. The danger isn't directly the explosions, the fire keeps people back, it's the heavy metal containers going off like rockets. When the fire started, the plant workers took the right steps: big and fast.)

Also a great lesson in disaster response.

Wikipedia (yes, I know, but it is at least an overview) suggests a look at the Black Tom and Texas City; as well as Port Chicago (not in Illinois)* and the 1944 Bombay Harbor explosion**. I do not think it is possible to be too careful with explosives. You'll note that the amount of damage and loss of life is directly connected to what's near the site of the explosion, which is why three of those five were godawful disasters, one was terrible, and one was just a big messy one.

Nowadays, ports are pretty picky about when and where and how explosives are handed.

*See also the Port Chicago Mutiny. 15% of all African-American military casusalities (killed and wounded) occurred as a result of this explosion.

**Fires in cotton bales are very hard to put out, unless you can open the bale and scatter it, which has its own drawbacks, as loose cotton blows around and will spread the fire. Fires in bales of cotton which have had any oppostunity to take on oils or grease are hopeless--500 pounds of burning, smoking fun just looking for a way to make your day worse. Cotton bales which are soaked in water are also amusing, in a different way. Press-sized rolls of newsprint soaked in water have their own entertainment value. (My landlord used to work on an L&N/CSX railroad wrecker crew. He has stories.)

'Minds me of the time I was sitting in my living room, and I heard an odd, rubbery creeeeek. Frowned. Heard it again. Got up...finally traced it to my front door. No, wait, it's my bicycle, which is sitting by my front door. Huh. Oh, seems to be coming from my back wheel. What the—

>>>BANG!!<<<

Once I got my brain started again, I worked out that I had apparently over-filled my high-pressure tires (110 psi, nominal) and a quarter-sized patch pushed through the (kevlar) tire and then finally blew.

I'm really glad the plug was aimed away from my face.

I'm assuming my old karate reflex of exhaling forcefully in anticipation of a punch would be appropriate, too, no?

That would be this one, in Tavares FL, yes?

As the man said, "Most sane people don't stick around for an event like this."

WESH in Orlando has images and video, here.

Well, it certainly won't hurt. See also Terry's #32, open-mouthed yelling.

I've heard that it helps to lie down (facing the blast), opening your mouth, putting your thumbs in your ears and your fingers over your eyes.

Given that the most common, and the most serious, blast injuries are to the lungs, anything you can do to protect your lungs is probably a good idea.

Doyle #35:

"... hoses designed to spray water on the large tanks in case of fire, did not go off as planned because they had to be manually activated."

Maybe they should rethink that....

Generally, back to the OP: When you're treating blast victims, multiple injuries tend to have multiplicative effects rather than additive effects. Someone with pulmonary injury and penetrating injury, someone with burns and broken bones ... is a hurting cowboy and needs to be carefully evaluated.

As far as blast waves go, I was a several miles away from this grain explosion when it happened:

http://www.inmaricopa.com/Article/2008/12/29/explosions-rock-arizona-grain-3-workers-injured-updated

It's amazing the amount of force something as simple as grain dust can pack. There was a railroad line up the road, and my first thought was that a train had derailed and the train's cargo had gone boom.

Sugar can also be surprisingly explosive.

The open-mouthed yell thing, I've seen it in newsreel footage of heavy artillery firing, and tried to find some examples. There's film on YouTube of the US Navy's 14-inch railroad guns in France, in 1918, and I don't see any sign of it when they fire. Maybe it was an Army thing. No sign of it on the clips of the German Paris Gun firing, but the camera is a good way off.

Those Navy railway guns were, if one newsreel can be believed, fired with the standard movie dynamite exploder. Pictures of various 14-inch guns, battleships and railway guns

Most large guns are fired electrically, since the internal pressure is likely to be too high for a percussion cap to withstand without blowing out (or being forced out and jamming the breech mechanism). Earlier attempts incorporated a steel ball as a 'non-return valve' to solve the problem, but electric ignition makes things much easier.

Yeah... basically, a normal fire is a pile of stuff burning: limited by the surface area, where fuel and oxygen combine. A liquid fuel can increase that surface area rapidly, especially if it gets thrown about -- that's why liquid fires can get out of hand so fast.

But even a pile of dust is going to have way more surface area than it looks like, and it can be scattered easily (especially since combustion produces lots of gasses). Once the fuel is dispersed through a volume of air, the whole surface limitation basically goes away, and stuff can burn as fast as the flame front can move. I think that's technically a deflagration rather than a true explosion, but it still sounds like BOOM!

Even stacking the old square bales outside required some forethought--you needed airspace among them for several reasons. As of this moment in time, this links to the Wikipedia Hay article with a picture of a truckload of hay on fire. One can only imagine the driver's feelings when he noticed the problem.

I know grain elevators have had to install complex ventilation systems to deal with the threat of dust explosions--more of that intrusive government regulation making people's lives harder. I doubt they prevent the problem completely, though. My brother-in-law lost a high school classmate to an elevator explosion--and there's Minneapolis's Great Mill Disaster

Depends on the speed of the reaction front (under the speed of sound, it is a deflagration, over the speed of sound, it is a brisade; if it generates a pressure wave it is an explosion).

All explosions create a low pressure area behind the shockwave, due to the momentum of the air in motion. Think of it as releasing a compressed coil spring.

This is Ingvar's cue to relate the physiological effects of firing the 84mm Carl Gustav anti-tank weapon.

Hopefully this will work -- this should be a google street view of a dairy farm near my old home that had a hay fire.

I lived approximately five miles away and could see the glow in the sky.

They're still using the pole barn that was over the hay, but you can see where the I-beams sagged and twisted. Note the vehicles underneath for scale -- that's a huge structure. The damage is a bit more dramatic when you can see it in person from the road, but it's still obvious it was a VERY hot fire.

Somewhere along hwy 347 between Maricopa and Phoenix, there's also a tractor trailer sized patch of asphalt that had to be resurfaced. A tractor trailer hauling hay changed lanes and sideswiped a motorcycle. The guy on the bike died, and the hay fire that resulted from the wreck burned for hours, closing traffic in both directions.

Hay fires -- definitely not to be underestimated.

(Canning wild blackberry jam is on the agenda for this weekend. I love the end results, but to this day, I still get a bad case of the nerves every time I remove a jar from the water -- even when I let them cool almost down to room temperature first!)

As happens, I've never fired one (nor have I fired the AT4, nor the AT4 CS; but I know a chap who was on the design team for the latter), but my understanding is that you want to have emptied your bowels well before you fire one, unless you want to have an assisted emptying.

Ah, in that case it must have been someone else with the 84mm anecdote, since the other end of the body was involved.

(Basically it's a recoilless rifle, all the propellant has burned before the projectile leaves the end of the barrel, and it acts like an enormous suction pump, lowering the air pressure in the vicinity of the firer. In the tale I remember, the firer had a bad cold and the weapon obligingly cleared his nostrils for him.)

Having successfully Lowered The Tone, I shall now shut up again.

P J Evans #49: Eggs that are put in a pan of water to cook and then forgotten. (The ceiling may never be clean afterward.)

My Mom did that once when I was a kid, and it wasn't. (We eventually put in drop ceilings.) She got more teasing for her rice disasters (much of why I like the rice cooker), but she never managed to make rice explode.

Crazy(Yeah, I know... inhuman, I am! Well, with a little help from the DH, who's suggestion about the recipe was immediately after I read Charlie Stross' post aloud to DH)Soph

Jim Macdonald @51--I'd suspected that was pretty close, by North Country standards. That must heave been an awful call to go out on, especially once the adrenaline faded.

Closer to Jim than to me, and I'm in the same province.

As of yesterday, the search for bodies is over. 42 found, out of 47 missing. 38 have been identified so far. The coroner's office isn't "giving up", they just don't think they'll find any more. It was an incredibly destructive explosion. The sister of one victim, still missing, said it's easy to see "how Marie-France could have been lost in it".

There's concern now over what first responders and long term investigators (and the inhabitants) have been exposed to. I saw a mention of Benzene. Certainly, many are suffering emotional stress.

Investigators are looking into the oil itself now. Apparently, it did not burn the way light crude is expected to burn:

"The train [snip] was carrying light oil from the Bakken oil fields of North Dakota where crude is drilled up from rock through a process known as fracking. Environmental groups and Canadian pipeline operator Enbridge Inc. have complained to U.S. federal regulators about the volatile and potentially unsafe chemical makeup of Bakken crude."

The tanker cars were shipped by CP from North Dakota to Montreal, where they were picked up by MM&A Railway. From what I can see here, that means the stuff went through several densely populated areas, including about 8 km from me.

I haven't been talking about this because I have had no idea what to say. It's too overwhelming. If you believe in the power of prayer/good thoughts, you could take a moment to send some Lac Megantic's way. They really need it.

It's a real heart-breaker.

On a lighter note, my mother's sister was making caramel pie one day, and as was her custom, she did what they tell you not to do -- put the can of condensed milk into a pressure cooker half full of water to boil for several hours. The can exploded, blew the lid off the pressure cooker, and sprayed the kitchen abundantly with caramel.

Given that this was her regular custom, and my mother's as well, and this was the only time it ever happened, I'm inclined to blame a weak point in the seam of the can. Nonetheless, I've never felt the slightest inclination to use that process myself; once is quite enough!

If the can is standing directly on the bottom of the pot, it could become overheated, so I put a small cooling rack in the bottom of the pot so water will circulate under the can(s). I also start with the cans in cold water, and when they've been boiled long enough, turn off the heat and let the pot cool to room temperature before removing the cans from it.

Now, it's possible the liquid inside the cans could expand enough to rupture the can if it has a weak seam. It's never happened to me—so far.

Dave: Re shrapnel, and yelling.

Modern Grendaes (US and British) are actually shrapnel devices (they have a frangible wire inside; much as with the ball in Shrapnel's shells).

The US army has (to the best of my knowledge) never been prone to yelling when firing artillery/mortars. The blast is out in front of the person(people) firing them.

We yell when setting of a grenade; or when we see one nearby. It's both to alert others, and to reduce blast damage.

It's certainly true that heating a can directly will cause it (eventually) to explode; the Mythbusters did this trick with a can of baked beans, and I'm sure it's been accidentally replicated more than once by people trying to cook without a pot. The pan of simmering water* would constitute a sort of bain-marie, cooking things along at a slower and more gentle rate, so that you don't build up too much pressure by getting the can too hot.

*My impression is that you want to avoid the sort of lively boiling you get with, say, pasta cooking--Xopher, Rikibeth, does that match your experiences?

1. Boiling water in an open vessel won't get above 100°C no matter what you do. Having the water bath boil more rapidly won't heat the contents any faster; it just means you'll have to top off the water more often.

2. A rapidly boiling water bath will make the cans rattle around in it. Noisy and a nuisance.

However, related to #1, a rapidly boiling water bath wouldn't add a significant risk of Exploding Can over a simmering bath. A few degrees below boiling isn't going to *slow* the can heating contents much, either.

Directly heating the sealed can without the buffering water bath, or sticking a lid on the water bath, or eek, using a pressure cooker? All up the risks.

For the most part, though, a simmer vs. a rapid boil is a convenience measure, not a safety one.

But Rikibeth is right: a hard boil isn't any hotter than a low simmer (though if there are big bubbles of actual steam I suppose they might be, so a simmer might be marginally safer).

Yes, good sense dictates not leaving the pot to boil along merrily without keeping an eye on things. The instructions I've seen suggest boiling the thing for 90 minutes to two and a half hours, so I can see why someone might well decide this was a good time to multitask, and forget about what was on the stove.

Xopher, how long were you heating your can?

More details, including descriptions of how very complicated blast injuries can be, in the full article.

(Link to the full article: http://www.nejm.org/doi/full/10.1056/NEJMcpc1314240?query=BUL)

By the way, the link to this post in the Index of Medical Posts is broken (no "L" in the "html").

He starts his coals in a chimney lighter, and had it sitting on the concrete. He walked up to the porch to get something and hears a "KABLAM". The chimney was on its side, he scooped the coals back in and continued. Until he realized there were hunks of concrete shrapnel all around the chimney and a big divot in the pad.

I'm glad he was on the porch. We've since had enough other trauma he didn't need to be hurt. It did it again, only with a smaller crater/fewer pieces, a little while later. He was not standing near it then either.

Hmm. If this was in March, is it possible that the heat of the chimney boiled some water trapped in the concrete, and it's the concrete pad that exploded?