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July 29, 2013

Trauma and You, Part Six: Blast Injuries
Posted by Jim Macdonald at 03:04 AM * 79 comments

As promised in Trauma and You Part Five: Burns this is the entry on injuries caused by explosions. Blast injuries are challenging: Practically any kind of traumatic injury is possible. The scene may be unsafe. There may be HAZMAT. It is possible that you’ll be facing a multiple-casualty incident (MCI). It is also possible that you’ll be operating inside a crime scene.

The first important thing to do is stay safe yourself. The second most important thing to do is get help rolling.


Before we start talking about your first-aid response to blast injuries, I want to talk a bit about explosions in general (in such a general way that it will have professional chemists, physicists, and firefighters rolling their eyes). I’m going to be talking about non-nuclear explosions here. For nukes — all this plus radiation.

You have a couple of different kinds of explosions: You have your steam explosions, where steam pressure exceeds the strength of the container. These can be referred to as mechanical explosions. You have your low explosives, such as gunpowder, which can be understood as very rapid burning, where the combustion produces gas pressure inside of a container. These (and many others) are chemical explosions. And you have your high explosives, such as dynamite where the energy comes from chemical bonds being broken. An open pan of water over heat will just boil away. A pile of gunpowder in the open will burn with a rapid Whoosh. Neither will explode without being confined in a container. A block of TNT in the open will still explode. “Brisance” is the shattering power of an explosion. Gunpowder has low brisance: when you’re digging tunnels in hard rock black powder will turn the rock into boulders. TNT has higher brisance: in the same tunnel TNT will turn the rock into gravel. Some explosives, for example HBX (for High Brisance eXplosive) are noted for their brisance.

The common elements in explosions are generally rapidly-generated/rapidly-released high-pressure gasses.

Regardless of the source of the explosion, some items are common from a responder’s point of view: pressure wave, heat, projectiles, and personnel displacement.

Your typical explosion begins with rapidly expanding, often hot, gas. In the cases of dust, gas, or aerosol explosions, the explosion doesn’t have a point of origin, but rather an area of origin. The rapidly-moving molecules strike other molecules, setting them in motion. They strike others, in turn, in an expanding sphere of pressure. Energy moves outward, rapidly. This is your pressure wave. It is generally just slightly faster than the speed of sound. Regardless of what Hollywood may show, you can’t outrun an explosion.

When the pressure wave strikes a person, the wave continues through that person’s body. Solid, and liquid-filled, organs and tissues are generally unaffected. Hollow structures, including the lungs, sinuses, auditory canal, and bowels, can sustain significant damage. In general, a mere 15psi overpressure can be fatal. Once the compression/decompression of the shockwave passes, that part of the explosion is done. It is fast, and brief. (In this video of the PEPCON explosion, you can actually see the pressure wave as it travels across the desert floor.)

The next item of concern is heat. You have hot gasses, and you have radiant heat. A human body is mostly water; the very brief heat of an explosion is unlikely, by itself, to create more than superficial burns. However, other flammable material (including but not limited to the patient’s clothing) may ignite, and that secondary fire may produce life-threatening burns.

The third mechanism of injury is projectiles. Fragments of either the explosive’s container or bits of scenery can be propelled with great force over long distances. Broken glass, masonry, gravel, wood — whatever was near the source of the explosion — will be moving through the air at high speed. This can produce either blunt-force or penetrating trauma if it strikes a person. Explosive fragments generally don’t penetrate deeply, but larger/heavier fragments can cause significant damage.

The last major source of trauma is personnel displacement. Following behind the pressure wave, the expanding gasses from the explosion form a blast wind that can pick up and move people, causing them to fall or strike other objects. You can get any kind of injury in this way; someone knocked into a body of water may drown.

The combination of pressure wave and blast wind may weaken structures. Building collapse can give you patients with crush injuries, along with the other blunt-force trauma, penetrating trauma, barotrauma, and burns that they have already suffered.

Fires may complicate rescue efforts. Weakened structures may complicate rescue efforts. Confined-space rescue, common in building collapses, is a specialty which requires equipment and training most folks don’t have. Stay safe yourself.

For examples of all these kinds of injuries, see The Fiery Keel of Antwerp’s Bridge.


The pressure wave and the heat of the explosion cause the primary injuries.

From The Fiery Keel::

The page, who was behind him, carrying his helmet, fell dead without a wound, killed by the concussion of the air.

Due to the incompressible nature of water, underwater explosions have very damaging pressure waves. Generally speaking, an underwater explosion’s pressure wave is damaging out to three times the distance as an in-the-air explosion, given an equivalent explosion. The pressure wave can be highly lethal. On the plus side, the pressure wave rapidly attenuates with distance, so your overpressure patients will generally be those quite close to the explosion. Nevertheless, underwater explosions and gas-cloud explosions can affect large areas.

The pressure wave moves perpendicular to the surface of the explosive. A person’s orientation to the pressure wave has a large effect on the resulting injuries. The severity varies directly with the surface area exposed. The worst injured will be those standing, facing directly toward, or directly away from, the point of origin. Those least injured are generally those lying on the ground, with their heads, or their feet, pointing to the point of origin. The same is true underwater, with the provision that overpressure effects are greater with greater depth.

Explosions are often associated with intense heat. While the burns received from the flash itself are generally superficial, other flammable materials ignited by the explosion may produce extensive and serious burns. A comparatively small explosion can spread flammable material over a wide area. Burns by themselves are seldom rapidly fatal. Do not be distracted by them from other, more critical, injuries. See Trauma and You Part Five: Burns.

The most common, and most serious, injury in blasts is lung injury. This may not be instantly obvious. Damage to the lungs may result in the lungs filling with blood, or may result in air entering the circulatory system or the chest cavity. Be alert for anyone showing signs of shock, labored breathing, coughing up blood or pink sputum, breathing unusually rapidly or unusually slowly, or who has unusual lung sounds. These may develop over time. Just because someone looks fine now doesn’t mean that they aren’t seriously injured. Any pulmonary symptoms make the patient a red tag (i.e. immediate transport).

Be prepared to perform artificial respiration if the patient stops breathing. Use oxygen if you have it, and use the least pressure necessary; ventilate only to moderate chest rise.

A patient with ruptured bowels does not require any special immediate treatment on-scene beyond basic life support. These injuries are rarely rapidly fatal; let a trauma center deal with them.

Do not overlook the possibility of Traumatic Brain Injury (TBI), especially Diffuse Axonal Injury (DAI). The symptoms may be quite subtle, and may not manifest immediately. Anyone who has been in or near a blast merits prolonged observation. Other than basic life support there are no special first-aid actions. See TMI about TBI.

Ear injuries are seldom life-threatening. Your patients may have hearing loss, which may make it difficult for them to answer questions or follow directions. They may be disoriented, and may go into psychogenic shock even in the absence of other injuries.

Secondary injuries are those created by blast projectiles. These can be parts of the explosive’s container, or a structure, or other parts of the environment propelled by the explosion. They travel rapidly, with great energy, although usually slower than bullets, and without bullets’ aerodynamic properties. They can cause serious injuries outside of the zone of the blast’s pressure wave.

From The Fiery Keel:

Parma himself was thrown to the ground, stunned by a blow on the shoulder from a flying stake.

Treat projectile injuries as you would any penetrating trauma. Assuming the patient has an airway and is breathing, control bleeding and treat for shock.

Some injuries caused by projectiles can be quite grotesque, up to and including traumatic amputation. Do not be distracted by grotesque injuries from more serious underlying injuries or conditions. See Trauma and You, Part Four: The Squishy Bits

Tertiary injuries are caused by personnel displacement and structural collapse.

From The Fiery Keel:

Houses were toppled down miles away, and not a living thing, even in remote places, could keep its feet.

Another young officer of Parma’s body-guard … rose like a feather into the clouds, and, flying quite across the river, alighted on the opposite bank with no further harm than a contused shoulder.

Traveling just behind the pressure wave is the blast wind. This consists of the actual heated-and-expanding gasses of the explosion. The blast wind has less strength but greater duration than the pressure wave. Its primary mechanism of injury is through picking up people and throwing them into fixed objects. People who are being propelled through the air by the explosion become projectiles themselves, and may cause injuries to other patients. Just because you find a patient at some distance from the explosion, do not assume that he or she was not far closer to the center of the event when it happened.

Compared to injuries from the pressure wave and projectiles, personnel displacement creates fewer and less serious injuries, but serious injuries are possible. These are mostly blunt trauma. See Trauma and You, Part Three: Sticks and Stones

The pressure wave and blast wind can cause structural damage in nearby buildings which may lead to their collapse. Don’t assume that just because a building didn’t collapse immediately that it is structurally safe.

If there was one explosion, assume that there will be more. With explosive events the hot zone is 1/2 mile (about five city blocks) in all directions, including vertically.

Be highly alert to your surroundings; gas leaks, downed power lines, weakened structures, fires, sharp metal, broken glass, or other hazards may make getting to your patients challenging. If you have patients in the hot zone, do what you have to in order to get them out of the hot zone.

You may be in an MCI. For more on that, see: Triage for Fun and Profit

A brief note on crime scenes: Follow the same path out that you followed on the way in. Touch nothing that you don’t have to touch to provide patient care. If you do have to move something, remember what it was you moved, where it was, and what you did with it. Take nothing with you that you don’t have to. Don’t clean up after yourself. If you must cut a patient’s clothing off, and there are holes in that clothing, cut around rather than through the holes. Don’t throw the clothing out. Immediately afterward, write up your recollections fully.

Okay, here we are at the end. There’s an explosion. What do I do, standing there in my shirtsleeves?

  1. Stay safe. If you’re that close hit the dirt until after the blast wind passes.
  2. Get help rolling
  3. Triage if circumstances require it.
  4. Provide basic first aid as appropriate (See Trauma and You, Part One: The Basics and Trauma and You, Part Two: Shock)
  5. Stay safe.

Copyright © 2013 by James D. Macdonald

I am not a physician. I can neither diagnose nor prescribe. These posts are presented for entertainment purposes only. Nothing here is meant to be advice for your particular condition or situation.

Creative Commons License
Trauma and You, Part Six: Blast Injuries by James D. Macdonald is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 License.

(Attribution URL: http://nielsenhayden.com/makinglight/archives/015024.html)


Index to Medical Posts
Comments on Trauma and You, Part Six: Blast Injuries:
#1 ::: Ralph Robert (Rob) Moore ::: (view all by) ::: July 29, 2013, 07:16 AM:

Absolutely fascinating. Always a pleasure to read something by someone who knows what they're talking about.

#2 ::: Lila ::: (view all by) ::: July 29, 2013, 09:54 AM:

I was recently privileged to attend a talk by Dr. Christina Hernon, who was one of the medical volunteers near the finish line of the Boston Marathon. One of the hazards they faced was something that never occurred to me--blood-spattered broken glass EVERYWHERE. So not only did responders have the risk of injury, but of contamination as well.

#3 ::: Dave Harmon ::: (view all by) ::: July 29, 2013, 11:13 AM:

Ralph Robert (Rob) Moore #1: Not disagreeing, but I wanted to note that your comment tripped my wetware spam-filter. :-) A false alarm,of course -- I see you've posted occasionally over several years.

#4 ::: Brian Kellett ::: (view all by) ::: July 29, 2013, 12:46 PM:

Nicely written up.

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)

#5 ::: Columbina ::: (view all by) ::: July 29, 2013, 12:54 PM:

So should I assume that, in the unlikely event that I know an explosion is ABOUT to occur but I don't have enough time to get the hell out, the best plan B is to lie down on the ground?

#6 ::: Ralph Robert (Rob) Moore ::: (view all by) ::: July 29, 2013, 12:55 PM:

Dave #3 - Interesting. Thanks.

#7 ::: Jim Macdonald ::: (view all by) ::: July 29, 2013, 01:21 PM:

#5 Columbina

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.

#8 ::: Lee ::: (view all by) ::: July 29, 2013, 01:53 PM:

Ralph Robert (Rob) Moore, #1: David wasn't the only one to have that reaction. I moused-over your URL link and then checked out your View All By as well. The specific trigger involved is "one or two sentences praising the post, with no details or discussion of the contents". IOW, it reads like copy-and-paste boilerplate, which is a common approach for spammers -- a couple of sentences that could apply to any post on any topic, and the payload in the URL link.

#9 ::: Jim Macdonald ::: (view all by) ::: July 29, 2013, 02:25 PM:

This is entirely aside from explosions and blast injuries, but for the folks mentioning spam, one of the Gnomes' Filters is:

/(that|who) .?(actually|genuinely|really|truly) .?(knows|understands) .?what .?(they're|they .?are) .?(discussing|talking .?about|sharing) .?(on|over) .?the .?(internet|net|web)/i

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.

#10 ::: Jim Macdonald ::: (view all by) ::: July 29, 2013, 02:32 PM:

Update to add:

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

Hi my friend! I want to say that this post is awesome, great written and include almost all vital infos. I'd like to see more posts like this.
Greetings! Very useful advice within this post! It is the little changes that produce the most significant changes. Thanks for sharing!
Thanks, I have just been searching for info approximately this subject for a while and yours is the best I've discovered till now. But, what concerning the bottom line? Are you certain concerning the source?

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

#11 ::: guthrie ::: (view all by) ::: July 29, 2013, 03:05 PM:

Can you or someone else elaborate on the whole overpressure thing? I've read about it often enough regarding nuclear explosions, but it's just a number that could be high or low or whatever. I mean my car tyres are usually at 31 or 32 psi, so thinking about that suggests to me that 15 is actually quite a strong shockwave if it's about a sudden burst of air at a pressure half that of my car tires.

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.

#12 ::: Jim Macdonald ::: (view all by) ::: July 29, 2013, 03:10 PM:

15 psi is a one-atmosphere overpressure, or, diving to a depth of approximately 33 feet of seawater.

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

#13 ::: Jim Macdonald ::: (view all by) ::: July 29, 2013, 03:57 PM:

Speaking of structural damage, at the Oklahoma City bombing, a total of 324 buildings were damaged including ten structures collapsed and thirteen condemned.

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.

#14 ::: Tom Whitmore ::: (view all by) ::: July 29, 2013, 04:18 PM:

Columbina @5 -- I'm going to disagree with Jim @7 here.

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.

#15 ::: Tom Whitmore visits the gnomes ::: (view all by) ::: July 29, 2013, 04:19 PM:

Can I recommend that the gnomes learn when to duck and cover?

#16 ::: Ralph Robert (Rob) Moore ::: (view all by) ::: July 29, 2013, 04:38 PM:

Lee at #8: I can see how that could be a trigger, especially after reading Jim’s examples at #10. In any event, I read Jim’s post this morning, and the amount of detail regarding injuries that arise from explosions impressed me. I saw it as an example of clear writing, and I appreciate he took the time to put it together. Next time I post here, I’ll make sure I have a cup of coffee first, so I’m a bit more talkative. Thanks for taking the time, Lee, to explain the issue. :)

#17 ::: guthrie ::: (view all by) ::: July 29, 2013, 04:57 PM:

Thanks Jim.

#18 ::: Dave Bell ::: (view all by) ::: July 29, 2013, 06:30 PM:

While few of us are likely to come under artillery fire, "blast projectiles"...

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.

#19 ::: Jim Macdonald ::: (view all by) ::: July 29, 2013, 06:33 PM:

#14 Tom

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.

#20 ::: Tom Whitmore ::: (view all by) ::: July 29, 2013, 06:49 PM:

We're agreeing forcefully here, Jim. I was addressing Columbina's specific statement "in the unlikely event that I know an explosion is ABOUT to occur but I don't have enough time to get the hell out". Let's build in the "drop" reflex before we start looking at how to proceed once the explosion happens. Explosions fall into the category of rare events: most of us won't have to deal with them at all. We're more likely to have to deal with small explosions than large ones; they're more likely to be smallish near ones than huge far ones. The reflex to drop will help in all cases. It's not sufficient to prevent damage, but it helps.

#21 ::: chris ::: (view all by) ::: July 29, 2013, 07:00 PM:

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.)

#22 ::: Jim Macdonald ::: (view all by) ::: July 29, 2013, 07:28 PM:

As far as pressure waves, my understanding is that they're comin' through and there isn't anything that you can stand behind that'll help. What will help is making your cross-section perpendicular to the wave the smallest it can be to minimize the amount of energy that your body will have to absorb. Shock waves travel through the earth just fine (which is why the West, Texas, explosion registered on seismographs).

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....

#23 ::: eric ::: (view all by) ::: July 29, 2013, 10:15 PM:

The PEPCON video might show the shockwave, but it's redubbed so that the explosion and the sound are synced, from a viewing distance that would be measured in miles.

#24 ::: Jim Macdonald ::: (view all by) ::: July 29, 2013, 11:50 PM:

It's hard to make out, but if the TV antenna on Black Mountain where the video of the PEPCON explosion was filmed from is at the top of Arden Peak Trail, then the linear distance to the site of the plant is on the order of six miles. The sound of the blast would have reached the observers 30 seconds after they saw it.

#25 ::: heckblazer ::: (view all by) ::: July 30, 2013, 12:33 AM:

It took some searching, but I found a copy of the Pepcon explosion video that wasn't re-dubbed. It looks like it took approximately ten seconds for the shockwave to reach the camera. Since the shockwave was pretty much by definition traveling faster than the speed of sound that would still be consistent with the cameraman being around six miles away.

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.

#26 ::: Errolwi ::: (view all by) ::: July 30, 2013, 05:01 AM:

heckblazer @25
Well people wanted to build a kindergarten on the ridge above the magazines for Devonport Naval Base, Auckland NZ, in the area zoned "No buildings here, ever, it's where the blast wave will come.", so nothing would surprise me.

#27 ::: Ingvar M ::: (view all by) ::: July 30, 2013, 05:10 AM:

Jim McDonald @ #22

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.

#28 ::: Dave Bell ::: (view all by) ::: July 30, 2013, 05:36 AM:

On cover and the blastwave:

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.)

#29 ::: NelC ::: (view all by) ::: July 30, 2013, 09:08 AM:

On the wind from explosions, I think it's a significant feature of large explosions rather than small ones. Mythbusters did a segment on it a while ago, where I think they went up to 10 or 20lbs of explosive with no observable effect on the flight of a dummy (they were busting the Hollywood myth of being propelled through the air in Hollywood fashion by an explosion). For a smallish planted bomb, I think any distance where the wind is significant you're going to be in worse trouble from the shock wave and shrapnel.

#30 ::: fidelio ::: (view all by) ::: July 30, 2013, 10:07 AM:

The December 1917 Halifax Disaster, which demonstrates the sort of explosion that produces a wind, the odd things a blast wave can do, and the dangers of looking out the window just before the blast wave hits.

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.)

#31 ::: fidelio ::: (view all by) ::: July 30, 2013, 10:23 AM:

For a more modern accidental explosion, there's Lac Mégantic, with the added feature of burning fuel oil in the storm sewers. Safe shipping by train of hazardous materials, from fuel oil to hydrogen cyanide, is a matter of careful regulation and constant argument, as is inland waterway safety--there are some very scary things travelling by barge as well.

#32 ::: Terry Karney ::: (view all by) ::: July 30, 2013, 10:45 AM:

Plan B is lie down, put your mouth away from the blast and yell; this gives your lungs a chance to evacuate the air as the pressure wave comes past (for reasons which ought to be obvious, I will heard to yell, "grenaaaade!", repeatedly, until either it goes boom, or I am too exhausted to continue).

#33 ::: Jacque ::: (view all by) ::: July 30, 2013, 12:14 PM:

Jim Macdonald @13: And since tires were mentioned, I've had to transport a gentleman who was injured when a truck tire he was inflating exploded.

'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.

#34 ::: Jacque ::: (view all by) ::: July 30, 2013, 12:26 PM:

Jim Macdonald @22: What will help is making your cross-section perpendicular to the wave the smallest it can be to minimize the amount of energy that your body will have to absorb.

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

#35 ::: Debra Doyle ::: (view all by) ::: July 30, 2013, 12:47 PM:

Dave@28: ...the fire in Florida...

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.

#36 ::: Jim Macdonald ::: (view all by) ::: July 30, 2013, 01:10 PM:

Jacque #34:

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.

#37 ::: Cygnet ::: (view all by) ::: July 30, 2013, 02:49 PM:

fidelio @ 30 -- Like hay*, cotton bales will spontaneously combust if they get wet enough -- at least the ones I'm familiar with, which are tractor-trailer sized compressed rectangles of raw cotton straight out of the field. I would suspect that transporting raw cotton by sea could be a bit risky.

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.

#38 ::: heckblazer ::: (view all by) ::: July 30, 2013, 09:30 PM:

Cygnet @37:

Sugar can also be surprisingly explosive.

#39 ::: Dave Bell ::: (view all by) ::: July 31, 2013, 04:17 AM:

Terry @32, Jim @36

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

#40 ::: Cadbury Moose ::: (view all by) ::: July 31, 2013, 05:15 AM:

Dave Bell @ #39

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.

#41 ::: Dave Harmon ::: (view all by) ::: July 31, 2013, 06:58 AM:

Cygnet #37 It's amazing the amount of force something as simple as grain dust can pack.
heckblazer #38: Sugar can also be surprisingly explosive.

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!

#42 ::: fidelio ::: (view all by) ::: July 31, 2013, 09:07 AM:

cygnet @37--Around here, if they can get away with it, farmers prefer to leave hay outside until it's dry--I suspect that's one of the reason the ginormous round bales are preferred now. My mother remembers, many years ago, neighbors losing their barn because of a hay fire--they didn't allow enough drying time before they put it up, and the barn was not well-ventilated.

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

#43 ::: Ingvar M ::: (view all by) ::: July 31, 2013, 09:09 AM:

Dave Harmon @ #41:

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).

#44 ::: albatross ::: (view all by) ::: July 31, 2013, 01:14 PM:

I seem to recall reading somewhere that a grain elevator type explosion/deflagration/boom event could actually cause an underpressure wave after the overpressure wave. I think this effect is supposed to be important with fuel air explosives, and I imagine it happens with grain elevator explosions (same mechanism, different fuel, right?).

#45 ::: Cadbury Moose ::: (view all by) ::: July 31, 2013, 02:16 PM:

Albatross @ #44

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.

#46 ::: Cygnet ::: (view all by) ::: July 31, 2013, 06:10 PM:

fidelio @ 42 -- oh, hay fires. Yes.

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.

#47 ::: Angiportus ::: (view all by) ::: July 31, 2013, 09:18 PM:

Usual expression of gratitude for the scientific information. Uncertainties remain. When a glass cookware item is put on the stovetop instead of the oven, and differential heating in its walls eventually causes it to shatter so violently that hundreds of pieces fly all over the kitchen, that doesn't come under some people's description of an explosion above because it wasn't hot gases or combustion--but no one who witnessed it, or cleaned up afterward, would have called it anything else. I would say that molecular bonds were broken; I stepped on one of the smallest pieces and suffered what I guess would be a quaternary injury. I know it wasn't gas pressure because that would have lifted the lid. But to this day I hate to think of what would have happened if anyone had been close to the stove when that thing let go.
I love me a good physics lesson, but not when someone gets hurt--or loses anything more valuable than a batch of spaghetti sauce. I hope that all you tell us of remains theoretical for us, and to this day I don't use glassware in cooking, no matter what the label says.
And then there was the time my parents put the last of the home-brew in a gallon glass jug...That one waited till the middle of the night before causing me to peel myself off the ceiling...

#48 ::: Jim Macdonald ::: (view all by) ::: July 31, 2013, 09:49 PM:

Sure, there are other kinds of explosions. Magnetic explosions, endothermic explosions, all sorts of stuff out there. That's why I used words like "generally" and "typically." If something makes a bang and sends fragments all over the place, I won't quibble.

#49 ::: P J Evans ::: (view all by) ::: July 31, 2013, 11:04 PM:

47
Eggs that are put in a pan of water to cook and then forgotten. (The ceiling may never be clean afterward.)
We had a 50-gallon water heater blow the inside seam. It may not have been an explosion, but it was audible throughout the house. (Fortunately it was in a location where all the water was outside the house.)

#50 ::: Cygnet ::: (view all by) ::: August 01, 2013, 12:33 AM:

I had a canning jar blow up on me once as I took it out of the canner. I was very lucky the contents were potatoes and not something sticky like jam. There was glass embedded in the ceiling, so I counted myself lucky to only have a few scratches and some first degree burns on my forehead from splattered potatoes.

(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!)

#51 ::: Jim Macdonald ::: (view all by) ::: August 01, 2013, 03:53 AM:

Speaking of Lac-Mégantic, that took place barely ninety miles by road north of me, and I've met some of the folks from the US who responded to the event.

#52 ::: Ingvar M ::: (view all by) ::: August 01, 2013, 05:55 AM:

Cadbury Moose @ #45:

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.

#53 ::: Cadbury Moose ::: (view all by) ::: August 01, 2013, 08:16 AM:

Ingvar @ #52

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.

#54 ::: Dave Harmon ::: (view all by) ::: August 01, 2013, 08:46 AM:

Angiportus #47: Mechanical explosion, thermal stress.

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.

#55 ::: P J Evans ::: (view all by) ::: August 01, 2013, 09:28 AM:

My father was dealing, at home, with a broken something from work. It involved taking alkali metals (sodium, potassium, or a mixture of the two) out of the something and putting them in a jar of oil. Unfortunately some of the alkali metals didn't get under the oil fast enough, and the jar blew up in his hand.
They never did get all the glass out; too small for ultrasound and X-rays weren't sufficiently 3D to locate the pieces. Fortunately he was wearing a lab coat and safety glasses.

#57 ::: Henry Troup ::: (view all by) ::: August 01, 2013, 11:09 PM:

Dave Harmon @#41
Flour is notorious for exploding. As is sawdust. Iirc, in both cases one has to be careful about plastic ducting, as a little static electricity can go a long way in the undesirable direction.
In the old days, coal dust was a problem.
Any finely divided oxidizable substance can be an explosion hazard.

#58 ::: crazysoph ::: (view all by) ::: August 02, 2013, 07:54 AM:

. o O ( Is it awful of me to wish for the rhubarb chutney recipe that was involved in the blast? )

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

#59 ::: fidelio ::: (view all by) ::: August 02, 2013, 10:55 AM:

Cygnet @46--that's a very sad pole barn. I understand why they haven't rebuilt it--they're more expenseive than you'd think for a structure without walls--but damn.

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.

#60 ::: Cheryl ::: (view all by) ::: August 02, 2013, 12:43 PM:

@59 fidelio

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.

#61 ::: fidelio ::: (view all by) ::: August 02, 2013, 02:22 PM:

Cheryl @60--It's a dreadful occurrence, and being nearer can only make that more obvious. I know down here in Tennessee it had me contemplating just how closely I live to three sets of active tracks and two rail bridges over the Cumberland River. And also the fighting we have going on over pipeline safety. (Keystone's not the only point of contention there...)

It's a real heart-breaker.

#62 ::: B. Durbin ::: (view all by) ::: August 02, 2013, 03:55 PM:

It doesn't surprise me that wet hay can spontaneously combust—one of the listed benefits of straw bale gardening is that as it's composting, the temperature of the bale rises, which means you can plant earlier in climates where the soil temperature is less than ideal until later in the season.

#63 ::: Lee ::: (view all by) ::: August 03, 2013, 12:01 AM:

fidelio, #61: There's an active rail line 4 blocks from our house. In the event of such an explosion along it, we'll be dead, full stop.

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!

#64 ::: Rikibeth ::: (view all by) ::: August 03, 2013, 01:35 AM:

Lee, you can get the same dulce de leche out of condensed milk just simmering the cans in a regular pot too. That's how my chef-instructor did it.

#65 ::: Xopher Halftongue ::: (view all by) ::: August 03, 2013, 02:05 AM:

I've made dulce de leche by boiling closed cans many times. In an open pot, with plain water boiling...it's hard to see how the liquid in the can would boil. Since it's got a lot of stuff dissolved in it, it would have to boil at a higher temperature than plain water, and as long as there's plenty of that plain water in the pot, it won't get hotter than the boiling temp, and therefore the liquid inside the cans won't boil. I think.

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.

#66 ::: P J Evans ::: (view all by) ::: August 03, 2013, 09:06 PM:

They were demolishing an old steam-generator plant in Bakersfield, and some of the debris got away. The onlookers were a thousand feet away (reported), and one of them got hit and lost a leg; he may lose the other one also.

#67 ::: Lizzy L ::: (view all by) ::: August 03, 2013, 10:28 PM:

*waves at Terry Karney* Nice to hear from you. It's been a while. Hope everything is okay.

#68 ::: Terry Karney ::: (view all by) ::: August 16, 2013, 09:06 AM:

Lizzy: I am well, just variably distracted. I have taken to twitter.

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.

#69 ::: fidelio ::: (view all by) ::: August 16, 2013, 10:08 AM:

All of the instructions I've seen for the cooking-the-can-of-condensed-milk trick note that you need to keep the can fully covered by the water throughout the process, and that means keeping an eye on things and topping up the water if needed. Some mention pressure differentials in a knowing sort of way while telliong you to make sure to do this.

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?

#70 ::: Rikibeth ::: (view all by) ::: August 16, 2013, 12:52 PM:

fidelio, there are a couple of reasons I can think of to use a moderate simmer rather than a full rolling boil for cooking sealed cans:

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.

#71 ::: Xopher Halftongue ::: (view all by) ::: August 16, 2013, 03:03 PM:

I agree with Rikibeth. But to me, the point is that the contents of a can in boiling water is not going to get hotter than the water, and the solution in the can has to have a higher boiling point than the water (as long as you don't make the mistake of salting the water as you would for pasta). Therefore no explodey.

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).

#72 ::: P J Evans ::: (view all by) ::: August 16, 2013, 03:31 PM:

71
Xopher, I understand it takes a lot of salt to raise the boiling point enough to matter.

#73 ::: fidelio ::: (view all by) ::: August 19, 2013, 09:08 AM:

If you aren't going to be keeping a close eye on the thing, or are a forgetful sort, the simmer is safer, though, because a neglected boil can end up leaving the can high and dry--at which point, see to your supply of cleaning paraphenalia and I hope you weren't in the room at the time...

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?

#74 ::: Lila ::: (view all by) ::: August 19, 2013, 09:14 AM:

If I were going to try that (and I might; I opened a can of condensed milk that had spontaneously caramelized due to long/hot storage and it was yummy)--I would set a timer to go off every 20-30 minutes to remind me to check the water level. I have boiled several teakettles dry in my time.

#75 ::: Lila ::: (view all by) ::: April 09, 2014, 07:38 PM:

This month's NEJM has an in-depth case study about the treatment of one of the Boston Marathon Bombing victims. The take-home: improvised tourniquets that don't use windlasses (tightening devices, e.g. a stick used to twist the tourniquet tighter) can make bleeding WORSE as they don't stop blood going out from the arteries but do stop blood coming back from the veins. According to the docs, "probably the best thing an untrained bystander can do for a traumatic amputation is pack the wound tightly."

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").

#76 ::: Paula Helm Murray ::: (view all by) ::: April 09, 2014, 08:30 PM:

Jim had an unpleasant experience last time he cooked outside (early March). We have a big backyard concrete 'pad' that connects the house and garage, I think there may have been a deck on it a while ago.

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.

#77 ::: Xopher Halftongue ::: (view all by) ::: April 09, 2014, 08:34 PM:

Oops, I must have stopped looking at this thread before it was finished, and never answered fidelio's question. Way too late now, of course, but: about four hours IIRC.

#78 ::: Cally Soukup ::: (view all by) ::: April 09, 2014, 08:38 PM:

I've never had a fire chimney starter explosion. I'm impressed by the directed nature of the blast, and I'm having trouble coming up with a mechanism for it. I wonder if the fact that I always start the coals by standing the chimney in the grill has something to do with it? What fuel does he use?

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?

#79 ::: Lila ::: (view all by) ::: April 09, 2014, 08:59 PM:

Cally, that was my impression; that it was a steam explosion. The same thing sometimes happens with rocks around campfires.

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