Honestly, I’m watching a war movie and a dude got hit by an IED. It got me thinking though, and I don’t quite get what is the lethal factor in an explosion?
There always seems to be fire in the movies, and it’s clearly a lot of force. But my question is what ACTUALLY happens to (I guess anything) that gets hit by a large bomb/explosion from a play by play/physics situation?
I feel like this is kinda dark, but I just had one of those curious moments and felt like this was the appropriate place to ask
In: Physics
Watch any Kurzgesagt video on Youtube involving explosions or nukes and you will get a good visual ELI5.
Basically your body can’t get out of the way of the explosion fast enough so your squishy bits get compressed. This compression can be enough to damage or shatter your squishy bits (or even your not so squishy bits if your close enough). This can cause enough damage to kill you but unless your standing over top of the explosive or in the fireball very unlikely to kill you.
Part 2 is shrapnel. Shrapnel goes waaaaaaaaaaaay farther than the pressure wave. And depending on distance and explosive type can be traveling at 1km/s +. This is the really dangerous part of an explosion. The shrapnel are essentially bullets and will kill you in the same way one from a gun will. It doesn’t really matter what your shrapnel is made of generally it’s traveling fast enough it doesn’t matter. However heavier pieces travel further. This is what kills you most likely in an explosion.
A good example of this is flashbang grenades. They are designed to not throw shrapnel out and unless your physically touching it your not going to risk dying or lasting disability (outside hearing damage). Despite having about the same amount of energetic material as the snake antipersonel grenades.
Burns aren’t as life threatening from explosives but can still be pretty damaging. Generally if you get burned and survive your explosive deflagrated instead of detonating and wasn’t super well confined. Again shrapnel is what will usually kill you. Especially if you’re close enough to worry about heat or pressure.
Unless your in a cave or building and then vacuum might be what does you in.
3 things:
1. Heat (only matters if it’s a really big bomb)
2. Shock (matters a bit more, but not much)
3. Debris (matters the most)
Heat we can safely ignore. Since the bomb is (probably) not a nuke, you aren’t vaporized. The movie bombs make these huge fireballs that are only possible if the bomb is utterly surrounded by gasoline or some other flammable.
The shock might throw you into the air. But unless the bomb is a nuke it won’t do anything direcly harmful (but it might disorient you or throw you off a cliff)
The debris is like bullets. Bullets = danger. The debris is basically the metal fragments of the bomb (or more if it’s like a frag grenade.)
The two primary risks for bodily injury due to an explosive are from objects being propelled by the explosive (shrapnel) and the pressure gradient created by the shockwave. The human body is pretty good at handling pressure changes…just not rapid pressure changes (which is how explosives work). And the damage (depending on the multiple factors) can be as simple as it “knocking the wind out of you” to collapsing your lungs or even as severe as liquifying your internal organs. You typically won’t see a lot of flame with commercial explosives. Some of the exceptions are with homemade explosives such as homemade ANFO where the ammonium nitrate isn’t fully saturated with fuel oil or there is simply too much fuel oil as commercially manufactured ANFO typically has excess fuel drained off prior to packaging.
Hollywood typically uses a lot of gasoline in their pyrotechnics for the visual effect. In reality, unless the goal is specifically the use of an incendiary explosive (such as napalm) you won’t see much fire (though an explosive could start a fire from dispersing the contents of a fuel tank).
Historically, the pressure wave has always been the primary source of injury. A good study on the topic is how trenches evolved during WWI through the use of sharp angles to reduce the effects of the shockwave though WWI was also where modern battle helmets became standard use as they weren’t commonly used during the wars of the “Napoleonic era” to reduce the effects of shrapnel (not bullets) injuring soldiers. The US Army did some fairly extensive testing in the late 1970’s and early 1980’s on the subject as well (nothing classified so it should be searchable) which is now the basis for how armored vehicles are designed increase survivability with the threat of IEDs. Of course, over the last 20 years things have also greatly changed and it has been discovered some vehicle types have better explosive survivability characteristics (i.e. the phasing out of the US HMMWV in certain environments for vehicles with higher ground clearance and better underbelly armor such as the MRAP and M-ATV).
Now this isn’t necessarily limited to military/counter domestic-terrorism application either. You see various technology manufactures who will test their equipment against explosives for various reasons especially in public safety application. For example, a two way radio manufacturer may test their portable radios to ensure the man-down emergency switch (triggers emergency mode after X seconds of the radio being horizontal instead of vertical) will survive a given explosion that could be survivable by the person carrying the radio but may otherwise incapacitate them or even that a mobile radio can be interfaced to the fuel shutoff switch of a car which turns off the fuel pump in the even of an accident (or can be triggered by an explosion) again to put the radio into emergency mode.
When I was blown up out on patrol, it was the blast concussion that effected me the most. I was inside an armored vehicle every time so shrapnel wasn’t an issue. Until it was. Only one of them was bad enough to “hurt.” Head ringing, bloody nose, possible shit in underwater . The injury that sent me home was a mortar that hit a truck outside of the trailer I was in. Shrapnel from that came through a wall and put a hole in my skull an inch above my eye. That experience was odd.
It felt like I got hit in the head with large piece of wood. My ears were ringing, I could hear everyone yelling get down. That’s about the only thing movies get right about blast. That brain confusion, the ringing, and the way you can hear but it sounds distant. I just stood there thinking wtf just happened. My body was in shock, I couldn’t feel shit, except numbness. Everyone looked up at me horrified, but impressed, pointing to my forehead. My hand didn’t even make it pall the way up before I noticed my arm was covered in blood…so was the floor. I walked over to the shop area and we waited until a medic could come. I was just chatting away as if it was nothing. Just another day where you have a two inch gap in your skin, exposing a hole a little less than an inch. Not sure if the piece of metal still lodged or the hanging flesh that drew everyones attention. Soldiers are a messed up breed of humans. After doc gave me some morphine, my memory kind of comes and goes. Not sure how much after that actually happened and how much I put together while talking with people after the fact about it. I honestly thought I would have more lingering effects.
An explosion can make you get pushed very fast. Imagine those hydraulic presses on youtube, but very fast and made of hot air. It squeezes you, depending on the strength and distance, aside from all the flying pieces of metal that also work like stray bullets.
As another comment mentioned, shrapnel is the number one problem regarding lethality when it comes to explosions.
However, the second is the pressure wave. You know when you are at a concert or a fireworks show and you can feel the air waves hitting your chest? Explosions do that same thing to but can range anything from “knock you on your ass” to “your lungs literally burst inside your chest cavity.”
Imagine if someone punched you. The force used would damage your muscles, and you would get bruises, as capillaries break.
If Mike Tyson punched you, the damage would be greater, perhaps breaking bones and damaging internal organs.
When the shock wave from an explosion hits someone, the force of the explosion is transferred into their body in a similar way to a punch, but is not so direct. It causes the same kinds of effects to the muscles, bones and organs.
Explosives that are designed to damage through this shock wave are generally refered to as concussion explosives, and used to be used commonly in grenades, for use in confined spaces.
Other explosives are used in similar ways, but are packed in containers that split apart and throw bits (called shrapnel) around at a very high speed. This shrapnel goes through the skin, and leads to bleeding.
The fire is just for the benefit of the movie. Movie explosives tend to include a lot of gasoline or other fuel to get that nice big fireball. With the exception of weapons that are designed to create fire, real-world war explosives don’t care about fire.
When an explosive weapon goes off, it essentially releases a whole lot of energy at once. And this is weaponized in two main ways.
There’s going to be a massive pressure differential as the explosive’s energy ‘pushes’ the surrounding air aside. This pressure wave is so powerful that it’ll pretty much rupture the soft parts of your body if you’re unfortunate enough to be in the blast radius. Even if your body manages to stay in one piece, it can just squish the soft bits like your organs.
Most explosives are also designed to produce shrapnel. Shards of the bomb’s casing, objects like nails that were packed in with the bomb. A hand grenade has that pineapple pattern just to create more surface are and thus more shrapnel when it explodes.
Shrapnel goes flying in every direction pushed by that pressure wave, that energy release when the bomb goes off. And it will shred anything nearby. It will cut through bodies, sever limbs, go straight through light materials like car paneling.
And of course, since bombs are weapons, most are designed to achieve specific things. Some landmines are spring-loaded so they jump up to chest height before exploding. Vehicle mines are often shaped in such a way that they guide most of the explosive force upwards into the vehicle above instead of exploding equally in all directions.
Anti armor munitions often have staged explosions to help them penetrate armor before doing something nasty to the crew inside a tank.
Thermobaric bombs are designed to create a long-lasting explosion that uses up all of the oxygen in an area, rupturing the lungs of anyone unfortunate to be in the very large blast area. It’s perfect for clearing out caves and tunnels where direct shrapnel wouldn’t hit people.
But the basic idea is that explosives produce a devastating pressure differential compounded by shrapnel.
i can think of two things that happen: you get burned very hard and you get ripped apart by the pressure if a bomb hits you directly
if the bomb explodes near you there are little things flying arround with a high speed that can also hurt you (think of bullets) and depending on the bomb and your distance to it the sudden pressure can make you loose balance
if you are near an exploding nuke you body just evaporates due to the heat
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