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Disclaimer

This seems a particularly stupid question, but the more I think about it, the less trivial I find it. Worldbuilding possess the most appropriate tags. It does not fit in physics-network usual problems, and we don't have a gun-enthusiast network that I know of (other than in a theoretical manner here, especially when we have to wipe out civilizations.).

Context

(Edit 2) This is an explanation as to why I need such a specific information. I've been advised to do so by Revetahw to avoid a closure for being off-topic. I first abstained to write it as not to drown the question in too many information. You can skip to the next part if it does not interest you:

You're still reading? Then hang on, cause you will need to handwave quite a few things. My main character is a mutant in a near sci-fi future. Among other things, he possess the ability to absorb shock. His body dampen more efficiently kinetic energy and actively transform it in another kind of energy. He is more resistant than a human, but not bulletproof. Thus, he needs to wear a costume made from magically-genetically-modified-spider silk. Thing is, spider silk reacts badly to heat, and albeit the enhanced silk is designed to withstand more heat, it's highly unadvised to stay near a fire. He is going to fight crime and military groups who may eventually use grenades. I need to know if I'm going to kill my character outright or not. Plus, I like being thorough in the non-"it's magical, just read on" aspects.

Question

How does a gun kill you? It accelerates a bullet to a supersonic speed by igniting powder in a controlled environment. The bullet shape allows it to impact you and focus its kinetic energy on a very restricted area, perforating the target (overly and deliberately simplified). TLDR, a fast bit of metal flies from the end of the cannon and punctures you.

How does a grenade kill you? Some mean person throws an explosive device at you. When the thing goes off, the powder ignites and breaks the outer shell, sending shrapnel flying in every direction in a big boom.

The boom is the part bothering me.

Against small caliber, the most common protection is a bulletproof vest, one that does not rupture when the bullet impacts it, allowing it to spread the kinetic energy on to a wider area. You do not get perforated, thus you do not die (at least not directly).

The suit of a defusing squad is far heavier and thicker and protects the whole body, not just the torso (but then again, why would you need your head?). I'm wondering if there is more to it than just stopping all the "bullets" (which shrapnel kind of is, just thrown all around).

  • Are the shrapnels hotter than a bullet from the explosion, thus impacting their penetration power? (A quick internet research indicates a small caliber round reach around 200°C, but the heat seems to vary a lot between the exit of the cannon and its eventual impact) Would that make the shrapnels burn their way through a regular bulletproof vest?
  • Is the blast from the explosion powerful enough to outright kill you, even without the shrapnel?

I do need this kind of information for a worldbuilding purpose, and since I'm not too keen on using myself as a guinea pig, I'd appreciate someone explaining to me what to take into account in case of grenade explosion, especially regarding their impact on usual protections in a gunfight.

PS: Keep in mind that I grossly simplified the interaction. I'm aware of the physics involved but in no way proficient in ballistics. I know how to operate a handgun, the way it works, but couldn't write the equations for the life of me.

PPS: I think it's worth adding a few things.

I can reasonnably assume different types of grenades kill you in different manners. For the sake of simplicity, let's keep to fragmentation grenade (example used in the question) and concussive grenade (pertinent to the shock wave problem). I can make an educated guess at how an incendiary 'nade would kill you. (The answer is: very unpleasantly).

Second, me joking about EOD having full body protections is merely to keep you awake during the long question. I understand someone wearing a bulletproof vest can not always wear a full body protection cause they need mobility. Whereas an EOD capable of outrunning the shockwave seems pretty unlikely. (Note that I'm not implying that the vest guy will outrun the bullet, but will attempt to get out of the way). However, I was unaware of ceramic being used in body armor, and will look into it.

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    $\begingroup$ Not all grenades rely on quickly sending bits of metal your way. An explosion by itself can also kill you quite nicely even without shrapnel. $\endgroup$ – Spoki0 Feb 1 at 14:45
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    $\begingroup$ A truck hitting you is technically "a piece of metal hitting you" but it's not a bullet nor a shrapnel. It can still kill you in a similar way to a grenade - by hitting you really hard. $\endgroup$ – VLAZ Feb 1 at 14:54
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    $\begingroup$ @VLAZ Falling onto metallic floor from sufficient height also enter the category of "piece of metal hitting you too fast for your own good". I think we can admit that an excess of kinetic energy, metal or not, is not recommended by medical professionals. $\endgroup$ – Nyakouai Feb 1 at 16:43
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    $\begingroup$ @Nyakouai I'm not a medical professional and I would also not recommend it. I'd expand that to medieval weapons, too. However, if at all possible, I'd recommend being hit by a giant block of gold that fell on you like an anvil in a cartoon. It's still lethal but your relatives can at least benefit from your demise. If it's also shaped like a cartoon anvil, it will be somewhat funny. So - if you have a choice, I'd go for that. $\endgroup$ – VLAZ Feb 1 at 16:51
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    $\begingroup$ Watch some of the mythbusters episodes. They explain shockwaves and how they kill you very well. $\endgroup$ – Scott Baker Feb 1 at 16:56
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What a wonderfully macabre question! This calls for cited sources!

First off, I'd like to point out that you are correct to notice the similarities between a grenade and a rifle round. Both have the same gross pattern: they set off some explosives near some metal that is going to be accelerated by the explosive. So if we start from that very simplified model, we can cover both the similarities and the differences between the two.

In both cases we start with a detonation. This is a combustion reaction which is fast enough to propagate a shock wave in front of it. The first thing we can do is contrast this with deflagration, where the combustion proceeds slower than the speed of sound. In both grenades and modern firearms (which use a nitrocellulose based explosive typically called "smokeless powder"), the reaction is a detonation. However, in black powder based firearms from previous eras or lower quality improvised grenades, the reaction is a deflagration. I'll assume that we are interested in the modern military grade equipment, given the wording of your question, so if you're interested in the deflagration case, simply skip the sections dealing with the direct consequences of detonation.

(Thanks to all the commenters posting on this, I've had to do more research and issue a correction. Explosives detonate, which is defined to be what happens when a combustion reaction propagates faster than the speed of sound. The propellants in ammunition are designed to deflagrate, which is burning with a flame front that moves slower than the speed of sound. My confusion was caused by the presence of supersonic bullet, which would clearly need to be propelled by something going faster than the speed of sound. The piece I missed was answered here: the high temperature of the expanding gasses increases the speed of sound in that medium. Also, the speed of sound that matters is apparently the speed of sound through the material (the powder itself), not the air surrounding the powder. That speed of sound is much faster. Firearms designers use this deflagrating "low explosive" intentionally, for many reasons including the fact that this means their propellant cannot generate the shock waves of a high explosive, and thus does not need to be regulated in the way we regulate high explosives. I can go to the store and buy smokeless powder without any questions. If I went to the store and asked to buy C4, questions would start coming my way. Thanks to everyone for pointing out my mistake!)

When you detonate an explosive, you create a shock wave. Shock waves are interesting little beasts.

If you want to skip the next few paragraphs on the physics of a shock wave, you can. However, I find its very helpful to understand what a shock wave actually is. That helps in understanding why the line between deflagration and detonation is such a big deal.

A shock wave is required because the simplistic laws of physics that we're used to break down. Usually we say that information about an object propagates ahead of it at the speed of sound. What this really means is that there are gas atoms which hit the object and are bounced in the opposite direction, traveling faster than the object itself. These eventually collide with other gas atoms, sending them scattering ahead of the object and so on and so forth. In normal every day circumstances, this process involves so many collisions that we can model it statistically. The result is that we can talk about "pressure" meaningfully, and we can talk about a "pressure wave" which propagates ahead of the object. All objects moving through the air have a pressure wave in front of them, though it is not always obvious. A fast moving modern car doesn't have very many insects striking its windshield because the pressure wave in front of it pushes the insects upwards over the windshield. An older car with worse aerodynamics may not generate a sufficient pressure wave to force the insect over the top of the car, and the result is... well.. messy.

When we get to events that move at the speed of sound or faster. As this happens, our nice clean statistical model of the gas breaks down. In the nice clean model we're used to, we say that every small region has a "pressure," and it pushes outwards in all directions equally. This works because, over the distances between collisions (the "mean free path length," on the order of 68nm), the velocity of particles on both sides of the object are close enough to use easy statistical distributions. However, as particle speeds approach the speed of sound, this changes. The differences in velocity get more and more pronounced until we can't sweep the differences under the rug with a simple differential equation. We have to account for more of the actual particle physics in this regime.

If you're skipping the physics lesson, this is a good time to rejoin the answer

So why is a shock wave such a big deal? Well when we account for the particle physics of objects at these speeds, we have to allow for what are basically discontinuities in pressure (modern measurements suggest a shock wave is about 200nm thick). The pressure can rise almost instantly. This matters because many objects, including human bodies, are very sensitive to sudden changes in pressure. Under normal conditions, such rapid pressure changes would call for an enormous amount of energy. However, if you can create a shock wave, you can create a rather large pressure differential with a much smaller explosive.

So what happens when a shock wave hits the body? For the most part, it can pass through freely, but if we find regions where the speed of sound changes dramatically, these sharp pressure changes can do damage.

The primary effect of such shockwaves is on the lungs. This effect is dominated by the impulse of the explosion (generally proportional to the integral of overpressure over the duration of the shock). In the case of the lungs, this impulse imparts a velocity to the cells lining the alveoli. Because they are thin, designed to stretch as we breathe, and right along an impedance boundary between flesh and air, they are very susceptible to this. The result of this damage is the rupture of the capillaries in the lungs, called pulmonary contusion. This is what medical doctors would call "Bad News." The damage can cause the alveoli to collapse, no longer participating in breathing. It can also cause pulmonary edema, filling the lungs with fluid and causing suffocation.

Other gas filled organs can be affected similarly, but in the literature, lung damage due to shocks is the primary issue.

Ear drum damage also occurs in response to such shocwaves. Being thicker than the walls of the alveoli, they respond to slower effects. The damage to the ear drum appears to be more associated with the actual overpressure than the impulse of the shockwave. A perforated eardrum is typically not fatal, but it can cause sudden disorientation and vertigo. Given that one is in an environment where there are grenades and/or flying bullets, this disorientation can lead towards a fatal incident shortly thereafter.

So this shows a major difference between grenades and bullets. In a bullet, the shock wave occurs quite far away and has rather low impulse by the time it arrives. The shockwave plays a very minor part. There is an argument that a supersonic bullet hitting flesh can generate its own shockwaves which can disrupt neural activity, known as hydrostatic shock, but it is a disputed theory.

Thus we see a major difference between the bullet proof vest and the EOD suit. You noticed that it covers the whole body, but it also covers it in a different way. The layers of an EOD suit are also designed to redirect and damp the shockwave. They do this using layers of varying acoustic impedance. EOD suits are also designed to protect in other ways, such as cushioning the spine so that an EOD expert thrown back by an explosion is unlikely to suffer catastrophic spinal injury.

Now some grenades stop here. Concussion grenades like the MK3 do their damage with these effects. A fragmentation grenade like the M67 adds a layer of metallic shrapnel. This shrapnel operates like a bullet. In fact, it is reasonable to model the effects of shrapnel exactly like we model the effects of bullets.

Bullets are really straightforward. Shove a metal slug through someone's body, and you force the bonds that hold their body together to give way. If any of those bonds were critical, the opponent is incapacitated.

Bullets come in supersonic and subsonic varieties. The fundamental difference between them would be that a supersonic bullet could cause a shockwave to propagate through the body. However, given that hydrostatic shock is a disputed theory, we can reasonably ignore that difference. Instead, we can just look at all bullets as the same sort of thing. Their damage is based on shape, energy, and momentum. Naturally, supersonic bullets can have substantially more energy, but other than that they aren't special.

A bullet entering a wound basically generates (subsonic) waves, pushing the flesh out of the way of the bullet just like the air was pushed around our windshield in the car example at the beginning of this answer. This pushing effect can tear tissue, and that's the primary cause of damage from a bullet (or grenade fragment).

If arteries, veins, or capillaries burst, blood loss will occur and may cause death. Damage to nerves can cause paralysis of the innervated region, and obviously damage to the brain can cause death. A bullet may break a bone, in which case those muscles can no longer effectively use that bone to create motion. It may also tear tings like tendons, which also prevent motion.

If a bullet or fragment strikes any area, it may cause infection. This is a major factor in abdominal wounds. Our intestines are quite full of bacteria kept safely within the body of the intestines. If the intestines are torn, they will spill this material out, creating a substantial risk of infection.

The kevlar and/or ceramics found in both bullet proof vests and EOD suits is focused on dealing with these objects. Both materials are very good at arresting physical objects before they enter the body. Bullet proof vests have a smaller coverage area because of tradeoffs. Those who wear bullet proof vests must move quickly and care about minimizing burden. Thus the vests only cover the regions where the lethality of a bullet wound warrants the burden of protecting it.

In the case of the EOD suit, mobility is less of a concern. The EOD technician is already where they need to be (which would be the place everybody else doesn't want to be). They do care about mobility, don't get me wrong, but the tradeoffs for someone intentionally going to the wrong sort of place are different. It's worth it to them to have full body coverage.

Which leaves me with a gem of wisdom I got from the comic Schlock Mercenary, by Howard Taylor. His The Seventy Maxims of Maximally Effective Mercenaries includes two which I am yet to find a veteran or active duty member who doesn't agree with, or at least have to give a nod at the wisdom of it all:

  1. A Sergeant in motion outranks a Lieutenant who doesn't know what's going on.
  2. An ordnance technician at a dead run outranks everybody.
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    $\begingroup$ +1 for quoting from the 70 maxims. $\endgroup$ – Criggie Feb 1 at 23:38
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    $\begingroup$ +1 for perfectly applied sarcasm and dark humor. $\endgroup$ – Philippe Feb 2 at 1:28
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    $\begingroup$ +1. And don't forget larger pieces of shrapnel have also a considerable kinetic energy: "... suddenly, with a great clanging thud, I was hit on the forehead and knocked flying onto the floor of the trench... a shrapnel bullet had hit my helmet with great violence, without piercing it, but sufficiently hard to dent it. If I had, as had been usual up until a few days previously, been wearing a cap, then the Regiment would have had one more man killed." -Reserve Lieutenant Walter Schulze. $\endgroup$ – RudolfJelin Feb 3 at 14:10
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    $\begingroup$ Nitpick: The powder in a gun deflagrates, while the TNT in the hand grenade detonates. For a gun, you generally do not want the strong, hard shockwaves of detonation. Instead, you ideally want the burning powder to quickly build up max pressure, and then to just add enough energy to keep that pressure as long as possible while the bullet accelerates out of the barrel. The longer the barrel, the longer you want the powder to burn. If you detonated the powder, it would damage the gun. $\endgroup$ – cmaster Feb 3 at 21:00
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    $\begingroup$ Nitpick #2: While bullets may be supersonic in the air (and consequently produce a sonic boom that's only heard by the target after the bullet has already hit), virtually no bullet is ever supersonic within the target's body. Simply because the target's body is mainly water, which has a speed of sound in excess of 1.4km/s = 5000km/h. That's pretty fast, it'd be about twice as fast as the concorde was... Thus, you'd need a hypersonic bullet (faster than 1.5km/s) in order to create a supersonic shockwave inside the body. Not that supersonic rounds aren't destructive enough already... $\endgroup$ – cmaster Feb 3 at 21:17
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The M67 grenade contains 180 g (6.5 oz) of composition B explosive.

The amount of explosive in a gun or rifle is way less than that, just few grams.

It follows that, close to the explosion, the damage of a grenade is dealt both from the fragments ejected in all the directions and from the shock-wave produced by the explosion.

When an acoustic wave propagates through different media, the amount of transmitted energy depends on the relative difference in acoustic impedance between the two media: the closer they are (i.e. water-flesh), the better energy is transmitted, else (i.e. air-flesh) it is reflected back in larger amount.

The human body is mostly made by flesh but has also some hollow places, like the intestines, lungs and stomach. The interface between these and the flesh can be approximated, from an acoustic point of view, to an interface between air and liquid.

The explosion happens in air, and when the shock-wave impinges on the body it is mostly reflected. But the amount which is transmitted through the body will be basically trapped between the outer shell (the skin) and the inner shell (lungs, stomach, intestine), wrecking havoc there.

This explains why explosions are way more lethal in water than in air (there is less reflected energy on the skin), and why the effect of the shock-wave is the more significant the closer the target is to the explosion point (the intensity attenuates with the square of the distance).

Incidentally, this is also way whoever gets an echo scan is spread with gel in the point where the scan is taken: to improve the acoustic coupling between the scanner and the body.

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    $\begingroup$ To your point about air vs. water explosions, Mythbusters did an interesting episode that tested the Navy's recommendation that floating on your back at the surface is the best way to survive an underwater explosion. This was confirmed, as it minimizes the flesh-water interface area, thereby minimizing the transmitted energy. $\endgroup$ – Nuclear Wang Feb 1 at 16:32
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    $\begingroup$ As for your comment about internal organs, "The interface between these and the flesh can be approximated, from an acoustic point of view, to an interface between air and liquid.", this is only true if your stomach/intestines/etc actually have gas in them. For the stomach, this is generally untrue (unless you've been drinking carbonated beverages, for instance), and the amount of gas in the small intestine is essentially zero. Flatulence occurs in the large intestine, of course (normal farting is 8-10 times a day) but the amount of gas in not large. $\endgroup$ – WhatRoughBeast Feb 1 at 17:08
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    $\begingroup$ This is an interesting explanation of how shockwaves can hurt or kill people, but it doesn’t really address the question of how damaging the shockwave of a grenade would be, if all shrapnel were ignored. While 180 g is a lot more than “a few grams,” that doesn’t mean it’s enough to create a life-threatening shockwave (or, perhaps a better question, how close one has to be to the epicenter of the shockwave for it to be life-threatening). $\endgroup$ – KRyan Feb 1 at 17:40
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    $\begingroup$ Related: Is a bomb's shockwave strong enough to kill? $\endgroup$ – Alexander Feb 1 at 19:25
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    $\begingroup$ -1 The explosive in a fragmentation grenade is there to drive the fragments, which are the lethal part. If you're close enough for the shockwave to hurt you, you'd still be more worried about the shrapnel. $\endgroup$ – Carl Kevinson Feb 1 at 19:39
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The shockwave from a fragmentation grenade is negligible. A concussion grenade, which has few fragments and which is specialized to kill directly through explosive overpressure, has only a 2m kill radius (https://en.wikipedia.org/wiki/Grenade#High_Explosive_(Offensive). A fragmentation grenade has less explosives than that, and would deal very little direct damage through explosive overpressure. It is the fragments that deal damage. There really isn't more to this than stopping all the fragments. A grenade explosion is not a particularly impressive event. There is just a puff of dark smoke and a bang, not a huge explosion.

There seem to be two misconceptions about body armor in your post.

  1. EOD technicians do not necessarily wear better armor than regular soldiers. Most soldiers in modern militaries wear hard body armor made of advanced ceramic composites over their torsos, not kevlar vests. Kevlar and other types of soft, fabric like body armor can only reliably stop pistol caliber rounds and are not of much use on the battlefield. EOD suits are made of many layers of foam, plastic, and soft body armor. They absorb explosions and fragments efficiently, but are not necessarily better against bullets or other kinetic projectiles (depends if they include ceramic components).

  2. EOD technicians do not only go after hand grenades. Many of the threats they deal with are much larger bombs that need more protection, so they wear more protective armor. Even if all they had to deal with was hand grenades, they would probably still wear their special armor. The majority of regular troops in the modern day see little to no combat, and even combat troops deal with grenades on an irregular basis. For them, covering all of the limbs and head in armor would restrict movement and breathing. However, EOD techs deal with explosives all the time, and expect to do so, so they wear armor to be prepared. (In reality, from what I have read, EOD techs typically try to shoot bombs with anti-material rifles or to disarm them with robots unless absolutely necessary)..

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  • $\begingroup$ The differing kill ranges make it very clear which is more deadly. $\endgroup$ – Loren Pechtel Feb 1 at 18:30
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When you get right down to it, both a gun and a grenade kill you with application of the same attribute;

Energy.

The difference is only in the shaping of that energy. Guns fire a bullet in a specific direction, meaning that the energy (in this case, kinetic) is applied in a very narrow and precise focus. In effect, a bullet applies a lot of kinetic energy into a very small window of effect. That means that you can be standing right near a gun being fired, but if you're not staring down the business end of the barrel, it simply won't affect you at all.

This is a simplification; you may (for example) be hit by the casing ejection, and there is some waste heat as a result of the bullet being fired, but it's the kinetic energy of the bullet that really counts in terms of terminal damage.

A grenade on the other hand is what we call an area of effect weapon. It doesn't focus the kinetic energy, but rather distributes it radially. A frag grenade gets its name from the fragments of metal and other debris that get launched from the point of explosion.

Radial blasts cause damage in all directions, but the range of effect is subsequently seriously reduced. Grenades, not requiring bullets et al are also capable of storing more potential kinetic energy than a single bullet, but most of that is going to be directed into places the enemy isn't.

The difference between the two is that a bullet creates a massive impact along a very specific directional line and over a much longer range; a grenade can release more energy overall, but over a much smaller range because of the radial distribution of that energy.

So; if you're standing right near a grenade when it goes off blowing shrapnel all over the place, it would be like being hit by a shotgun blast at close range; flak vests et al are going to be the order of the day in order to have any hope of survival. But, the further away you are, the much greater the chances of your survival by comparison to a bullet fired from a gun.

I don't have exact figures on me, but at very close range grenades will probably have a similar kinetic energy release as what one could expect from a bullet at much further ranges. A grenade may contain (say) enough charge to fit in 50 bullets, and the fragmentation of the casing means that you're facing a fair percentage of that at very short range. But the omni-directional dispersal pattern of that energy means that the tradeoff is that the charge is used very inefficiently, unless your enemy has surrounded the grenade in all three dimensions with very close proximity. This is why they're often used to clear machine gun nests, trenches, and other fortified positions as opposed to being used in an open battlefield where people are more dispersed and more capable of avoiding the device when they see it.

Ultimately, the key thing to remember is that the radial dispersion pattern means the energy dissipates at a rate proportional to the cube of the distance from the explosion with grenades, meaning that they are strictly a short range weapon, best deployed in tight, enclosed spaces containing only enemy combatants.

Guns, on the other hand, are a point and click interface designed to work at range but only in the direction you specify.

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  • $\begingroup$ Good answer, I would also mention rifling which goes even further at making sure energy is delivered to one spot $\endgroup$ – Andrey Feb 1 at 14:59
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    $\begingroup$ this answer fails to account the root of the question, how a shockwave kills. $\endgroup$ – John Feb 1 at 15:13
  • $\begingroup$ @John looks like that part was added as an edit after the fact $\endgroup$ – Tim B II Feb 1 at 21:10
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One could say that a grenade kills you in the same way that a fall onto a hard-enough surface kills you. The (brief but) strong force from the blast/impact on the floor can deform the body up to a point where bones break and/or organs experience acceleration big enough to destroy tissue. Also, the shock wave may travel through the body and cause damage at places not directly impacted on. This is an effect that is also seen with projectiles (some more than others): A bullet is not like a small rod slowly piercing through the body but also causes shockwaves along its path through the tissue. These shockwaves can affect a much wider channel than the projectile itself. You could be hit by a 9mm bullet but have a 'tunnel' of destroyed tissue around the trajectory of multiple times that diameter.

Then of course there are indirect causes of death: Even when the blast or the projectile doesn't kill you instantly, tissue, organs and blood vessels may be damaged causing you to bleed to death or die from some kind of organ failure within some time after the event.

So I guess the main difference is really, as you said, that a projectile works by piercing into the body while a blast works by massive acceleration of large parts of the body.

That's also one reason why the bomb squad uses as heavy an armor as is practical: A large mass can absorb more energy for a given acceleration. Hence, the heavier the armor is the slower it will move and hit your body in response to a blast.

(The sequence of events here is detonation -> shockwave hits armor -> some energy gets reflected, some absorbed -> due to the absorbed energy the armor starts moving -> the armor impacts on your body's surface -> force is applied to your body. The slower the armor the less peak force is applied to your body.)

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It all depends on how you use both tools. For instance it's much more difficult to club someone to death using a grenade than it is to use a rifle.

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    $\begingroup$ Thanks John. Though I'm not an eminent member of SE, I think we mostly keep playful answer in comments. But I do appreciate the input. Didn't the mutants from Fallout had some sort of boomstick? (In the form of explosive hammer with a 'nade strapped to it?) $\endgroup$ – Nyakouai Feb 2 at 14:07
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Okay so a quick simple answer that might help. As someone who is ex army(uk) and worked in both aerospace and for a civilian testing company I've seen a few different things.

The way the bullet works on the body depends on the shape of the round as well as its calibre, there Are a huge number of other factors but we'll keep it simple.

A 5.56mm round which is fired by the UK main rifle was not designed to kill, it can but that's not it's main function, it was designed to injure. The main reason for this is down to numbers, it takes 1-2 people to look after an injured person. In this fashion you actually create less casualties.

The 7.62 round which is a NATO standard round is much heavier round and so creates a more devastating wound and is more likely to kill.

Depending on the entry/velocity of the round bullets can go straight through, slow and stop in the body and can even ricochet off bone and end up in a different part of the body or leave in a different part.

There are many different types of round and they all have different effects, a hollow point has a huge power and because of its shape, mushrooms and has a devastating effect( the US's number 1 home defence pistol round) but it is, in bullet speeds, quite slower. There are fragmentation rounds that essentially shatter and create shrapnel inside the body.

As for grenades, it's not just the debris that kills, if you are close enough the pressure wave itself can kill. Think of all the movies where a grenade is thrown in a lake and suddenly fish start bobbing up. Generally these are killed by a pressure wave rather than the actual grenade shrapnel.

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Not military but as long-term martial artist with military SF tastes, am widely-read.

One thing I've read about choice of weapons in broad combat is sometimes it's about inflicting a slow death - you want opposing soldiers dealing with their own injured rather than clean kills. Fragmentation grenades are particularly effective in generating injuries which require time-consuming treatment due to insertion of many small fragments. So another way they kill is slow death through infection/bleeding.

What I didn't notice in the answers above is discussion of the speed of fragments.

This explosive speed paper as cited in Quora answer to Do fragments from a grenade travel faster than a bullet? puts the speed right in the middle.

A quick search based on the initial velocity of a perfectly spherical fragment from the composition-b explosive of an American M-61 fragmentation grenade yielded 480 meters per second. This is higher than the initial velocity of most pistol cartridges- .45 ACP and 9x19mm parabellum cartridges from pistol-length barrels fall about 10–30% below this, including +P and +P+ variants, and about 50–60% of a 5.56 NATO cartridge fired from a rifle-length barrel.

So you can regard a frag grenade up close as a bunch of tiny, mid-range bullet impacts plus overall explosive front.

Having read your spoiler, that gives you some interesting things to consider about responding to multiple impacts and distributed, focused point impacts vs one big one ;-)

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