Explosives: Lethality of 1 pount of TNT

[schnuersi]

Originally Posted by kure

range damage
0 42
1 14
2 7
3 4,666666667
4 3,5
...
This is realy bit low, at range 3+ there is no real danger. At range 2, this is a major wound.

I really doubt someone who takes 5 or 4 points of damage (rounded up) in reality will call this "no real danger". It won't take out a badass Char who doesn't feel pain and isn't alive. So because GURPS is "just" a game explosives don't hurt as much as they do in real life.

Explosions in confined spaces create more concussion effect not because the shockwave travels back and forth and does damag everytime it passes. While this effect exists it only contributes a little. More importat is the dissipation speed of the presurised gas. While it will dissipate allmost instantly in the open it will take time if it has just a small door or window to dissipate thru. While this time is only measured in fractions of a second it means beeing hit by a shockwave in the open or beeing exposed to several (maybe dozens or hunderets) atmospheres of presure for a short time. And this is quite dangerous.
Furthermore you have to look a the hit locations. The concussion ignore armor unless completly sealed (today no armor in common use qualifies). It attacks eyes ears and the lungs - wich qualyfies for an attack against the vitals. It will deafen the victims and possibly blind them - maybe even permanatly. Adittionally they will be stunned and/or disoriented for some time. So i think it isn't really nessesarry to reflect the shockwave back and forth.
If an explosion occures in the open use the regular rules. If it occures in a small room (wich isn't blown appart) double the distance at wich damage decreases. So if a pound of TNT is placed in the middle of an average flat room (5m by 5m and 2,5m high) everyone will take 14 points of damage unless he is standing right next to a wall (someone right in the middle will take the full 42 dam) . Furthermore everyone standing in front of the door will either be hit by the door or if there is no door take regular damage with distance calculated from door step.
While this is not a siencific proven formular i think it is acurate and simple enough to be usefull in a game.

[Anthony]

Realistically, 1 lb of TNT has a good chance of killing by overpressure at about one hex. It's a major danger from fragments at a number of times that range (good chance of lethality at about 3 hexes).

Explosions bouncing around in rooms is rarely an issue; the overpressure required to destroy a non-armored building won't cause worse than burst eardrums on a human. The major added hazard from explosives indoors is the chance of dropping the ceiling or collapsing the building on the victims.

[schnuersi]

Originally Posted by Anthony

Explosions bouncing around in rooms is rarely an issue; the overpressure required to destroy a non-armored building won't cause worse than burst eardrums on a human. The major added hazard from explosives indoors is the chance of dropping the ceiling or collapsing the building on the victims.

A pound on TNT simply placed on the ground will not destroy a building made of stone. It will ruin the furniture and may start a fire but the building itself will stay intact. If it is detornated below the roof and the roof is a conventional construction of wooden frame and rooftiles it will blow of the tiles and some parts of he frame. But these will be blown away and only some will fall down to the place they started from.

[Anthony]

Originally Posted by schnuersi

A pound on TNT simply placed on the ground will not destroy a building made of stone.

I would classify a stone building as armored. In any case, the 50 psi or so required to actually kill a human from overpressure will definately flatten anything not built like a bunker.

[Luther]

Schnuersi, interesting discussion.

Anthony, have you a reference for the 1 yard lethality radius? The document you referenced* doesn't discuss casualty rates. The best info I've found is that 62 psi have a 50% casualty rate, and 92 psi almost 100%. However it didn't give exposure times, so I've to guess from the rest of the document that these are figures in the open. It would be useful to find the psi-casualty relationship given exposure times. I've already collected quite a bit of material about structure damage, so that's the missing bit.

Others. Please guys let's collect some real world data before going off tangent and suggesting house rules. I've the feeling the new explosion rules in 4e are quite right for a game.




* EFFECTS OF EXPLOSIONS AND PERMISSIBLE EXPOSURES

[Rupert]

If your source was talking about explosions, the exposure time is "very short". What matters is the onset rate - divers routinely expose themselves to over 50 psi without ill effects, and deep dives produce pressures of 200+ psi.

[Anthony]

Originally Posted by Luther

Schnuersi, interesting discussion.

Anthony, have you a reference for the 1 yard lethality radius?

Sorry, no, that was just extrapolation to about what point would produce sufficient overpressure to be lethal. In any case, lethality is mostly a function of peak static overpressure (the shock wave) not dynamic overpressure, and thus exposure time is negligible (about as long as the shock wave takes to pass, which is under a millisecond for a human perpedicular to the blast front).

[Luther]

Originally Posted by Rupert

If your source was talking about explosions, the exposure time is "very short". What matters is the onset rate - divers routinely expose themselves to over 50 psi without ill effects, and deep dives produce pressures of 200+ psi.

Of course we are talking about explosions, Rupert. That's the whole point of the thread. Since you ask for details, I'm actually talking about static overpressure, that is overpressure after the blast wave (which is called dynamic). Exposure time vary according to external condition -- it's longer in enclosed spaces -- and heavily affects casualty rates.

[Luther]

Originally Posted by Anthony

Sorry, no, that was just extrapolation to about what point would produce sufficient overpressure to be lethal.

And how much psi would be lethal according to you data? Is it in the open, on in enclosed spaces?

In any case, lethality is mostly a function of static overpressure (the shock wave) not dynamic overpressure, and thus exposure time is negligible (about as long as the shock wave takes to pass, which is under a millisecond for a human perpedicular to the blast front).

From what I've studied, this isn't the case. I may be wrong, but I understand that, even for static overpressure, exposure time is very relevant -- think about lung and eardrum injuries. Our body can stand a fast overpressure peak better than a prolonged one, the stress on tissues is much lower.

[Kromm]

Originally Posted by Luther

I may be wrong, but I understand that, even for static overpressure, exposure time is very relevant -- think about lung and eardrum injuries. Our body can stand a fast overpressure peak better than a prolonged one, the stress on tissues is much lower.

Sure, but the shock front caused by an explosive is essentially a transient, and its peak overpressure is in fact all that matters. Differences in peak shape from one explosive to the next for an explosion in atmosphere are essentially negligible from the body's point of view, although they do matter for the demolition of solid materiel in contact with the charge. "Static overpressure" is almost meaningless when speaking of the effects of explosives on human beings.