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Old 04-24-2015, 09:54 PM   #1
PTTG
 
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Default GURPS stats for a tank cooking off?

I had a generic german WWII tank in bad repair that suffered two flares and a stick grenade inside. I determined that this caused the ammo to cook off, and the fuel in turn.

A PC is 5 yards away. How much damage does this do? I figure there's a certain amount of luck involved, but what sort of effects does this do?
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Old 04-24-2015, 11:14 PM   #2
Buzzardo
 
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Default Re: GURPS stats for a tank cooking off?

I'm basing my response on pictures of such things that I've seen over the years. I've never been in a tank or seen one explode in person (and I'm happy about the latter). You can find a few pictures by doing a Google image search for "Exploded WWII Tank" (without the quotation marks). (You'll also get a couple interesting diagrams of WWII tanks.)

The only certainty is that there'll be a tremendous fire. The turret may or may not come off. If it does come off, it's likely to just fall off one side or the other. Popping up 30 feet in the air and landing 30 feet away is cinematic.

Unless shrapnel from the explosion hits the PC, the PC should be able to move away quickly enough to avoid damage. Moving may expose the PC to attacks from the enemy, but very few people would stick around to get cooked.
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Old 04-24-2015, 11:27 PM   #3
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Default Re: GURPS stats for a tank cooking off?

Well, it should probably be a Regular Contest of Cooking Skill vs Cooking Skill, but the tank will take a penalty due to lacking No Fine Manipulators.
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Old 04-25-2015, 02:02 AM   #4
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Default Re: GURPS stats for a tank cooking off?

Quote:
Originally Posted by Langy View Post
Well, it should probably be a Regular Contest of Cooking Skill vs Cooking Skill, but the tank will take a penalty due to lacking No Fine Manipulators.
And the winner is!
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Old 04-25-2015, 02:59 AM   #5
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Default Re: GURPS stats for a tank cooking off?

Quote:
Originally Posted by PTTG
I had a generic german WWII tank in bad repair that suffered two flares and a stick grenade inside. I determined that this caused the ammo to cook off, and the fuel in turn.

A PC is 5 yards away. How much damage does this do? I figure there's a certain amount of luck involved, but what sort of effects does this do?
Iím not certain that the effect youíre looking at is an actual ammo cook off, so letís go over the possibilities. First, Iím assuming that youíre talking about the stored ammunition and not a round already loaded into the tankís gun. A round loaded into the tankís gun is going to be pretty much immune to both the grenade and the two flares. Neither the shockwave from the explosion of the grenade nor the shrapnel are going to get through the breech or the chamber, which are inches thick steel. Even if both flares landed on the breech block, it will take considerable time to heat the breech and then the chamber and then for the heat of the chamber to transfer to the brass cartridge case which has to get hot enough to set the propellant off inside. Alternatively, the breech block might get hot enough to transfer its heat to both the base of the cartridge case and the primer, setting the primer off. In either case, the round will fire out of the barrel at whatever the tank is ďaimedĒ at, at the moment of detonation.

The stored ammunition would have greater exposure to the effects of both the grenade and flares. Unless the stick grenade was an incendiary grenade, it canít cause a cook-off, though it might cause a sympathetic detonation if it went off close enough. The two flares would need to land among the ammunition to cause a cook-off. Again it has to heat the cartridge case first which will then cause the propellant to burn or possibly explode. If the propellant burns, it will fire at relatively low velocity compared to that attained by it exploding when the primer is struck. The flares will not be able to cause sympathetic detonation of the projectile. What happens when the projectile is ďfiredĒ by cook-off is a bit of a question. Ammunition for modern rifled guns wonít arm the fuze until the round is spinning rapidly enough to set back the safeties. This is to prevent an explosion from occurring at the muzzle of the gun. If this was also true of WWII era rifled ammunition, the cook-off wonít spin the projectile at all, preventing the fuze from functioning, causing the round to effectively be a ďdudĒ.

If you get sympathetic detonations of one or more projectiles, they will explode for their rated damage. Assume the fuel tanks are protected by between half and a third of the tankís DR on that side, as the fuel tanks are generally inside the armour and possibly better protected from external explosions than internal explosions. The fuel will spill into the compartment and will probably catch fire. There is no danger of an explosion unless the gasoline vapourises, in which case you can get a powerful explosion. If the fuel is diesel; well, one of dieselís advantages is that it wonít explode; itíll just burn.

For the PC, if he is outside the tank, he only has to worry about the damage that fully penetrates the armor, so figure the damage and subtract the DR. On the other hand, if heís 15 feet away from the explosion but inside the tank, he may be a goner. Even if he is in the driverís compartment and avoids the effects of the explosion, he has to contend with the fire. Quick-disconnect headsets were a post-WWII development. Many persons who wore radio headsets, which often included drivers and commanders of armoured vehicles where the radio had an intercom facility for communication among the crew, could not discard the headset quickly enough and were burned to death as a result.
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Old 04-25-2015, 07:52 AM   #6
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Default Re: GURPS stats for a tank cooking off?

I'd say the numbers given by the Fragile (Explosive) disadvantage look fairly reasonable: 90d for a 150 HP tank. That's about equivalent to 56 lbs of TNT, or a couple of dozen shells worth of propellant going up at once.

I'd let the tank's armour protect those outside it to some extent (although it would also increase fragmentation damage). Say around thirty dice less for an inch and a half of steel.

Divide the remaining damage by 15 for distance and the unfortunate PC will be hit by 4d Crushing damage with another 1d Cutting for each fragment which hits.

Note that things get a lot better at even one yard further away: then you only take 1d+1 Crushing and don't have to worry about fragments.
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Old 04-25-2015, 08:21 AM   #7
Anaraxes
 
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Default Re: GURPS stats for a tank cooking off?

Quote:
Originally Posted by Langy View Post
the tank will take a penalty due to lacking No Fine Manipulators.
... but gets an familiarity bonus when the secret ingredient turns out to be depleted uranium. Allez cuisine!
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