From v04.n849 Thu Jul 30 13:43:17 1998 Date: Mon, 4 May 1998 11:03:16 -0700 (PDT) From: Anthony Jackson Subject: Rules on Conventional Explosives Again, comments wanted; these rules are probably more generally useful than nuclear weapons, and seem to reality-check fairly well. A method of simplifying this (so as to not use table lookup) would be nice, but I didn't have any great inspiration for how to do that. While discussion of nuclear weapons is occasionally interesting, by and large it isn't particularly relevant to PCs, and for the most part are going to fall under the category of 'plot device'. Conventional explosives are _far_ more likely to be directly important to PCs, and while the GURPS rules on explosions are less obviously broken for conventional explosives than for nuclear weapons, they don't really work quite right for conventional explosives either -- in fact, based on my research it appears that they are far more broken than I originally realized. Explosions cause damage via both direct overpressure (concussion) and by throwing objects around (shrapnel, translation injuries, hitting barriers). Overpressure generally is order +1/2 in total weight of explosives, -3/2 in distance, which means that the radius of destruction (via overpressure) is roughly order 1/3 in distance. Shrapnel is extremely variable, and these numbers are slightly questionable but probably reasonable. Blast ratings: for simplicity, explosives are just given a 'blast rating', reflecting the distance at which they have a particular destructive ability. This is a fairly low resolution method of handling damage -- a ten-fold increase in destructive force is only +2 blast rating -- but likely to be sufficient for the requirements of gaming. Blast ratings are normed such that 1d of damage is a +0; thus, 1 pound of conventional high explosive is a +2, one ton is a +9. Note that if dealing with secondary explosions from energy weapons (fusion/etc) double and subtract 2. Blast Dmg Frag Blast Dmg Frag Blast Dmg Frag - -3 1d-4 1d-2(6) -2 1d-3 1d-1(8) -1 1d-2 1d(10) +0 1d 1d+1(12) +1 2d 1d+2(14) +2 3d 2d(16) +3 6d 2d+2(16) +4 10d 3d(17) +5 6d*3 4d(18) +6 6d*6 6d(19) +7 6d*10 8d(20) +8 6d*18 10d(21) +9 6d*30 6d*2(22) +10 6d*55 4d*4(23) +11 6d*100 5d*4(24) The 'dmg' column indicates concussion damage to a human; to determine the actual column used for blast, add up the blast rating of the weapon and the range penalty; minimum effective range is 1 yard (treat 'touch' range as a range modifier of -3, 'internal' as -4). For larger than human victims, add half their size _or_ half the range mod, whichever is less. For vehicles, add +2 and modify for size as above. For buildings, add +3. If you have cover, reduce by 1 level for moderate levels of cover, 2 levels for near total cover. Knockback: to determine knockback distance, multiply damage by 10 * range from blast to victim, and divide by the weight of the victim; this distance will not exceed twice the damage rolled (yes, larger blasts throw you further at the same overpressure). The 'frag' column indicates expected fragmentation damage, and the chance of being hit by a fragment. Add any cover modifiers, and twice the size of the target, to the chance of being hit by a fragment. These numbers are subject to adjustment for the type and quantity of stuff available to be hurled around. Note that the maximum chance to hit is 16. If fragments hit, you are hit by a number of fragments equal to the amount by which the fragmentation roll succeeded (at least 1), on a critical success roll for a normal critical success in ranged combat for one fragment. A building is assumed to have a size of +2 on each hex. I tried this as an example, comparing with the expected results (per the military standards for munitions storage), the destructive effects look about right, though damage to vehicles is possibly somewhat low. For reference, here are the expected effects at particular ranges for 1000 lb equivalent of high explosives (this per standard explosive safety regulations). 20 yards: personell generally killed (due to blast, fragmentation, and hitting surfaces), unreinforced buildings are totally destroyed, most ground vehicles crushed and/or overturned. Direct overpressure will not kill at this range. 30 yards: unreinforced buildings essentially destroyed, personell likely to be killed or seriously wounded by blast, fragmentation, or translation, unarmored vehicles will be damaged beyond practical repair. 37 yards: unreinforced buildings likely to be essentially destroyed, personell likely to be seriously injured, eardrum rupture likely (20%), aircraft will be disabled and are likely to catch fire, ground vehicles will have serious surface damage and minor internal damage. 60 yards: unreinforced buildings suffer 50% damage, serious fragmentation damage likely, major surface damage to vehicles, aircraft are probably disabled. 80 yards: 20% damage to buildings, minor fragmentation hazard, minor damage to vehicles, minor navigation hazard, aircraft probably are no longer airworthy but can be repaired easily. 100 yards: 10% damage to buildings, other forms of damage unlikely to disable or seriously wound. May cause loss of control for aircraft. 130-170 yards: 5% damage to buildings, possible injuries from broken glass, other hazards minor.