Alright, I've been considering this and playing with it a bit. For the sake of this project, there are a few rules I need to keep in place, such as:
The calculation cannot use logs at all ever. The most complex operator it can use is division
The calculation must work on scales as small as 1 meter
Must scale reasonably well enough for someone to blow up a building
Must make reasonable sense
Must not completely ruin game balance
Must not require a bazillion notes
It must be something a knucklehead like me can come up with (this rule can be tossed out the window if someone else helps
)
The biggest restriction is the lack of exponents and logs. That is obviously a major kink when the formula is completely one of well, exponents and logs. However for the 3 meter to 15 meter range, which is where most of our combat happens, we can hit it APPROXIMATELY by just dividing the power by 2 every meter. This is a very rough number, but I don't think anyone will argue it's hard to remember or to use. At 2 meters, divide by 4, at 3 meters divide by 8 (alright, we're getting into exponents here, but only incidentally).
The first problem here is calculating the initial blast power. I read the TM 5-1300 and boy, those guys could use a lesson in including notation, because they throw numbers all over the place without mentioning if it's kilos or feet. However, it's pretty clear that if you're holding a piece of TNT against your chest, you're going to die. Since in combat we don't generally see that situation, it's more reasonable to assume that the point of explosion will be at least 1 foot away from whatever it is we're concerned about and just put a special rule about 'if the explosive is physically on top of whatever is being blown up, multiply the power by X for that purpose'. Secondly, we need to cut off the peak of our logarithmic graph so we can fit it into what is basically a geometric graph. This unfortunate loss in accuracy does help however, in that it allows a shadowrunner sitting on a grenade to survive the blast, since it will be less than what a point blank explosive blast would be (but still enough to kill most NPCs). This is an unanticipated but ultimately positive concession.
If we wanted to increase realism, we would having a large 'divide by' number for closer in and a smaller one for farther out, so perhaps from 0-3 meters it divides by 10 every meter, then it divides by 2 from then on, or perhaps divides by 2 every 10 meters from 20 meters out. This could greatly increase the realism without violating the rules above, but it becomes ungainly and makes math more difficult in that a person 4 meters out has to divide the power by 1,000 then by 2, adding steps. I'd prefer to avoid this unless really necessary, but I'm open to thoughts and questions.
For the sake of math, we'll stick to TNT, since that's the basic number they always use in explosive calculations. Grenades will act like a smaller mass of TNT, C4 and the like as a larger mass. It appears the initial blast is just a function of mass * power, so if we say C4 is four times as powerful as TNT (just pulling numbers out of my butt), 1 kilo of C4 is equal to 4 kilos of TNT.
Disregarding other things like shrapnel and the like, which greatly increase the deadliness of a blast, .45 kilos is about 1,000 psi at 1 foot and 11 psi at 5 (if we go off of kzt's chart above). Unfortunately, any starting number in this range of 2 meters shifts the graph up because it's still dividing by such a large number. So in this case we may want to move out to 3 meters, figure that's approximately where most explosive damage will happen, and figure out a good base by multiplying by 4.
At 6 psi wooden utility poles are snapped and people are still pretty darn dead, so we can be pretty satisfied that multiplying this by 4 will still mean people are pretty darn dead (and also doesn't give us a good number to start with). At 4 meters we're close enough to 'threshold for significant human mortality' to use that. Human mortality means Deadly damage. With an average body of 3, we're looking at a power of 3 or 4 most likely. Winding back up, that means at our 'point blank', we'd be going off of around 32D.
At tis point we're hitting a new problem - shadowrun does not change from Deadly to Serious to Light very easily. With the current numbers, at 4 meters it would be killing people, at 8 it would be .5D. I do not yet have the best solution to having explosive blasts 'stage down' which was one of the initial complaints people had. This really would be better served by saying explosives cause 10 boxes of damage and lose 1 box of damage every X meters. But we don't currently have that, so we'll have to make do with something else. Fortunately, the Shadowrun damage track sort of supports having something akin to an exponential decrease in power, since Deadly does almost twice as much damage as Serious.
So since no one can roll below a 2, we can simply say when Power reaches 2, the Damage Level decreases by 1 (from Deadly to Serious) and Power increases again. A body 3 person can expect to get 2 successes from a 2D attack, staging it to Serious, so we can choose any power above 5 or 6 without seriously influencing his odds. A body 1 person is basically SOL no matter what. A body 6 person can expect 5 successes against a 2D, equivalent to 4S. So the working compromise I'd suggest is:
Every time power reaches 2, decrease the Damage Level by 1 and increase the power to 5. When the damage code is less than 1L, no damage roll is required.
(Of course, SR4 players probably won't have this problem.)
*WHEW*
Given that, with TNT as a round start, we can figure out other things like grenades and C4. Like I said above, the easiest way to do this right now is standardize everything by power and set it so you're buying different quantities (i.e. - when you see C4 listed in Street Gear, it's for the equivalent of 1 kilo of TNT, so maybe this is a quarter kilo of C4). Unfortunately, this becomes awkward when dealing with grenades, so we probably will have to break down and just write basic damage codes across standardized weights i.e. if TNT causes 32D at 'point blank', C4 causes 128D (or maybe just 32 Moderate Naval Damage?) A grenade meanwhile just causes 8D.
It's also noted that special circumstances will change these numbers. When I was looking at the examples of blast power in the army book, I mostly went off unobstructed groundburst. If that explosive is detonated in the air, its power is halved. Otherwise power is reflected as shown in the main SR3 book. With a little thought, we can implement rules for shaped charges - the detonation is automatically guided a particularly route, significantly decreasing or completely eliminating the blast effects in other directions. This is especially relevant for AV warheads.
Blasts are very effective against materials, and cause more damage to materials than to people by and large (i.e. - our combat rules are designed for fighting between fleshy people, not against walls. Demolitions cause a lot more damage to walls than say axes and punches would). To reflect this, barrier ratings are reduced by half.
Finally, and perhaps most importantly, the danger of the blast to people is greatly increased by the other stuff around. A grenade throws up shrapnel, a stick of dynamite in a box of nails will cause tremendous damage to fleshy people around (although not significantly more to stable structures). These rules would probably count as flechette - damage level increases by one (so Deadly becomes LN) against unarmored opponents. I don't think armored opponents would get the benefit of double impact or impact + ballistic, however, since they'd still need to deal with the shockwave. Honestly, I'd consider saying it's just a flat increase to damage level against fleshies, and that's it. There's a difference between throwing tiny shards of glass and throwing pieces of telephone pole, so which way we rule would depend on which case is likely more common.
Some explosives don't just cause a shock wave but also cause a burst of extreme heat. Examples of this would be gasoline exploding, which creates a giant fireball. In these cases the damage level would be increased against fleshies, but can be staged down with fire resistance.
A note here, if we turned to a unified explosive force degradation mechanic, there would be no difference between offensive and defensive grenades with the same damage code. Frankly, I don't know how they work anyway, so I wouldn't mind an explanation. If grenades rely primarily on the shrapnel thrown up rather than the shockwave, it may mean they are better served by the current mechanic (an arithmetic decrease in power, since they'll constantly decrease in power based on air resistance or something).
Alright, at this point I'm sure I've made a thorough fool of myself, but hopefully I've made a better fool of myself than whoever wrote the initial rules. So I open myself up to comments and criticisms.
Better or worse than the current rules? Simple? Too simple? Too difficult? How absolutely terrible is my math? Any other terrible botches? Would you use it over the current rules?
Thanks for your attention, all.