If one were to change the current SR rules to mirror reality more closely, how would explosives look? How do explosives lose power over distance and what other factors should be properly remembered? Does anyone else have house rules for explosives in their games?

Note that that's purely blast, which is a wave propagating in three dimensions. A piece of debris or shrapnel launched by the explosion will lose velocity according to standard projectile mechanics, which is why hand grenades can cause casualties out to hundreds of meters (though to say they don't do so reliably would be an understatement).

~J

What would you say the "reliable" casualty range on a fragmentation grenade would be, Kage?

Chris

Old style (ww2) grenades had crappy frag patterns. The case shattered into a fairly small number of large pieces and dust. Large pieces will go a long way, but "big sky, little bullet." So the chance of soemone getting hit is small, but the damage is huge if you do and the large pieces can kill you at over 100 yards away.

Modern frag grenades (technically "defensive grenades" - which is the inverse of what the FASA boy geniuses called them) use many prefragmented pieces, either notched wire, inner scored body, or ball bearings. This produces a much denser pattern of small fragments. Which have a predictable lethal range and will still do (likely) non-lethal damage a ways past that. The fuze pieces will still go a long distance, but you have to be very unlucky to get hit by that.

For example, the M-67 fragmentation grenade
"Capabilities -- can be thrown 40 meters by average soldier. The effective casualty-producing radius is 15 meters. ALTHOUGH THE KILLING RADIUS IS 5 METERS AND THE CASUALTY PRODUCING RADIUS OF THIS GRENADE IS 15 METERS, FRAGMENTS CAN DISPERSE AS FAR AWAY AS 230 METERS."

The 230 meters is (IIRC) the fuze.

According to this page, fifteen meters for the M67 grenade.

Of course, that's just for that one grenade. Different grenades have different casualty radii.

~J

Alright, so for the blast effect, every meter it would decrease by a ^1/3, however shrapnel and grenade effects would be better simulated by some sort of blind fire mechanic where there's a 90% chance of hitting any given item within 15 meters.

That sound right?

No no, the power would be proportional to 1/(x^3), with x being the distance from blast center.

~J

So, I'm gonna guess that that is a loose approximation rather than suggest (if I am reading the formula correctly that [Blast effect at r] = [blast at r = 0]/(r^3) ) that if you are 1 cm away from the blast point than the effect is 1 million times stronger than at the blast point. (I suppose I should be using the smallest units possible though....) Can someone help me figure how to make this work so that someone standing 1m away from a grenade (or 10 kilo explosive) doesn't take the exact same damage as someone standing on said explosive? (and still have a reasonable decrease in power)

Basic issue that SR misses is that the damage you take isn't dependent on the mass of the explosive, it's dependent on the combination of distance and mass. So a 1 pound charge at 1 foot is much worse that a 20 pound charge at 20 feet.

Ultra-short range:

You get significantly increased damage from a contact blast.

For TNT you get a contact blast at distances of R=0.136 ft * Weight^(1/3)
Multiplier of 1 for 500 pounds or less, up to 3 at 3000 pounds or more.

TM-1300 doesn't describe the physics of a contact blast in detail, but double damage or more would seem reasonable. They want you to store bulk explosives at least a foot off the concrete floor to minimize contact blast cratering.

The major points on the blast chart (Fig 2-7 in TM 5-1300) are
Contact=10,000 PSI
1=R/W^(1/3) 1000 psi
5=R/W^(1/3) 11 psi
10=R/W^(1/3) 6 psi
50=R/W^(1/3) 0.75 psi
100=R/W^(1/3) 0.4 psi
(oops edited to fix operator)

TM 5-1300 mentions that only superficial damage occurs beyond 100=Rx ft/lb^3. Broken windows, etc.

In terms of what blast does

Overpressure, psi Expected Damage
0.04 Very loud noise (143 dB); sonic boom glass failures
0.1 Breakage of small windows under strain
0.15 Typical pressure of glass failure
0.30 10% of windows broken
0.5 Windows shattered, limited minor damage to house structures
0.7 Upper limit for reversible effects on humans
1.0 Partial demolition of houses; corrugated metal panels fail and buckle; skin lacerations from flying glass
2.0 Partial collapse of walls and roofs of houses
2.4 Eardrum rupture of exposed populations
2.5 Threshold for significant human lethality
3.0 Steel frame building distorted and pulled away from foundation
5.0 Wooden utility poles snapped
10 Probable total building collapse. Lungs hemorrhage
20 Total destruction. 99% fatality due to direct blast effects

http://www.aristatek.com/explosions.aspx

1=R/W^(1/3) 1000 psi

1 is 1 foot, R is radius? Also 1 foot? W is weight of the explosives (in pounds?)

So it would be strength at 1 foot = 1/(W^(1/3)) * 1,000 psi?

Hrm... I know I'm missing something, since that would mean 1 lb. would give off 1,000 psi whereas 9 lbs would give off 333 psi.


(Thanks for the clarification)

Looking at my log chart, it would be approximately 3.02, so 3,020 PSI? Seems to make sense... Same answer multiplied by 9^1/3. That makes the math a little simpler (and it has been way too long since I used logs, so any simpler is better).

Thank you a *TON* for the help. Now to simplify it to a 'close enough' mechanic...

I'd be interested in what you come up with.

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.

Offensive grenades kill primarily by concussion. Hence they have a fairly small deadly radius and can be thrown by any soldier such that the thrower is outside the area where they will take significant effect. This is really useful on the attack, as guys attacking are not in cover, hence they are called Offensive grenades. (You do get some fragments from the fuze, but that is fairly minor.)

Defensive grenades primarily are designed to produce a lethal cloud of fragmentation. The shock wave can still kill you, but the primary mechanic is fragmentation and has a rather large radius of danger, larger than an average soldier can throw it. This is ok when the person throwing the grenade is in hard cover like a foxhole, it kind of sucks when you are in the open. Hence these are called Defensive grenades.

Shadowrun rules naturally gets it backwards.

Overall your idea looks reasonable for small values of explosive and distance, but for car bombs not so good...

With large quantities instead of dividing by 2 it would divide by some much larger number, however the Shadowrun damage system doesn't really work well for hugely destructive forces like nuclear bombs and car bombs, unless you feel fine throwing out 10,000ND attacks. I'm not too interested in reworking the complete Shadowrun damage system, although I suppose you can just say '500 lbs of TNT means everything within a radius of X is destroyed, no chance to resist. Past that use the standard rules, dividing by Y.'

The easiest way to do it would be to calculate power based on mass and distance separately, particularly since a single explosive might damage multiple objects at multiple distances. First determine damage at one meter and then modify based on the inverse cube law. This way, we avoid using roots and logs multiple times per explosion.

I'm not quite following. Would you be kind enough to write out an example?

Lets say that the power of an explosive at 1 meter is the function f(m) The power at 2 meters would be f(m)/2^3 at five meters f(m)/5^3 at half a meter f(m)/0.5^3 = f(m)*2^3 and at one millimeter would be f(m)/0.001^3 = f(m)*1000^3.

f(m) might involves roots and logs, but once it is calculated it is simple to determine the damage at any given distance.

Of course, with nuclear weapons we'd use the inverse square law to determine damage from heat and radiation, rather than the inverse cube law (we might have to calculate blast, heat, and radiation damage separately in such a case.

Simple for you and me (well, you) isn't simple for the 'average' player. Your rule would work and work well almost regardless of quantity or distance, but it uses logs and exponents which, for MOST people would make it too complex (heck, last night to buy gas I was calculating 4 gallons * 2.75 per gallon and the cashier looked at me like I was crazy).

I don't know about you, but while I can get approximate answers to common logarithms, exponents, and fractional exponents pretty easily, addition and non-exponentiating multiplication seem to continually defy me.

~J