Demolition Rules ?

[rust]

In my new campaign some of the characters will have to blow up quite a lot

of stuff during mining and terraforming operations, including parts of a moun-

tain chain.

While BRP includes rules for the Demolition skill, some basic data on explosives

and spot rules on the damage explosions can cause to characters, I do not

know how to handle the use of explosives to destroy huge objects, for exam-

ple soft and hard rock.

The basic question I am unable to answer is: How much explosive does a cha-

racter need to destroy a certain volume of rock ?

I could of course try to convert rules from GURPS or another system, but per-

haps someone has already found and perhaps even tested the solution to my

problem.

Thank you very much for your help !

Edit.: Problem solved, I will use the Heredium rules for explosives.

Edited November 24, 2008 by rust

[Atgxtg]

It kinhd of depends of what something is trying to blow up, what kind of explosive you are using, and how you place the charge. It takes a lot of explosive to actually destroy (break up) a buidling, bridge or some rock, but much less to take out a support and cause said object to collapse under it's own weight. The while point of the demolitions skill is to allow someone to recognize and take out the supports so that an object collaspes, rather than blowing it apart.

I can dig out some stuff for blowing up buildings, bridges and the like. I've even got so real world stuff for determining how much you need to cut through steel bars (and train tracks). But you might be better off keeping it abstact:

For a simple guideline, I'd suggest using the damage listed for explosives in the rules (I think BRP has the old CoC xd6 +1 d6 per so much more explosive on the weapon charts) and compare the damage inflicted to the SIZ of the object on the resistance table to see if the explosive force is enough to knock the object down.

A demolitons skill roll could kick up the "success level" of the explosive attack on the object, making it more likely to take down a big object with less explosive. A successful demolitions roll could inflict double damage, a "special success" do max damage (or triple), and a critical might do 4x damage.

This way you only need to give bridges, building and rock a SIZ rating based on their mass and go from there.

[rust]

This way you only need to give bridges, building and rock a SIZ rating based on their mass and go from there.

Thank you, that makes it indeed much easier !

[Guest Vile Traveller]

There's some layman introductory information on quarrying here, particularly under resources:

Planning for minerals home

I think you can probably make up something which seems reasonable in game terms by following Atgxtg's advice on size. The process is most efficient when you break material away from the face in chunks of exactly the right size - i.e. as big as can be handled by the PCs' equipment. It's easier and takes less explosive to break up rock into big pieces than into small ones, but you have to be able to haul those pieces away. Fines are the worst byproduct of the process, because that stuff gets everywhere and is useless as a construction material.

You should give the rock texture some thought, too, because that makes a lot of difference to what you get when you blast. Partially decomposed granite (it reacts with rainwater and becomes friable) can just turn to gravel if you're not careful. Gravel is very useful, but it's better to make it by crushing rather than blasting because you get less fines.

Anyway, there's quite a lot of information out there. I just happen to know a bit about it because I'm currently working on a quarry restoration.

[rust]

Thank you very much for the info and the very interesting link !

[Atgxtg]

rust,

I did a little digging and am working on a table with explosive strengths, amount you need to blow up/demolish things like doors, walls, vehicles building and bridges, along with modifiers for things like extra set up time, shaped charges and tamping.

I am going to set up it to list the amounts in standard M112 blocks of C-4 with about 1 lb of explosive charge. I(ll include a table with the Releative Strengths of other explosives, so a character can figure out how much nitro, TNT, dynamite, or black powder to use if he doesn't have any C-4 handy.

Hopefully I'll have it done tonight and can post it tomorrow. I just have to expand the BRP C\4 damages from 4 oz. on up to get the damages and figure out the resistance for various materials to being blown up.

[rust]

I am very much looking forward to it !

[Atgxtg]

I am very much looking forward to it !

Sure, put the pressure on.

Actually it'S fun to do stuff like this. I just hope it doesn't suck or doesn't make sense with the rest of the BRP rules.

One problem I'm already noticing is that the "double amount +50% damage" rule from CoC might not work well with th AP/HP ratings for vehicles. A M183 satchel pack will probably do enough damage in BRP terms (about 30d6) to blow a tank to bits. I don't think it would be quite as easy in reality. But hey, a character actually has to get close enough to place the charge on the tank in the first place, so he can probably use a break.

[Atgxtg]

rust,

Since I won't be getting my copy of BRP until after Christmas, I was wondering if you could check the BRP spot rules for explosives and see if doubling the amount of explosive increases both damage and burst radius by 50% (as in CoC).

The CoC spot rule is causing a lot of problems with demolitions and the effect explosices have during game play. I suspect that whoever thought up the doubling/+50% rule failed to consider that increasing the damage also increasesthe area of effect, and that doubling the number of dice every time you quadruple the amount of explosives ends up giving small to moderate sized conventional weapons bombs damage capability and area of effect that exceeds thermonuclear devices.

Even rounding the numbers down, a conventional bomb packed with 500 lbs. ton of TNT (something that could be dropped from a plane) does over 500d6 damage with a range increment over 250 yards/meters. This pretty much ensures that it will obliterate (inflict at least 100d6 damage) to any target within 60miles/100km.

To be fair, I believe that the doubling rule was never intended to be used for anything larger than, say, a sachel charge, or maybe two dozen sticks of dynamite.

As far a demolitions goes, this makes it hard for a character to survive his attempt, and makes it pretty easy to trash anything short of a battleship with a 20 lb. satchel charge. So I guess I'll need to tweak things.

[rust]

Since I won't be getting my copy of BRP until after Christmas, I was wondering if you could check the BRP spot rules for explosives and see if doubling the amount of explosive increases both damage and burst radius by 50% (as in CoC).

I did not find any such rule in BRP, neither in the Explosions entry of the Spot

Rules chapter nor in the Equipment chapter.

The only rule repeated in both chapters is: Damage is expressed in dice per

meters, damage done each meter past the initial radius decreases by 1D6

per meter.

Nothing about the doubling of the amount of explosives or any potential con-

sequences for damage and burst radius, at least not where it would be easy

to find.

[rleduc]

Maybe it is just me, but my first thought for scaling explosives would be to use the cube root of the amount to increase damage – something like this:

[table]Amount|Damage

1|x1

2|x1.25

4|x1.58

8|x1.99

16|x2.51

32|x3.17

64|x3.99

128|x5.03

256|x6.34

512|x7.99

1024|x10.07

2048|x12.69

4096|x15.99

8192|x20.15

16384|x25.39

32768|x31.99

65536|x40.31

[/table]

[Atgxtg]

Maybe it is just me, but my first thought for scaling explosives would be to use the cube root of the amount to increase damage

We think a lot alike here. I also think that increasing the blast radius at the same time is part of the problem since increasing the damage automatically increases the area of effect anyway.

I got out an Army Field Manual (5\2590) and seeing how the math looks.

[sdavies2720]

[table]...|...

8|x1.99

...|...

[/table]

The cube root of 8 is 1.99? Do you want to do extra math with a calculator?:ohwell:

Steve

[rleduc]

Just me being lazy and using Excel to quickly approximate the values. Sorry if it offends. (I used the “power” function to the power of .33 – obviously this is only a quick approximation of the true value – but it shows the trend). Since this problem only comes up in my games once every few years, and since I usually game with scientists (and corresponding graduate students), in the past we have just done “back of a napkin” calculations in game and gone with that.

[Kloster]

Just me being lazy and using Excel to quickly approximate the values. Sorry if it offends. (I used the “power” function to the power of .33 – obviously this is only a quick approximation of the true value – but it shows the trend). Since this problem only comes up in my games once every few years, and since I usually game with scientists (and corresponding graduate students), in the past we have just done “back of a napkin” calculations in game and gone with that.

Some players complain having to divide by 5 (for specials), others calculate cubic root on the fly!!!

That's life.

Apart to that, and not being a demolition expert, the rule I've learned in the army (were I was briefly exposed to explosives usage) was roughly doubling the damage for increasing the charge by a factor 8 to 10 (depending on the type of charge and what was to be blown). This is why it is more useful to use several small charges than 1 big.

Runequestement votre,

Kloster

[rust]

... roughly doubling the damage for increasing the charge by a factor 8 to 10 ...

Thank you for a very useful rule of thumb.

[sladethesniper]

For untamped charges, see below. For a tamped charge, use half...

Approximately 10 cubic meters of rock are disintegrated, 50 lbs of C-4

Approximately 50 cubic meters of rock are disintegrated, 200 pounds of C-4

Approximately 90 cubic meters of rock are disintegrated, 250 lbs of C-4

Approximately 160 cubic meters of rock are disintegrated, 500 lbs of C-4

Approximately 370 cubic meters of rock are disintegrated, 1000 lbs of C-4

Approximately 650 cubic meters of rock are disintegrated, 2000 lbs of C-4

Those are rough estimations going for easy "weights" of C-4...

There is lots of stuff online about actual demo math.

-STS

[rleduc]

Yeah – that data is almost perfectly linear (cubic rock disintegrated) = 1/3xpounds C-4 +0.6. Note that the response measure is in cubic units.

I’ll stick to cube root of the increase in explosive = final damage roll.

[Atgxtg]

Sorry for the dealy, I got "shanghaied" to do some apartment renovating, and since I have to move into the aforementioned apartment by the end of the month, I haven't had much time to work on this.

But, here is a quick heads up on where I stand:

I got a copy of an army filed manual (FM5-250) for demolotions, and the cube root thing is about right for brecching charges (making holes through walls), but probably doens't quite hold up for cutting charges and other types of demolotions.

I7m working on converting the formulas into easy to use BRP terms, but CoC's increasing the damage and range increment by 50% per doubling causes some whacky results.

What seems to work out best is to use a standardized blast radius for all explosives, since increasing damage dice increases the blast radius anyway. Sothing like -1d6 for each 50% increase in distance might do it. That way I can use the Reletive Effectivness values to allow the system to work with just about any explosive.

What is looking good to me at the moment is to use something like x2 explosive=+1d6 damage. It is easy, and seems to hold up well in game terms. It also keeps a 10 kg satchel charge from doing 50d6 to everything within 20m, and killing everybody within a 1km radius, making demoliions skill kind of pointless.

I'm also seeing if I can make it all compatible with my old armor and vehcile rules.

What I've got for a working model is giving the object a resistance value based on the SIZ of the hole, with a modifer based on material and thickness. I need to compare it to the sample protection values in the BRP rules to see how well it will work in game play.

BTW, it it helps FM 5-250 has all sorts of formulas and tables that explain how much explsoivieve you need to do just about anything. I found it online, and could put some of the more pertinent stuff up here if desired.

My only worry is that the FM is real world info, and not the kind of thing that we might want to spread around. While we find it useful for gaming, there are probably some poeple out there who might want to know how to blow up bridges for less friendly reasons.

[rust]

Thank you for the information.

I will take a look at the FM, it is available on the net.