Think Tank: Going Boom!

In an armoured room deep in the heart of the Dark Harvest’s secret bunker, a lone ginger Igor sits and scratches away with pen and parchment; creating ideas and information for his master.

These are his musings.

This week, I’m continuing to follow up on the fortified churches story with a quick look at explosives, and how a GM can support your desire to Blow Something Up.

Some science and games mechanics follow, along with a couple of maniacal giggles!

Dynamite

“Dynamite is an explosive made by soaking sawdust in nitro-glycerine and forming the mixture into sticks.” – Resistance, p146.

How does it work? Well; the “active” constituent of dynamite, nitro-glycerine, undergoes detonation in the presence of heat according to the following chemical equation:

4C3H5N3O9(l) + heat ⇒ 6N2(g)+12CO(g)+10H2O(g)+1O2(g)

Now, if you never studied chemistry at school, the important point here is that 4 parts of liquid nitro-glycerine will produce 29 parts of nitrogen, carbon monoxide, water vapour and oxygen (or using a rough approximation, 1 wine bottle filled with pure nitro-glycerine will produce enough gas to fill 1,100 wine bottles of gas! These gases will expand in a bubble, trying to fill the available space around them as quickly as possible, until the gas pressure balances out with normal air pressure. The practical upshot of this is that the explosion produces a shockwave which travels outwards at a speed of over 7 kilometres per second, and it’s this shockwave that causes all the damage.

Why am I telling you all this? Good question. There are some points we need to take away from this when we talk about the rules for using dynamite in Dark Harvest:

  1. The more dynamite you use, the bigger the bang. This is just a simple multiplication: 3 sticks of dynamite will produce 3 times as much gas as 1 stick, and it’s that gas expansion that does the damage.
  2. If you pack multiple sticks of dynamite into a small space, you will get added bang for your buck, but only in a smaller radius of explosion. If the detonation shockwave encounters resistance as it expands (say a wall), it will destroy whatever is in its path, and carry it along with it as it continues to expand. The extra mass it has picked up will do more damage against the next thing it his, but moving all this extra material takes energy out of the shockwave, and causes it to stabilise faster. This is the basic principle behind all fragmentation grenades.
  3. There is a minimum safe distance for a dynamite explosion. The shockwave will eventually peter out, and that’s the point where it’s safe to stand.
  4. Skill plays a factor in how effective a dynamite detonation is – how much explosive and how tightly packed it is will determine the size of the explosion, and how far away you need to get before you’re safe (which determines the length and composition of the fuse you intend to use).

System Notes

Area Effect

For those not in possession of a copy of Resistance, here’s the weapon effect that applies to dynamite, with a slightly different example to what we published in the book:

A weapon with an area effect will deliver damage to everyone within a circle centred on where the weapon goes off. Anyone unlucky enough to be standing at Ground Zero should take damage equal to the normal damage of the weapon, plus extra dice equal to its Area Effect rating. Anyone within a radius equal to the Area Effect rating in yards will take the normal weapon damage, and anyone beyond that, out to twice the Area Effect rating in yards will take damage equal to the normal weapon damage, less the Area Effect rating.

Example: A thrown stick of dynamite, damage rating 8D, Area Effect (2) will do 10D damage at Ground Zero, then 8D out to 2 yards from the point of detonation, then 6D out to 4 yards.

OK so far? Right then, here’s the new bit. When combining explosives, you multiply the damage code by the number of devices (2 sticks of Dynamite = 16D), and add one to the Area Effect rating for each additional device (Area Effect(3) for two sticks of dynamite). Yes, this can get crazy, but we are talking about BIG explosions here.

Damaging Buildings

The other thing we need to consider when blowing something up is how strong it is. This is really for the GM to decide, but to give you some idea, the wall of a simple house will have around 15 Hit Points, and a more substantial townhouse around 25 Hit Points. More heavily constructed walls (say a barracks) may have around 40.

Proper fortifications like Tàrga Mures will have been built to resist explosives, and will have upwards of 80 Hit Points in a section of wall, but will also have a Fortification rating. Each point of Fortification on a structure will add a Black Die to the roll made by the demolitions expert… Which brings us to the mechanics!

Blowing Things Up

Finally! This is simple – a demolitions roll is a lot like a normal attack. Roll Wits + Demolitions, adding in any Black Dice for Fortification (and any other difficulties or penalties that are appropriate). Any additional successes on this roll will add extra dice into the damage roll.

Example: The slightly crazy Neculai bundles six sticks of dynamite together and lights it in an attempt to destroy the wall of a small house. He lights the fuse and gets well back. His Wits + Demolitions gives him five dice, and the roll gives him a 1, 1, 2, 4, 6, 2 (the 6 gave him another die to roll). Three successes means two additional dice on the damage roll. The damage done at Ground Zero is therefore 58D (48D for the explosive itself, 7D for Area Effect, and 3D for Demolitions). Without taking up lots of space, this generated 24 successes! (I would recommend a dice rolling app for this roll, by the way!)

Twenty-four successes is more than enough to take out the wall (15 Hit Points, with no Fortification) – and remember that with the Area Effect code changing, anyone within 7 yards of Ground Zero will have taken 61D, and anyone within 14 yards will have taken 54D! (I do hope that Neculai’s fuse was long enough…)

So there you have it – a quick guide to explosives. See you next time the time-lock operates on the Think Tank!

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