How To Model Cascade Failures?

[Pursuivant]

How would you model the sort of "golden BB" damage that progressively destroys a complex system?

Obviously, it starts with a critical hit or equivalent.

If you've got a vehicle loaded with volatiles or explosives, the path towards destruction is obvious. A hit to the fuel tank/ammo bunker triggers an explosion which damages adjacent fuel bunkers/ammo, etc. until the the whole thing turns into a mushroom cloud.

But what about turbine engines where a little bit of damage turns into a lot of damage as as one bit of shrapnel turns into lots of shrapnel which shreds the entire engine?

How do you model it in terms of point costs? Looking at it as a disad, it starts with Vulnerability or Weakness. Maybe Vulnerability 4x to fragment damage, with either a minor limitation or feature that the damage cascades rather than being delivered all at once?

For systems that are take damage from normally non-damaging effects, combine Vulnerability and Weakness, Perhaps add Self-Destruct if there are systemic effects which will quickly kill the system even if it survives the initial damage.

For example, say you've got a vehicle with an engine which completely blows apart if it encounters seawater (e.g., a steam engine with very hot boilers, which will fail catastrophically if they get doused with cold water). Maybe treat the potential damage from seawater as a Weakness, then apply Vulnerability to the damage from that weakness. If damage reaches 50% or more but isn't enough to destroy the system, it begins to suffer from Self-Destruct as the remaining parts fail. (Treating damage of X+ from a given source as a substitute for Age.)

[Anthony]

Within the level of detail of GURPS, you model it as hitting vitals or a critical hit. It's not really any different from the lucky hits that can kill a human.

[Engurrand]

GURPs models cascade damage by allowing complex machines with moving parts to have a vitals hit location. The release of the engine's own energy toward its destruction is one of several possible explanations for why a single bullet might do that x3 damage.



Machines may also use the mechanics for Fragile and/or Explosive, or may have explosive cargo of course. Most gas engines should be Flammable and you can get a lot of drama out of that 1d-1 burn damage (ignoring DR) that progressively takes down airplanes and cars. After taking vitals shots, bleed damage (representing the slow cascade of failure) has added an interesting dramatic element to many a scene.



If the object is gear, purchased with money, then I often have to remind myself to resist the impulse to stat it up using character traits. Much easier and completely sufficient to make note of any special vulnerabilities in the write-up. For example, a gas bomb applied to the air intake on any air-breathing gas engine will annihilate the engine in a few seconds. GURPS doesn't model this, but it's very easy to apply the x3 wounding modifier for a vitals hit to the cyclic fire damage in that case.



Where it gets complicated is when you have mechanical PCs and NPCs who do need character sheets. I once had a Patron on my record that was a sentient USS Akron, flying aircraft carrier. Stating it up was an exercise.

[mburr0003]

I'd do it as a 'vitals' hit that instead of dealing all the damage at once, deals it in small chunks over a brief span of time.

[Varyon]

Originally Posted by mburr0003

I'd do it as a 'vitals' hit that instead of dealing all the damage at once, deals it in small chunks over a brief span of time.

Note GURPS typically handles massive bleeds - which similarly would be more realistically modeled as occurring over a brief span of time - as simply outright damage. This is part of what makes Vitals (particularly those fluffed as hits to the kidneys) and even Skull hits have such a high damage multiplier, and is the sole reason behind vein/artery hits having an increased multiplier over normal cutting damage. So there's precedent in treating such effects as though they occur instantly.

[Anthony]

Originally Posted by Varyon

Note GURPS typically handles massive bleeds - which similarly would be more realistically modeled as occurring over a brief span of time - as simply outright damage.

Which in turn somewhat justifies consciousness rolls working as they do, though failed death checks are still treated as immediate. It would be interesting if a failed death check didn't immediately incapacitate you.

[Varyon]

Originally Posted by Anthony

It would be interesting if a failed death check didn't immediately incapacitate you.

Consider the following: Any normal Failure on a Death Check doesn't necessarily immediately incapacitate the character. Instead, it results in a further -2 to HT checks to stay conscious each round. If the character opts to Do Nothing, they must still make the check, but without this extra -2. Regardless of how well the player rolls (and how high the character's effective HT is), the character can only maintain consciousness for 1d minutes, after which point they either fall unconscious (if they failed the death check by only 1 or 2) or drop dead (if they failed the death check by 3 or more). For purposes of healing the character through supernatural or superscience means, the character is considered Mortally Wounded if they failed by 1 or 2; if they failed by 3 or more, either treat as Mortally Wounded but with a large penalty to remove this condition until the 1d minutes run out, or treat as having no way to prevent death. Any Critical Failure means the character simply drops dead immediately upon being struck with the fatal blow.

[Pursuivant]

So, for quick death to non-human targets from combat damage, retain (or add) the Blood and Vitals hit locations.

Vitals represents critical parts where a single hit can immediately shut the target down.
Blood represents progressive damage (including possible fluid loss, like hydraulic fluid or oil) which will eventually kill the target.

I could also see the following quirks:

Fast Bleeding: 0.5x time between bleeding checks, a very weak form of Hemophilia.

Fragile Vitals (Explosive or Flammable): Fragile (Explosive or Flammable) but just for your Vitals.

Vulnerability to Brain/Vitals Hits (-1 per level): 1x multiplier per level to damage beyond the usual multiplier for brain/vitals hits.

Vulnerability could also be defined as fast-bleeding, with increased damage being linked to the rate at which you bleed out or otherwise cascade fail. Treat this as a special effect.

Fragile (Brittle, Explosive or Flammable) nicely covers cascade failure for targets which carry volatile fuel or explosives which fall apart quickly once they take any serious damage.

Killing damage can be defined as a "fast cascade failure" which happens over a few seconds. Alternately, it can represent a slower cascade failure after a hit which delivers the lethal damage. Remember that GURPS defines people as dead if they're so badly injured that they can't act or survive, even if they're not quite dead. Realistically, people or machines might take several minutes to die after a fatal hit. In the case of humans, you might have agonal breathing or other reflexive instincts just prior to death. Some creatures (e.g., chickens and turkeys) have much more vigorous instinctive reactions. Call it another quirk.

Die Hard: You don't just fall over when you're killed. Instead, unless you are reduced to HP x - 5 or fewer HP, you engage in some sort of vigorous but useless instinctive activity for HT seconds after you fail a death check. Merely destroying your vitals or brain isn't sufficient to stop your reaction as long as the rest of your body is functional. For example, you might flail wildly or run in a random direction. This might distract enemies or cause other problems, possibly allowing your comrades to escape or avenge you.

I'm still trying to figure out good options for cascade failures from non-combat events. So far I've got Weakness with a modified form of the Trigger enhancement linked to Vulnerability.

Exposure to your Weakness triggers damage which continues for a set amount of time even if you're no longer exposed. Add Temporary Affliction/Disadvantage if there are effects other than damage.

I'll glom them together to create a new disadvantage rather than monkeying with the details of defining Weakness + Vulnerability as a disadvantageous power.

It's tempting to handwave cascade failure for gadgets as just being part of how they operate, but I've learned the hard way that inevitably someone will want a gadget as a Power or Ally/Dependent/Enemy, so I always try to provide at least basic character point stats.

[Pursuivant]

Originally Posted by Varyon

Consider the following: Any normal Failure on a Death Check doesn't necessarily immediately incapacitate the character. Instead, it results in a further -2 to HT checks to stay conscious each round.

This would be a good perk, as a sort of limited form of Hard to Kill.

[whswhs]

Originally Posted by Pursuivant

So, for quick death to non-human targets from combat damage, retain (or add) the Blood and Vitals hit locations.

Vitals represents critical parts where a single hit can immediately shut the target down.
Blood represents progressive damage (including possible fluid loss, like hydraulic fluid or oil) which will eventually kill the target.

I think that a mechanic like bleeding could work well for a ship that springs a leak below the waterline.