Size Modifier and poison

[Anders]

Someone over in Discord talked about how you need more poison for larger creatures - which is true. Now, there are a lot of complications here, including metabolic rate, fat percentage, distribution volume, and other fun stuff, but we're not writing the Deadly Spring*. I suggest we simply use Size Modifier as a proxy for mass and modify resistance rolls by Size Modifier. Larger creatures get a bonus, smaller creatures get a penalty. A negative Size modifier has a lot of upsides so I don't think we need to change the cost of Size Modifier.

* sorry Doug, I couldn't resist

[Tinman]

I usually just use the SM as a bonus to the HT roll.
As just happened in an adventure of mine: A player tried to use a tear-gas grenade to escape a pursuing T-rex. TL8 tear-gas is HT-4, T.rex* is SM+5 so his bonus is net HT+1. Unfortunately, T.rex has a HT14 to start so it didn't work out too well...



*Lands Out of Time p.27

[Anders]

Yeah, exactly. Use SM as a modifier to HT.

[Fred Brackin]

Originally Posted by Tinman

I usually just use the SM as a bonus to the HT roll.
As just happened in an adventure of mine: A player tried to use a tear-gas grenade to escape a pursuing T-rex.

Possibly not a good example of the principle. The mucus membranes of a T-rex's eyes and nostrils should be just as sensitive as those of an SM+0 creature and get irritated just as easily. The active agents in CS gas don't have to reach an effective dose level in the bloodstream to have their usual effect.

[Anthony]

Size isn't particularly relevant against area poisons; sure, it takes a larger dose, but it's a bigger target, it's going to absorb a larger dose. Against injected poisons this is just another case of the scaling problems with hit points.

[Varyon]

Originally Posted by Anders

Yeah, exactly. Use SM as a modifier to HT.

Note this means "proper dosage" scales linearly with height, which I suspect is a bit off (I'd expect it to be the square or perhaps cube*). For example, take a poison that is HT-3 to resist and does 1d tox. If you double the dosage, it becomes HT-5 to resist and does 2d tox (B439) - but an SM+2 target (nominally twice as tall as the SM+0 one) would be at HT-3, and should have twice the HP of an equivalent SM+0 target, such that 2d tox causes the same proportional wounding to an SM+2 target as 1d tox does to an SM+0 one. There is the issue that doubling the dosage also makes it work twice as fast for poisons with delays and/or intervals; it is probably appropriate to have SM modify both HT and the delay/interval (+1 step on the Size and Speed/Range Table - x1.5, x2, x3, x5, etc - per +1 SM) to make things match up perfectly (so now a double dose of poison has proportionally exactly the same effect on an SM+2 target as a single dose has on an SM+0 one).

*LD50 and similar values are typically expressed as being per unit body mass, which would have dosage scaling more with the cube of height.

[Ulzgoroth]

Originally Posted by Anthony

Size isn't particularly relevant against area poisons; sure, it takes a larger dose, but it's a bigger target, it's going to absorb a larger dose. Against injected poisons this is just another case of the scaling problems with hit points.

If the poison's effect isn't surface-targeted the target's dose requirement and area poison absorption probably won't scale in the same proportion, though.


...And of course it's only part of the scaling problems with hit points for poisons whose effects are mediated in hit points. But when that applies, it's a fair point...

[Donny Brook]

Originally Posted by Varyon

Note this means "proper dosage" scales linearly with height, which I suspect is a bit off (I'd expect it to be the square or perhaps cube*). For example, take a poison that is HT-3 to resist and does 1d tox. If you double the dosage, it becomes HT-5 to resist and does 2d tox (B439) - but an SM+2 target (nominally twice as tall as the SM+0 one) would be at HT-3, and should have twice the HP of an equivalent SM+0 target, such that 2d tox causes the same proportional wounding to an SM+2 target as 1d tox does to an SM+0 one. There is the issue that doubling the dosage also makes it work twice as fast for poisons with delays and/or intervals; it is probably appropriate to have SM modify both HT and the delay/interval (+1 step on the Size and Speed/Range Table - x1.5, x2, x3, x5, etc - per +1 SM) to make things match up perfectly (so now a double dose of poison has proportionally exactly the same effect on an SM+2 target as a single dose has on an SM+0 one).

*LD50 and similar values are typically expressed as being per unit body mass, which would have dosage scaling more with the cube of height.

It scales linearly with SM, but SM does not scale linearly with height.

[Pursuivant]

LD50 can vary based on target age, health, species, etc. and exact delivery method. GURPS models those factors as a HT-based resistance roll.

Roll vs. Physician, Poisons, or Veterinary to get the dosage right if you're only trying to drug your target, Poisons if you're trying to kill them. Biology, Guns, Law Enforcement, Naturalist or other skills might substitute if you're dealing with members of a specific species and are using common, commercially-available drugs with standardized equipment.

[Varyon]

Originally Posted by Donny Brook

It scales linearly with SM, but SM does not scale linearly with height.

"Height" here is a stand in for "effective linear dimension" - a quadruped uses its length instead of its height, a somewhat-elongated sphere uses ~1.5x its longest dimension, a sphere uses ~2x its diameter, etc. If you are maintaining the same basic shape, the function would indeed be linear with height (and pretty much any other linear measurement on the target).

Are you saying poison/drug dosages in real life are linear with what GURPS calls SM? That is, the appropriate dosage for an SM+3 elephant is around three times that for an SM+0 human? Because that's how the GURPS poison rules work, and that seems rather off to me (but then, I'm nowhere near an expert on the subject).