Game mechanics for poison gas?

[molonel]

In one of my upcoming adventures, there is going to be a gas attack during a huge festival.

I use a lot of third party resources. I just flipped through Toxicant, which I purchased off of RPGnow. But I haven't found anything that suits my needs, yet.

Are there any 3rd party supplements that deal with how to simulate a poison gas attack in a d20 Modern game?

 

[(Psi)SeveredHead]

I don't think there are any good rules for poison gas, but I've cobbled something together from Iron Heroes and Spycraft II. What are you looking for? Save DC? Damage? Duration? What party level?

 

[molonel]

The party will be somewhere between level 4 and level 6 when this occurs. They have infiltrated a cult that I modeled on the Bhagwan Shree Rajneesh and added a Cthulhu-esque flavor. There will be a gas attack intended to wipe out the cult as part of a ritual. The party will - hopefully - be away when the attack occurs, but I want it to be deadly and emulate that with an appropriate save DC, damage, and duration. I prefer to have the stats if I need them. I'd prefer it be an inhalation gas rather than a contact gas so that a gas mask is an effective piece of equipment if they need it.

 

[jdrakeh]

Poison gas is yellowish green and similar to a fog bank but, of course, poisonous. Gas vapors automatically kill any living creature with 3 or fewer HD (no save). A living creature with 4 to 6 HD is slain unless it succeeds on a Fortitude save with a DC of 15 (in which case it takes 1d4 points of Constitution damage on your turn each round while in the cloud).

A living creature with 6 or more HD takes 1d4 points of Constitution damage on your turn each round while in the cloud (a successful Fortitude save halves this damage). Holding one’s breath doesn’t help, but creatures immune to poison are unaffected by the spell.

Posion gas disperses at a rate of 10 feet per round, rolling along the surface of the ground. Figure out the cloud’s new spread each round based on its new point of origin, which is 10 feet farther away from the point of origin where it was originally unleashed. The gas dissipates, becoming inert, after X minutes (X is whatever the GM wants it to be adjusted for lethality).

Because the vapors of poison gas are heavier than air, they sink to the lowest level of the land, even pouring down den or sinkhole openings (this makes dispensing it via ceiling mounted ventilation systems the preferred method of distribution).

[Edit: This is a modified form of the Cloud Kill spell from the 3.5 D&D DMG]

 

[Justin D. Jacobson]

Still not sure exactly what you are looking for, but my Poisoncraft book has rules for building your own poisons among other things.

 

[hobgoblin]

while not 3rd party, d20 modern have some bits about gas attacks iirc.

still, thats about tear gas grenades, as used by riot police.

 

[(Psi)SeveredHead]

Here's what I have: CR 8 gas attack.

1d6 Con damage per round of exposure (or 3d6 hit points per round if you want to be nicer), Fort save DC 15. Reduce the CR to 6 if the PCs are likely to only be affected for one round.

Status effects have a base CR; blinding poison shouldn't have a CR below 4, paralyzing and Con poison shouldn't be below 6.

The save DC was determined by math and should be passed half the time; if your PCs have high Fort saves (mine usually do) then the CR should be adjusted a point downward.

IMC gas masks give a +4 bonus to the Fort save rather than granting total immunity; I don't think equipment should ever be more important than character abilities.

 

[molonel]

Here's what I have: CR 8 gas attack.

1d6 Con damage per round of exposure (or 3d6 hit points per round if you want to be nicer), Fort save DC 15. Reduce the CR to 6 if the PCs are likely to only be affected for one round.

Status effects have a base CR; blinding poison shouldn't have a CR below 4, paralyzing and Con poison shouldn't be below 6.

The save DC was determined by math and should be passed half the time; if your PCs have high Fort saves (mine usually do) then the CR should be adjusted a point downward.

IMC gas masks give a +4 bonus to the Fort save rather than granting total immunity; I don't think equipment should ever be more important than character abilities.

That is exactly along the lines I was thinking, only better put together, clearer and more precise. Thank you.

And I agree about the gas masks.