Zinna's mage hand slowly works the dagger under the gem and begins to cut but she finds that whatever the cord attached to the gem is made of, it is not so easy to cut. At one point the mage hand makes a furtive movement that does succeed in finally cutting the cord but it pulls up on the cord with a quick jerk at the same time. You can hear a click come from the ceiling in the chamber as though some for of mechanism has been tripped a thick yellowish cloud suddenly falls from the hole in the ceiling and quickly spreads throughout the chamber and toward the corridor.
Being closest to the door Zinna can attempt to close the door before the cloud escapes into the hall but will need to make a successful Dexterity save DC 12; If Zinna fails this save then everyone in the corridor will be exposed and will need to make CON saves.
Zinna looks on as the cord is almost cut through. Then she hears a click. Seeing the yellowish cloud coming out of the ceiling she grabs the door and attempts to slam it closed. " Run" She calls out. Zinna prays to Inasyah that the door will stop the cloud.
Zinna moves to slam the door shut and does, in fact, manage to close the door but in doing so some of the toxic gas, or whatever it is, is sucked out into the hallway burning everyone eyes, skin, and lungs. Everyone in the corridor takes 2d10 poison damage and gain the poisoned status (And may continue to take damage) but those who succeed on a DC 12 CON save take half damage and are not poisoned.
So I will need everyone to roll CON saves as well as 2d10 for damage, remember to halve that damage if you succeed DC 12 CON save. For those wanting to describe the effects if they fail the save look up mustard gas; though this stuff is not mustard gas per se its effects are basically the same.
Edited: Aericsteele on 19th Apr, 2017 - 9:01pm
Zinna, Leo, and Corren stagger toward Mradoric's position at the intersection they are coughing and struggling to breathe for a moment. They feel their skin and eyes burning as the cloud of yellowish smoke briefly overcomes them but the exposure was minimal enough that it only caused slight reddening and irritation of their exposed skin rather than full blistering and they are quickly able to clear out their lungs before anyone suffers any permanent or severe damage (Corren takes 1hp; Zinna takes 5 damage, and Leo takes 7 damage).
In response to Leo's question it's hard to say how long the cloud will linger in the room; the door is closed but you don't know whether that hole in the ceiling may act as some form of ventilation. The gem did remain behind in the room though.
Corren's throat seems to clear faster than the others, probably because he was exposed to less gas than the others. He finally catches his wind enough to say, "Whatever it is, I don't think they value it much. Setting the tap was enough. And it might not be worth much at all, just as bait. I'm going to try the other door." As the gas settles he moves back to the farther door, readying his tools to go after the locking mechanism.