Vent the gas is an objective in the Story Mission, The Cost of Progress in Borderlands 2: Commander Lilith and the Fight For Sanctuary
- Having made it to to the top of the infested portion, head over to the right (North) from the large bay windows.
- This will lead you into the Experimentation Room.
- In here, deal with the Infected Bruiser.
- After that, go over to the Western side of the room, to the right of the door, to find the wheel valve needed to activate the next set of fans.