Item description:

Go right and down. I long hallway with 2 doors, go in first door.
(Same room from before)

Down in smoke: There is a guard in this room knocked out right next to a fire extinguisher.
Be a decent amount back from him. In the area between lockers/doors should be good.
Tap RT to pull out tranq gun. Press LS to aim, and point laser at bottom left side of extinguisher. When he wakes up, shoot extinguisher by pressing X.