How do you get past the laughing gas on Batman Arkham Asylum

There are a few different scenes in the game where there is laughing gas. In all of them, you must remain off the ground at all times - otherwise you'll die & have to start over at the nearest checkpoint.

Travel throughout the room on the higher platforms/etc. From up there you will have to search the walls below you for these red switches - aim & throw a batarang at them one at a time & the air vents/circulation turns on & the room eventually clears of all gas.