How do you switch off the gas in the medical facility when trying to rescie..

Ok after you beat the two goons out the front and talk to cash(the guard)then look up and use your grappling hook to get to the vent shaft to gain access to the room. Once you're in then equip your batarang and hold down RT(aim)look for the 1st fan switch, which is below you and to your left, so walk right along the cat-walk turn left and walk right sideways have look around you should get a lock on throw batarang to turn fan on.

Now the second fan, walk back along the catwalk so you are above the switch you just activated run and jump and glide strait ahead (A and forward you should know that lol) run and jump strait ahead again turn right run and jump once more.

You grab on to the side of the cage box thing automatically, climb up on top of it an turn around so you face the way you just came from and throw batarang at switch below to activate second fan, now you can take down the bad guy hanging with the batarang he smash's the roof of the room he is hanging over. That gives you access to the third fans switch, jump to the platform next to the room the bad guy just fell into and activate fan with batarang.