We have seen that after an emergency landing when the airplane needs to be evacuated promptly, evacuation slides get deployed immediately. I am not sure if normal air is being inflated in those slides or do they use some other gas in them?
They are filled with carbon dioxide, oxygen and nitrogen. See here for reference.
From the linked article:
Slides inflate with an initial boost from a canister of compressed carbon dioxide and nitrogen. The canister provides only about one-third the volume needed to inflate the slides. The remaining volume is supplied by ambient air, channeled into the slides through aspirators.
When the inflation mechanism is triggered—by a lanyard pulled by the slide as it tumbles from its storage case—gas from the canister accelerates through the aspirators at high speed, creating a vacuum that sucks ambient air into the aspirators through louvers. When the slide is fully inflated, the louvers close.