Submarine Sabotage

You are currently serving aboard the USS Ibis, the first of the US Navy's top-secret Puny class submarines. The Puny class is an attack submarine that packs maximum firepower into a minimum-sized hull. It relies on speed and stealth to surprise the enemy.

The USS Ibis is currently on a training exercise in the North Atlantic, just off the coast of Newfoundland. You were doing some routine maintenance at the aft end of the submarine when the sirens sounded. You thought this might have been a training exercise until you noticed a whitish-coloured gas approaching you from the aft bulkhead. Training and instinct took over. You couldn't get to a gas mask in time, so you dived into the nearby airlock and closed the air-tight hatch behind you.

You are now alone and have no idea what is happening throughout the rest of the sub. You can't leave the airlock through the inner hatch (the one you entered by), or you'll get gassed, and you can't leave through the outer hatch, or you'll drown. What can you do?