Yeah, that worried her. A lot.

"Poison gas?! That's not--it's--"

Oh, bugger, she cursed in her head. There's really no time to talk about it out loud. When the Doctor had trouble with the lever, Maria quickly looked around the room, picking up a sturdy lamp and running back to the window.

"We could break it open!"

Of course, it wouldn't be the cleanest break, they'd likely get scraped up, but they'd be alive. And that was the important thing.