Yeah, I've seen some stuff disputing how people could have been gassed when there were doors with cracks and/or space around the edges for gas to escape.

But I don't really think that's a valid argument. Now, I wasn't there to see it but I'd be willing to bet that, if there were wooden doors, well, cracks in the doors or not, if you pump enough chemical into that room, the occupants of that room are still going to die.