I haven't played through Dead Air since they've changed over to the redone VS maps, but are the freezer doors still unbreakable by Tanks but the survivors can shoot through them? Is that what you're talking about? If so that is a major oversight on Valve's part.
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On a separate note apparently you can back up to a certain set of double doors in one of the No Mercy survivor maps and have a tank hit you with your back to the door and the door breaks open allowing you access to a very hard to penetrate 'killbox' room.
...also I got to 6:40 on the Lighthouse map in a pub before my entire team got Smoker'ed (two) / Hunter'ed (two) all at the same time, how long have you guys lasted?