Warhead Quarantine Crate Glitch
I know many of you already know this, as I have taught many people this glitch in-game, but there is a glitch to "lock" the metal crate in Warhead Quarantine.
Basically, you can survive inside the metal box and none of the zombies can get in.
All you have to do is get someone to die right outside the door. (This is harder than it sounds.)
a) You can get a friend to suicide outside the door for you
b) You plant mines right outside the door, so when zombies step on it they die and lock the door.
The zombies can still infect you through the walls and ceiling, so make sure you stay in the middle and crouched at all times.
As the zombies try to attack you through the wall, you can knife them till they die.
The door can become "unlocked" if the person who "locked" the door (died outside it) leaves the room.