I'd like to add some input as a player who hates that map. It's a long tunnel with two entrances, neither of which are 2-person-limit crouch spots. I think of them as "double wide" crouch spots, meaning you can have, at most, 4 zombies assaulting it simultaneously (2 from each end).

Unless a special exception is made for this spot, the humans can entirely cade one entrance, and then they can cade half of the other entrance, without breaking any rules. However if all that cading was done, only 2 humans would be allowed to defend from zombies. Other humans could stay inside to maintain the integrity of the barricades, but they wouldn't be allowed to shoot the zombies. This is my interpretation of the rules as a player.

However if you've ever played this map you'll know that this is one of 3 or so spots that are viable to defend. The result is that 15 players tend to congregate inside the vent. Any props that find their way inside end up getting blown out by 15 hails of machine gun bullets. The counter against this is that if too many players go in at once, usually one of them becomes a zombie, scores lots of easy kills, and then the rest of the map turns into a hide-and-seek match looking for the couple of players who saw the clusterfuck and said "Fuck that" and ran somewhere else. Occasionally you'll see the last human hiding in the secret disco room, and then the following round 15 people go there.

It's really a terrible map, mostly because of the low number of viable spots. Someone should make a thread to have it removed.