There are basically 3 narrow hallways, and on purpose. :)

One which is basically a T shaped hallway to join the main center area and the two middle level rooms. It's not terribly long.

The other is the one with the vents and smoke. There is a specific reason for that - the health boost. It's supposed to be dangerous to go through there, like a gauntlet hallway.

The last is the L shaped one that wraps around the lowest water room. That is meant as a snipers area, and a dangerous access point to a health boost that sits in the exit hole at the far end.