It's been a few years since I last spec'd out a comms room, but we were pushed to nitrogen instead of halon for the machine rooms I last put together. The point was that it was an oxygen displacer. Pp, there was a cat flap-like arrangement in the wall for the purpose. There was still a few seconds programmed in to get out, but you had to tell it you were inside to benefit from that, or maybe that was an override, it's been a few years. Apparently you'd definitely know about it when it went off.