How the Purge button works

In The Cabin in the Woods movie the need for the Facility to have a purge button is unexplained. Given the ultimate consequences of its use, what is its logic?

(If you haven't seen this one before, you're doing yourself a disservice by not watching the real movie first. Go get it!)

Basing my opinion on that of an anonymous contributor to the Cabin wiki and what one can see on the theatrical release, I think that the elevator lobby was not meant to pour out the army of nightmares. The area can be described as a capital letter 'T' with the vertical line having the elevator doors with the guard booth at its bottom. On either side of the horizontal we have two exit doors  one leading to Administration  (the one towards the giant snake slithered away) and one to Engineering (from where the two security squads came from). Both these doors, along with that of the guard area look entirely unsuited to hold off anything, so one can safely assume that the Purge was not intended to be directed towards this lobby, but somewhere else, only resulting in what we saw in the movie to malfunction, quite possibly due to Marty's tampering with the wires to make the cubes run backwards. Or maybe to an oversight, for once Dana's and Marty's cube was located, it was directed to the lobby area for their retrieval, but so were the rest. This would also explain the small interval between activation and release.

So what for?

The Purge, judging by its name, was meant to get rid of everything on one go. Possibly, the creatures were not immortal in the sense in that they had an 'expiration' date and had to be renewed from time to time. Possibly then the current batch of creatures might get all tainted at once from 'something' as to make them unsuitable for the Ritual making it necessary to vacate their quarters  offseason for a new batch of nightmares (bred? captured?) from the Facility's departments (Zoology a top candidate). The elevator lobby would be then the loading area and quite sensibly the the Purge button would be there and not in the main control room, which monitored the Ritual proper.

So where to?

Maybe a safe disposal place within the Facility where the creatures could be controlled and dealt with. Or as the  anonymous contributor said, to the surface. Maybe there, they would turn on themselves saving the trouble to exterminate each one, or they would just die off by themselves (daylight? their expiration date?) . Releasing them all to ensure the Ritual's completion seems like an overkill, but maybe still an option.