If the vast majority of inmates were in the shelter, it would be prudent to lock it down in order to protect them. [A little cold and heartless, but that was the military mind at work. With a more optimistic tone.] There appear to be several individuals engaging the monsters throughout the dome, so perhaps we will be lucky.
[And sure enough, there was the elevator leading down, and no apparent barricade, or sign of forced entry.] Hm. Convenient.