Trip did mention that the catwalk was the maintainence shaft running aloing "each" nacelle, so I assumed that the crew was distributed between the two nacelles.

Actually, a bigger plot point is why Phlox was so adamant that T'Pol find space for his zoo - after all, didn't he say that Sickbay was shielded and it was possible for some of the crew to survive there? Why not leave his pets in there, and have people escorted to Sickbay in suits if the need arose?