Goto Dengo nods. Only a few meters beyond where they turned into this passage is a ventilation shaft that goes all the way to the surface. It has a sharp sideways jog in the middle that Goto put there so that when Captain Noda filled it up with rubble (which he has presumably done by now), the diagonal tunnel—their escape route—would not be blocked. If Rodolfo went up that shaft, he found a cul-de-sac, with no air bubble in the top.