The bottles are a major maintenance item only. I don't remember any hatch or access to that part of the aeroplane. The bottles occupy a small space between the central wing carry through box and the rear of the hold. You obviously want as much hold space as possible, so the rear of the hold will come down as close as possible to the wing box. The bottles are quite large. I do not think aircon plumbing comes through here- I think it goes under the wing box- the engineers here will know. I have checked my Pilot Technical Manual, but these are not pilot accessible areas so the manual gives scant information. The bottles feed into a universal cabin ring main, so there would be NRVs at each bottle as well as pressure reducing valves, and a big stopcock on each bottle. Can any divr say what happens if all the gubbins on the end of an Oxygen cylinder blows off suddenly? Or the end blows off? What happens to the bottle?
It did occur to me that the TWA accident began in this general location, but I am quite sure that the investigators would have discovered if a similar cause could be involved. But the bottles are very close to the wing box which is the largest fuel tank on the aeroplane.