I don't think to many people here familiar with PVHO. I suggest you refine your question and inquire to the current and ex naval sorts that are present in the forum. American Bureau of Shipping, Det Norske Veritas, Lloyd's Register, and Germanischer Lloyd would also be a potential reference for you. I know what it is, I've seen some built while working some naval yards (pressure vessels for human occupancy) and I know version 2 is short coming, but I am no expert. sorry I couldn't be of more help.