Goto Dengo is not a diver, and knows very little of diving medicine. But his father used to speak of how caissons were used to send workers deep underwater, to build things or to mine. That is how he learned about caisson disease, and how he learned the rule of thumb that most men will not suffer its symptoms if you have them decompress for a while at half the original air pressure. If they stop and breathe for a while, the nitrogen will come out of the tissues. Once this is done, the air pressure may be halved again.