Again I will answer the points made by Tardmaster, the post will most likely be censored but anyway. Over a number of decades going back to the seventies we dived the WW1 wrecks on the south coast of Ireland, depths ranged between 130 feet on the SS FOLIA, to 240 feet on the SS PINEWOOD, half a dozen other wrecks fell somewhere between these. All the dives were made with 1 diver in the water on a safety line to a stand by diver in the boat. We recovered tons of non ferrous cargo and machinery, and carried out hundreds of dives . We never had an accident. The viz. could be anywhere from 50 feet to 5 feet. The rescue Tardmaster spoke of was carried out in shallow water, perfect conditions and a controlled environment, this rescue would be impossible in the conditions we worked in. On the subject of narcosis, all the dives were made on air with bottom times from 40 minutes to 20 minutes. To limit the effects of narcosis the dives were built up over the season by slowly increasing depth and shortening bottom times.