The search for means to allow man to descend deeper has been a continuing process. People ask themselves - how to dive deeper and what to use - Saturation Diving or Liquid Breathing?
By the early twentieth century deep diving research had enabled divers to reach depths in excess of 90 metres; at this depth the narcosis induced by nitrogen incapacitated most men.
After the First World War the Royal Navy diving research tried to extend their depth capability beyond 60 metres. Equipment was improved, the submersible decompression chamber was introduced, and new decompression schedules were developed. These used periods of oxygen breathing to reduce decompression time. Dives were made to 107 metres, but nitrogen narcosis at these depths made such dives unrewarding and dangerous and scientists want to know - how to dive deeper.
Liquid breathing trials, in which the lungs are flooded and the body supplied with oxygen in solution have only been conducted in laboratories and hospitals(diving history). The potential advantages of liquid breathing are the elimination of decompression sickness as a problem, freedom to descend to virtually any depth, and the possibility of the diver extracting the oxygen dissolved in the water.
Hydrogen diving, using hydrogen in gas mixtures for deep diving, was first tried by Arne Zetterstrom, a Swedish engineer. His pioneering work on the use of hydrogen in a diver's gas mixture is still being developed. He demonstrated that hypoxia and risks of explosion could be avoided if the diver used air from the surface to 30 metres, changed to 4% oxygen in nitrogen, and then changed to 4% or less oxygen in hydrogen. In this manner the diver received adequate oxygen and the formation of an explosive mixture of oxygen and hydrogen was prevented.
In 1945, Zetterstrom dived to 160 metres in open water, but unfortunately an error was made by the operators controlling his ascent. They hauled him up too fast and he died from hypoxia and decompression sickness. The error was accidental and was not related to his planned decompression schedule.
The cheapness of hydrogen compared to helium, and the probability of a helium shortage in the future, may mean that hydrogen will be more widely used in deep dives. French workers have reported good results using a mixture of hydrogen and helium as diluting gas.
Other European workers have followed Zetterstrom with radical approaches to deep diving. The Swiss worker, Keller performed an incredible 305 metres (1000 ft) dive in the open sea in December 1962. He was assisted by Buhlmann who has developed and tested several decompression tables.
Modern gas mixture sets ( not liquid breathing systems) have evolved as the result of several forces. The price of helium has become a significant cost, and this - combined with a desire to increase the diver's mobility - has encouraged the development of more sophisticated mixed gas sets. The most complex of these have separate cylinders of oxygen and diluting gas. The composition of the diver's inspired gas is maintained by the action of electronic control systems which regulate the release of gas from each cylinder. The first of these sets was developed in the 1950s, but they are still being refined and improved.
Saturation diving is probably the most important development in commercial diving since the Second World War. Behnke, an American diving researcher, suggested that caisson workers could be kept under pressure for long periods and decompressed slowly at the end of their job rather than undertake a series of compressions, and risk decompression sickness after each.
A US Navy Medical Officer, George Bond and others adopted this idea for diving, the first of these dives involving tests on animals and men in chambers. In 1962 Robert Stenuit spent 24 hours at 60 metres in the Mediterranean Sea off the coast of France.
Despite the credit given to Behnke and Bond it might be noted that the first people to spend long periods in an elevated pressure environment were patients treated in a hyperbaric chamber. Between 1921 and 1934 an American, Dr Orval Cunningham, pressurized people to a pressure equal to a dive to 20 metres for up to five days and decompressed them in two days (Saturation Diving Procedure).
Progress in saturation diving was rapid with the French-inspired 'Conshelf experiments and the American 'Sealab' experiments seeking greater depths and durations of exposure. In 1965, the former astronaut Scott Carpenter spent a month at 60 metres, while two divers spent two days at a depth equivalent to almost 200 metres. Unfortunately, people paid for this progress, as lives were lost and there has been a significant incidence of bone necrosis induced by these experiments.
In saturation diving systems, the divers either live in an underwater habitat or in a chamber on the surface. In the latter case, another chamber is used to transfer them under pressure to and from their work site. Operations can also be conducted from small submarines or submersibles, with the divers operating from a compartment that can be opened to the sea. They can either move to a separate chamber on the submarine's tender or remain in the submarine for their period of decompression. The uses of this equipment offers several advantages. The submarine speeds the diver's movement around the work site, provides better lighting and carries extra equipment. Also, a technical expert who is not a diver can observe and control the operation from within the submarine.
Operations involving saturation dives have become routine for work in deep water, the stimulus for this work being partly military and partly commercial. Divers work on the rigs and pipelines needed to exploit oil and natural gas fields. The needs of the oil companies have resulted in strenuous efforts to extend the depth and efficiency of the associated diving activities. Diving firms are now prepared to sign contracts that may require them to work at over 500 metres.
Man is pursuing other avenues in his efforts to exploit the sea. Armoured diving suits withstand the pressure exerted by the water and allow the diver to avoid the hazards of increased and changing pressures. In effect, the diver becomes a small submarine. The mobility and dexterity of divers wearing earlier armoured suits were limited and they were not widely used. The newer suits such as the British 'JIM' and the Canadian suit made by Hard Suits have become accepted pieces of diving equipment. They can be fitted with claws for manipulating equipment. The Hard Suit product is of interest because its joint system is more mobile than that of JIM, reducing the work input needed for movement. The Hard Suit and the WASP, a compromise between a diver and a one-man submarine, have propellers to aid movement, and the designers are now aiming for depths beyond 660 metres (2000 ft). Thay say that thay know how to dive deeper.