In 1962 a Swiss guy named Hannes Keller reached a depth of 300 meters on a breathing mixture of helium and oxygen. He used a different technique: he went down in a small diving bell in which the pressure was a little higher than that of the outside surrounding water. In this way he could open a hatch once he arrived on the bottom and swim to his job. The gas was supplied to him from the bell by an umbilical. An umbilical can be defined as a multifunctional life-line. It runs down from the surface ship to the bell and from the bell to the diver. It has been further professionalised in later years and is still in use today. It may supply things like breathing gas, electricity (for the lights and tools), hot water, communication wire and any other source that is needed under water.
In fact Keller created the pillar for future military, scientific and commercial diving.
Dr. Bond was the director of the US Navy Submarine Medical Center in 1957. He deserves the credits for developing saturation theories. He found that the tissues of animals and humans would eventually become completely saturated with the inert gas after a particular time of exposure to it. They would then be filled up and not absorb anymore.
As long as the diver stayed at the depth where he saturated, his decompression period would be unaffected, even if he stayed days or weeks.
What is saturation diving and how does it work ?
Depending on the depth and the time the diver stays there, the tissues in the divers body collect gasses from the surrounding environment relatively quick until a point of saturation is reached.
After a deep dive a diver has to decompress. His decompression time is often much larger than his actual diving time. For example: a dive to 180 meters for 1 hour will take the diver 38 hours to decompress ! If it takes several deep dives to finish a job, the total time will be very long (and expensive)!
After reaching the point of
saturation the decompression time makes no difference anymore. Did the
diver stay under the pressure for this one dive of 1.5 hours or for one week ?
He has to decompress for a certain equal time (depending on the depth).
So, ways had to be found to bring and keep divers under the pressure of the dive depth, let them finish the complete job and decompress them only once.
Experiments were carried out by Jaques Cousteau with his Conshelf underwater habitat and by the Experimental Diving Unit, lead by Dr. Bond. In the early 1960-ies they developed underwater habitats Sealab I and II. In Sealab I four divers lived in a depth of 65 meters for 10 days. In Sealab II teams of 10 divers stayed underwater for periods of 15 days in a depth of 70 meters. Heliox was used as the breathing gas.
These experiments were very valuable but the underwater habitats turned out to be very expensive and complex to maintain. Life support umbilicals were extremely vulnerable due to currents, storms etcetera. In the 1980-ies all underwater habitats had disappeared. It was preferred to leave saturation complexes on the surface support ship.
Surface Saturation Complexes
|The first Surface Saturation System was the SDC (Submersible Diving Chamber). A well known SDC in the 1960-ies was the Seashore. It had a cabin that could transport two divers to a maximum of 200 meters. Divers left the cabin through a hedge to start their job. After work was finished the cabin was brought back on deck and connected to the Deck Decompression Chamber (DDC). Here they waited till they were needed again. After the whole job was finished the divers underwent full decompression in the DDC.|
Modern ways of saturation diving
The principal is as follows. The divers are brought under the pressure of their next job in a surface pressure chamber. This system is often called a Deep Diving System (DDS). A DDS is sometimes portable but many times to bulky to transport and mounted permanently on diving vessels. The DDS will be the home for the saturation divers for some weeks. It contains medical facilities as well as showers, toilets, beds, tables, heating, a built in breathing system (BIBS) etcetera. Food, drinks and other things the divers need are supplied through a small attached pressure vault.
As soon as the divers are under the pressure of that specific dive sequence and all systems are checked they can start their job by entering the Personnel Transport Cabin (PTC). This is a small diving bell attached to the DDS and under the same pressure. heating, communications equipment, video cameras etcetera. In the PTC the divers enter the water and they descend to their job. Since the pressure there is the same they can immediately exit the PTC and start their work. Like in the first attempts of Hannes the diver is supplied with his breathing gas, communication facilities, hot water to heat his suit and electricity for his tools and lights by the umbilical (an umbilical also comes down from the diving vessel to the PTC.
When his "turn" is over he re-enters the PTC and his mate can go out to do his part of the job. There is always one guy left behind in the PTC. He is called the "bellman" and he monitors the systems. After the shift is over they will surface in the PTC that will be re-locked to the DDC. Now the divers can rest, sleep, eat, shower and relax until their next dive.
A saturation team of 6 divers can operate continually , with one diver always on the job, 24 hours a day for up to 30 days or longer.After the whole dive sequence is finished, the divers will be decompressed inside the relatively comfortable and safe environment of the DDC. A complete shift may take more than a month but the use of conventional surface supplied diving equipment would take a lot longer since the divers would have to decompress after each dive.
An unknown large number of experiments in this field has taken place. They all had different goals. They tried to reach greater depths, design new equipment or develop new underwater working procedures for welding, cutting and demolition.
Many different types of saturation diving systems have been developed by different companies. Some of them are portable, some of them can be air lifted to remote locations but most of them are mounted on diving vessels.
Saturation divers are brave and special people with unique abilities to operate in hazardous conditions.Saturation diving is currently the best way to work in deep water. However, the development of atmospheric diving suits looks very promising as well.
Toisa Polaris Saturation Diving System
England completed the installation of a "new" saturation system
on board the Norwegian vessel Toisa Polaris in 1999. This 18 man system
features two 3 man state of the art diving bells. The system is a
refurbished system. Many systems were built to go as deep as 400 meters
but many of them have never even been there ! Refurbishing is cheaper than
a new system. There are enough "second-hand" systems available
in the downsizing oil-market.