The Kursk sank in over 300 feet (91 m) of water. When a SCUBA diver makes a dive to that depth, he experiences the pressure of the water around him, which is approximately 10 times the pressure at sea level. At this pressure, the gasses that make up the air in his lungs, particularly nitrogen, dissolve into his blood and tissues. With the gasses in his blood and tissue, he can remain at that depth for a short period of time -- less than 5 minutes. If he stays down longer than that, he runs the risk of developing decompression sickness, also known as "the bends," when he surfaces, and he'll have go through the decompression process to avoid getting sick. Because the Norwegian divers knew they would have to stay longer at that depth, and therefore would have to undergo decompression, they used a technique called saturation diving.
Saturation diving is based on the principle that the pressure of the dissolved gas in the blood and tissues is the same as that of the gas in the lungs. Basically, a diver goes down to a depth, perhaps 300 feet, and remains there until no more gas can dissolve in the tissues -- the tissues are saturated with nitrogen. Once the saturation point has been reached, the time required for decompression will be the same no matter how much longer the diver stays at that depth, whether it be a minute, an hour, a day or a week. This principle has been used for divers who live and work in undersea habitats. It was used by the divers in the submersible oil rig in the film "The Abyss."
One idea that is being researched to prevent the need for saturation diving and decompression at great depths is liquid breathing, which was also shown in "The Abyss." Instead of breathing gas, the diver breaths a non-compressible, liquid perfluorocarbon compound that contains oxygen. Because no gas phase is in contact with the blood, and nitrogen is not used, the danger of forming nitrogen bubbles does not exist. In the 1960s, it was shown that rats could survive for up to 20 hours when immersed in such a mixture. Potentially, liquid breathing could allow a diver to reach depths of up to 3000 feet (914 m). Liquid breathing is still under research, and has been focused on helping to save pre-mature infants and patients with acute lung injuries.
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