News reports have said that the Russians trapped in a submarine on the ocean floor couldn't swim to the surface because they'd almost certainly face a fatal case of something called "the bends." Fear of the bends also explains why rescue craft have to surface very slowly, over the course of several hours. What are the bends, and why do they happen?
"The bends"--a condition caused by the formation of nitrogen bubbles in the body's tissues--affects divers or submariners if they surface too quickly. On the surface, the air we breathe is roughly 20 percent oxygen and 80 percent nitrogen, which is the maximum amount of nitrogen our bodies can safely take in. Normally this nitrogen is diffused from our body's tissues into the blood, enters the respiratory system, and is exhaled. But underwater--at depths of 20 feet or more--higher pressure prevents the body from expelling this nitrogen easily, and it builds up. If divers rise slowly to the surface and the external pressure around them decreases gradually, the nitrogen can be expelled. (They use dive tables and computers to figure the safe rate of ascent.) But if they surface too quickly, the nitrogen can't be processed fast enough, and it forms bubbles in the body's tissues. In the nervous system, such bubbles can cause convulsions, paralysis, and death. Bubbles often form in knees, elbows, and other joints, making them difficult to straighten--hence the name "the bends."