Scuba diving is a sport that many people (including me) enjoy. Those who practice the sport pursue a number of activities including the exploration of shipwrecks, underwater photography, spear-fishing, lobstering, and just the plain fun of underwater exploration.
The letters that make up the word SCUBA stand for Self Contained Underwater Breathing Apparatus. A scuba diver wears a considerable amount of specialized equipment including:
The tanks that a recreational diver uses contains regular air under high pressure (typically 3000 PSI or pounds per square inch). This pressure is far too high for the diver to breath directly without bursting his/her lungs. This is why a regulator is needed. The regulator provides air to the diver at the same pressure as his/her surroundings. Hence if a diver is at a shallow depth the regulator will provide low pressure air for the diver to breath. If the diver is at a deep depth, the regulator will provide air at a much higher pressure. The regulator makes breathing at 100 feet feel just as easy as it feels on the surface.
The composition of the air around us is approximately 78% nitrogen, 21% oxygen, .03% carbon dioxide, and .97% other trace gases. The gas that causes the most problem in diving is nitrogen. Under water, the pressure of the surroundings cause the nitrogen that the diver breathes to dissolve in the blood and body tissues. As a diver goes deeper and spends more time underwater a greater amount of nitrogen will build up in the his/her body.
When a diver completes a dive, he/she must be very careful when coming to the surface. If the diver surfaces too quickly, the nitrogen in his/her tissues may form bubbles. We can visualize these bubbles to be similar to those that occur when you first open a bottle of soda. When the lid is on the bottle and the pressure inside is high, there are no visible bubbles because the gas (carbon dioxide in this case) is fully dissolved. When you pop the top, the bubbles form because there is less pressure holding the dissolved gases into the solution. Like the bottle of soda, if a diver surfaces too quickly, nitrogen bubbles will form in his/her body.
Unlike the harmless bubbles that form in a bottle of soda, nitrogen bubbles in a scuba diver can kill. These bubbles can form in many places and in nearly all cases will cause considerable damage. For example, nitrogen bubbles that form in the brain may cause blindness, dizziness, paralysis, unconsciousness, and convulsions. Bubbles that form in the joints, bones, and muscles cause intense pain. Bubbles that form in the blood can block circulation, and kill tissue. Bubbles that form in the spinal cord can cause paralysis. When bubbles form in the body of a diver, we refer to this as the bends or decompression sickness .
When a diver is bent, the treatment is to place him/her in a decompression chamber. Here the diver is placed under high pressure so that the nitrogen bubbles will redissolve in the blood and tissues. The pressure in the chamber is then slowly reduced so that the diver can "blow off" the dissolved nitrogen without forming large bubbles.
I have witnessed the ravages of the bends first hand. A dear relative of mine got the bends while diving in the Bahamas where she worked. Immediately after the accident, she was paralyzed from the chest down. This was the result of nitrogen bubbles forming in her spinal cord. After multiple decompression chamber therapy sessions (about a month), extensive rehabilitation therapy, and by the grace of God, she is able to walk today.