As you go down, your ears begin to hurt. This is because the pressure outside the eardrums increases with the depth. The moment you feel the pressure, you must pinch your nose and gently blow. This opens your Eustachian tubes and equalizes the pressure on each side of the eardrums. If you do not equalize the pressure, your eardrums will burst at about 30 feet. For this reason, never dive after a heavy cold or flu, as it may not be possible to clear the Eustachian tubes.
Compressed tanks contain the constituents of air, that is, 80 percent nitrogen and 20 percent oxygen. Breathing pressurized nitrogen sometimes produces a feeling of intoxication known as nitrogen narcosis. This becomes a problem when diving at depths of 75 feet (22.5m) or deeper. A diver’s companion must be alert for the signs. A diver may suddenly start behaving strangely, attempt to remove the face mask, or make indistinct and fumbling communication signs. The other diver must get the person to the surface as quickly as possible without producing decompression sickness (the “bends”). Once the person has surfaced, the narcosis wears off, leaving no aftereffects.
Decompression sickness depends on the amount of time a diver is at a certain depth as well as the depth itself. The diver experiences acute muscle cramps and breathing difficulties. He or she must be treated immediately. The only safe way of doing this is to get the diver to the nearest decompression chamber.
If you miscalculate the amount of air that you have left in your tank and consequently run out, it is extremely dangerous to hold your breath and rise to the surface. As you rise, the air in the lungs expands as it decompresses, and the lung may rupture. You must blow air out as you rise. Skilled divers sometimes share the air from one tank with their companion as they surface.
