Breathing under water is complicated by the water pressure. At a depth of only 10 m, the water pressure is double what the air pressure was at the surface. As a result the air in your lungs and the lungs themselves are compressed.

Scuba divers can go to greater depths and stay under water longer because they take a supply of oxygen with them. For deep diving (100 m or more), this oxygen is not supplied in a normal air mixture, because at this depth the nitrogen in the air is poisonous. The mixture the divers breathe is 98% helium and 2% oxygen. This is supplied to the lungs at the same pressure as the environment.

If divers return to the surface too quickly, nitrogen bubbles form in their blood and body tissues. They block the capillaries and the nerve cells especially in their brain don't get enough oxygen. In addition oxygen actually passes out of the blood into the lungs. i.e. the wrong way. This condition is known as the bends. First the divers often lose consciousness, then there are signs of paralysis and they finally die because the lungs are damaged.

Therefore before diving rapidly to a depth of even 10 m, divers must completely fill their lungs to prevent them from collapsing. Before returning to the surface, they must empty their lungs to prevent them from rupturing. Last but not least the divers must return to the surface slowly.

l. 3 to compress - zusammendrücken; l. 5 bubbles - Bläschen; l. 8 bends - Taucherkrankheit; l. 9 to lose consciousness - das Bewußtsein verlieren; l. 9 paralysis - Lähmung(en); l. 13 to rupture - (zer)reißen;

1. What happens in your body when you drive and what problems may this cause?

2. What must divers do to avoid these problems.