Most air ducts are made of nitrogen and oxygen in a ratio of four to one. Nitrogen is a gas that does not have any chemical activity that passes into the body during breathing without causing any chemical change or after-effects.
However, the water pressure increases as the depth increases, and to keep a diver breathing normally, the pressure of the air mixture he breathes in must increase. At a depth of about thirty meters, for example, the diver will need to breathe air whose pressure increases four times the atmospheric pressure, and if this mixture is normal air, the fat tissues in the human body must absorb nitrogen more quickly than it appears in the rest of the body tissues. And since the brain and central nervous system are made up of fat and fat by 60 percent. So the gas affects them strongly, and hinders their normal movement. The result is that the diver is drugged with nitrogen, which is very similar to the intoxication caused by drinking an intoxicating substance.
Another risk associated with deep-sea inhalation of a nitrogen mixture is hypotensive disease (bends). If the diver goes down very quickly to the depth of the sea, the nitrogen present in the fatty tissues will expand and form a bubble in the brain, spinal cord or joints, and cause a number of pathological symptoms, including paralysis and severe pain.
Divers can avoid these conditions by inhaling a mixture of helium and oxygen instead of air. Helium is also an inactive, inactive gas that does not interact with body tissues, and its absorption rate is less than that of nitrogen. However, it generates more heat and faster than nitrogen, which leads to a loss of body heat of the diver relative to the temperature of the surrounding water, so a diver who inhales the mixture of helium and oxygen is forced to automatically wear a hot diving suit. Finally, there is another disadvantage of helium gas is its effect on the sound, as it becomes inhaled sound like Donald Duck's sound .. for a temporary period.