Course Outline

Additional gas will dissolve in body tissues under pressure. Oxygen is metabolized (used by the body) as you descend; however, nitrogen gets absorbed into your body tissues as the surrounding pressure increases. When the tissues have absorbed gas equal to the surrounding water pressure, it is called saturated. This state must be avoided.

Tissues high in fat absorb a lot while other tissues absorb less. Tissues that have a large blood flow will absorb and release gas more quickly than tissues with less blood flow, such as tendons, cartilage, or fat. While under pressure, the increased gas circulating in the blood stream is contained; but as you ascend, the gas will need to be eliminated. If the pressure is released slowly, the nitrogen outgases slowly and will safely travel to the lungs where you breathe it out. However, if the pressure drops too quickly (rapid ascent), nitrogen forms larger bubbles in the blood and that can be harmful. While tiny bubbles generated by slow and controlled ascent are harmless, larger bubbles can get stuck and create blockages in your circulatory system. They may block blood circulation and/or compress nerves causing pain.

Signs and Symptoms

Signs and symptoms would vary from pain to irritation to soreness and swelling. Divers may say that they have the bends or have been bent. This happens when nitrogen bubbles block parts of the circulatory system (small veins of joints, elbows, knees, or shoulders), causing pain that divers may seek to relieve by bending those joints. Even very experienced divers can get bent, so take this very seriously. There is a wide range of symptoms from skin rash to articular pain and neurological problems, and they tend to come on gradually. The biggest problem is denial by the patient and delayed response. Regardless of the severity of the symptoms, consider all cases of decompression sickness to be serious.


Treatment is simple: Discontinue diving, administer 100% oxygen, and seek professional medical attention as soon as possible. It is important to have the correct contact information for the closest diving emergency facility/re-compression chamber because treatment by such a facility will most likely be necessary.


By following safe and proper diving procedures, you can avoid DCS. While it is very difficult to exactly predict how much nitrogen is absorbed by the wide range of human bodies, there are models and algorithms that give fairly accurate approximations.

Open circuit dive tables let divers determine how much nitrogen is absorbed, how long they can safely remain at a certain depth, and how quickly they may dive again. Dive computers do the same thing only more quickly and more accurately, and they are recommended for the diving course. You will be trained to make a safety stop on every dive as a precaution to help avoid decompression sickness.

The following are a few precautions you can take to stay as safe as possible.

  • Make sure you ascend slowly—9 meters/30 feet per minute or less.
  • Stay well hydrated before and after the dive.
  • Do not exceed your no decompression limits (NDLs).
  • Be more conservative with cold or strenuous dives.
  • Do not dive if you are unwell.
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