Scuba Diving International (SDI) Computer Nitrox Practice Exam

What typically causes decompression sickness in divers?

1. An excess of oxygen in the body

2. An excess of nitrogen and ascending too quickly

3. Poor visibility underwater

4. Staying at depth for too long

The correct answer is: An excess of nitrogen and ascending too quickly

Decompression sickness, often known as "the bends," is commonly caused by an excess of nitrogen in the body combined with a rapid ascent to the surface. When divers descend, they breathe air that includes nitrogen, which is absorbed by the body. As a diver ascends, the pressure decreases, and this nitrogen is supposed to be eliminated from the body. If a diver ascends too quickly, however, the rapid change in pressure can cause nitrogen bubbles to form in the body, leading to various symptoms of decompression sickness, which can range from mild joint pain to severe neurological issues. The other potential causes listed—such as an excess of oxygen, poor visibility underwater, and staying at depth for too long—are issues divers may face but do not directly cause decompression sickness. An excess of oxygen can lead to toxicity, but it is not related to the formation of nitrogen bubbles. Poor visibility can make diving more dangerous but doesn't contribute to decompression sickness. Staying at depth for too long can lead to other complications, but it’s the rapid ascent with a buildup of nitrogen that's directly responsible for decompression sickness.