Scuba Diving International (SDI) Computer Nitrox Practice Exam

What safety risks are increased by not setting the FO2 on your dive computer?

1. Increased risk of nitrogen buildup

2. Increased risk of equipment failure

3. Increased risk of oxygen toxicity and decompression sickness

4. Increased risk of poor visibility

The correct answer is: Increased risk of oxygen toxicity and decompression sickness

Not setting the FO2 (Fraction of Oxygen) on your dive computer can significantly increase the risk of oxygen toxicity and decompression sickness. When diving with a nitrox mix, the FO2 setting is crucial because it informs the dive computer about the proportion of oxygen in the gas being breathed. When the FO2 is not properly set, the dive computer cannot calculate safe limits for nitrogen and oxygen exposure. This miscalculation can lead to either exceeding the safe exposure to oxygen, which raises the risk of oxygen toxicity, especially during deeper dives or longer exposure times. Additionally, it can also wrongfully calculate no-stop limits and ascent rates, increasing the likelihood of decompression sickness due to inadequate surface intervals or ascents that do not match your actual breathing gas mix. In essence, the FO2 setting aligns the dive profile with the specific gas mixture to minimize risks associated with diving, particularly those related to the physiological impacts of nitrogen and oxygen at varying pressures underwater.