PADI Divemaster Certification Practice Exam

What is the maximum percentage of oxygen that standard regulators can safely be used with EANx blends?

1. 30%

2. 35%

3. 40%

4. 45%

The correct answer is: 40%

Standard regulators are designed to operate safely with a wide range of gas mixes, including EANx (Enriched Air Nitrox) blends, which contain higher percentages of oxygen than regular air. The correct answer indicates that standard regulators can typically be used safely with oxygen levels up to 40%. This limit is important because as the percentage of oxygen increases, so does the risk of oxygen toxicity. Oxygen toxicity can become a hazard at depths and with exposure times that scuba divers commonly encounter. Therefore, manufacturers of standard diving equipment specify a safe upper limit for the use of their regulators with enriched air. While regulators may technically function properly with percentages higher than 40%, using them above this threshold can compromise safety due to the increased risk of oxygen toxicity. Deep diving operations or extended exposure times at higher oxygen levels usually require special equipment specifically rated for higher oxygen use to mitigate these risks. This underscores the importance of adhering to safe operational guidelines when using enriched air while diving.