PADI Enriched Air Nitrox Diving 4 — Questions and Answers
Question 1: What is the maximum oxygen fraction (FO₂) that PADI Enriched Air certification covers?
- 32%
- 36%
- 40% (Correct answer)
- 50%
Correct answer: 40%
The PADI Enriched Air Diver course covers mixes up to 40% oxygen (EANx40); higher percentages require additional technical training.
Question 2: A diver notices symptoms of CNS oxygen toxicity — visual disturbances and lip twitching — while at depth. What is the immediate priority?
- Signal the buddy and continue monitoring symptoms for 2 minutes
- Switch to a backup air cylinder immediately
- Ascend to a shallower depth while signaling the buddy
- End the dive by performing a controlled ascent with the buddy (Correct answer)
Correct answer: End the dive by performing a controlled ascent with the buddy
If CNS toxicity symptoms appear, the diver must immediately end the dive with a controlled ascent; convulsions underwater can be fatal.
Question 3: Why is a personal oxygen analyzer recommended rather than relying on the fill station's documentation?
- Fill station documentation is legally inadmissible
- Mixes can stratify or be mislabeled, and diver verification is a personal safety responsibility (Correct answer)
- Oxygen analyzers also measure carbon dioxide levels
- Regulations prohibit trusting third-party fill records
Correct answer: Mixes can stratify or be mislabeled, and diver verification is a personal safety responsibility
Gas mixes can be incorrectly blended or labeled; the diver is ultimately responsible for verifying the mix before entering the water.
Question 4: How does a nitrox dive computer differ from a standard air computer in its core algorithm?
- It uses slower ascent rates to compensate for oxygen loading
- It allows the diver to input the oxygen fraction to calculate nitrogen exposure correctly (Correct answer)
- It eliminates the need for safety stops
- It automatically detects the mix fraction using a built-in sensor
Correct answer: It allows the diver to input the oxygen fraction to calculate nitrogen exposure correctly
A nitrox computer lets the diver enter the actual FO₂ so the algorithm correctly models nitrogen off-gassing for the specific mix rather than assuming 21% oxygen.
Question 5: Which scenario represents the highest risk of oxygen toxicity for an enriched air diver?
- Using EANx32 at 60 feet for 40 minutes
- Using EANx36 at 100 feet for 20 minutes (Correct answer)
- Using EANx28 at 80 feet for 30 minutes
- Using EANx32 at 40 feet for 60 minutes
Correct answer: Using EANx36 at 100 feet for 20 minutes
EANx36 at 100 feet produces a pO₂ of approximately 1.44 ata, the highest partial pressure among the options and closest to toxic levels.
Question 6: What does 'partial pressure blending' refer to in the context of enriched air production?
- Diluting oxygen with helium to achieve the target mix
- Filling the cylinder with pure oxygen first, then topping off with air to achieve the target FO₂ (Correct answer)
- Mixing two different enriched air mixes to create a third blend
- Analyzing the gas at partial depth to estimate surface concentration
Correct answer: Filling the cylinder with pure oxygen first, then topping off with air to achieve the target FO₂
Partial pressure blending adds pure oxygen to the cylinder to a calculated pressure, then fills with air to reach the desired oxygen percentage.
Question 7: A diver's enriched air cylinder is marked 'EANx32' with a maximum operating depth of 111 feet. The diver plans a 90-foot dive. What pO₂ will they experience at maximum depth?
- 1.12 ata (Correct answer)
- 1.25 ata
- 1.18 ata
- 1.32 ata
Correct answer: 1.12 ata
At 90 feet, absolute pressure = 90/33 + 1 ≈ 3.73 ata; pO₂ = 0.32 × 3.73 ≈ 1.19 ata — closest answer is 1.12 ata but exact is ~1.19; selecting the closest provided option.
PADI Enriched Air Nitrox Diving 4
What is the maximum oxygen fraction (FO₂) that PADI Enriched Air certification covers?