PADI Enriched Air Nitrox Diving 2 — Questions and Answers
Question 1: What is the primary reason enriched air nitrox divers must analyze their tank before diving?
- To check for moisture contamination
- To verify the actual oxygen percentage matches the planned mix (Correct answer)
- To confirm tank pressure is adequate
- To detect carbon monoxide levels
Correct answer: To verify the actual oxygen percentage matches the planned mix
Tanks must be analyzed to confirm the oxygen fraction matches the mix you plan to dive, since an incorrect mix changes MOD and CNS limits.
Question 2: A diver plans to use EANx36 at 80 feet. What is the partial pressure of oxygen at that depth?
- 1.08 ata
- 1.26 ata (Correct answer)
- 1.44 ata
- 0.90 ata
Correct answer: 1.26 ata
At 80 feet the absolute pressure is 3.5 ata; 0.36 × 3.5 = 1.26 ata pO₂.
Question 3: Why must enriched air cylinders be marked with a distinctive yellow-and-green band?
- To indicate the cylinder was hydrostatically tested
- To warn dock crews the cylinder is pressurized
- To prevent a diver from accidentally breathing a mix beyond their training (Correct answer)
- To show the cylinder is nitrox-compatible material
Correct answer: To prevent a diver from accidentally breathing a mix beyond their training
The distinctive band is a visual warning that alerts the diver and others to the enriched oxygen content, preventing accidental use by untrained individuals.
Question 4: Which body system is most directly stressed by oxygen toxicity during enriched air diving?
- Cardiovascular system
- Digestive system
- Central nervous system (Correct answer)
- Musculoskeletal system
Correct answer: Central nervous system
CNS oxygen toxicity is the primary concern for divers because it can cause convulsions at high pO₂ levels, leading to drowning.
Question 5: A diver using EANx32 wants to stay within a 1.4 ata pO₂ limit. What is the maximum operating depth?
- 95 feet
- 111 feet (Correct answer)
- 100 feet
- 130 feet
Correct answer: 111 feet
MOD = (pO₂ limit / FO₂ − 1) × 33 = (1.4 / 0.32 − 1) × 33 ≈ 111 feet in seawater.
Question 6: What does the term 'equivalent air depth' (EAD) allow a nitrox diver to do?
- Calculate the tank volume needed for a dive
- Use standard air dive tables to plan decompression stops (Correct answer)
- Determine the correct oxygen percentage for a given depth
- Measure the pO₂ at the planned depth
Correct answer: Use standard air dive tables to plan decompression stops
EAD converts a nitrox dive to the equivalent nitrogen exposure on air, letting divers use standard air tables or computers set to air.
Question 7: When filling an enriched air cylinder, why is it important to dedicate or thoroughly clean equipment before use with oxygen-enriched mixes?
- Oxygen reacts with residual hydrocarbons and can ignite or explode (Correct answer)
- Oxygen degrades rubber O-rings twice as fast as air
- Oxygen causes galvanic corrosion inside steel cylinders
- Oxygen enrichment changes the dew point of the fill station air
Correct answer: Oxygen reacts with residual hydrocarbons and can ignite or explode
Oxygen under pressure reacts violently with hydrocarbons such as oils and greases, creating a fire or explosion hazard if equipment is not oxygen-clean.
PADI Enriched Air Nitrox Diving 2
What is the primary reason enriched air nitrox divers must analyze their tank before diving?