NAUI NITROX CERTIFICATION EXAM
ACTUAL 2025/2026 | QUESTIONS AND
100% CORRECT ANSWERS
1. The _____ in the air you are breathing limits the time you can stay at depth.
• Answer - Nitrogen
Rationale: Nitrogen is not metabolized by the body and accumulates in
tissues during a dive. Its slow release limits bottom time due to
decompression sickness risk.
2. In the early twentieth century, a quantitative model for nitrogen loading and dive
tables were developed by _____.
• Answer - John Scott Haldane
Rationale: Haldane (1908) developed the first practical decompression
model based on nitrogen uptake and release in hypothetical tissue
compartments.
3. We say that nitrogen is an inert gas. This means _____.
• Answer - Our bodies do not use the nitrogen we breathe
Rationale: Inert gases are physiologically inactive; they dissolve in tissues
but are not metabolized or used in any biochemical process.
4. Credit for developing and introducing nitrox diving techniques for standard
scuba goes to ______.
• Answer - Dr. Morgan Wells
Rationale: Dr. Morgan Wells, a NOAA diving officer, pioneered the use of
nitrox for recreational scuba in the 1970s, including the first NOAA nitrox
tables.
,5. NAUI sanctioned enriched air nitrox training in ______.
• Answer - 1992
Rationale: NAUI (National Association of Underwater Instructors) was the
first recreational diving agency to offer a formal nitrox certification course
in 1992.
6. Two benefits of diving with nitrox are ______.
• Answer - Longer dive times and shorter surface intervals
Rationale: Reduced nitrogen intake allows more bottom time within
no-decompression limits and faster off-gassing, shortening surface intervals.
7. What does the "x" stand for in the term EANx?
• Answer - The percentage of oxygen in the mix
Rationale: EANx stands for Enriched Air Nitrox; the “x” is a variable
representing the oxygen percentage (e.g., EAN32, EAN36).
8. In 1878, Paul Bert established that ______, liberated as bubbles following
sudden decompression was the cause of decompression sickness.
• Answer - Nitrogen
Rationale: Paul Bert demonstrated that decompression bubbles consist
mainly of nitrogen, proving it is the primary cause of DCS.
9. Nitrox is a ______ breathing gas.
• Answer - Enriched air (oxygen-enriched)
Rationale: Nitrox contains more than 21% oxygen, typically 32% or 36%,
with the balance nitrogen.
10. What is the maximum oxygen percentage allowed for recreational nitrox diving
according to NAUI?
, • Answer - 40%
Rationale: NAUI recreational nitrox limits oxygen to 40% to keep maximum
operating depth (MOD) within recreational limits and reduce oxygen
toxicity risk.
11. The maximum partial pressure of oxygen (PO₂) recommended for recreational
diving is _____.
• Answer - 1.4 ATA (with contingency up to 1.6 ATA)
Rationale: PO₂ above 1.4 ATA increases the risk of central nervous system
oxygen toxicity; 1.6 ATA is the absolute limit for short exposures.
12. The formula for Maximum Operating Depth (MOD) is _____.
• Answer - MOD = (PO₂_max / FO₂) – 1 (in atmospheres absolute, then
convert to feet/ meters)
*Rationale: MOD = (1.4 / FO₂) – 1 gives depth in ATA; multiply by 33
ft/ATA for feet or 10 m/ATA for meters.*
13. Calculate the MOD in feet for EAN32 using PO₂ = 1.4 ATA.
• Answer - 111 feet
*Rationale: 1..32 = 4.375 ATA; 4.375 – 1 = 3.375 ATA × 33 ft/ATA =
111.4 ft (rounded to 111 ft).*
14. Calculate the MOD in feet for EAN36 using PO₂ = 1.4 ATA.
• Answer - 95 feet
*Rationale: 1..36 = 3.889 ATA; minus 1 = 2.889 ATA × 33 = 95.3 ft →
95 ft.*
15. What is the MOD for EAN32 if you use a contingency PO₂ of 1.6 ATA?
, • Answer - 132 feet
*Rationale: 1..32 = 5 ATA; 5 – 1 = 4 ATA × 33 = 132 ft. This is the
absolute depth limit for EAN32.*
16. Oxygen toxicity affecting the central nervous system (CNS) is also called
_____.
• Answer - The Paul Bert effect
Rationale: CNS oxygen toxicity, named after Paul Bert, can cause
convulsions, tunnel vision, and loss of consciousness.
17. The lung (pulmonary) form of oxygen toxicity is known as _____.
• Answer - The Lorrain-Smith effect
Rationale: Pulmonary oxygen toxicity results from prolonged exposure to
high PO₂, causing inflammation, coughing, and reduced vital capacity.
18. Which type of oxygen toxicity is more relevant to recreational nitrox diving?
• Answer - CNS oxygen toxicity (Paul Bert effect)
Rationale: Recreational dives are short enough that pulmonary toxicity is
unlikely; CNS toxicity from high PO₂ at depth is the primary concern.
19. The most common early symptom of CNS oxygen toxicity is _____.
• Answer - Visual disturbances (tunnel vision, flickering lights)
Rationale: Early signs include vision changes, ringing in the ears, twitching,
nausea, and irritability.
20. If a diver experiences CNS oxygen toxicity symptoms underwater, the
immediate action is _____.
• Answer - Reduce depth (ascend) and breathe a lower PO₂ gas
Rationale: Decreasing depth reduces PO₂; the diver should also switch to a
lower oxygen gas if available.
ACTUAL 2025/2026 | QUESTIONS AND
100% CORRECT ANSWERS
1. The _____ in the air you are breathing limits the time you can stay at depth.
• Answer - Nitrogen
Rationale: Nitrogen is not metabolized by the body and accumulates in
tissues during a dive. Its slow release limits bottom time due to
decompression sickness risk.
2. In the early twentieth century, a quantitative model for nitrogen loading and dive
tables were developed by _____.
• Answer - John Scott Haldane
Rationale: Haldane (1908) developed the first practical decompression
model based on nitrogen uptake and release in hypothetical tissue
compartments.
3. We say that nitrogen is an inert gas. This means _____.
• Answer - Our bodies do not use the nitrogen we breathe
Rationale: Inert gases are physiologically inactive; they dissolve in tissues
but are not metabolized or used in any biochemical process.
4. Credit for developing and introducing nitrox diving techniques for standard
scuba goes to ______.
• Answer - Dr. Morgan Wells
Rationale: Dr. Morgan Wells, a NOAA diving officer, pioneered the use of
nitrox for recreational scuba in the 1970s, including the first NOAA nitrox
tables.
,5. NAUI sanctioned enriched air nitrox training in ______.
• Answer - 1992
Rationale: NAUI (National Association of Underwater Instructors) was the
first recreational diving agency to offer a formal nitrox certification course
in 1992.
6. Two benefits of diving with nitrox are ______.
• Answer - Longer dive times and shorter surface intervals
Rationale: Reduced nitrogen intake allows more bottom time within
no-decompression limits and faster off-gassing, shortening surface intervals.
7. What does the "x" stand for in the term EANx?
• Answer - The percentage of oxygen in the mix
Rationale: EANx stands for Enriched Air Nitrox; the “x” is a variable
representing the oxygen percentage (e.g., EAN32, EAN36).
8. In 1878, Paul Bert established that ______, liberated as bubbles following
sudden decompression was the cause of decompression sickness.
• Answer - Nitrogen
Rationale: Paul Bert demonstrated that decompression bubbles consist
mainly of nitrogen, proving it is the primary cause of DCS.
9. Nitrox is a ______ breathing gas.
• Answer - Enriched air (oxygen-enriched)
Rationale: Nitrox contains more than 21% oxygen, typically 32% or 36%,
with the balance nitrogen.
10. What is the maximum oxygen percentage allowed for recreational nitrox diving
according to NAUI?
, • Answer - 40%
Rationale: NAUI recreational nitrox limits oxygen to 40% to keep maximum
operating depth (MOD) within recreational limits and reduce oxygen
toxicity risk.
11. The maximum partial pressure of oxygen (PO₂) recommended for recreational
diving is _____.
• Answer - 1.4 ATA (with contingency up to 1.6 ATA)
Rationale: PO₂ above 1.4 ATA increases the risk of central nervous system
oxygen toxicity; 1.6 ATA is the absolute limit for short exposures.
12. The formula for Maximum Operating Depth (MOD) is _____.
• Answer - MOD = (PO₂_max / FO₂) – 1 (in atmospheres absolute, then
convert to feet/ meters)
*Rationale: MOD = (1.4 / FO₂) – 1 gives depth in ATA; multiply by 33
ft/ATA for feet or 10 m/ATA for meters.*
13. Calculate the MOD in feet for EAN32 using PO₂ = 1.4 ATA.
• Answer - 111 feet
*Rationale: 1..32 = 4.375 ATA; 4.375 – 1 = 3.375 ATA × 33 ft/ATA =
111.4 ft (rounded to 111 ft).*
14. Calculate the MOD in feet for EAN36 using PO₂ = 1.4 ATA.
• Answer - 95 feet
*Rationale: 1..36 = 3.889 ATA; minus 1 = 2.889 ATA × 33 = 95.3 ft →
95 ft.*
15. What is the MOD for EAN32 if you use a contingency PO₂ of 1.6 ATA?
, • Answer - 132 feet
*Rationale: 1..32 = 5 ATA; 5 – 1 = 4 ATA × 33 = 132 ft. This is the
absolute depth limit for EAN32.*
16. Oxygen toxicity affecting the central nervous system (CNS) is also called
_____.
• Answer - The Paul Bert effect
Rationale: CNS oxygen toxicity, named after Paul Bert, can cause
convulsions, tunnel vision, and loss of consciousness.
17. The lung (pulmonary) form of oxygen toxicity is known as _____.
• Answer - The Lorrain-Smith effect
Rationale: Pulmonary oxygen toxicity results from prolonged exposure to
high PO₂, causing inflammation, coughing, and reduced vital capacity.
18. Which type of oxygen toxicity is more relevant to recreational nitrox diving?
• Answer - CNS oxygen toxicity (Paul Bert effect)
Rationale: Recreational dives are short enough that pulmonary toxicity is
unlikely; CNS toxicity from high PO₂ at depth is the primary concern.
19. The most common early symptom of CNS oxygen toxicity is _____.
• Answer - Visual disturbances (tunnel vision, flickering lights)
Rationale: Early signs include vision changes, ringing in the ears, twitching,
nausea, and irritability.
20. If a diver experiences CNS oxygen toxicity symptoms underwater, the
immediate action is _____.
• Answer - Reduce depth (ascend) and breathe a lower PO₂ gas
Rationale: Decreasing depth reduces PO₂; the diver should also switch to a
lower oxygen gas if available.
