ADCI Surface Supplied Mixed Gas Diver Certification
Practice Exam
Based on ADCI (Association of Diving Contractors International) standards and
commercial diving practices, here is a comprehensive practice exam for Surface Supplied
Mixed Gas Diver Certification. Questions are formatted with multiple-choice answers,
correct answers, and detailed rationales.
1. What is the primary purpose of using mixed gas in surface-supplied diving?
A) Reduce equipment cost
B) Increase visibility
C) Reduce nitrogen narcosis and oxygen toxicity
D) Improve communication
Correct Answer: C
Rationale: Mixed gas reduces nitrogen levels and allows controlled oxygen
percentages, minimizing narcosis and toxicity at depth. Helium is non-narcotic and
allows safer deep diving operations.
2. Which gas is commonly used to replace nitrogen in mixed gas diving?
A) Carbon dioxide
B) Helium
C) Argon
D) Hydrogen
Correct Answer: B
Rationale: Helium is used because it is non-narcotic, has low density, and reduces
breathing resistance at depth. It does not produce the narcotic effects associated with
nitrogen.
,3. What is the maximum recommended partial pressure of oxygen (PPO₂) during
working dives?
A) 0.5 ATA
B) 1.0 ATA
C) 1.4 ATA
D) 2.0 ATA
Correct Answer: C
Rationale: 1.4 ATA is commonly accepted as a safe working limit to reduce oxygen
toxicity risk. For light work or rest periods, 1.6 ATA is sometimes permitted as an upper
limit.
4. What condition is most associated with high partial pressures of oxygen?
A) Hypoxia
B) Oxygen toxicity
C) Decompression sickness
D) Barotrauma
Correct Answer: B
Rationale: Elevated oxygen partial pressures can lead to central nervous system (CNS)
oxygen toxicity, causing convulsions, visual disturbances, and potentially drowning.
5. Which symptom is a sign of nitrogen narcosis?
A) Tremors
B) Confusion
C) Rash
D) Muscle cramps
Correct Answer: B
,Rationale: Nitrogen narcosis affects the central nervous system, causing confusion,
impaired judgment, euphoria, and overconfidence - similar to alcohol intoxication.
6. What is the main advantage of helium in breathing mixtures?
A) High density
B) Narcotic effect
C) Low density
D) Reactivity
Correct Answer: C
Rationale: Helium's low density reduces breathing resistance at depth and makes it
easier for divers to ventilate, especially during heavy work.
7. Which gas mixture is commonly used for very deep commercial dives exceeding
100 meters?
A) Nitrox
B) Air
C) Trimix
D) Helium only
Correct Answer: C
Rationale: Trimix combines oxygen, helium, and nitrogen to reduce both oxygen
toxicity and nitrogen narcosis, making it suitable for extreme depths. A small amount of
nitrogen is often retained to help mitigate High Pressure Nervous Syndrome (HPNS).
8. What does PPO₂ stand for?
A) Parts Per Oxygen
B) Pressure per oxygen liter
C) Partial pressure of oxygen
D) Pressure of pure oxygen
, Correct Answer: C
Rationale: PPO₂ refers to the partial pressure of oxygen a diver experiences, which is
critical for avoiding oxygen toxicity. It is calculated as depth in ATA multiplied by the
fraction of oxygen.
9. What is the primary risk of exceeding 1.6 ATA PPO₂ in a mixed gas dive?
A) Decompression sickness
B) Nitrogen narcosis
C) Oxygen toxicity
D) Hypercapnia
Correct Answer: C
Rationale: Exceeding 1.6 ATA PPO₂ can lead to CNS oxygen toxicity, causing
convulsions underwater, which is extremely dangerous and often fatal.
10. What is the main reason helium is added to a trimix breathing mixture for
deep dives?
A) Reduce oxygen toxicity at depth
B) Reduce nitrogen narcosis and gas density
C) Increase partial pressure of oxygen
D) Reduce carbon dioxide retention
Correct Answer: B
Rationale: Helium reduces narcotic effects from nitrogen and lowers gas density,
making breathing easier at depth. It also reduces work of breathing.
11. Which device is essential for controlling the breathing gas delivered to a
surface-supplied mixed gas diver?
A) Depth gauge
B) Submersible pressure gauge
Practice Exam
Based on ADCI (Association of Diving Contractors International) standards and
commercial diving practices, here is a comprehensive practice exam for Surface Supplied
Mixed Gas Diver Certification. Questions are formatted with multiple-choice answers,
correct answers, and detailed rationales.
1. What is the primary purpose of using mixed gas in surface-supplied diving?
A) Reduce equipment cost
B) Increase visibility
C) Reduce nitrogen narcosis and oxygen toxicity
D) Improve communication
Correct Answer: C
Rationale: Mixed gas reduces nitrogen levels and allows controlled oxygen
percentages, minimizing narcosis and toxicity at depth. Helium is non-narcotic and
allows safer deep diving operations.
2. Which gas is commonly used to replace nitrogen in mixed gas diving?
A) Carbon dioxide
B) Helium
C) Argon
D) Hydrogen
Correct Answer: B
Rationale: Helium is used because it is non-narcotic, has low density, and reduces
breathing resistance at depth. It does not produce the narcotic effects associated with
nitrogen.
,3. What is the maximum recommended partial pressure of oxygen (PPO₂) during
working dives?
A) 0.5 ATA
B) 1.0 ATA
C) 1.4 ATA
D) 2.0 ATA
Correct Answer: C
Rationale: 1.4 ATA is commonly accepted as a safe working limit to reduce oxygen
toxicity risk. For light work or rest periods, 1.6 ATA is sometimes permitted as an upper
limit.
4. What condition is most associated with high partial pressures of oxygen?
A) Hypoxia
B) Oxygen toxicity
C) Decompression sickness
D) Barotrauma
Correct Answer: B
Rationale: Elevated oxygen partial pressures can lead to central nervous system (CNS)
oxygen toxicity, causing convulsions, visual disturbances, and potentially drowning.
5. Which symptom is a sign of nitrogen narcosis?
A) Tremors
B) Confusion
C) Rash
D) Muscle cramps
Correct Answer: B
,Rationale: Nitrogen narcosis affects the central nervous system, causing confusion,
impaired judgment, euphoria, and overconfidence - similar to alcohol intoxication.
6. What is the main advantage of helium in breathing mixtures?
A) High density
B) Narcotic effect
C) Low density
D) Reactivity
Correct Answer: C
Rationale: Helium's low density reduces breathing resistance at depth and makes it
easier for divers to ventilate, especially during heavy work.
7. Which gas mixture is commonly used for very deep commercial dives exceeding
100 meters?
A) Nitrox
B) Air
C) Trimix
D) Helium only
Correct Answer: C
Rationale: Trimix combines oxygen, helium, and nitrogen to reduce both oxygen
toxicity and nitrogen narcosis, making it suitable for extreme depths. A small amount of
nitrogen is often retained to help mitigate High Pressure Nervous Syndrome (HPNS).
8. What does PPO₂ stand for?
A) Parts Per Oxygen
B) Pressure per oxygen liter
C) Partial pressure of oxygen
D) Pressure of pure oxygen
, Correct Answer: C
Rationale: PPO₂ refers to the partial pressure of oxygen a diver experiences, which is
critical for avoiding oxygen toxicity. It is calculated as depth in ATA multiplied by the
fraction of oxygen.
9. What is the primary risk of exceeding 1.6 ATA PPO₂ in a mixed gas dive?
A) Decompression sickness
B) Nitrogen narcosis
C) Oxygen toxicity
D) Hypercapnia
Correct Answer: C
Rationale: Exceeding 1.6 ATA PPO₂ can lead to CNS oxygen toxicity, causing
convulsions underwater, which is extremely dangerous and often fatal.
10. What is the main reason helium is added to a trimix breathing mixture for
deep dives?
A) Reduce oxygen toxicity at depth
B) Reduce nitrogen narcosis and gas density
C) Increase partial pressure of oxygen
D) Reduce carbon dioxide retention
Correct Answer: B
Rationale: Helium reduces narcotic effects from nitrogen and lowers gas density,
making breathing easier at depth. It also reduces work of breathing.
11. Which device is essential for controlling the breathing gas delivered to a
surface-supplied mixed gas diver?
A) Depth gauge
B) Submersible pressure gauge
