ADCI Surface Supplied Mixed Gas Diver Certification Exam
Questions and Correct Answers Updated
QUESTION 1:
Which of the following best describes the primary advantage of using helium-oxygen breathing
mixtures (heliox) for deep surface-supplied diving operations?
A) Reduced oxygen toxicity risk
B) Increased nitrogen narcosis
C) Increased work of breathing
D) Enhanced carbon dioxide retention
CORRECT ANSWER: A) Reduced oxygen toxicity risk
RATIONALE: Helium replaces nitrogen in the gas mix, lowering narcotic effects and minimizing
oxygen toxicity risks at depth. Helium’s low density also reduces work of breathing compared to
nitrogen-rich mixtures.
QUESTION 2:
At what maximum partial pressure of oxygen (ppO₂) should a diver’s breathing mix be
maintained during the working portion of a mixed-gas dive?
A) 0.5 ATA
B) 1.3 ATA
C) 1.6 ATA
D) 2.0 ATA
CORRECT ANSWER: C) 1.6 ATA
RATIONALE: A ppO₂ of 1.6 ATA is the accepted maximum safe working limit for oxygen exposure
during mixed-gas operations, beyond which oxygen toxicity becomes a significant hazard.
QUESTION 3:
True or False: Nitrogen is used instead of helium in deep diving because it is less expensive and
non-flammable.
CORRECT ANSWER: False
RATIONALE: Nitrogen is more narcotic than helium and unsuitable for deep diving, despite being
cheaper. Helium’s inertness and low narcotic effect make it preferable for mixed-gas operations.
,QUESTION 4:
During saturation diving or prolonged mixed-gas operations, why is thermal protection critically
important?
A) Water conductivity leads to rapid heat loss from the diver
B) Helium gas increases body temperature
C) Carbon dioxide buildup is eliminated in cold water
D) Increased hydrostatic pressure warms the suit
CORRECT ANSWER: A) Water conductivity leads to rapid heat loss from the diver
RATIONALE: Helium conducts heat much more efficiently than air; therefore, without thermal
protection, a diver quickly loses body heat, risking hypothermia.
QUESTION 5:
What is the purpose of a “bailout bottle” in surface-supplied mixed gas diving?
A) To provide air to inflate the diver’s drysuit
B) To replace primary gas with oxygen
C) To serve as an independent emergency gas supply
D) To reduce decompression obligation
CORRECT ANSWER: C) To serve as an independent emergency gas supply
RATIONALE: A bailout system ensures self-rescue capability if the primary surface gas supply is
interrupted, maintaining diver safety.
QUESTION 6:
When calculating equivalent air depth (EAD) for decompression, what main factors are
considered?
A) Depth and helium-to-oxygen ratio
B) Depth and fraction of nitrogen
C) Temperature and breathing rate
D) Duration and oxygen percentage
CORRECT ANSWER: B) Depth and fraction of nitrogen
RATIONALE: EAD accounts for the narcotic potential of nitrogen at a given depth, aligning
mixed-gas decompression with air tables where applicable.
,QUESTION 7:
Which of the following best defines “bounce dive” in mixed-gas operations?
A) A series of short, shallow dives
B) A single deep dive with decompression prior to returning to surface
C) A saturation dive of extended duration
D) A dive with variable pressure cycles
CORRECT ANSWER: B) A single deep dive with decompression prior to returning to surface
RATIONALE: Bounce dives involve short exposure at depth followed by decompression, unlike
saturation dives where divers remain compressed for days.
QUESTION 8:
Which component removes carbon dioxide from the diver’s breathing gas in a rebreather or
habitat system?
A) Oxygen sensor
B) Scrubber canister
C) Demand regulator
D) Pressure relief valve
CORRECT ANSWER: B) Scrubber canister
RATIONALE: The scrubber absorbs CO₂ using a chemical medium (commonly soda lime),
preventing hypercapnia.
QUESTION 9:
What is the principal symptom of central nervous system oxygen toxicity?
A) Headache
B) Muscle cramps
C) Convulsions
D) Nausea
CORRECT ANSWER: C) Convulsions
RATIONALE: CNS oxygen toxicity can cause convulsions without warning, posing a severe
drowning risk if it occurs underwater.
QUESTION 10:
In a properly functioning surface-supplied system, check valves are used to:
, A) Prevent backflow of gas from the diver’s side
B) Allow free flow in both directions
C) Increase gas pressure to the diver
D) Maintain constant temperature
CORRECT ANSWER: A) Prevent backflow of gas from the diver’s side
RATIONALE: Check valves provide one-way gas flow, ensuring that gas pressure fluctuation or
hose rupture does not send gas backward into the supply line.
QUESTION 11:
Why is helium’s high thermal conductivity a concern for divers using heliox mixtures?
A) It causes overheating at depth
B) It accelerates nitrogen absorption
C) It promotes rapid body heat loss
D) It interferes with voice transmission
CORRECT ANSWER: C) It promotes rapid body heat loss
RATIONALE: Helium transfers heat more efficiently than air or nitrogen, cooling divers quickly
and requiring adequate heating systems.
QUESTION 12:
Which of the following instruments continuously monitors the diver’s depth and bottom time
during a surface-supplied mixed gas dive?
A) Cross-check gauge
B) Pneumo-fathometer
C) Depth recorder logger
D) Oxygen analyzer
CORRECT ANSWER: B) Pneumo-fathometer
RATIONALE: The pneumo-fathometer measures depth by back-pressuring a small line of air
against water at the diver’s location, giving accurate depth readings.
QUESTION 13:
The term “surdural time” in mixed-gas diving typically refers to:
A) The interval before decompression can start
B) The total time spent under pressure
Questions and Correct Answers Updated
QUESTION 1:
Which of the following best describes the primary advantage of using helium-oxygen breathing
mixtures (heliox) for deep surface-supplied diving operations?
A) Reduced oxygen toxicity risk
B) Increased nitrogen narcosis
C) Increased work of breathing
D) Enhanced carbon dioxide retention
CORRECT ANSWER: A) Reduced oxygen toxicity risk
RATIONALE: Helium replaces nitrogen in the gas mix, lowering narcotic effects and minimizing
oxygen toxicity risks at depth. Helium’s low density also reduces work of breathing compared to
nitrogen-rich mixtures.
QUESTION 2:
At what maximum partial pressure of oxygen (ppO₂) should a diver’s breathing mix be
maintained during the working portion of a mixed-gas dive?
A) 0.5 ATA
B) 1.3 ATA
C) 1.6 ATA
D) 2.0 ATA
CORRECT ANSWER: C) 1.6 ATA
RATIONALE: A ppO₂ of 1.6 ATA is the accepted maximum safe working limit for oxygen exposure
during mixed-gas operations, beyond which oxygen toxicity becomes a significant hazard.
QUESTION 3:
True or False: Nitrogen is used instead of helium in deep diving because it is less expensive and
non-flammable.
CORRECT ANSWER: False
RATIONALE: Nitrogen is more narcotic than helium and unsuitable for deep diving, despite being
cheaper. Helium’s inertness and low narcotic effect make it preferable for mixed-gas operations.
,QUESTION 4:
During saturation diving or prolonged mixed-gas operations, why is thermal protection critically
important?
A) Water conductivity leads to rapid heat loss from the diver
B) Helium gas increases body temperature
C) Carbon dioxide buildup is eliminated in cold water
D) Increased hydrostatic pressure warms the suit
CORRECT ANSWER: A) Water conductivity leads to rapid heat loss from the diver
RATIONALE: Helium conducts heat much more efficiently than air; therefore, without thermal
protection, a diver quickly loses body heat, risking hypothermia.
QUESTION 5:
What is the purpose of a “bailout bottle” in surface-supplied mixed gas diving?
A) To provide air to inflate the diver’s drysuit
B) To replace primary gas with oxygen
C) To serve as an independent emergency gas supply
D) To reduce decompression obligation
CORRECT ANSWER: C) To serve as an independent emergency gas supply
RATIONALE: A bailout system ensures self-rescue capability if the primary surface gas supply is
interrupted, maintaining diver safety.
QUESTION 6:
When calculating equivalent air depth (EAD) for decompression, what main factors are
considered?
A) Depth and helium-to-oxygen ratio
B) Depth and fraction of nitrogen
C) Temperature and breathing rate
D) Duration and oxygen percentage
CORRECT ANSWER: B) Depth and fraction of nitrogen
RATIONALE: EAD accounts for the narcotic potential of nitrogen at a given depth, aligning
mixed-gas decompression with air tables where applicable.
,QUESTION 7:
Which of the following best defines “bounce dive” in mixed-gas operations?
A) A series of short, shallow dives
B) A single deep dive with decompression prior to returning to surface
C) A saturation dive of extended duration
D) A dive with variable pressure cycles
CORRECT ANSWER: B) A single deep dive with decompression prior to returning to surface
RATIONALE: Bounce dives involve short exposure at depth followed by decompression, unlike
saturation dives where divers remain compressed for days.
QUESTION 8:
Which component removes carbon dioxide from the diver’s breathing gas in a rebreather or
habitat system?
A) Oxygen sensor
B) Scrubber canister
C) Demand regulator
D) Pressure relief valve
CORRECT ANSWER: B) Scrubber canister
RATIONALE: The scrubber absorbs CO₂ using a chemical medium (commonly soda lime),
preventing hypercapnia.
QUESTION 9:
What is the principal symptom of central nervous system oxygen toxicity?
A) Headache
B) Muscle cramps
C) Convulsions
D) Nausea
CORRECT ANSWER: C) Convulsions
RATIONALE: CNS oxygen toxicity can cause convulsions without warning, posing a severe
drowning risk if it occurs underwater.
QUESTION 10:
In a properly functioning surface-supplied system, check valves are used to:
, A) Prevent backflow of gas from the diver’s side
B) Allow free flow in both directions
C) Increase gas pressure to the diver
D) Maintain constant temperature
CORRECT ANSWER: A) Prevent backflow of gas from the diver’s side
RATIONALE: Check valves provide one-way gas flow, ensuring that gas pressure fluctuation or
hose rupture does not send gas backward into the supply line.
QUESTION 11:
Why is helium’s high thermal conductivity a concern for divers using heliox mixtures?
A) It causes overheating at depth
B) It accelerates nitrogen absorption
C) It promotes rapid body heat loss
D) It interferes with voice transmission
CORRECT ANSWER: C) It promotes rapid body heat loss
RATIONALE: Helium transfers heat more efficiently than air or nitrogen, cooling divers quickly
and requiring adequate heating systems.
QUESTION 12:
Which of the following instruments continuously monitors the diver’s depth and bottom time
during a surface-supplied mixed gas dive?
A) Cross-check gauge
B) Pneumo-fathometer
C) Depth recorder logger
D) Oxygen analyzer
CORRECT ANSWER: B) Pneumo-fathometer
RATIONALE: The pneumo-fathometer measures depth by back-pressuring a small line of air
against water at the diver’s location, giving accurate depth readings.
QUESTION 13:
The term “surdural time” in mixed-gas diving typically refers to:
A) The interval before decompression can start
B) The total time spent under pressure
