ADCI Surface Supplied Mixed Gas Diver
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1. What is the primary purpose of using mixed gas diving over air or
nitrox?
A. Reduce dive costs
B. Extend bottom time and reduce nitrogen narcosis
C. Simplify decompression schedules
D. Avoid surface decompression
B. Extend bottom time and reduce nitrogen narcosis
Mixed gas allows divers to reduce nitrogen exposure and mitigate
narcosis, enabling deeper and longer dives safely.
2. Which gas mixture is commonly used for dives deeper than 100
meters?
A. Nitrox 32
B. Trimix
C. Heliox
D. Air
B. Trimix
Trimix combines oxygen, helium, and nitrogen to reduce narcotic
effects and manage oxygen toxicity at extreme depths.
, 3. What is the maximum allowable partial pressure of oxygen (PPO2)
at depth to prevent CNS oxygen toxicity?
A. 0.5 ATA
B. 1.6 ATA
C. 2.0 ATA
D. 2.5 ATA
B. 1.6 ATA
A PPO2 of 1.6 ATA is generally considered the maximum safe exposure
for working dives to prevent CNS oxygen toxicity.
4. Which gas is added to a breathing mix to reduce nitrogen
narcosis?
A. Oxygen
B. Carbon dioxide
C. Helium
D. Hydrogen
C. Helium
Helium is non-narcotic and reduces the narcotic effects of nitrogen at
depth, making deep dives safer.
5. What is the primary risk associated with high oxygen partial
pressures?
A. Hypothermia
B. CNS oxygen toxicity
C. Carbon monoxide poisoning
D. Nitrogen narcosis
B. CNS oxygen toxicity
High oxygen partial pressures can lead to seizures and CNS oxygen
toxicity, a critical hazard in mixed gas diving.
, 6. What is the function of a gas panel in a mixed gas surface-
supplied dive?
A. Monitor decompression time
B. Control the composition of breathing gases delivered to the
diver
C. Measure dive depth
D. Track diver’s heart rate
B. Control the composition of breathing gases delivered to the diver
The gas panel ensures the diver receives the correct mix for each
depth, preventing oxygen toxicity and narcosis.
7. Which decompression model is most commonly used for mixed
gas diving?
A. Haldanean
B. Thalmann (VVAL-18)
C. Bühlmann ZHL
D. US Navy 1955
B. Thalmann (VVAL-18)
VVAL-18 is widely adopted in commercial diving for mixed gas
schedules because it is validated for helium-containing mixes.
8. What is the main purpose of a back gas in mixed gas diving?
A. Provide surface breathing gas
B. Serve as a bailout supply for emergencies
C. Cool the diver
D. Replace helium at depth
B. Serve as a bailout supply for emergencies
Back gas acts as a redundant supply if the primary surface-supplied
gas fails, allowing the diver to safely ascend.
, 9. Which device is used to measure the oxygen fraction in a gas mix?
A. Flow meter
B. Oxygen analyzer
C. Depth gauge
D. Gas chromatograph
B. Oxygen analyzer
Oxygen analyzers are essential for verifying the oxygen content before
diving to prevent oxygen toxicity.
10. What is the primary risk of using helium in a gas mix?
A. Carbon monoxide formation
B. Hypothermia due to high thermal conductivity
C. Nitrogen narcosis
D. Hypercapnia
B. Hypothermia due to high thermal conductivity
Helium conducts heat quickly, increasing the risk of diver hypothermia
if thermal protection is inadequate.
11. What is a safe ascent rate for mixed gas decompression
dives?
A. 30 m/min
B. 9–10 m/min
C. 1–2 m/min
D. 20 m/min
B. 9–10 m/min
Controlled ascent rates prevent decompression sickness by allowing
inert gases to off-gas safely.
12. Which of the following is a primary symptom of
decompression sickness?
A. Headache
Certification Exam With Actual Questions
& Verified Answers, Plus Explained
Rationales/Expert Verified For Guaranteed
100% Pass 2026/Latest Update/Instant
Download Pdf
1. What is the primary purpose of using mixed gas diving over air or
nitrox?
A. Reduce dive costs
B. Extend bottom time and reduce nitrogen narcosis
C. Simplify decompression schedules
D. Avoid surface decompression
B. Extend bottom time and reduce nitrogen narcosis
Mixed gas allows divers to reduce nitrogen exposure and mitigate
narcosis, enabling deeper and longer dives safely.
2. Which gas mixture is commonly used for dives deeper than 100
meters?
A. Nitrox 32
B. Trimix
C. Heliox
D. Air
B. Trimix
Trimix combines oxygen, helium, and nitrogen to reduce narcotic
effects and manage oxygen toxicity at extreme depths.
, 3. What is the maximum allowable partial pressure of oxygen (PPO2)
at depth to prevent CNS oxygen toxicity?
A. 0.5 ATA
B. 1.6 ATA
C. 2.0 ATA
D. 2.5 ATA
B. 1.6 ATA
A PPO2 of 1.6 ATA is generally considered the maximum safe exposure
for working dives to prevent CNS oxygen toxicity.
4. Which gas is added to a breathing mix to reduce nitrogen
narcosis?
A. Oxygen
B. Carbon dioxide
C. Helium
D. Hydrogen
C. Helium
Helium is non-narcotic and reduces the narcotic effects of nitrogen at
depth, making deep dives safer.
5. What is the primary risk associated with high oxygen partial
pressures?
A. Hypothermia
B. CNS oxygen toxicity
C. Carbon monoxide poisoning
D. Nitrogen narcosis
B. CNS oxygen toxicity
High oxygen partial pressures can lead to seizures and CNS oxygen
toxicity, a critical hazard in mixed gas diving.
, 6. What is the function of a gas panel in a mixed gas surface-
supplied dive?
A. Monitor decompression time
B. Control the composition of breathing gases delivered to the
diver
C. Measure dive depth
D. Track diver’s heart rate
B. Control the composition of breathing gases delivered to the diver
The gas panel ensures the diver receives the correct mix for each
depth, preventing oxygen toxicity and narcosis.
7. Which decompression model is most commonly used for mixed
gas diving?
A. Haldanean
B. Thalmann (VVAL-18)
C. Bühlmann ZHL
D. US Navy 1955
B. Thalmann (VVAL-18)
VVAL-18 is widely adopted in commercial diving for mixed gas
schedules because it is validated for helium-containing mixes.
8. What is the main purpose of a back gas in mixed gas diving?
A. Provide surface breathing gas
B. Serve as a bailout supply for emergencies
C. Cool the diver
D. Replace helium at depth
B. Serve as a bailout supply for emergencies
Back gas acts as a redundant supply if the primary surface-supplied
gas fails, allowing the diver to safely ascend.
, 9. Which device is used to measure the oxygen fraction in a gas mix?
A. Flow meter
B. Oxygen analyzer
C. Depth gauge
D. Gas chromatograph
B. Oxygen analyzer
Oxygen analyzers are essential for verifying the oxygen content before
diving to prevent oxygen toxicity.
10. What is the primary risk of using helium in a gas mix?
A. Carbon monoxide formation
B. Hypothermia due to high thermal conductivity
C. Nitrogen narcosis
D. Hypercapnia
B. Hypothermia due to high thermal conductivity
Helium conducts heat quickly, increasing the risk of diver hypothermia
if thermal protection is inadequate.
11. What is a safe ascent rate for mixed gas decompression
dives?
A. 30 m/min
B. 9–10 m/min
C. 1–2 m/min
D. 20 m/min
B. 9–10 m/min
Controlled ascent rates prevent decompression sickness by allowing
inert gases to off-gas safely.
12. Which of the following is a primary symptom of
decompression sickness?
A. Headache
