Certification Exam Practice Questions

ADCI Surface Supplied Mixed Gas Diver Certification Exam Practice Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• What is the primary purpose of using mixed gas instead of air for deep

diving?

a) To reduce oxygen toxicity only

b) To reduce nitrogen narcosis only

c) To reduce both nitrogen narcosis and oxygen toxicity

d) To increase dive speed

Rationale: Mixed gas, such as heliox or trimix, is used in deep diving

to reduce the risk of both nitrogen narcosis and oxygen toxicity, which can occur when breathing air at great depths. 1 / 4

• Which gas mixture is commonly used for dives below 100 meters?

a) Air

b) Nitrox

c) Trimix

d) Helium

Rationale: Trimix contains oxygen, nitrogen, and helium and is used

for deep dives to mitigate both nitrogen narcosis and oxygen toxicity.

• Oxygen toxicity becomes a major concern when the partial pressure of

oxygen exceeds:

• 0.5 ATA
• 1.6 ATA
• 2.0 ATA
• 1.0 ATA

Rationale: Central nervous system oxygen toxicity becomes

significant when PO2 exceeds 1.6 ATA during diving.

• Which device monitors depth and partial pressure of oxygen during a

dive?

a) Depth gauge

b) Pressure gauge

c) Oxygen analyzer

d) Compass

Rationale: An oxygen analyzer is used to monitor PO2 in the

breathing gas to ensure safe limits are not exceeded. 2 / 4

• What is the most important factor when planning a mixed gas dive?

a) Water temperature

b) Gas mixture and depth profile

c) Visibility

d) Current speed

Rationale: Proper planning of gas mixtures and depth profiles is

critical to avoid oxygen toxicity, nitrogen narcosis, and decompression sickness.

6. The main reason helium is added to deep diving mixtures is:

a) To increase density

b) To reduce nitrogen narcosis

c) To increase oxygen content

d) To improve buoyancy

Rationale: Helium is an inert gas with low narcotic potential, which

reduces nitrogen narcosis in deep dives.

• What is the primary hazard of rapid decompression from deep mixed

gas dives?

a) Nitrogen narcosis

b) Oxygen toxicity

c) Decompression sickness

d) Hypothermia

Rationale: Rapid ascent without proper decompression can cause

dissolved gases to form bubbles, leading to decompression sickness. 3 / 4

• Which mixed gas is known for being very light and easy to breathe at

depth?

a) Air

b) Nitrox

c) Heliox

d) Trimix

Rationale: Heliox, a mixture of helium and oxygen, is less dense and

reduces breathing resistance at great depths.

• Which factor most affects decompression obligations?

a) Water visibility

b) Dive suit thickness

c) Depth and bottom time

d) Current speed

Rationale: The depth and duration of a dive determine the amount of

inert gas absorbed, which dictates decompression stops.

• What is the purpose of a decompression stop?

a) To rest the diver

b) To check equipment

c) To allow inert gas to safely leave tissues

d) To reduce oxygen exposure

Rationale: Decompression stops allow dissolved inert gases to be

eliminated slowly, reducing the risk of decompression sickness.

• / 4