Commercial Diver Certification Exam

Commercial Diver Certification Exam Practice Test Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• Which gas is commonly used in surface-supplied diving to prevent

nitrogen narcosis at depth?

• Oxygen
• Helium
• Nitrogen
• Carbon dioxide

Rationale: Helium is used in breathing mixtures (like heliox) because it

reduces the narcotic effect of nitrogen at depth.

• / 4

2. The primary purpose of a diving helmet is to:

• Protect the diver from cold water
• Provide a supply of breathing gas
• Increase buoyancy
• Measure underwater depth

Rationale: A diving helmet supplies air or gas mixtures to the diver while

maintaining a sealed environment.

• The maximum allowable working pressure for a standard commercial

diving air supply system is typically:

• 50 psi
• 100 psi
• 300 psi
• 500 psi

Rationale: Standard commercial diving air systems are designed to safely

operate up to 300 psi.

• Which diving mode allows the diver to receive gas through a hose

connected to the surface?

A) SCUBA

• Saturation 2 / 4

• Surface-supplied diving
• Freediving

Rationale: Surface-supplied diving uses a hose or umbilical to supply

breathing gas from the surface.

5. Decompression sickness occurs when:

• A diver stays underwater too long
• Dissolved gases come out of solution too quickly
• The diver inhales contaminated gas
• Water temperature is too cold

Rationale: Rapid ascent can cause nitrogen bubbles to form in tissues,

leading to decompression sickness.

• Which piece of equipment measures depth underwater?
• Compass
• Flow meter
• Depth gauge
• Regulator

Rationale: Depth gauges indicate how far a diver is below the surface,

critical for safe ascent.

• / 4

7. In commercial diving, a “bell” is primarily used for:

• Storing tools
• Measuring underwater pressure
• Transporting divers to depth safely
• Communication

Rationale: A diving bell allows divers to be safely lowered and raised while

maintaining gas supply.

• The recommended ascent rate to reduce decompression sickness risk is

approximately:

• 50 ft/min
• 30 ft/min
• 10 ft/min
• 60 ft/min

Rationale: A slow ascent of around 30 feet per minute helps nitrogen safely

off-gas.

• Which gas is toxic at high partial pressures and limits diving depth?
• Helium
• Oxygen
• Nitrogen
• Hydrogen
• / 4