What procedure is used to analyze the breathing gas before use, and what parameters are checked?

• A. Pre-dive gas analysis to verify oxygen content (for mixed gas/nitrox) and detect contaminants; verify cylinder identity and pressure.
• B. Visual inspection of gas color and smell.
• C. Post-dive gas sampling for trace elements.
• D. Gas analysis only checks moisture content.

Answer: (A)

Before a dive, the breathing gas is analyzed with a gas analyzer in a pre-dive gas analysis. The key purpose is to confirm the oxygen content of the mix, which determines safe depth limits and decompression requirements for nitrox or mixed gases, and to detect contaminants that could pose a hazard, such as carbon monoxide, hydrocarbons, or excessive moisture. The procedure also verifies that the gas in the cylinder is the correct one by checking the cylinder’s identity and labeling, and it notes the cylinder pressure to ensure there is enough gas for the planned duration. Visual checks or smelling the gas aren’t reliable for confirming composition or safety, and post-dive sampling isn’t relevant to preparing for the dive.