Breathing gas contamination

A member has reported an incident involving the contamination of a diver’s breathing gas.

COâ‚‚ contamination was found to be present in three cylinders of a diver’s breathing gas (96/4%). The discovery was made after a gas transfer to the vessel Kelley tubes during ‘routine’ testing. Subsequently, a full gas chromatographic analysis (to determine if additional contamination products were present) revealed levels of 3600 ppm COâ‚‚ with no other significant findings. The supplier’s gas quads were then analysed, with readings of 850 and 110 ppm COâ‚‚ noted in these.

A full inspection of the gas plant and routeing onboard was then made, which confirmed that there was no cross-contamination within the system. The ‘dirty gas’ was scrubbed and an investigation as to the source of the contamination was initiated.

The investigation also revealed that:

• the supplier’s quality certificate indicated a maximum allowable concentration of 300 ppm COâ‚‚. The company’s own standard is < 10 ppm for breathing gas;
• the quality standard referenced by the supplier was the UK Ministry of Defence standard 68-284 – Compressed Breathing Gases for Aircraft, Diving and Marine Life-Support Applications. This document sets a maximum limit of 5 ppm COâ‚‚ for oxygen/helium gas mixtures.

The company has removed the suppler from its ‘approved vendor’ list and now requires independent laboratory certification for all gas. Calibration frequency for the gas analyser and instrument limitation for detecting the lowest level of impurity is also to be studied.