Helium gas quad – gas variances across quadrants

What happened?

During a planned mobilisation of five Helium gas quads (2% O₂, 98% He), one of the gas quads was found to differ from the others.  All of the quads were labelled and certified as being 2.05% O₂.  One quad, however, was stencilled as 12% O₂ and 88% He.

When the gas man began his analysis of the quad, the first quadrant indicated 1.21% O₂.  Each quadrant was subsequently analysed and provided the readings below:

• 1) 1.21%
• 2) 1.40%
• 3) 3.73%
• 4) 1.84%

The intention was to store the quad onboard for use at a later time rather than decant all of the gas into Kellys.  This quad was rejected by the diving support vessel (DSV) and returned to the supplier.

What were the causes?

It was established that there was a human error.

• Poor production checks resulted in the incorrect stencilling;
• Poor mixing of gasses before filling.

What lessons were learnt?

• Always make sure that the contents match with the quad markings, the paperwork supplied and is tested on site;
• When the manufacture recharges 64-cylinder quads, they may fill the four quarters separately (16 cylinders) of the unit, accounting for the variations.

The average of the quad was just above 2%, but the different quarters may have varied.  In this case, if the vessel were to have decanted or used the gas directly from each quarter, they would not have received the required 2% mix.  If the entire quad were decanted (all 4 quarters at the same time), this would have provided the 2% mix.

Our member noted that this is not a common occurrence, but that all personnel should be made aware that differences in gas ratios may occur in quads and check with individual suppliers whether quadrants need to be sampled individually.

Members may wish to refer to:

• High potential near-miss: Poor Oâ‚‚ content in supplied air – diver temporarily lost consciousness
• Failure to follow gas quad procedure
• Substandard nitrogen quads delivered to shipyard