Incorrectly calibrated CO₂ analyser allowed high levels of CO2 to enter divers’ breathing air

Two divers were working on the seabed. They were supported by a bellman in a diving bell.

The divers had difficulties with breathing and physical tasks. Initially this was communicated to the bellman, but he did not inform the dive supervisor (DS).

When reported directly to the supervisor, he checked the reclaim system which appeared to be working correctly.

Shortly after, an alarm sounded on the CO₂ analyser for the divers’ reclaim return.

The DS observed that the analyser readings were incorrect. Divers also reported that they were experiencing agitation, breathing difficulties and headaches.

The divers were asked to flush their helmets, go on an open circuit, and return to the bell stage to change onto a secondary breathing mix.

After the analyser was changed, the CO₂ reading was still not in line with normal operating conditions. The CO₂ absorbent was also changed in the divers reclaim system.

The dive was aborted, and divers recovered to the bell.

The CO₂ absorbent had saturated, so high levels of CO₂ entered the reclaim loop and into the divers’ breathing gas.

The operating procedures did not contain sufficient details on how to calibrate and set the alarms for the CO₂ analysers. They were not calibrated correctly so did not go off at the expected levels.

The fault code on the CO₂ analyser was an unknown fault code – its significance was not recognised.

The initial symptoms experienced by the divers were not considered significant enough to cause alarm.

Review diving operating manuals to ensure reflection of manufacturer’s current recommendations – changes made by manufacturers should be disseminated to all workers.

Ensure high CO₂ scenarios are reviewed and that appropriate actions are fully detailed.

Dive system operating procedures should be comprehensive and should include information on how to calibrate and set up analysers, and how to set alarms.

Ensure that you fully understand systems that have single point failures – establish effective risk control and mitigating barriers.

All workers carrying out safety critical roles should be fully trained and competent to do so.

The divers reported their symptoms to the bellman, but they were not considered significant at first.

• What would you do in this situation?
• How would you feel about challenging authority?

How do you know how to calibrate correctly all the equipment that you use?

What would you do if an unknown fault code appeared on your equipment?

Are you fully up-to-date with all your diving procedures? What should you do if not?

What safety measures do we have in place to prevent something like this happening on our site?