Uncontrolled decompression during gangway move

A member has reported that a man-way trunk and its adjacent entry lock on a hyperbaric chamber were depressurised to surface when a fitting on the man-way was struck by a gangway. The system was pressurised to 270fsw and vented to the surface in ten minutes through a ¼” penetrator. The system held four divers in saturation.

The were no injuries and, other than the fitting, no further damage was caused.

Initial findings of the investigation are that:

• the trunk fitting was unprotected from direct contact with the gangway;
• the crew had lost control of the gangway while raising it to allow a materials barge alongside;
• there had been a valve on the internal aspect of the trunk, but this had not been secured after the valve was hit;
• the loss of pressure in the adjacent entry lock was attributable to a misalignment of the chamber inner door, which was immediately and easily realigned following the incident.

The potential for a less benign outcome for this incident was significant. Investigations are ongoing and the company will be issuing an internal memorandum on the issues surrounding this incident.

In the meantime, it has passed this alert to IMCA as a ‘heads up’ and a reminder that to expect and prepare for the unexpected is good advice. The company has asked all of its dive team members to scrutinise the arrangement of similar fittings on other diving spreads and to report any results which could predict the occurrence of a similar incident. Any proposed system modifications will then go through the company’s management-of-change process.

Particular points to be noted are:

• hyperbaric evacuation systems and other dive equipment on deck should be adequately protected from being struck by other objects;
• all internal doors within a hyperbaric system should be aligned properly.