As part of its Safety Flashes, IMCA describes a case of a missing Tether Management System (TMS) door found during offshore installation activities.
The incident
The ROV team confirmed that the remaining doors on the TMS were attached. The aluminium TMS door (2m x 1m x 4mm thickness, approximate weight 15kg) is secured to the TMS frame with 2 pins on top of the door and 2 stainless steel latches on the bottom.
In this instance, both the bottom latches failed to allow the door to detach from the TMS frame whilst subsea.
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The water depth at the dive location was approximately 1400 meters. The vessel was located approximately 830m from the nearest subsea asset. The surface current was approximately 1.5–2.0 knots. The door was not found.
Analysis of the DROPS cone determined it was very unlikely that the TMS door would have struck or damaged any of the subsea assets.
Probable causes
IMCA investigation noted that there had been no check to confirm secondary retention was in place on the TMS doors as described in the company ROV Operations Checklists. The securing pins at the top of the door did not contribute to the incident.
Actions and recommendations
- Check and ensure that all fixings are in good working order and that where required, secondary retention is used;
- Review pre-dive/post-dive checklists and add any additional items as required based on the existing condition of the TMS. Purely as an example, for this specific TMS, our member added “confirm that tie wraps are in place”;
- Consider the potential environmental, safety, schedule, and legislative impacts from items dropped/lost at sea.
