Dropped Object – door detached from TMS during dive

What happened

During offshore installation activities a Remotely Operated Vehicle (ROV) and Tether Management System (TMS) recovered to deck was observed to have a TMS door missing.  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 allowing the door to detach from the TMS frame whilst subsea.

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.

What went wrong?

Our members’ 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 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.

Members may wish to refer to:

• Near miss: dropped magnet during dry docking
• Near miss: Potential dropped object due to unsecured door  
• Equipment damage – dropped ROV/tether management system (TMS)