Skip to content

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.

Showing a TMS door in place
Showing a TMS door missing
A bottom securing latch
A failed latch

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:

Safety Event

Published: 16 June 2021
Download: IMCA SF 17/21

Relevant life-saving rules:
IMCA Safety Flashes
Submit a Report

IMCA Safety Flashes summarise key safety matters and incidents, allowing lessons to be more easily learnt for the benefit of all. The effectiveness of the IMCA Safety Flash system depends on Members sharing information and so avoiding repeat incidents. Please consider adding [email protected] to your internal distribution list for safety alerts or manually submitting information on incidents you consider may be relevant. All information is anonymised or sanitised, as appropriate.

IMCA’s store terms and conditions ( apply to all downloads from IMCA’s website, including this document.

IMCA makes every effort to ensure the accuracy and reliability of the data contained in the documents it publishes, but IMCA shall not be liable for any guidance and/or recommendation and/or statement herein contained. The information contained in this document does not fulfil or replace any individual’s or Member's legal, regulatory or other duties or obligations in respect of their operations. Individuals and Members remain solely responsible for the safe, lawful and proper conduct of their operations.