ROV free-fall incident

A member has reported an incident which resulted in a work-class remotely operated vehicle (ROV) free-falling approximately 10 metres into the sea during a recovery operation. No injuries occurred and only minor damage was sustained by the ROV, but the incident could have been severe with possible loss of life or damage to the vessel if the fall had occurred at a different stage of the recovery operation, or in bad weather conditions.

The company’s site investigation revealed that the fall was caused by a lapse in the procedures used to safely recovery ROVs, probably due to complacency because of the stillness of the weather and over-confidence, due to the large number of times that the process had been completed. A contributing factor to the incident may also have been the fail-safe condition of the docking device.

The umbilical snapped at the outlet to the sheave block and is suspected to have failed due to a combined over tension from both the umbilical winch and the initial movement of the A-frame inboard. A block-to-block position with the lifting wire meant that the docking device was pulled by the umbilical to a non fail-safe position and subsequent snapping of the umbilical prevented the docking device from capturing the ROV again in time to prevent its fall.

The following actions were recommended as a result of the company’s investigation:

• further investigations into the design of the docking device to improve its fail-safe features;
• verification of the strength of umbilicals via destruction testing of a cut-back on a yearly basis;
• review of launch and recovery procedures to verify risk assessments;
• improved training of personnel specifically aimed at launch and recovery scenarios;
• review of lifting equipment to instigate visual indicators (colour banding, flags, lights, etc.) to represent the safe working areas and warn of ‘danger zone’ operational envelopes.