In its latest safety flash, IMCA provides lessons learned from an incident where an ROV got trapped inside the platform structure due to strong tidal current.
The incident
As a result the tether was damaged, and the ROV lost power and telemetry. Attempts to free the slightly positive ROV and pull it carefully out of the structure, but these were not successful.
Ultimately, the vessel was needed elsewhere, and the tether was cut and secured to the jacket. Upon returning to the platform the next day, the damaged tether parted during a new rescue attempt.
The ROV drifted away from the platform and after a few hours the signal from the ROV’s beacon was lost. A new vessel was summoned to search for the lost ROV with its WROV, but the ROV was not found. The incident occurred during a routine platform jacket inspection.
Probable cause
- Emergency procedures were not detailed enough to cover the scenario that actually occurred; the workboat was not launched in time to secure the ROV in the short interval it was at surface during rescue attempt from the platform;
- The ROV crew was understaffed: There were two operators, but the complexity of the operation warranted a three person team;
- The ROV transponder interrogation rate was set too high – too frequent – resulting in premature exhaustion of the beacon battery.
- Insufficiently detailed instructions, risk assessment of hazards, and emergency recovery procedures;
- Understaffed team.
Lessons learned
- Procedures revised to include more details; environmental limitations and more details for a recovery scenario;
- Added a current reading on ROV pilot user interface (GUI).
