Failure of underwater pan and tilt rotator unit

A member has reported an incident in which there was a small explosion and fire on a remotely operated vehicle (ROV). Personnel had reported having experienced minor issues with the upper pan and tilt unit fitted on the ROV camera whilst it was subsea. Once the unit was recovered, they intended to connect it to a computer and run the on-deck camera analyser software.

An explosion blew the single axis driver assembly (SADA) with the camera unit attached (approximately 5kg weight) away from the main rotator unit. The explosion resulted in the SADA with camera becoming separated (the 6 x 5mm grommet screws connecting the SADA to the camera pan and tilt main housing were sheared) and propelled at a high speed away from the pan and tilt main housing. Flames were noticed coming out of pan and tilt rotator unit and extinguished.

There were no injuries.

Our member noted that the origin of the over-pressure that led to the explosion is still unknown and under investigation with the unit manufacturer.

The lessons were as follows:

• Never be in the line of fire;
• Maintenance/repair work on the pan and tilt units should be reduced to ALARP – as low as reasonably practical;
• Ensure there is a robust management of change process – ensure that there is proper risk assessment when the situation has changed, as in this case.

Members may wish to refer to the following similar incident (key word: overpressure)

• Fatality: Pressure build-up leading to sudden release of mechanical plug