Unplanned rotation of drilling machinery

What happened

A large diameter subsea drill had completed drilling operations and was returned to the vessel’s deck for planned maintenance. Part of the maintenance programme required the drill support system to be energized. As the system was energized, the drill bit unexpectedly started rotating for around 40 seconds. The retention fastenings, used to secure the drill during maintenance, parted, tangling in the rotating drill-bit. Nobody was in the vicinity at the time and there were no injuries.

What went wrong – lessons learned

• Operating procedures were not fully followed by the drilling team, which led to the operating console drill-bit rotation switch being left in the ‘on’ position;
• The was no warning that the system was “live” and that the bit would turn;
• There was no engineering barrier, such as an automatic interlock system which would have prevented inadvertent operation;
• Shift handover was not adequate and did not ensure all safety practices were followed;
• The control measures identified during the task risk assessment and subsequently included in the operating procedure, placed too great a reliance on individuals being aware of the situation (e.g. being aware of the position of control switches etc.) and also a reliance on following administrative controls / check sheets.

Actions taken

• Following an equipment design review, an isolation interlock was integrated into this equipment;
• Additional procedural steps requiring operator intervention (switching off) were now included in improved operating procedures;
• Improved monitoring of compliance and communication within work teams;
• The importance of engineering controls over and above administrative controls has been reiterated.

Members may wish to refer to:

• Hand injury when caught in machinery [an unrecognised situation caused a stopped and un-isolated machine to restart suddenly]
• Agitator started moving during mud tank cleaning – leading to injury [procedures concerning isolation of moving or rotating equipment were not followed]
• UK HSE: Poor control of work – worker suffered serious injuries [a worker was distracted while arranging isolation, and the isolation was not completed]
• Near-miss (HIPO): Engine started and running whilst crew member working on shaft generator [an unplanned change which was not properly managed]