Skip to content

Unplanned release of stored energy: Worker struck and injured by tensioning tool

What happened?

The International Association of Oil & Gas Producers (IOGP) has published Safety Alert 293 about an incident in which a worker was struck on the head and seriously injured when a tensioning tool came loose and hit him.

A four-yearly task was in progress, to check the tension of bolts on the bearing of a floating storage and offloading (FSO) unit turret. During moving the bolt tensioner, a part (the puller, weighing 13kg) fell between the bearing stud bolts of the inner (static) and outer (rotating) bearing races. Before it could be removed the FSO weathervaned, trapping and compressing the tensioner part between the two rings of bolts. A crew member went to investigate further. As he crouched over the tensioner part, it suddenly came free and struck him in the head causing serious injury. He was promptly medevaced to hospital onshore.

Turret working location
Tensioner part trapped between bearing race stud bolts

What went wrong? What were the causes?

  • The risk of a tensioner part falling and becoming trapped between the stud bolts was not recognised in the job safety analysis (JSA), work procedure or turret vendor documentation;
  • This risk was not recognised by the crew member, who placed himself ‘in the line of fire’;
  • No stop work authority was applied when the task deviated from the expected work process;
  • The design of the turret bearing races and stud bolts location allowed the tensioner part to become trapped and compressed when the FSO weathervaned.

Actions taken

  • Provide additional safeguarding tools and equipment to prevent the tensioner puller from dropping in between the inner and outer stud bolt or even this tool and equipment could help to support the re-tensioner while moving along the race;
  • Investigate a manual handling tool that will reduce the risk of accidentally dropping the tensioner parts;
  • Review the JSA and work procedure to include routine and unexpected risks and provide troubleshooting guidance. Include JSA to consider weather limits for the work and use of a tug on the FSO stern;
  • Reinforce use of stop work authority if work deviates from normal conditions. Investigate if this task should be performed by a specialist contractor rather than the FSO crew;
  • Develop ‘line of fire’ awareness training;
  • Share information with other operating assets with a FPSO and future project FSO, to design out the hazard, e.g. put the two bearing races and rings of bolts at different elevations.

Members may wish to refer to the following incidents relating to the unplanned release of stored energy:

Safety Event

Published: 21 December 2017
Download: IMCA SF 32/17

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.