Dangers in Uncontrolled Release of the Bridal Gear Under Tension

By
Mfame Team
-
3637

Summary

North Sea Atlantic, which was built in 2014, is a 144 m multipurpose offshore vessel, designed for survey, pipe lay and sub-sea construction projects. North Sea Atlantic sailed from Lerwic, UK on 16 July 2015 to an offshore construction site in BP Foinaven Oilfield, 150 km West of the Shetland Islands. North Sea Atlantic was working on the Riser Preinstallation Project, involving the construction and deployment of 14 dynamic risers. The risers were loaded on the Opening Vertical Lay System (OVLS) table where buoyancy modules, Duraguard® riser protection and other ancillaries were stowed for the project. In buoyancy module installation, a clump weight is used to assist with the lowering of the riser to the seabed for connection to the hold down pile.

The clump weight is connected to the riser upper tether clamps on the OVLS table, and is lowered down on the seabed through the moon pool along with the riser. The tether clamps are then hooked up to the pre-installed driven pile and the clump weight is recovered to deck. The associated rigging arrangement included a two leg bridal gear, connected to the clump weight. The hook-ends were fastened with messenger lines to remotely operate/open the hooks.

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Two leg bridal gear with remotely operated hooks

Each leg of the bridal gear is joined to a shackle which in turn is linked to the OVLS winch wire leading to the forward port side winch.The riser and the clump weight are held in constant tension to control any untoward movement. This arrangement allows the lowering of the clump weight into the moon pool through the OVLS doors without making contact with the riser. A ‘management of change’ carried out prior to the accident had introduced changes in the operational procedure relating to the clump weight deployment.

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Schematic drawing of two leg bridal gear and rigging arrangement

On 22 July 2015, the rigging crew was doing pre-installation work on the 11th riser (W-5P). There was moderate to fresh breeze. The swell was Southwest with an average height of 1.0 m. The work permit issued on 17 July 2015 was re-issued at 1148 and accepted for work carried out between the 1200 and 0000 work shift. Wires under tension were an identified risk, listed in this permit.

The deck foreman conducted a Toolbox talk on:

  • loading and deployment of the clump weight;
  • continuing the building of the riser; and
  • general deck duties and housekeeping.

The Toolbox talk identified risks to riggers and simultaneous operation of winches. The riggers were reminded that anyone can call ‘all stop’ to break the operations in the event of witnessing an unsafe act or condition.

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The lead rigger pulling on the messenger line to release bridal hook

The crew manifest listed eleven riggers from the Philippines and two British deck foremen. The majority of riggers worked on the 1200 to 0000 shift. One of the rigger reported for duty at 1200 in his role as lead rigger. This crew member was an experienced lead rigger, having worked for 12 years on board the Company’s off-shore vessels. He had been assigned for 12 months on board North Sea Atlantic, working on a rotation of 12 weeks on and 6 weeks off.

Cause of the Accident

The immediate cause of the accident was the momentarily snagging of the hook and uncontrolled release of the bridal gear under tension.

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Image showing the snagging of the hook and position of the lead rigger right above the area

Safety Actions Taken

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Hook with damaged extension ‘beak’ after the accident

Following the accident, the Company carried out an internal investigation and took the following safety actions as part of a holistic action plan to avoid similar accidents in the future:

  1. Safety information was issued for fleet wide distribution;
  2. Snag potential assessments carried out in order to establish ‘no go’ snapback zones;
  3. In consultation with the manufacturer, the ROV hook has been modified to remove the extension beak;
  4. Toolbox training was facilitated for all crew members serving on the vessel;
  5. Time out for safety meetings is being held across the fleet to assess equipment, procedures, risk and on board activities;
  6. A training package on Toolbox talk has been developed by the Company and is being implemented across the fleet;
  7. A working group has been established to revise internal procedures and the Company’s risk assessment process;
  8. Procedures were adopted to ensure that feedback on the operations are analysed and lessons learned were captured;
  9. A PUWER assessment was carried out on the winches in order to assess ergonomic design;
  10. An exercise was adopted to raise awareness of fire hazards;
  11. The on board management team has embarked on a ‘Stop the Job’ campaign;
  12. An internal Safety Notice has been drafted and issued to all vessels in the fleet; and
  13. The internal investigation findings were reviewed from a ‘just culture’ perspective so as not to apportion blame.

Recommendations

In view of the safety actions taken by the Company, no recommendations were made.

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Source: Transport Malta

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