High potential near miss – unsecured sheave

What happened?

A hydraulic control lever on a console was inadvertently activated, resulting in the unplanned movement of part of the equipment on a drilling derrick on a vessel.  A power swivel crept upwards making contact with a tagline connected to a sheave assembly, leading to a situation where equipment weighing 40kg was left suspended over crew.

What went wrong?

Investigation identified that the tagline’s change in orientation caused the upper sheave to invert, resulting in the sheave’s hinged gate to open.  With the sheave gate open, an assembly with a combined mass of 40kg was left hanging on its winch wire above the manned working platform. 

What were the causes

  • It was concluded that the potential for unintended activation of the control lever(s) had not been adequately considered during the console’s design;
  • Once in service, lessons learned from similar incidents had not been consistently applied to all similar consoles;
  • Poor situational awareness: crew failed to notice the uncontrolled rise of the power swivel – they were alerted by a member of crew positioned on the bridge who observed the power swivel making contact with the sheave assembly;
  • Safe systems of work across departments with overlapping responsibilities for the inspection, supply, installation and use of the sheave assembly, had failed to identify the sheave’s lack of a secondary restraint and subsequent DROPS risk.

What actions were taken?  What lessons were learned?

  • Review similar control panels and consoles to mitigate or remove risks arising from inadvertent activation of controls;
  • Review and develop a common company standard for winch sheaves and their installation in the context of company operations;
  • Improve visibility for workers involved in control locations for this kind of operation – e.g. through better use CCTV systems to better aid operator visibility;
  • Review all operations where there is shared or overlapping business or project responsibility to ensure that task risk assessments and associated methodologies clearly define roles and responsibilities.