Chain on lifting assembly snagged, allowing heavy tool to fall

A measurement-while-drilling (MWD) tool was being hoisted with an original equipment manufacturer (OEM) lifting assembly up the v-door with a derrick full of pipe.

One worker on the rig floor was standing between the racked pipe to watch the tool and give instructions to the tugger (winch) operator. A second worker was guiding the tool up the stairs.

The 10m-long tool was 8m above the drill floor when it fell, grazing the first worker’s hardhat and the back of his gloved hand, resulting in a hematoma above the right eye and a bruised right hand. The second worker was narrowly missed by the falling tool.

Investigation findings:

• The two workers had independently inspected the tool and lifting assembly before it was picked up. They verified that the retaining pin was in place.
• The retaining chain of the lifting assembly snagged on the racked pipe which allowed for the pin to release from the gate, allowing the tool to fall.
• This weak point of the design was previously identified, and an improved T-locking handle push pin was available but not all field kits had received the upgrade.
• The worker on the floor was positioned to provide both verbal and visual direction to the tugger operator but was standing in the drop zone to achieve that.
• Due to potential damage to the bottom of the tool, and the skate v-door design, the second worker had to guide the MWD tool up the stairs, which was also in the drop zone.

Contributing factors:

• The OEM design was susceptible to this failure.
• The upgrade for the lifting assembly was missed on the load-out.
• Inadequate hazard assessment of the existing, older-style assembly.
• Worker was positioned in the drop zone to give verbal and visual direction to the tugger operator, rather than at the top of the stairs giving only verbal direction.

• Assess and update all lifting assemblies with OEM-approved modification.
• Regularly audit all mechanical lifting equipment.
• Identify line of fire and drop zones when handling tools and modify work practices accordingly.

• How can something like this happen here (e.g. on our site)?
• What safety measures (i.e. procedures, controls/barriers) do we have in place to mitigate the risk?
• How do we know the risk controls/barriers are working?
• What improvements or changes should we make to the procedures, controls/barriers or the way we work?