Safety Awareness - May 2021


Dropped sensor plate during operations.


What Happened

The client while drilling, a piece of stainless-steel angle iron (730 grams) dropped from the Top Drive onto the rig floor. There was no-one on the rig floor at the time of the incident. It was identified that the plate had come from the compensator system on the Top Drive. The plate triggers a sensor. The dropped object had fallen 6 meters.


Contributing Factors

  • The Top Drive was new and supplied with the sensor plate fitted. (The unit was installed on the rig at the end of 2020.)
  • The plate was secured by 2 x 6mm bolts and locking nuts.
  • Due to the location of the plate and the vibrations it was subjected to, the two securing 6mm bolts had failed. The end of the bolt that was located was broken off.
  • The bolt size was small for the purpose it is intended.
  • The weight of the sensor plate (730 grams)


Corrective Actions

  • New sensor plate fitted (299 grams)
  • 8mm bolts and locking nuts used for installation
  • Secondary retention fitted to plate
  • Other fitted items that came with the new Top Drive were inspected to ensure fit for purpose.


ModuResources wishes to thank our client for sharing this safety awareness alert.