High potential near miss: Dropped object during piggyback drilling operations
- Safety Flash
- Published on 16 July 2019
- Generated on 18 September 2025
- IMCA SF 17/19
- 2 minute read
During piggyback drilling operations, a driller inadvertently operated the sample winch control lever instead of the power swivel fast rotation control lever as intended.
What happened?
Activating the sample winch caused a tool to rise from its storage position, resulting in it snagging on a safety hoop of the adjacent vertical fixed access ladder.
The tool (weighing 11 kg) separated from the wire and fell approximately 8 m onto the drill floor below. There were no injuries and no equipment was damaged.
What were the causes?
- The operating driller moved the wrong lever unintentionally.
Investigation noted the following:
- The tool (an ‘overshot’) was connected to the sample winch wire via a weak link shear pin designed to separate at 450 kg. The sample winch has a working load limit of 1.2 tonne.
- The experienced driller had not operated this particular type of drill rig control console for several years; however, he had received a short period of familiarisation training during the previous shift under the guidance of the back-deck supervisor.
- The control console ergonomics and inspection and maintenance requirements had not been properly considered:
- the possibility of inadvertent operation of the wrong lever had not been identified when the piggyback drilling equipment was installed some months before the incident
- there is no evidence that this had been taken into account (in 1995) when the piggyback drill was designed.
- the possibility of inadvertent operation of the wrong lever had not been identified when the piggyback drilling equipment was installed some months before the incident
- There had been ineffective checking and assessment of the suitability or fitness for purpose of this equipment.
What lessons were learned?
- Undertake a design review and complete a design risk assessment on all similar drilling rigs:
- to include the operational and human interface with the drill rig and associated equipment
- planned preventative maintenance check sheets should be updated to reflect the findings of this assessment.
- to include the operational and human interface with the drill rig and associated equipment
- Control consoles should be clearly labelled to identify all controls and their function.
- Develop a thorough familiarisation assessment process for the operation of this kind of equipment.
Related Safety Flashes
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IMCA SF 12/19
28 May 2019
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IMCA SF 03/02
1 April 2002
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