The prevention of entanglement in the rotary parts of drilling and piling rigs


This guidance summarises how inspectors should approach applying and enforcing legal requirements relating to the use of rotary drilling and piling rigs. It explains the most common rig uses, and describes the steps inspectors should expect owners, employers and operators to take to prevent people becoming entangled in the rotating parts. The guidance is not applicable to rigs where the drill string or pile does not rotate but is driven by impact, percussive, ultrasonic or hydraulic force.


Entanglement in the rotating parts of drilling and piling rigs has caused fatalities and serious injuries including amputations. Historically rotating parts on many of these machines have not been guarded despite requirements in the Provision and Use of Work Equipment Regulations (PUWER) 1998 and the Supply of Machinery (Safety) Regulations (SMSR) 2008.

The purpose of this guidance is to address the key issues that inspectors should consider during inspection and provides initial enforcement expectations.


If an unguarded rig is seen during an inspection inspectors should treat it as a matter of evident concern given the level of risk. (Note exemptions in Appendices 3 and 7).

Inspectors should:

  • Pay close attention to any drilling or mini-piling operations seen during routine inspections.
  • Ensure guards prevent access to the dangerous rotating parts, including to the side and rear of the drill string around the mast.
  • Check the operation of the interlock to ensure that the rotational power stops on activation, that full speed is not possible with the gate open and that slow rotation is only on hold-to-run control or inching.

Where the rig is unguarded but trip-wires are in place, inspectors should strongly challenge this choice of injury mitigation. See the initial enforcement expectation (IEE) in Appendix 1 and guidance specifically on trip wires in Appendix 6.


A drilling rig is a machine that creates holes (usually called boreholes) and/or shafts in the ground. They can sample sub-surface deposits, test rock, soil and groundwater physical properties, and are used to drill holes for blasting as well as to install sub-surface fabrications, such as piles, underground utilities, instrumentation or wells. See Appendix 3 for images and information specific to the different uses of drilling and piling rigs.

Typically, in all rotary rigs, a 'drill-head' supplies rotational power to the 'drill-string' rotating it into, and out of, the ground. The drill-string can be a smooth shaft driving a drill / cutter / short auger or a continuous flight auger (CFA).

The issues

Drilling and mini-piling rig operators and others in the area may be at risk of serious injury or death through becoming entangled in the rotating drill-string and crushed against the supporting mast or neighbouring structures. The risk is far higher when operators need to work close to, or approach, the machine such as when adding and removing sections of drill-string by hand, taking samples, removing spoil or simply walking close by on uneven or slippery ground.

The rotating drill-string and drill head is a dangerous part of machinery and access to it must be prevented so far as practicable in line with the hierarchy set out in PUWER Reg 11(1) and associated ACOP (see Further References). Appendix 4 sets out the hierarchy that should be applied in selecting safeguarding measures for drilling and piling rigs. Where guarding is appropriate and achievable, guard design and construction should be such that it is suitable to withstand site conditions and cannot be easily defeated. Appendix 5 provides key points to be addressed.

Many drilling crews are paid bonuses for extra holes/piles or exceeding targets in terms of depths achieved in a given time. If they perceive the guard is slowing them down, they may be tempted to defeat the safeguards. Whilst there is no evidence of a well designed guard slowing operations the perceptions may remain. The safeguards must be robust, maintained and the workers monitored at the work-site. One example of rig operation that sets out to defeat the safety systems without dismantling interlocks is the use of bent wire or similar to lock hold-to-run devices in place. This may be spotted out of use but hooked onto the rig near the control position.


No special visits or organisational requirements are involved.

Further references


Construction Sector Safety Unit, Specialist Group (SG) (Mechanical)


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Updated 2020-12-15