SIM 02/2011/04
Construction Division Staff, Quarries Inspectors, Mines Inspectors, Agriculture Inspectors, Construction Inspectors
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 of the requirements of the Provision and Use of Work Equipment Regulations (as amended) 1998, the Supply of Machinery (Safety) Regulations 2008 (and earlier enactments of this legislation).
This SIM does NOT cover issues surrounding rig stability. Guidance on this can be found from Federation of Piling Specialists, CIRIA & HSE guidance on temporary works.
The purpose of this SIM is to explain the most common drilling and piling rig uses and describe the steps owners, employers and operators need to take to prevent people becoming entangled in the rotating parts. It address the key issues that inspectors may wish to consider and provides initial enforcement expectations.
Examples of commonly seen machines.
A drilling rig is a machine which 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 also used to drill holes for blasting as well as to install sub-surface fabrications, such as piles, underground utilities, instrumentation, tunnels or wells. The links at the end of this SIM provide information specific to the different uses of rigs.
Typically, in all 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 casing or a continual flight auger (CFA).
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 the 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 is considered to be a dangerous part of machinery.
Access to the rotating part must be prevented so far as is practicable in line with the hierarchy set out in PUWER Reg 11(1) and associated ACoP.
For new rigs the Supply of Machinery (Safety) Regulations 2008 (SMSR) apply.
are practicable for machines or applications where sections do not need to be routinely added or removed or the process is completely automated and enclosed. Fixed guards need to be secured so that a tool is needed to remove them, eg bolted to the mast or frame. Full-size CFA piling rigs fall into this category and there is separate HSE/FPS guidance freely available on-line and at Appendix A.
are practicable to prevent access to the rotating part where access to the drill string is routinely needed during the work process. Opening the guard should activate the interlock so that rotation stops. Where some rotation is needed to make or break threaded connections, the rotational speed should be limited on re-start with the guard open to a speed as low as practicable and no more than 15rpm. Inching controls giving ¼ rotation per control operation should be considered.
Full rotational speed should only be available with the guard shut and all controls should be “hold to run”.
Interlocked guards are practicable for vertical, horizontal and inclined drilling operations.
Guards must not be removed to enable working close to structures; rather the borehole/pile location redesigned or the guard should be redesigned.
(See Appendix A and Appendix B for more specific mini-piling guidance).
Trip wires do not prevent access to the rotating part but may mitigate injury. An example where the use of trip-wires instead of guards has been successfully justified has not been found. Separate guidance can be found at Appendix A.
are still in the developmental stage. Protective devices are defined in the “new” Machinery Directive (2006/42/EC) in that they must stop moving parts of machine before a person can touch them and moving parts cannot start up while they are within the operator's reach. Protective devices are still a developing technology with radar, light, infrared, ultrasonic, proximity/RIFD being investigated. HSE Construction Sector would like to be informed of any such devices found in the field.
Whilst the inspection of drilling/piling rigs is not a programme priority, if an unguarded rig is seen during an inspection it should be treated as a matter of evident concern given the level of risk.
Inspectors should do the following:
Where the rig is unguarded but trip-wires are in place, strongly challenge this choice of injury mitigation. See the IEE and specific trip wire guidance in Appendix A
If the rotating parts of a drilling rig are adequately guarded the EMM Benchmark gives a nil/negligible risk of serious personal injury whereas operating an unguarded rig, even with trip wires, gives an Actual Risk of possible risk of serious personal injury resulting in a Risk Gap of Extreme. The legal standards are defined and set out in PUWER Regs 10 & 11 and the associated ACoP.
The IEE is therefore a Prohibition Notice. This will be the case for unguarded rigs, poorly guarded rigs, those with defective or defeated interlocks and those relying on trip wires.
Activity prohibited: Use of the rig (specify make, model, serial number or other unique ID) with the drill-string or drill-head rotating.
Matters giving rise to the risk: persons are liable to come into contact with the dangerous rotating parts and suffer a serious personal injury.
Contraventions: HSWA 2(1) & 3(1), PUWER 1998 Reg 11(1)
Because: You have not prevented access to the rotating parts of machinery through the provision of an interlocked/fixed* guard when it is practicable to do so.
(* delete as appropriate.)
The existing CEN for Drilling rigs EN 791 is currently in the final stages of revision and is being combined with EN 996 (Piling rigs) with a much clearer requirement for guarding in line with the current Machinery Directive (2006/42/EC). The new standard will be pr EN 16228.
The 2006 Machinery Directive states “The moving parts of machinery must be designed and constructed in such a way as to prevent risks of contact which could lead to accidents or must, where risks persist, be fitted with guards or protective devices.”
If a rig is found that was manufactured/supplied since the Supply of Machinery (Safety) Regulations 2008 came into force with no guard; enforcement including prosecution under SM(S)R should be considered.
If an Inspector is considering taking enforcement action under the Supply of Machinery (Safety) Regulations 2008 they are advised to contact HSE Construction Sector to discuss.
HSE does not dictate what materials are used to construct the guards or what the actual design should look like but there are some key points that need to be addressed.
The materials selected should be robust enough to withstand expected site conditions; tubular/box steel frames with mesh infill are most common but polycarbonate and conveyor belt rubber have also been used effectively.
The purpose of the guard is to prevent access so the guard must extend far enough around the drill string to achieve this.
The BDA guidance advises that in vertical, or near vertical, operations the guard should extend from 500mm from the ground at its base to 2000mm above ground level, or the operators position if elevated, as a minimum. In piling operations the 500mm can be problematic due to spoil and up to 750mm is acceptable. Prevention of access can also be achieved through reach distances by using an off-set guard rather than purely relying on height.
(NB BDA’s “Guidance Notes For The Protection of Persons From Rotating Parts and Ejected or Falling Material Involved in the Drilling Process” is a priced publication available from the British Drilling Association ( www.britishdrillingassociation.co.uk); limited copies are owned by HSE for reference.)
In inclined or horizontal drilling applications the entire drill string may be within reach and the entire length need to have access prevented.
Interlocks need to be sufficiently robust to withstand site conditions, the vibration that comes with drilling operations and not easily defeated. Simple roller switches are unlikely to withstand vibration which can exacerbate through the structure of the guard and are easily defeated, as are some plunger style devices. Coded magnets are more difficult to subvert.
Where possible the interlock should be such that if it is not connected or operational rotational power is not available.
In terms of motivation, 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 go to great efforts to overcome the safeguards. Whilst there is no evidence of a well designed guard slowing operations the perceptions may remain, this, plus peripatetic working, demands that the safeguards be robust, maintained and the workers monitored at the work-site.
Some companies have managed to monitor their crews remotely in that any disconnection of the interlock is logged within the system electronically and the data downloaded at the depot with re-education or disciplinary action taken accordingly.
Trip wires do not prevent access to the rotating parts of machinery but may mitigate injury when entanglement occurs if they are properly sited, designed, maintained and operational.
The use of trip wires instead of interlocked guards is lower in the hierarchy and must be robustly justified in a written risk assessment with evidence of why guards are not practicable. To date HSE have not come across a situation where if the job had been properly planned and the guard adequately designed an interlocked guard could not be used.
If a dutyholder produces robust evidence that guards are not practicable, and having consulted with SG who agree, there potentially may be a need for them to rely on trip wires. Then the following points must be addressed:
Where the drill string can rotate in either direction there should be at least one trip wire on each side. The wires should not be more than 150mm from the outside rotating edge.
The switch should trip when the wire is pulled no more than 200mm in any direction.
The trip wires must have a spring mounting at one end and the switch should act in either direction NOT a rigid mount at the end remote from the switch.
Rotation should stop if the wire breaks or a component in the system fails.
Meeting all these requirements is extremely challenging and unlikely to be achievable on drilling rigs with large heads, sliding heads and/or capable of drilling differing diameter holes.
Drilling rigs are used in many industries for a variety of purposes, the main ones are listed below with photographs and specific guidance:
This covers a multitude of activities including taking samples or cores up to great depths for the purposes of determining such things as foundation design, looking for water sources and mineral resources, developing geothermal energy systems and designing routes for tunnels. Other purposes include grouting and soil anchoring in unstable areas, rock-bolting, de-watering. They can work by impact, rotation or sonic wave application – usually a combination of two of the three.
Geotechnical rigs can be used to work in the vertical and horizontal planes or inclined between the two; guarding is practicable in all orientations. In inclined or horizontal applications the entire length of drill-string that is within reach will need to be guarded.
Drill mast attachments can be fixed to excavators for geotechnical work; these will also need to be guarded.
Vertical & inclined drilling rigs, both guarded.
Unguarded & guarded drill mast attachments on excavators
Are used usually in restricted access or low headroom areas such as existing buildings to produce cast in-situ piles. Operators will frequently work without guards to enable them to work closer to existing walls or other obstructions. This increases the risk of them being crushed against the structure if they become entangled.
The designer, structural engineer and client should be challenged under CDM duties to remove risks at the design stage and to re-visit the design accordingly. Can pile locations be moved – this may involve deeper piles, cantilevers or a marginal loss of space in the finished structure.
Also, if trying to work around obstructions could an intelligent guard design be accommodated? Concertina doors, side opening gates, cylindrical rotating gate designs can facilitate guard use in restricted spaces.
Sliding and side opening guard designs.
Rock-bolting rigs are rare in the UK but PUWER Reg 11 applies. Seek SG advice.
Are used mainly in quarries and mines to drill holes for explosives to be inserted. This is usually a one-person operation in an excluded area with extra sections added automatically.
Guarded surface production rig
Are a form of trenchless technology gaining in popularity due to the ability to insert utilities pipes without the need to excavate along the route.
Whilst it is practicable to guard the areas of drill string accessible down to, and including, the “rocking” clamps, the area of drill string protruding beyond this must be managed by the contractor.
HDD rig with clamps and lower end of drill string shown to be guarded.
On models such as these the drill string is more exposed and must be guarded.
On very large HDD rigs the rocking clamps will also need guarding and if there is a walkway along the drill string access to the rotating part needs to be prevented – a fixed barrier may suffice.
Have an articulated arm that can swivel through 180 degrees to insert bolts in submerged tunnel sections or create holes for explosives in blasting to create tunnels.
Guarding Jumbo’s has been problematic and SG advice should be sought.
Are geotechnical rigs but on a floating barge that is manoeuvred into position when the legs are extended to the river or sea bed below and the rig works to take samples from the same. Guarding standards are the same as those expected on land but other issues may include them relying on rope-ladders for access rather than man-riders or other means and poor emergency arrangements.
Once the barge is jacked clear of the water it is HSE jurisdiction and a construction site; CDM etc will apply as long as it is within GB’s borders.
Jack-up rigs in the Thames
Are towed trailers used to drill large diameter holes usually in concrete either for large building alterations (riser installation) or installing airport runway lighting or similar.
Guarded & unguarded trailer rigs.
