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Guarding is a legal requirement in the UK; HSE guidance and PUWER 1998 (as amended) assists towards compliance and highlights the requirements to prevent people from entering a 'danger zone'. 'Danger zone' means any zone in or around machinery in which a person is exposed to a risk to health or safety from contact with a dangerous part of machinery or a rotating stock-bar.
Employers must ensure measures are in place to prevent employees from being exposed to dangerous parts of machinery. A 'dangerous part' of machinery is determined by risk assessment; if the hazard could present a reasonably foreseeable risk to a person, the part of the machinery generating that hazard is a 'dangerous part'.
The hazard to be overcome is mechanical contact or being caught by the dangerous moving part. Mechanical contact is divided into the categories including:
Crushing- the body is trapped between two moving parts or one moving part and a fixed object.
Shearing - a part of the body is trapped between two parts of the machine.
Cutting or severing - contact is made with a moving sharp-edged part
Entanglement - loose items such as clothing or hair get caught on a rotating machine and the person is drawn in.
Drawing or trapping - a part of the body is caught between two moving parts and drawn into the machine.
Impact - the body is struck by a powered part of the machine.
Stabbing or puncture - sharp parts of the machine, or parts or material ejected from the machine, penetrate the body.
Friction or abrasion - contact is made with a fast-moving surface which may be smooth.
The main regulation considering this is PUWER 1998 Regulation 11 Dangerous Parts of machinery states:
(1) Every employer shall ensure that measures are taken in accordance with paragraph (2) which are effective-
To prevent access to any dangerous part of machinery or to any rotating stock-bar; or
to stop the movement of any dangerous part of machinery or rotating stock-bar before any part of a person enters a danger zone
(2) The measures required by paragraph (1) shall consist of -
the provision of fixed guards enclosing every dangerous part or rotating stock-bar where and to the extent that it is practicable to do so, but where or to the extent that it is not, then
the provision of other guards or protection devices where and to the extent that it is practicable to do so, but where or to the extent that it is not, then
the provision of jigs, holders, push-sticks or similar protection appliances used in conjunction with the machinery where and to the extent that it is practicable to do so, and the provision of such information, instruction, training and supervision as is necessary.
(3) All guards and protection devices provided under sub-paragraphs (a) or (b) of paragraph (2) shall -
be suitable for the purpose for which they are provided;
be of good construction, sound material and adequate strength;
be maintained in an efficient state, in efficient working order and in good repair;
not give rise to increased risk to health and safety;
not be easily bypassed or disabled;
be situated at sufficient distance from the danger zone;
not unduly restrict the view of the operating cycle of the machinery, where such a view is necessary;
be so constructed or adapted that they allow operations necessary to fit or replace parts and for maintenance work, restricting access so that it is allowed only to the area where work is to be carried out and, if possible, without having to dismantle the guard or protection device.
Looking specifically at rotary drilling rigs we can apply a hierarchy of control measures so that compliance is met.
1 Provide a fixed guard.
A fixed guard is a physical barrier that prevents a person from coming into contact with dangerous moving parts. The guard may be shaped to fit the machine quite closely (enclosing guard), or it may be more like a fence around the machine (perimeter guard). It may have openings in it, but these must be designed in such a way that it is not possible to reach in and contact dangerous parts (distance guard). The basic principles are;
It completely prevents access to dangerous parts.
It is fixed in place.
Fixings require a tool for removal - the guard must not be removable by finger force alone.
2 Moveable Interlocked Guards.
An interlocked guard is designed to be removed or opened as a normal part of routine machine operation. When the guard is removed, a safety interlock system prevents machine operation. The basic principles are;
Power to the machine is disabled and the machine will not operate until the guard is in place.
Either the guard is locked shut until it is safe for the guard to open, or the act of opening the guard stops the dangerous parts and disables power. The closing of the guard must not start the dangerous parts. (Continue to read section on reduced rotation)
3 Pressure Sensitive Equipment
Pressure Sensitive equipment is a range of protective devices that do not put a physical barrier between the operator and the dangerous part of machinery. Instead, some form of sensor is used to detect the presence of the operator and stops the machine. The use of sensitive protective equipment is intended to minimise the severity of an injury and is often used as an additional control measure for example in combination with an interlocked access gate. Examples of sensitive protective equipment:
Pressure mats - mats placed on the ground around the item of machinery that, if stood upon, their weight activates the trip and the dangerous moving part will stop.
Trip bars/wires - wires, wands or rods placed close to dangerous parts which, when touched, will stop the machine movement. This is a complex method and finding the equilibrium between practicability and exposure is very difficult.
Photoelectric devices - devices which shine beams of light to form a curtain, covering the unguarded area, across an access point. If the beams are broken then the machine is stopped.
To explain the relationship between regulation 11 and the hierarchy:
Where access is not required part (2) (a) level 1 Fixed Guard applies.
Where frequent access is required part (2)(b) level 2 Moveable Interlocked Guard applies or
Where access is required part (2) (b) a combination of level 2 Moveable Interlocked Guard and level 3 Sensitive Protective Equipment applies.
In general Part (2) (c) does not apply.
Advanced protective devices -are available but are not in widespread use. They are defined in the Machinery Directive (2006/42/EC) in that they must stop moving parts of machine before a person can touch them and moving parts can only be operated in ROM while they are within the operator's reach. Protective devices are still a developing technology with radar, light, infrared, ultrasonic, proximity/RIFD being investigated. (Note that systems which depend on the person carrying a transponder do not provide collective protection). Current UK research suggests that some proximity devices can be effective at preventing someone reaching into or entering the protected zone, whilst coping with small pieces of spoil and water spray. Inspectors may find drilling rigs fitted with proximity devices undergoing field trials in the UK and Construction Sector Safety Unit would like to receive any observations. Once the technology is proven in practice these systems may move up the hierarchy.
It should be noted the use of Pressure Sensitive Equipment instead of fixed or moveable interlocked guards is the lowest in the hierarchy and must be robustly justified in a written risk assessment with evidence of why guards are not practicable. Machines supplied from 2014 should only be fitted with Sensitive Protection Equipment as a secondary or additional protective device.
The guard must be positioned not more that 500mm above the drilling table or the ground, if it is higher than this the drill string must be guarded, potentially using casing, however the casing itself would need to be guarded should it rotate. Please note casing clamps should be provided in such a condition that prevention of crushing or entrapment (dangerous moving part) is controlled.
It must extend to a minimum of 1600mm above the ground and / or working platform, attention should be paid the Operators standing on working platforms the guard should extent to such a height that the rotating part cannot be touched from the working position.
Application: When the guard is open;
The rotation and feed must stop.
Rotation and feed can be engaged once it has been stopped for maintenance or application of tooling. This is referred to as restricted operating mode (ROM) and must satisfy the following criteria;
It should be at a speed as low as practicable and no more than 30 revolutions per minute (rpm), and
A jog control should give no more than half rotation per control operation, and
Feed speed should be restricted to 15 metres per minute or 10 centimetres per activation, and
An indicator should be automatically activated to warn the operator that the drilling rig is in ROM, and
All controls should be 'hold to run' during ROM and on releasing the rotation control, motion should stop within half of a revolution, and
Full rotational speed should only be available on restart with the guard shut, and
Rotating or moving parts within reach distance should be restricted speed/motion during ROM.
'Hold to run' controls require the operator to hold the control at all times to operate the machine. Releasing the control for whatever reason will stop the machine from operating and within half of a revolution.
To return to full rotation or feed the guard must be closed and a separate positive action from the operator must be carried out.
The guarding should at all times fail to safe. If the guarding is not working correctly the rig must be rendered inoperable with immediate effect.
Daily checks to ensure compliance;
Measure / check the distances to ensure the operator(s) cannot touch any dangerous parts from the operating positions.
Ensure the heights from ground level / work platform to the top and bottom of the guard are correct, suitable and sufficient.
Check any contacts on interlock switches and guard pivot points are free from any detritus.
Activate full rotation and open the guard or trip the protective sensory equipment to ensure the dangerous rotation stops.
An indicator illuminates and / or sounds.
Close the gate, or clear the sensing area, and ensure rotation does not commence without a separate positive action.
If ROM is required ensure it is operated only by hold to run controls and
rotates less than 30RPM and on release of the hold to run stops within half of a revolution, and
feeds at less than 15m per minute and on release of the hold to run stops within 10 cm
NON-COMPLIANCE WITH ANY OF THESE CHECKS THEN DRILLING MUST NOT COMMENCE.
Author: Jon Christie, Chair of Safety Committee, British Drilling Association