09 June 2008
Michael Ellis

There has been a dramatic reduction in the past 30 years, since the advent of the Health and Safety at Work Act, in the worst accidents linked to contact with moving machine parts. Fewer than 10 of the average of 45 people killed each year in manufacturing in the past 10 years died because of contact with moving machinery, compared with 68 deaths in 1973 alone.

But the fact remains that working around machinery with exposed moving parts, whether it's in a machine workshop, a school kitchen or even a sports field (see Greenkeeper's severed fingers land council in court) carries the potential for accidents, and ones with a high severity. Limbs that come into contact with or are drawn into moving machinery often end up crushed or severed. There were 3269 over-three-day injuries caused by moving machine parts in 2006-07.

Out of the box

Though the Health and Safety at Work Act and the Provision and Use of Work Equipment Regulations 1998 (PUWER) broadened the responsibilities of those responsible for machine safety to take in safe working methods as well as the machines themselves (see box on page 40), later legislation was designed to ease these duties by making machinery more intrinsically safe.

The EC Machinery Directive, translated into UK law in the Supply of Machinery (Safety) Regulations, emphasised risk avoidance at the drawing-board stage and promoted safety by design. 

But research suggests that the conformity assessments required to verify machine safety at the manufacturing stage have failed to fully achieve their purpose. A study by Aston and Loughborough universities found that 12 years after the legislation came into force, ignorance of its requirements and supporting standards means unsafe machinery is still being sold and used.

A cynical view is that less scrupulous manufacturers address the superficial issues, issuing safety documentation and putting the CE mark on their goods, without getting to the root of the problem. The recently published third amendment to the Machinery Directive (amending Directive 95/16/EC) should help drive greater consistency; the HSE is likely to amend the Machinery Supply Regulations later this year.

Ignorance, apathy and inconsistent enforcement all contribute to the problem. For example, the authorities spend more time going after purchasers of machinery than suppliers, who may be responsible for the root causes of safety problems. In 2006-07, the HSE prosecuted 100 companies for PUWER offences and none for breaching the Supply of Machinery (Safety) Regulations. The executive issued a total of 1851 enforcement notices citing PUWER but only 17 referring to the Supply Regulations.

Machine purchasers are often left with new and old machines of the same type with differing compliance levels. Families of the same machine may be fitted with totally different levels of safeguards. All of which means that you can't just rely on the fact that there are regulations to say machines should be supplied with appropriate guards; you need to check for yourself.

Think ahead

Whatever the reason you want to ensure a machine is adequately guarded, the way to make sure is by a thorough risk assessment. The European standard BS EN ISO 14121-1:2007 Safety of Machinery: Risk Assessment Principles (available here at £118) provides a sound assessment methodology.

The assessment should cover the hazards that come with the machine's moving parts, which include the crushing, severing, shearing and entanglement mentioned above. You should be considering the probability that any of these (that is, the risk) could happen, despite any installed guards.

As well as normal operation, the assessment should take in risks during cleaning, setting, maintenance and fault diagnosis procedures - in some industries, more accidents happen during maintenance than during normal use. You also need to try and think beyond the hardware to include allowance for human behaviour and build in some anticipation of human error or possible misuse.

All these factors are better considered in front of the machine itself rather than behind a desk and with maximum feedback from the operators; let the people who will use the machine say where they think it might put them at risk, not just through inadequacy of guarding but from an ergonomic point of view as well.

Pattern recognition

There are too many individual guarding devices to stop contact with moving parts of machinery to list here, but they fall broadly into four groups:

• fixed guards, fastened permanently round part of a machine or forming an enclosure for the whole machine
• interlocks, where a moveable guard is connected to the machine's power system and the equipment will not operate until the guard is closed
• automatic guards, in the form of gates or bars that come between the operator and the danger zone while the machine is activated and move out of the way when it is turned off
• trip guards, which use proximity triggers such as photoelectric cells or pressure mats to shut down machines when anyone moves into the danger zone.

These are listed above in the order they fit in the hierarchy of controls (which can be summarised with the mnemonic FIAT). Complete exclusion, where practical, from a machine's danger zone is obviously the safest option and, at the other end, trip guards such as photoelectric barriers, which shut down the machine when the light beams are broken, guarantee the least protection. If the area of spread of the light beams is too limited, people may be able to reach over or round the beams and avoid tripping them.

Mind the gap

What looks like adequate guarding on a machine is often anything but. The most basic fault with closed guards is that the openings for feeding in materials or components are often too large, so operators can access danger zones. A machine tool with a gap large enough to accommodate the operator's hand as well as the component is not properly guarded.

Guard grilles on feed and discharge openings on machines such as mixers and grinders obviously need to be large enough to allow materials through, but if they are too large they will not protect users. The operator of a coffee grinder at a university café was clearing a blockage in the hopper by pushing the beans down. But the grille mesh was wide enough to let her fingers through, where they were chopped by the grinding blades.

The same principle of ensuring devices designed to prevent access actually do so applies, on a larger scale, to perimeter guarding or full enclosure of large machines such as industrial robots.

One fatal accident occurred when the operator entered a perimeter guarded area on an automated drilling machine which was safeguarded with fixed guards and interlocked gates and sliding doors.

Instead of following the entry procedure, which meant immobilising the machine before entry to change drills in the magazine, he walked along the perimeter guard to get through a gap of some 36cm and get close to the machine while it was still turning, where he was trapped and fatally injured. The gap represented a relatively small chink in the armour, but it was enough.

Interlocks should be configured so that they immobilise the machine immediately they are activated. With machines that operate at high speeds there may be a run-down time of several seconds after the power is cut and if the interlock allows operators to lift before the moving part is still they will still be at risk.

Interlocks should also be designed to "fail to safety" so that the machinery cannot be operated if they are broken or tampered with. On many imported machines, interlocks will fail to danger.

Even the best guards available need regular inspection and maintenance. If welds on fixed guards such as bars, grids and grilles break or bolts become loose and fall off, the guard may no longer provide an effective barrier.

Removable fixings should only be removable for authorised personnel, so security bolts which need a special tool to remove them are the most sensible option; guards held in place by spring clips or wing nuts are almost asking to be removed.

---

Making machines safer

The following action points will help reduce the risk of injury from machinery.

• Carry out machine-specific risk assessments.
• Use fixed guarding when practicable.
• Ensure fixed guards adequately enclose danger zones and can only be removed or adjusted using special tools (unless they are "fixed adjustable" guards).
• Check interlocks are positively operated, fail to safety, and conform to
  BS EN 1088.
• Ensure that dangerous parts of machinery can be adequately isolated, accounting for all potential sources of energy (including momentum), before operators can access danger zones.
• Undertake regular guard inspections, based upon levels of risk, including trip devices such as light-sensitive or pressure-sensitive systems.
• Document inspections adequately in a concise comprehensible format.
• Ensure stop, start and setters' controls are clearly and unambiguously marked and adequately shrouded or similarly protected.
• Ensure interlocks and similar guards are only overridden subject to special risk assessments.
• Allow access into danger zones only where absolutely necessary, and under the constraints of Regulation 22 of PUWER; that is, if full isolation is not possible, the use of setters' hold-to-run devices and similar be implemented at the design stage.
• Monitor working procedures to check for changes from safe practice.

---

Starting point

Inadvertant operation of machinery is a common cause of accidents. And it's not always simply a case of operators or others falling against the controls. At an engineering press shop, as a machine cutting finished lengths of steel strip was powering down, a metal bar rolled off the bed of the machine onto a foot pedal, engaging the clutch. There was enough momentum in the flywheel to bring the blade down and injure a worker, even though the machine was turned off.

For smaller, hand-operated machines, guarding the stop and start controls is a way to avoid accidental operation by anyone, or anything. Pedals, treadles and hand-operated controls and control buttons should all be shrouded: placed under protective covers or hoods that allow operators easy access but would deflect anything falling onto them.

On larger machines, controls should not only be shrouded but also located far enough away from the danger point that operators cannot use the controls while they are close to moving parts.

On machines fitted with interlocked guards or photoelectric safety devices, its preferable to specify a two-hand control for starting movement. These controls should be shrouded or placed so they can't be operated accidentally.

It shouldn't be possible to span both controls with one hand only, or to operate the controls with one hand and another part of the body, and the controls should be configured to stop the machine immediately if one of them is released.

Human nature

As long as machines are operated, maintained or repaired by humans, the human factors corner of the safety triangle (on page 38) will be the one that arguably needs the greatest attention, since human behaviour is the least easy to predict of all the factors.

But that is not to say it is unpredictable; when operators bypass safety controls on machines there is usually some form of reasoning behind their actions, however flawed.

One frequent cause is that safe operation of the machine conflicts with other demands on the users. If a guard slows production, operators under pressure to maintain productivity are likely to remove it.

In one case brought by the HSE, the grille preventing operators getting close to the blades in a machine chopping foam rubber blocked routinely with rubber pieces halting production. So the grille had "disappeared" some time in the couple of years before an employee reached up the exist chute into the blades and lost three fingers.

In cases where the guard itself causes occasional blockages, one answer is to enlarge the protective grill to stop it blocking and, if this allows employees to get their arms through, to extend the chute so that the guard is sufficiently far from the hazardous zone that they cannot get limbs in far enough to contact moving parts.

Guards may make operation less ergonomic for some users. An accident occurred on a gravity-fed food slicer (bacon-slicing machine) due to a guard being removed by the operator who was very small and had to take it off to operate the slicer normally. The manager responsible had assumed that because the machine was CE marked and had been approved by the organisation's safety department that it was safe in all circumstances, so had failed to carry out a risk assessment after commissioning.

Even where the guards cause no problem, if they hinder access to a piece of machinery that needs frequent attention, they may be bypassed if they are not robust enough. In foundries where the mixers and grinders which combine materials for making forms or moulds discharge the product through a chute, these chutes commonly block because the mixture begins to set off rapidly and operatives put their hands up the chutes to unblock them. There are cases where employees have crowbarred the bars of a grill apart to get their hands in to remove blockages.

In catering operations, the need for frequent cleaning means guards may be left off. The answer is either to fit interlocked guards or to train staff more thoroughly in why the guards are essential. Training is essential to make people understand why guards are necessary despite any inconvenience they may cause. Few people are completely reckless about their safety. (In one food factory where the operators had cut a hole in the fixed guard to allow access to the moving parts, they had padded the hole's ragged edges to avoid cutting their hands.)

Users may believe that some forms of guarding actually compromise their safety (as on some drilling machines where the guards hinder visibility, forcing them to lean in closer to the danger zone).

It is always worth investigating such claims to see if they are valid and should trigger a change of guard; the rest of the time it's simply a case of more training, explaining the nature of the greater hazard the guard is separating the operator from.

People may be used to long safe use of a certain machine, bypassing any guards, and will judge the risk to themselves based on that experience. They may change their minds if they are shown the bigger picture, and see the total of accidents involving similar machinery across the country.

Ultimately, PUWER is quite clear, as are the supporting standards, in requiring physical enclosure. It is well documented that reliance upon behavioural safety is a flawed concept; most accidents involving machinery normally involve a combination of unsafe hardware, inadequate systems of work and behavioural issues, whether this be human error, disregard or ignorance.

---

What PUWER says about guarding

The main regulation governing machine guards is Regulation 11 of the Provision and use of Work Equipment Regulations 1998 (www.opsi.gov.uk/SI/si1998/19982306.htm), which says the following.

Dangerous parts of machinery
11(1) Every employer shall ensure that measures are taken in accordance with paragraph (2) which are effective -
(a) to prevent access to any dangerous part of machinery or to any rotating stock-bar; or
(b) 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 -
(a) 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
(b) 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
(c) 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, but where or to the extent that it is not, then
(d) the provision of information, instruction, training and supervision.

(3) All guards and protection devices provided under sub-paragraphs (a) or (b) of paragraph (2) shall -
(a) be suitable for the purpose for which they are provided;
(b) be of good construction, sound material and adequate strength;
(c) be maintained in an efficient state, in efficient working order and in good repair;
(d) not give rise to any increased risk to health or safety;
(e) not be easily bypassed or disabled;
(f) be situated at sufficient distance from the danger zone;
(g) not unduly restrict the view of the operating cycle of the machinery, where such a view is necessary;
(h) 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 the work is to be carried out and, if possible, without having to dismantle the guard or protection device.

(4) All protection appliances provided under sub-paragraph (c) of paragraph (2) shall comply with sub-paragraphs (a) to (d) and (g) of paragraph (3).
(5) In this regulation - "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.

---

Good sources of further guidance on machine guarding include the Department for Business, Enterprise and Regulatory Reform, which has information on the Machinery Directive, and the Manufacturing Technologies Association, which has codes covering a wide range of machine tools ranging from basic manually operated equipment to sophisticated CNC machinery centres.

The BSEN Standards and British Standards, for example BS EN 1050 and BSPD 5304 are available here.

Finally the HSE has useful pages on its website, which is available here.

Michael J Ellis is a consultant and visiting lecturer at the Department of Human Sciences, Loughborough University, and a former HSE inspector.

Categories:
Article, Manufacturing / engineering, Work equipment