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Keeping guard of machine safety

Keeping guard of machine safety Machine guards are often treated rather casually and continue to be the cause of many severe injuries that could have been prevented had the appropriate guards been used, says Paul Laidler of TUV SUD Product Service.

The Health & Safety Executive Register of Convictions shows that 62 per cent of breaches under the Provision and Use of Work Equipment Regulations (PUWER) have been committed under Regulation 11 - Dangerous Parts of Machinery. So what are the Machinery Safety Directive (2006/42/EC) requirements and how should guard safety be tackled in the workplace?

For those who are tasked with managing workplace safety, the changes that are likely to be of particular interest are those that concern machines' essential health and safety requirements (EHSRs). These cover aspects such as guarding that manufacturers must build into their machine before it can carry the CE marking. Section 1.4.2.1 of the EHSRs requires that all fixed guards must be removable only with the aid of tools and the fixing systems must remain attached to the guards or to the machinery when the guards are removed. While a similar requirement was contained in the previous Machinery Directive, the fixing systems must now remain attached to the guards when the guards are removed. This means that ordinary machine screws and bolts can no longer be used as a means of attaching guards unless provision is made for the screws or bolts to be held captive when the guard is removed.

Section 1.4.1 now also requires that guards must protect against the ejection of falling materials and objects. For example, if a grinding wheel explodes, can the guarding contain that explosion? One of the other requirements of Section 1.4.2.1 states that guards should be incapable of remaining in position when their fixings have been removed. This means that some careful thinking will be required to ensure, for example, that guards on the top of machines are not retained in position by gravity when their fixings have been removed.

One of the key statements to take into account when assessing machinery is in Section 5.7 of the BS EN 1088 standard (Safety of machinery - Interlocking devices associated with guards - Principles for design and selection). This section of the standard states that: "If the specification of the safety interlocking device is such that it is possible to defeat the safety function solely by a reasonably foreseeable action at the interlocking device itself and if the device itself is to be relied upon to prevent defeat, it should provide measures to minimise the possibility of defeat."

Exactly what constitutes 'a reasonably foreseeable action' that could defeat the interlock is explained as an intentional attempt to defeat the interlock either manually or with the aid of some readily available object. In other words, it describes instances when operators are not using machinery correctly or choosing to take short-cuts during production. The standard goes on to explain that the extent to which these measures are applied should be decided on the basis of a risk assessment and it's clear that interlock systems used in the workplace need to be carefully considered and designed.

The standard goes further by stating that "defeat in a reasonably foreseeable manner" includes the removal of actuators and switches with the intention of disabling an interlocking device. However, this begs the question of how is it possible to fix switches and actuators in such a way that they can't be removed with normal tools? Welding or gluing may seem the obvious answer, but

BS EN 1088 does not recommend this. The standard actually suggests alternative measures such as regular checking of the interlock device by some form of safety control system.

However, the approach most strongly supported by BS EN 1088 is for companies to recognise the reasons why operators attempt to defeat interlocks, and to address these in the machine design. For example, can the machine design be modified so that the guard no longer inhibits productivity and the operator will not try to defeat the interlock?

So far, we have looked at new machines, but many of HSE's prosecutions are down to existing machines being used in the workplace and an in-house maintenance team not being fully aware of the requirements and falling foul of the law. For example, a new guard retro-fitted onto an existing machine also requires CE marking as it is considered part of the machine. The additional guard must be put through the entire CE marking process including risk assessment and the compilation of a technical construction file (of which the Directive states what must be included, such as calculations, drawings and test results).

Clearly, achieving full standards compliance for a guard to carry the CE marking is no trivial task. CE marking, along with the design and manufacture of guards, now requires specialist expertise as guards perform an indispensable function to minimise the risk of injury as well as meeting the multitude of regulatory requirements.

Since the changes to the Machinery Directive, a considerable level of expertise is now needed to ensure that guards satisfy all regulatory requirements. The plea of ignorance is not acceptable as failing to comply with the Machinery Directive, whether knowingly or unknowingly, can have serious and far-reaching consequences for machinery designers, the businesses that use them and their operators.
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