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Safe maintenance and the influence of machine guard design

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Jeremy Procter, a Member of BSI's MCE/3 committee (Safeguarding of Machinery), former Convenor of the European Standards Committee responsible for Machine Guards (CEN TC114 WG11), and Managing Director of Procter Machine Guarding, explains the role that machine guarding plays in improving safety during maintenance operations.

Safe maintenance and the influence of machine guard designWhen you look at the statistics, it is easy to see why the European Agency for Safety and Health at Work (EU-OSHA) is co-ordinating the European Healthy Workplaces Campaign on Safe Maintenance 2010-2011, the UK part of which was launched in June 2010 by the HSE (Health and Safety Executive) in conjunction with organisations representing employers, workers and other interested bodies - including the Trades Union Congress (TUC) and EEF, The Manufacturers' Organisation. The HSE's analysis of data from recent years indicates that 25-30 per cent of manufacturing industry fatalities in Great Britain were related to maintenance activities.

In this context, maintenance activities include inspection, testing, measurement, replacement, adjustment, repair, upkeep, fault detection (troubleshooting), servicing, lubrication and cleaning. It should also be borne in mind that maintenance activities fall within two categories: proactive (preventative) and reactive (corrective). Most accidents occur during corrective maintenance, and note that the need for corrective maintenance can be due to a lack of preventative maintenance. In some cases inadequate preventative maintenance can contribute towards catastrophic failures, injuries and even fatalities. Leaving aside these extreme situations, the unexpected nature of reactive maintenance tends to result in these activities being less well planned, and they might also involve work that was not foreseen by the original machine manufacturer, hence the machine maintenance manual lacks specific instructions.

Risk assessment

It might be assumed that guards always need to be removed for maintenance, so their design has little bearing on the safety of maintenance operations. However, this assumption is incorrect and the design of the guarding can make a significant difference. Machine designers should therefore give due consideration to the outcome of the initial risk assessment (which needs to cover maintenance as well as normal operation) and, ideally, they should discuss maintenance operations with personnel from all shifts, as it is not unknown for maintenance operations to be undertaken differently during night shifts or weekends than during office hours due to fewer managers being present at these times.

When designing machine guards (and, if necessary, other aspects of the machinery) it is best to provide means by which maintenance operations can be performed without having to open or remove the guards. For example, external grease points can be installed, viewing panels can be incorporated in guards, and facilities for making adjustments can be made accessible from outside the guards. As an aside, remember that the need for maintenance can be reduced by using higher-specification bearings and other components with higher reliability and a longer operating life.

Designers need to be wary of simply designing guards that meet the nominal requirements of the standards. Take, for example, BS EN ISO 13857, Safety of machinery - Safety distances to prevent hazard zones being reached by upper and lower limbs, which assumes that people will not use steps, chairs or other objects in an attempt to reach over guards; in reality, operators might well do so unless the guards are made sufficiently high or a top cover is installed.

Other hazards

In the vast majority of cases machine guards provide protection against moving parts of machinery - and these hazards cease to exist when the machine has stopped for maintenance. However, some machines also have hot surfaces, sharp edges or other hazards that continue to be present even when the moving parts are stationary. Designers should therefore take this into account when performing the risk assessment, designing the guards and providing measures such as warning signs and maintenance instructions. If necessary, additional physical guards can be provided to prevent accidental contact with sharp blades, for example.

BS EN ISO 13857 has already been mentioned, but there are numerous other standards relating to machine guarding (for more information, see On Your Guard - A Designer's Guide to Machinery Guarding Standards, which is available free of charge from Procter Machine Guarding). In addition, specific machine types are covered by C type standards that may contain detailed requirements relating to guarding. Designers therefore need to ensure that they are working to all of the applicable standards.

Clearly a thorough risk assessment and subsequent risk reduction measures by the machine designer can make a significant difference to the safety of maintenance operations, as can carefully prepared maintenance instructions. Nevertheless, maintenance managers still need to ensure that a risk assessment is undertaken before maintenance work is started. This is especially true if the machine has been modified or upgraded since the original instructions were prepared, or if the machine is getting old (the state of the art may have moved on since the instructions were prepared, so some procedures described in the instructions would no longer be regarded as adequately safe). In addition, fixed guards do not need to be interlocked so, if these need to be removed, lock-off procedures must be followed to ensure that the machine cannot be restarted.

Similarly, when the maintenance has been completed, procedures need to be followed to ensure that the guards have been replaced before the machine is restarted.

Access requirements

So far we have considered hazards relating to moving machinery, hot surfaces and sharp edges, but a considerable number of accidents occurring during machinery maintenance involve falls from height. Machine designers should consider whether suitable access is available for performing maintenance operations, or whether fixed access platforms should be installed. Indeed, end users are likely to find that fixed access platforms are cheaper in the long run than having to erect scaffolding structures each time maintenance is required.

Something else to consider in terms of machine guarding and safer maintenance is how to prevent access to the work area. With guards removed and potentially hazardous parts of machinery exposed, it is important to use signs, barriers or temporary perimeter guarding to prevent unauthorised access. This point is emphasised by the EU-OSHA in its campaign literature.

The idea of improving the safety of maintenance operations is not a new one; in 1985 the HSE published Deadly Maintenance - A Study of Fatal Accidents at Work and a separate report Deadly Maintenance - Plant and Machinery. The situation in the UK and Europe has improved since 1985, but there is still scope for further improvement. The foregoing explains the role that guarding plays in safer maintenance, with implications both for machine designers and those responsible for machinery maintenance.

Anyone interested in using better guard designs to make maintenance safer can follow the link to download a free copy of On Your Guard - A Designer's Guide to Machinery Guarding Standards.

 
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