| A Designer's Guide to Machinery Guarding Standards |
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There is no hiding from the the fact that guarding is a crucial element of a machine or production line, yet the guarding design is often left until last and not given as much thought as the parts that are seen to relate directly to productivity. Nevertheless, guards usually control the interaction between man and machine, so it should be remembered that their design can be a significant factor in optimising a machine's performance. A perceived difficulty with designing guards is that there are numerous regulations and standards that must be complied with. In fact, as the designer becomes familiar with the 'rules', the 'game' becomes easier. Alternatively, specialists such as Procter Machine Guarding can be employed to undertake the complete design, fabrication and installation. This guide seeks to direct the reader towards the main standards, as well as providing some advice on how the standards can be applied. At the end there is list of sources of additional information.
The Importance of GuardingMost employers today have at least a basic understanding of safety issues and accept that their employees are one of the company's biggest assets. But many still see machine guarding expenditure as a necessary evil rather than a key investment that can really help deliver improved productivity.If guards are well designed they will not interfere with efficient operation; ill-considered guards invariably do. Worse than that, poorly designed guards encourage operators, maintenance staff and management to bypass them, leading to poor production and high risks for all concerned. Machinery Safety RegulationsMachinery safety in the UK is driven by two main sets of regulations: The Supply of Machinery (Safety) Regulations 2008 (which requires all machines sold in the EU to carry a CE mark) and The Provision and Use of Work Equipment Regulations 1998 (PUWER 98). In addition, there are The Health and Safety at Work etc Act 1974 and The Management of Health and Safety at Work Regulations 1999.To comply with the requirements of The Supply of Machinery (Safety) Regulations 2008 ,a machine needs to pass these tests:
Guarding StandardsIn practice, the way suppliers and users of machines can most easily meet their legal obligations is to ensure that their machines, guards and other safety devices are designed to conform with harmonised European standards (Euronorms). These standards have been developed to ensure an equally high standard of machine safety across the EU. The good news for users of machines in the UK is that these standards incorporate most of the principles of BS 5304:1975 and 1988 (the Code of practice for safety of machinery), which served British industry well for a long period and, although no longer current, is now available from BSI as a Published Document, PD 5304:2005.The main machinery safety standards applying to machine guarding is downloadable here. Other type of machinery, from packaging machines to sewing machines, also have their own requirements. A full list of standards harmonised to the Machinery Directive is available on the European Commission's website. Additional information is also available from the HSE's website - from the Topics menu select Equipment at Work; from the Industries menu select Engineering and Manufacturing. Risk Assessment and ReductionToday the accepted approach to the design of any machine guarding system is based on risk assessment. BS EN ISO 12100:2010 (which recently replaced BS EN ISO 14121-1, which itself replaced BS EN 1050) sets out different methods, which must take account of the probability and degree of possible harm relating to any foreseeable injury. More guidance on Risk Assessment can be found the in the HSE's free leaflet Five steps to risk assessment INDG163(rev2), which was revised and simplified in 2006.A free Risk Assessment Calculator is also available from Procter Machinery Guarding. This is based on the requirements of BS EN ISO 14121-1 and is designed to be simple to use, making extensive use of checklists (see 'Useful Resources' below). Once a machine has been assess, if the resultant risk is considered unacceptable, measures must be applied to reduce the risk rating - which often includes guarding. This process is repeated until the measures applied reduce the risk to an acceptable level. Working with the StandardsBS EN 953, which is the main guarding standard, covers all machinery from simple drive couplings to very complex installations involving robots, conveyors and processing machinery. The standard lists those aspects of machinery, people and the design and construction of guards that need to be considered.Machine aspects to be considered are, of course, the functions of the machine and the hazards arising from these. Obvious ones include entanglement or impact from moving parts, and less obvious ones are, for example, the potential for ejection of broken tools, hazardous materials and invisible emissions including noise and radiation. Guards should minimise exposure to these hazards by the selection of appropriate materials, construction methods and correct safety distances - as specified in BS EN ISO 13857:2008. Before Starting the DesignThe successful design of machine guards needs a clear understanding of all the ways in which people interact with machines at all phases of the machine's life including commissioning, production and maintenance. Before designing any guarding, the designer should talk to the operators and maintenance staff that will use the machine; if the machine operates for more than one shift per day, the designer needs to talk to the operators and maintenance staff from all shifts because the working practices may not always be the same.Well-designed guards should permit machines to be loaded, unloaded, cleaned and maintained efficiently without exposing people to hazards (remember that around half of all accidents and 25-30 per cent fatal injuries occur while maintenance is being carried out). Design GuidelinesMachinery guarding can be constructed from a variety of materials and the skill of the designer lies in creating a system that will be fully compliant with the regulations, yet will also be user-friendly, cost-effective and aesthetically pleasing. The main choice of infill materials is between sheet steel, welded wire mesh and clear polycarbonate - though sheet steel guards can also be provided with mesh or polycarbonate windows.On machines where process viewing is necessary, adequate lighting must be provided to ensure compliance with BS EN 1837:1999, Safety of machinery. Integral lighting of machines, and to discourage operatives from attempting to bypass the guarding. If ejected parts are an issue, sheet steel or polycarbonate are typically chosen, while welded wire mesh (weldmesh) is cost-effective for many other applications. In corrosive environments or where frequent washdowns are required, stainless steel is preferred. Noise reduction is increasingly important today, so acoustic foam or other sound-deadening material can be added to sheet metal paneling. Sealing around guards can also help to reduce noise levels, and sealing is highly beneficial if fluids or dust are present. If heavy use or abuse is anticipated, heavy-duty materials should be selected. Designers need to be aware of an important change in BS EN 953:1997+A1:2009 relating to fixings for fixed guards. There is now a requirement that fixings for fixed guards shall remain attached to the guard or the machinery when the guard is removed. While this appears to make the situation clear, in fact designers need to be clear about whether or not a guard (or other component with a secondary safety function) is a 'fixed guard' and whether or not it is foreseeable that the guard will be removed for maintenance, cleaning or other reasons (if not, then there is no need to use retained/captive fasteners). More information about fixings for fixed guards is available in a free White Paper from Procter Machine Guarding, How to specify fixings for machine guards. When designing either fixed or moving guarding, the designer should refer to BS EN ISO 13857:2008, the standard that covers safety distances to prevent hazard zones being reached. A free Safety Distance Calculator is available from Procter Machine Guarding for establishing the required safety distances and heights of machine guards in accordance with BS EN ISO 13857:2008 (see 'Useful Resources' below). |
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