Guarding needs to be well designed if a machine is to operate safely and efficiently. Furthermore, guards should not be expensively over-engineered, nor should they detract from the machine's aesthetics. In all cases, however, they should be designed in accordance with the applicable national and international standards. These ten tips about machine guarding standards will also be useful for production managers, health and safety managers, health and safety representatives and others with an interest in the subject.
1. Compliance is not mandatory
This first point may come as a surprise, but there is no legal requirement (at least in the UK and Europe) to comply with machine guarding standards. However, compliance with the relevant standards, especially those harmonised to the Machinery Directive, is generally the shortest route to demonstrating that the Essential Health and Safety Requirements have been met, so compliance is strongly recommended.
2. PD5304, an informative ex-standard
PD5304:2005: 'Guidance on safe use of machinery', is available from BSI and has the status of a Published Document. Although not a standard, it is essentially the same as BS5304:1988, the old british standard for machinery safety, and contains a wealth of useful guidance and practical examples of guard design. Many of today's machine safety standards incorporate principles contained in PD5304, but lack the illustrative examples found in PD5304.
3. EN953, the main standard
EN953 (and the British Standard equivalent BS EN953:1998): 'Safety of machinery - Guards - General requirements for the design and construction of fixed and movable guards', covers all types of 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. However, using EN953 does not mean that other standards can be ignored; for example, see point 4 below.
4. Protecting upper limbs
EN294 (and the British Standard equivalent BS EN294:1992): 'Safety of machinery - Safety distances to prevent danger zones being reached by the upper limbs', contains tables and data to enable guards to be designed with an acceptable combination of height, horizontal distance from the hazard, and aperture size (for guards with mesh infill, or other openings in guards). Unfortunately the standard is not as user-friendly as might be hoped, and the results can be ambiguous. Procter Machine Guarding has therefore developed a spreadsheet-based safety distance calculator with simple menu selections that simplify the task and avoid ambiguities. The safety distance calculator is available free of charge on request or can be downloaded from the company's website.
5. Protecting lower limbs
EN811 (and the British Standard equivalent BS EN811:1997): 'Safety of machinery - Safety distances to prevent danger zones being reached by the lower limbs', is similar in many respects to EN294 (see point 4 above). However, in reality it is seldom used, as guards usually extend to floor level or to a level below which access by the lower limbs is not possible.
6. An amendment to EN1088
In 2007 an amendment was published for EN 1088 (and the British Standard equivalent BS EN1088:1995): 'Safety of machinery - interlocking devices associated with guards, principles for design and selection'. The aim of the amendment is to promote better safety system design so as to reduce the reliance on the correct functioning of safety interlocking devices. There is also a recommendation to use coded interlocks, rather than simple devices that could be overridden by, for example, a maintenance worker with a 'spare' actuator, or guard designs that shield the interlocks when the guards are opened, thereby preventing a second actuator from being inserted in the interlock.
7. New risk assessment standard
For over a decade machine builders have used EN1050 (and the British Standard equivalent BS EN1050:1997): 'Safety of machinery - Principles for risk assessment', as the starting point for designing machine guards. It is also likely that many are still using this standard, even though it was withdrawn and superseded by EN ISO14121-1 (and BS EN ISO14121-1:2007) in 2007. Although the new standard: 'Safety of machinery - Risk assessment - Principles', is broadly similar to EN1050, it contains some notable differences. Procter Machine Guarding has therefore updated its risk assessment calculator, which is based on an Excel spreadsheet, to take account of the changes. The risk assessment calculator is available free of charge on request or can be downloaded from the company's website.
8. Machine-specific standards
So far we have discussed general machine safety standards, but it should be remembered that there are dozens of standards, known as Type C standards, relating to specific classes of machinery. For example, BS5667-18:1979 is 'Specification for continuous mechanical handling equipment - Safety requirements, conveyors and elevators with chain elements - Examples for guarding of nip points'. Designers should check whether any Type C standards are available for the machine they are designing, as these standards can be extremely useful and avoid the need to work 'from first principles'.
9. Other official guidance
Standards are very helpful when designing machine guarding, but there are also other sources of official guidance. For example, here in the UK the HSE (Health and Safety Executive) has published a document known as HSG43: 'Industrial robot safety', which contains detailed information about how to safeguard robots. Although this publication has not been updated for several years, meaning that some of the standards references are now out of date, it is still widely considered to be 'essential reading' when safeguarding robots.
10. A free guide to machine guarding standards
Points 1-9 above are based on material contained in 'On Your Guard - A designer's guide to machinery guarding standards'. This is recommended reading for anyone involved in specifying or designing machine guards, as well as production managers, health and safety managers, health and safety representatives and others that require an understanding of this important subject. 'On Your Guard' is available free of charge on request from Procter Machine Guarding or can be downloaded from the company's website.