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Machine Safety Components
News Release from: Procter Machine Guarding | Subject: Machinery guarding
Edited by the Engineeringtalk Editorial
Team on 06 July 2004
Understanding BS EN953:1998
Jeremy Procter looks at the standard governing general requirements for the design and construction of fixed and movable machine guards.
Any machine placed on the market within the EU must be CE marked in accordance with the Machinery Directive - and this includes machinery that is built in-house for use in-house One of the most critical aspects of compliance with the Machinery Directive is guarding, for which several standards are applicable, the most important being BS EN953:1998, "Safety of machinery - Guards - General requirements for the design and construction of fixed and movable guards"
This article was originally published on Engineeringtalk on 16 Apr 2004 at 8.00am (UK)
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This guide seeks to direct the reader towards the main machinery guarding standards, as well as providing some advice on how the standards can be applied.
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Although there are no statistics, it is doubtful that every machine builder has a copy of it - or is even aware of its existence - judging by some of the machinery that appears in factories today.
Furthermore, as with any standard, it has to be applied correctly in order to achieve the aim of reducing risks to an acceptable level.
For example, moving guards, whether manually operated or powered, must not present a hazard in themselves, perhaps as a result of crushing, pinching or cutting (if a sharp edge is not protected).
Another example is that sheet-metal guards can sometimes be the cause of drumming noises if they are positioned close to machinery that vibrates.
In this respect it should be noted that although BS EN953 is principally concerned with the protection of persons from mechanical hazards, it does also refer specifically to nonmechanical hazards such as noise, fumes, radiation (typically from lasers or welding processes) or explosion.
Further reading
Free software assesses machinery risks
Procter Machinery Guarding is giving away a free Risk Assessment Calculator based on the requirements of BS EN1050, the standard for machinery risk assessments.
Free guide to machinery guarding standards
Procter Machinery Guarding is giving away a free guide to machinery guarding standards.
Low cost for modular perimeter guarding system
Having signed an exclusive distribution agreement, Procter Machinery Guarding is now able to supply the Satech low-cost modular perimeter guarding system to customers in the UK and Ireland.
Some engineers, especially if designing machinery for use in-house, are tempted to carry out a risk assessment assuming that the intended (experienced, conscientious) machine operator will always be the one using it.
However, BS EN953 makes it clear that guarding design requires the "proper consideration of foreseeable aspects of the machine and operation throughout the foreseeable life of the machine".
This implies that the guards must be designed for use by less experienced, less conscientious operators - perhaps even at another company, as it is possible that the machinery may be sold.
The machine designer must also consider all aspects of the machinery's use beyond loading and unloading, including maintenance and unplanned events such as tool or workpiece breakages.
As far as practical, the guards (and machinery) should be designed so that maintenance can be carried out without having to remove the guards and expose the maintenance technician to hazardous parts.
As for the containment of projectile parts in the event of a tool or workpiece breakage, this is why PMMA (often called Perspex) is not usually acceptable for clear guards; PMMA can shatter, whereas the more expensive polycarbonate alternative does not.
Nonetheless, guards should still provide an adequate view of the process, and they should not be "overengineered" to such an extent that ergonomic aspects suffer.
For instance, doors should not be made so heavy or awkward to use that there is a temptation to bypass them.
If weight becomes an issue, consideration should be given to power-operating the guard, though the standard does give maximum values for force and kinetic energy, relating both to guards equipped with a "safe edge" that retracts the guard if it is obstructed, and to those that have no "safe edge".
Many machine designers today are using light curtains or similar electrosensitive protective devices for parts of machinery where frequent access is required.
Although such devices are not discussed in BS EN953, they should be borne in mind, especially if a designer is getting bogged down trying to design a large, moving guard that meets the force and kinetic energy requirements mentioned above.
Annexes A and B of BS EN953 provide useful flow diagrams to assist designers with selecting the right type of guard from fixed guards, distance guards, enclosing guards, movable guards with or without interlocking, self-closing guards and adjustable guards.
Again, designers should remember that electr-sensitive protective devices can be a highly effective option, especially when used in conjunction with suitable fixed, distance and/or enclosing guards.
Other useful sections in BS EN953 refer to hygiene and cleaning requirements for machinery used in the food/beverage industry, anti-climb measures, the benefits of retained fasteners for fixed guards, and the need to verify the guard design through examination, inspection, testing or calculation.
Lastly, designers must be aware that BS EN953 is not the only standard relating to guards.
A list of others is included within the body of BS EN953, and although some relate to specific applications (such as EN1127, "Explosive atmospheres", or EN1672-2, "Food processing machinery"), others are applicable generally (for example EN294, "Safety of machinery - Safety distances to prevent danger zones being reached by the upper limbs").
Machinery guarding can make the difference between life and death, so designers must face up to their responsibilities and work to meet the requirements of all relevant standards.
For more in-depth advice about BS EN953, other guarding standards or, indeed, to discuss specific machinery guarding projects, please contact Procter Machinery Guarding.
Information about machinery guarding in general can be found on the Procter Machinery Guarding website, or the Angel Machine Guarding website (www.angelmachineguards.com) has details of the modular machine guarding system from Procter Brothers. Request a free brochure from Procter Machine Guarding ...
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