Welcome to the machine01 March 2008

Studying the latest version of the Machinery Directive in its draft form, it is apparent that, contrary to the common charge of Euro gobbledegook, here is a sound, best practice design guide for machinery designers, builders, operators and maintainers, written in plain and useful English.

Despite the off-putting 191 pages of ?Implementing the new Machinery Directive 2006/42/EC in the UK - A Consultation Document', what you will find is a lot of useful stuff. That's particularly the case in Annex 1, entitled ?Essential health and safety requirements relating to the design and construction of machinery', and just 30 pages long, originally published in the official journal of the European Union on June 9 2006.

Sense and safety
Much of it is common sense. Requirements range from what should be the blindingly obvious - para 4.1.2.3, 'Machinery, lifting accessories and their components must be capable of withstanding the stresses to which they are subjected' - to sensible advice, not always currently followed, such as that in para 1.2.1, 'The machinery must not start unexpectedly'.

That particular item is followed by a number of other requirements, which are well worth designers reading and inwardly digesting, but which in older designs of machinery are totally ignored. 'Guards must be fixed by systems that can be opened or removed only with tools,' declares para 1.4.2.1. There are many dangerous machines in use across the world that have no guards at all and, whereas their operators are usually sensible, there is always the risk of the unexpected hazard, such as a slip or somebody with a heavy load barging into a machine operator concentrating on managing his or her machine.

Most of the requirements are easy to fulfil, but that's not always the case. Consider item 1.5.3, 'Where machinery is powered by sources of energy other than electricity, it must be so designed, constructed and equipped as to avoid all potential risks associated with such sources of energy'. Avoiding all potential risks is a tall order. Similarly, in para 1.5.10, the directive states: 'Undesirable radiation emissions from the machinery must be eliminated or reduced to levels that do not have adverse effects on persons'. Even the smallest amount of radiation has some adverse effect, even when it's less than the amount emanating from the natural environment.

Real world protection
Seriously though, some regulations will require changes to current design and working practices. For example, in para 1.6.3, the directive warns, 'After the energy is cut off, it must be possible to dissipate normally any energy remaining or stored in the circuits without risk to persons'.

At the present time, capacitors in motor drives - especially the very large ones, for example, in inverters on wind turbines - can retain lethal amounts of electrical charge when the turbines are stopped for inspection and maintenance. Maintenance engineers usually use insulated wire with a resistor to discharge these capacitors, often in a highly unsafe manner, but it is only very recently that commercial products for the job have become available.

Some of the new directive's requirements are clearly written in the light of specific accidents, the thought of which makes the reader wince. An example comes from para 3.5.1: 'The battery housing must be designed and constructed in such a way as to prevent the electrolyte being ejected on to the operator in the event of a rollover or tipover'.

And para 1.5.14: 'Machinery must be designed, constructed or fitted with a means for preventing a person from being enclosed within it, or if that is impossible, with a means of summoning help'.

Despite the desirability of the requirements of the directive, BERR (the Department for Business, Enterprise and Regulatory Reform - formerly the DTI) notes that the provisions of the directive do not become applicable until December 29 2009. Its solution is the statementthat: 'From the practical and technical point of view, manufacturers are encouraged to review their products without delay, and adapt them as necessary to take account of the new directive. While machinery placed on the market before 29 December 2009 must continue to comply with Directive 98/37/EC, it can be assumed that a product that complies with the essential requirements of the new Machinery Directive continues to comply with the current directive.'

For a free download of the full Machinery Directive document in its current consultation version go to: www.berr.gov.uk/consultations/page41465.html.

CE Marking alone is no guarantee
Best practice in terms of plant installation, commissioning and maintenance remain key, if equipment and machinery safety features are not to be compromised. As Peter Millington, health and safety consultant and trainer with SETA (the Southampton Engineering Training Association), says, having a CE mark on a machine does not mean in and of itself that it is safe. 'It is still down to the users to install and maintain the machine in a competent manner,' he warns.

As an example of how not to do things, he cites Totton-based Change of Style, which installed a robotic granite kitchen worktop-cutting machine in 2000, but disabled the light curtain and hinged guards. This eventually led to the death of 22 year-old employee David Bail, who suffered massive head injuries when he was caught in the machine and crushed on May 23 2003.

Managing director Michael Shaw received a two year suspended prison sentence for a manslaughter conviction, plus a £70,000 fine for himself and his company. His son and fellow director Gavin Shaw was fined £1,500 for one breach of health and safety legislation. He was cleared of a charge of manslaughter on the direction of the judge, due to lack of evidence.

Technology advances improve safety
Recent developments demonstrate the power of new technologies to reduce risks associated with all sorts of plant and machinery - and to improve users' safety compliance.

Sensor manufacturer Sick UK, for example, has developed a particularly easy to install infrared light curtain safety camera that fits into a corner made from aluminium profile. Its V300 works with reflective strips fixed to the two opposite sides and covers a maximum area of 1m by 1m. When the operator presses the teach button, it automatically finds the strip, while for larger openings, or machines that require guarding on two adjacent sides, a pair of units can be synchronised to offer greater flexibility than is normally possible with optical light curtains. The reflector strip forms a background target and the system has a detection capability equivalent to a 20mm resolution light curtain. The device can cope with a certain about of dirt build up and damage or gaps in the reflective strip, although it probably needs to be cleaned after a year. The system conforms to the requirements of SIL 2, Category 3 (EN 954) or Performance Level d (BS EN 13849). The company is currently working on another version for SIL 1 Performance Level c applications.

Also suitable for guarding two adjacent machine access or cell enclosure guards are twin headed switches now available from Euchner. These are double-headed versions of the company's STP and SGP safety switches, suitable for applications involving locking forces up to 2,500N. Types available are SGP Twin - supplied without guard locking, but which can be padlocked to ensure that the switch actuators cannot be removed - and STP Twin, with a shot bolt that can be key operated or automatically released when a monitored machine has stopped or is otherwise safe. The mechanical key release feature can be used as a lockout for the guard locking function to prevent unintentional locking - ensuring that personnel cannot be trapped within a machining or production cell if a safety door is closed accidentally.

Finally, for safely discharging capacitors, look at Seaward Electronic's SD300. The device can be attached to capacitor banks of up to 1,200 microFarad at voltages up to 1kV, allowing them to discharge safely, and indicating completion on analogue meters on each phase, as well as LEDs.

Two-hand push button operation, to initiate and maintain energy discharge, ensures that the operator cannot come into contact with the live circuit. Other safety features include an automatic pre-use self test, providing protection against prolonged connection to live operating circuits, as well as monitoring of critical component temperatures, with automatic cut off. Once activated, stored energy is discharged within 30 seconds.

Points
- CE marks on a machine are no guarantee of safety good installation and maintenance remain key
- Machine guards must be fixed by systems that can opened or removed only with tools
- On electrically-operated machinery, it must be possible to dissipate any energy remaining without risk to individuals
- Machinery must be designed, constructed or fitted with a means for preventing persons from being trapped inside
- Machinery and plant must not be able to start unexpectedly

SOE

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