Jeremy Procter, Convenor of the European Standards Committee responsible for Machine Guards, and Managing Director of Procter Machinery Guarding, discusses parts 1 and 2 of EN ISO 12100, the machinery safety standard.
[Note that EN ISO 12100-1 and EN 12100-2 have both been superseded by EN ISO 12100:2010 - Ed, 31 December 2010]
EN ISO 12100 Safety of machinery - Basic concepts, general principles for design is one of the most important machinery safety standards. It is harmonised to the Machinery Directive, so complying with its requirements (and those of other relevant harmonised standards) will generally be the shortest route to demonstrating that the Essential Health and Safety Requirements of the Directive have been met. EN ISO 12100 consists of two parts; Part 1 deals with Basic terminology, methodology and Part 2 is the Technical principles. Each part states that the other is 'indispensable for the application of this document.'
EN ISO 12100-1:2003 and EN ISO 12100-2:2003 are Type A standards (basic safety standards) and therefore have a dual purpose: they are for use when designing machinery and they are also for use in developing Type B and Type C standards. Note, however, that a Type B standard (eg EN ISO 13849-1, Safety of machinery, Safety-related parts of control systems, Part 1: General principles for design) or a Type C standard (eg BS5667-18:1979 Specification for continuous mechanical handling equipment - Safety requirements, conveyors and elevators with chain elements - Examples for guarding of nip points) takes precedence if it deviates from any provision within EN ISO 12100-2 or any other applicable Type A standard. Both parts of EN ISO 12100 also recommend that the standard be incorporated in training courses and manuals to 'convey basic terminology and general design methods to designers.'
Looking in detail at Part 1, there are three main clauses in addition to the scope and normative references.
Clause 3 of EN ISO 12100-1, extending to around seven pages, is devoted to terms and definitions. This covers everything from 'machinery', 'hazard' and 'risk' to 'adequate risk reduction', 'common cause failures' and 'common mode failures.' Although Clause 3 does not contain a formal definition of a machine's lifecycle, Clause 5.3 explains this in some detail.
Clause 4, 'Hazards to be taken into account when designing machinery,' can be treated as an extensive checklist of hazards, ranging from mechanical, electrical and thermal hazards to hazards generated by noise, vibration and 'neglecting ergonomic principles in machine design.' Nevertheless, the standard acknowledges that there is a more detailed list of hazards and hazardous situations available in ISO 14121 (now EN ISO 14121-1:2007 Safety of machinery. Risk assessment. Principles).
Clause 5, 'Strategy for risk reduction,' contains what might be termed the real 'meat' of the standard. Sub-clause 5.1.3 and the corresponding flowchart (figure 2) lay down the basic steps to be taken:
Subsequent sub-clauses address each of these steps in more detail.
Another fundamental concept that is introduced (in Clause 5.4) is the 3-step approach to eliminating or reducing risk by protective measures. These three steps are:
'Adequate risk reduction' is defined in Clause 3 ('risk reduction at least in accordance with the legal requirements under consideration of the current state of the art') but Clause 5.5, 'Achievement of risk reduction objectives,' gives a practical checklist that users will find more helpful. Beware, however, that there is a reference to the 'lowest practicable' level of risks from hazards, and the standard does not define this term.
On the subject of risk reduction, the recently published ISO/TR 14121-2:2007 Safety of machinery - Risk assessment - Part 2: Practical guidance and examples of methods' is intended to assist designers in complying with EN ISO 12100 by providing additional guidance on the selection of appropriate protective measures for achieving safety.
While the foregoing discusses the body of Part 1 of the standard, there are also some additional information included. Annex A provides a schematic representation of a machine, though this is likely to be of limited use to most readers, and there are 14 pages of a trilingual (English, German and French) index of specific terms and expressions used in the standard, which is unlikely to be of use to most machine designers. The bibliography lists eleven ISO and IEC standards that machine builders may well wish to consult, though the bibliography in Part 2 is far more extensive).
Part 2 of the standard (Technical principles) generally contains practical advice that can be implemented when designing machinery. Clauses 1 and 2 are the scope and normative reference, and Clause 3 ('Terms and definitions') simply refers the reader to Part 1.
Clause 4, 'Inherently safe design measures,' gives examples of geometrical factors that should be considered. This goes into considerable detail, such as (in Sub-clause 4.2.1) 'sheet metal edges shall be deburred, flanged or trimmed.' No less than five pages are devoted to Clause 4.11 and its numerous sub-clauses for 'Applying inherently safe design measures to control systems,' and note that Sub-clause 4.11.7 covers 'Safety functions implemented by programmable electronic control systems' - these control systems are becoming increasingly popular for all but the simplest of machines.
Clause 5, 'Safeguarding and complementary protective measures,' contains plenty of information that will be useful to machine designers on a day-to-day basis. One example of this is Clause 5.2, 'Selection and implementation of guards and protective devices' and the accompanying flowchart, which give guidelines to help designers select the correct type of guard to use: fixed guards; interlocking guards with or without locking; adjustable guards; or other protective devices. However, machine designers should be aware that although Sub-clause 5.2.3 refers to two-hand control devices, these should only be used if a risk assessment shows the residual risk is reduced to an adequate level for persons other than the operator.
Sub-clause 5.2.5, 'Selection and implementation of sensitive protective equipment' (such as light curtains, laser area scanners and pressure sensitive mats), provides useful guidance. Note that the standard refers to 'draft IEC 62046' but in fact the second edition of this Technical Specification has recently been published as IEC/TS 62046 Safety of machinery - Application of protective equipment to detect the presence of persons.
One of the advantages of modern safety-related control systems is that they can assist with reducing cycle times if, for example, sensitive protective equipment is used to initiate the cycle when the operator has cleared the hazardous area. In such situations care must be taken to ensure that safety is maintained at all times, and this is aided by Sub-clause 126.96.36.199, 'Additional requirements for sensitive protective equipment when used for cycle initiation.'
EN 953:1998 Safety of machinery. Guards. General requirements for the design and construction of fixed and movable guards deals specifically with the guarding design, but the subject is also covered to a lesser extent in EN ISO 12100-2 Clause 5.3, 'Requirements for the design of guards and protective devices.' Note that EN ISO 12100 refers to ISO 13852 and ISO 13853 (identical to EN 294 and EN 811), but in April 2008 these standards were withdrawn and replaced by a single standard EN ISO 13857:2008 Safety of machinery. Safety distances to prevent hazard zones being reached by upper and lower limbs.
Where fixed guards are held in place by fasteners, Sub-clause 188.8.131.52 of EN ISO 12100-2 reminds readers that the guards should not remain in place without their fasteners. This poses an interesting problem for designers intending to use guards installed from above, where gravity would be capable of holding the guards in position.
Clause 6, 'Information for use,' outlines what shall be provided. However, the standard also directs readers to IEC 62079 (equivalent to EN 62079) Preparation of instructions. Structuring, content and presentation and the new Machinery Directive 2006/42/EC, which comes into force on 29 December 2009, also provides an extensive list of what a machine's instructions must contain.
Note that Clause 6.4 states that 'Written warnings shall be drawn up in the language(s) of the country in which the machine will be used for the first time and, on request, in the language(s) understood by operators.' With the increased use of Eastern European labour in countries such as the UK, machine designers and specifiers should be aware that there is a real possibility that the operators' language will not be the same as the native language of the country in which the machine will be first used.
The bibliography at the back of EN ISO 12100-2 is far more extensive than that in Part 1. Fifty documents are listed but, as has been shown above, some of these have since been with withdrawn and superseded.
Given how fundamental EN ISO 12100 Parts 1 and 2 are to machinery safety, it would be difficult for any machine builder to justify not having a copy, even though the two parts are not cheap (£150 each) and, as with all standards, they have a finite shelf life. Indeed, the ISO website states that both parts are to be revised, though no timescale is given. In truth, however, it is likely that almost every machine builder that does not currently own a copy will find something of use in both parts.
Procter Machine Guarding has published a PDF document called On Your Guard, A Designer's Guide to Machinery Guarding Standards, which is available from the Free downloads section of the company's website.