ISO/TR 14121-2 for machinery risk assessments - a review

When ISO 14121-1:2007, Safety of machinery - Risk assessment - Part 1: Principles, was published in September 2007 it was generally well received. However, in contrast to the standard it replaced, namely ISO 14121:1999 and its European equivalent EN 1050, it lacked the Methods for analysing hazards and estimating risk contained in Annex B of the old standard. The reason for this is that the new standard has a second part ISO/TR 14121-2:2007, Practical guidance and examples of methods, which contains considerably more information and is far more helpful than the old Annex B.

Note that ISO/TR 14121-2 is a Technical Report rather than a conventional standard document. The reasons behind this are explained in a Criticism of the ISO Technical Report ISO/TR 14121-2, which should be read in conjunction with this present review.

ISO/TR 14121-2 in detail

ISO/TR 14121-2 complements ISO 14121 (which is identical to EN ISO 14121-1, BS EN ISO 14121-1 and other national standards). It therefore contains numerous cross-references to Part 1; for example, readers are referred to Part 1 for all terms and definitions bar one.

Clauses 1, 2 and 3 of ISO/TR 14121-2 cover, respectively, the Scope, Normative references, and Terms and definitions. The bulk of the document is taken up with Clause 4, Preparation for risk assessment, Clause 5, Risk assessment process, and Clause 6, Risk reduction. Clause 7 covers Risk assessment iteration and Clause 8 covers documentation. Readers will also appreciate the two very useful Annexes: Annex A gives examples of methods for several steps of the risk assessment process; and Annex B contains an example application of the process of risk assessment and reduction.

Given the title of this Technical Report, readers may be pleasantly surprised to learn that it includes risk reduction as well as risk assessment. However, given the iterative nature of the risk assessment process, a failure to include risk reduction might have been viewed as an omission.

Clause 4 - Preparation for risk assessment

This clause states that the objective, scope and deadlines for the risk assessment should be defined at the outset. It also notes the benefits of using a team for the risk assessment, and discusses the composition of the team and the role of the team members.

While Clause 5 provides information on the criteria for selecting appropriate methods and tools for each step of the risk assessment process, Clause 4 highlights that consideration should be given to the machinery, the likely nature of the hazards, the purpose of the risk assessment, and the skills, experience and preferences of the team undertaking the assessment.

Clause 5 - Risk assessment process

This Clause is effectively a detailed explanation of the risk assessment process shown in Figure 1 of ISO 14121-1, except for a few steps - such as determination of the limits of the machinery, and hazard identification - where readers are referred back to ISO 14121-1.

Other useful information in Clause 5 includes a discussion of the merits and limitations of top-down and bottom-up approaches to hazard identification, and the appropriateness or not of creative thinking during different stages in the risk assessment process.

Sub-clause 5.4.4 lists the four main risk estimation tools as:

• Risk matrix
• Risk graph
• Numerical scroring
• Quantified risk estimation

In addition, hybrid tools can make use of a combination of the above methods. Detailed discussions of each tool are provided.

Clause 6 - Risk reduction

As well as referencing ISO 14121-1, this Clause also points readers towards ISO 12100-2, Safety of machinery - Basic concepts, general principles for design - Part 2: Technical principles. While this latter standard contains more detail, Clause 6 of ISO/TR 14121-2 nevertheless contains approximately four pages of useful guidance on topics ranging from 'Elimination of hazards by design', 'Risk reduction by design' and 'Safeguarding' through to 'Training', 'Personal protective equipment' and 'Standard operating procedures'.

Clause 7 - Risk assessment iteration

This clause highlights the need to repeat all stages of the risk assessment after the protective measures have been incorporated.

Annex A - Examples of methods for several steps of the risk assessment process

Six examples are provided as follows:

• Hazard identification by application of forms
• Risk matrices
• Risk graphs
• Numerical scoring
• Quantified risk estimation
• Hybrids

This last example is a hybrid method of numerical scoring and a risk matrix. In all six examples, considerable detail is provided, including graphs and tables where appropriate. Most of the examples conclude with a discussion of the method and its suitability for different types of machinery. For a reader who is trying to decide which risk assessment method to use, a good starting point might be to read all the discussion sub-clauses before studying the detail of the examples.

Annex B - Example application of the process of risk assessment and reduction

This Annex considers the risk assessment and risk reduction process for a single-spindle vertical moulding machine. Although it is described as 'non-exhaustive' it nevertheless contains considerable detail. Running to around 21 pages, the example includes diagrams, tables and circuit diagrams.

Conclusion

While ISO/TR 14121-2 contains plenty of information that will be useful to many people, the document is not without its critics. You can read what Peter Still, a member of one of the BSI committees that dealt with the preparation of the current editions of ISO 14121-1 and ISO/TR 14121-2, has to say at www.machinebuilding.net/n/n1057.htm.

Copies of ISO/TR 14121-2 are available in PDF or paper format, in English or French, from ISO at www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=42712, but it is recommended that Peter Still's comments be read first.