Where safety requirements are set out in product standards in the form of measurable values, methods suitable for their measurement must be adequately defined at the same time. KAN has presented a clear guidance document which is to assist standards committees in formulating measurement provisions in the most succinct and user-friendly way possible, yet at the same time in the necessary detail.
For the purposes of occupational safety and health and product safety, results based upon measurements must be reliable. Unsafe products may for example otherwise be declared good, thereby giving rise to hazards; conversely, the sale and use of safe products could be prohibited, possibly leading to litigation.
KAN study breaks the ground
Measurement tasks which can be performed with standard instruments and from which reproducible results may be expected even without description of a measurement method can generally be classified as trivial. This can be assumed to be the case for example for the measurement of the majority of dimensions and time quantities.
A study presented by KAN (pdf) in 2010 had revealed however that for a not inconsiderable number of non-trivial measurement provisions in machine and PPE standards, either the measurement methods stated are unsuitable, or no measurement methods are stated at all or referred to. Among the variables affected here are those of force, velocity, vibration, load-bearing capacity, wind speed and energy. This deficit appeared to be particularly serious for the measured variables of force and velocity, measurement of which is frequently required, and for that of vibration, since the Machinery Directive requires not only that the emission value of this variable be stated, but also its uncertainty of measurement. A similar situation may exist in other product areas.
KAN therefore subsequently formulated specific comments concerning individual machinery and PPE standards, and presented them to the German mirror committees. In the course of the study and during discussion of individual comments with the standards committees, it became clear that it is not even easy to reach agreement upon which measurements are trivial.
Criteria for measurement provisions
When factors are present which may influence the reliability of the test result, they must be defined clearly. The measurement method concerned together with all relevant influencing factors must then be described with sufficient precision either within the standard itself or by way of a reference. In order to support the standards developers in this task, a KAN working group has drawn up a very clear guidance document containing a two-page checklist:
• Comprehensive arrangements already exist in the basic rules governing standardization work concerning the essential requirements which must be met during the formulation of measurement provisions (Section 6.3.5 of DIN 820-2:2012-12, "Standardization – Part 2: Presentation of documents (corresponds to CEN/CENELEC Internal Regulations Part 3:2011/modified ISO/IEC Directives – Part 2:2011)). The first page of the checklist, containing seven questions, was based upon these arrangements. The questions are intended essentially to assure that the set of standards does not entail duplication of effort, superfluous provisions and unnecessary work for the standards developers.
• Based upon the KAN study, the crucial influencing factors affecting measurement provisions were defined in closer detail: the test object, test arrangement, performance of the test, test person/test subject, and interpretation. It emerged that these influencing factors and their parameters could be classified intelligently. The somewhat vague provisions of the above standardization rules were also supported precisely – for example whether a test method is to be standardized, and if so in what form and at what point. The second page of the checklist was based upon these findings.
KAN proposes that this short checklist be trialled as a supplement to the experience and intuition of the expert members of the product standard committees. Should it prove useful for facilitating the formulation of measurement methods in a succinct and user-friendly manner but at the same with the necessary detail, it could be incorporated into the basic rules of standardization work.