## 2 Metrological Study of the Regulatory Framework on the Occupational Exposure to Vibrations  
### European Directive 2006/42/CE on Machinery  
Exposure to vibrations at workplace normally has to do with the use of different equipment and machinery which are the source for such vibrations. However, there are countless different types of tools, vehicles, and machines use in very different sectors, such as agriculture, transport, or manufacturing among others, and each of these devices has different operating conditions.  
European Directive 2006/42/CE [19], for the commercialization and commissioning of machinery, must be considered together with OH&S regulations regarding exposure to vibrations. This directive sets the conditions for which a certain machine can prove to be safe and allows them to be manufactured.  
Consequently, this regulation includes requirements that manufacturers and suppliers must include in their machinery before putting them into market. Among these requirements, some essential health and safety requirements are established by the European Directive, including those related to vibrations when applicable:  
Figure 1: Examples of fields where the best possible measurements are especially relevant.  
* When the machine or workstation includes the installation of seats and it is subject to vibrations, it is required to design the seat so that it helps to reduce the exposure to vibrations for the operator (Section 1.1.8 within the CEN/TR). In general, the machine is required to be designed in such a way that the vibrations are reduced to the lowest possible level (Section 1.5.9 within the CEN/TR). However, apart from this indication, after critically analyzing this European Directive, it can be concluded that a specific reference level is not established. Without any other indication, it is not possible to establish a general acceptable level of vibration. Moreover, no indications are given regarding how to measure it; then, each supplier, manufacturer, or final user may calculate or estimate the level of vibrations in a different manner. As a result, high differences might appear, and the different methodologies will make it impossible to obtain a reliable comparison, even between similar machines.
* Some specific values are given in the case of handheld/hand-guided machinery. Section 2.2.1.1 within the CEN/TR establishes a set of reference values for vibrations (2.5 m/s\({}^{2}\)), which, when exceeded, must be informed in the instructions, together with the uncertainty of the vibration measurement. Nevertheless, no specific information is provided on which procedure must be followed for measuring vibrations or how to estimate the uncertainty of those measurements. The case where harmonized standards are not applied is considered, indicating that, in such circumstances, the vibration must be measured using the most appropriate measurement code.  
Although some indications are given regarding the exposure to vibrations, this directive does not specifically explain the procedures and technical considerations when studying the vibration levels. As the Prevention Services Regulations state [20], risk assessment must employ methods that provide confidence in its outcome. As it is commented, the lack of indications on how to measure or estimate the quality of those measurements and the obstacles for comparing the results for similar machines can lead to non-reliable results or estimated values about the level of vibration.