The EU draft "Vibration" Directive (individual directive of Framework Directive 89/391/EEC on the introduction of measures to encourage improvements in the safety and health of workers at work) proposes two different and equally valid procedures for determining the exposure limit value and exposure action value: the equivalent continuous acceleration over an eight-hour period calculated as the highest (r.m.s.) value, or the highest vibration dose value (VDV) in accordance with ISO 2631-1:1997 "Mechanical vibration and shock - Evaluation of human exposure to whole-body vibration". The two methods, however, yield different results for different signal types, depending upon the respective component of vibrations containing occasional shocks. The possibility cannot therefore be excluded of the exposure limit value not being exceeded when the r.m.s. value is determined, but violation of the limit value being ascertained on the basis of measurement of the vibration dose. The evaluated severity of the hazard may therefore vary according to the evaluation procedure selected. This conjecture is to be examined for actual vibration loads on mobile machinery, and the order of magnitude of the differences ascertained.
The energy-equivalent r.m.s. value of the acceleration under consideration (equivalent continuous acceleration over an eight-hour period) and the vibration dose value in accordance with ISO 2631-1:1997 are to be determined for uniform motion and for travel influenced by vibration involving occasional shocks on a number of different types of mobile machines (earthmoving machinery, industrial trucks, etc.) The number of evaluations is to be specified following a survey of the available measured data from previous in-company measurements in consideration of the different results yielded by the two procedures proposed as alternatives. Stringent, typical operating conditions for the machines are to be assessed.
Measurement of the action values and the exposure limit values for equivalent continuous acceleration over an eight-hour period on the one hand and of the vibration dose value on the other also yield different results for vibrations with a minor shock component in accordance with ISO 2631-1:1997, Section 6.3.3. The vibration dose value produces a less favourable result in the majority of cases. The results of the two assessment methods differ, in some cases widely, for vibrations with a shock component. For example, z-axis vibration on the seat of an off-road vehicle resulted in the exposure action value for the vibration dose value being exceeded after only eight minutes of travel, whereas the daily vibration exposure reached only approximately 32% of the corresponding exposure action value. Similar variations arose for a tractor harrowing dirt clods and for certain activities performed with earth movers and wheel loaders. Variations also arose however in the railway sector in cases where tracks and seats were in poor condition. The procedures described as being equivalent according to the EU directive proposal in terms of equivalent continuous acceleration and vibration dose value therefore lead in many cases to different assessment results. The project results will be reflected in the German position on the current draft directive to be published by the German Federal Ministry of Labour and Social Affairs (BMA). They will also be considered during national transposition of the EU directive in a corresponding OH&S regulation.
-cross sectoral-Type of hazard:
Arbeitsbedingte Gesundheitsgefahren, Lärm/VibrationenCatchwords:
Arbeitsumwelt (Belastungen, Gefährdungen, Expositionen, Risiken), Gefährdungsbeurteilung, VibrationDescription, key words:
EU draft "Vibration", exposure limit value, exposure action value, r.m.s.value, equivalent continuous acceleration, vibration dose value, vibration including shocks, differences