Earth Moving Machine Whole-body Vibration and the Contribution of Sub-1Hz Components to ISO 2631-1 Metrics

Abstract

Occupational exposure to whole-body vibration (WBV) is a hazard linked to several adverse health effects. The most widely reported pathogenic effects of WBV exposure include the occurrence of lower back pain [1][2][3][4] although other reported effects include increased prevalence of herniated discs and neck-shoulder disorders 5) . Vibration can also adversely affect comfort and performance 6) . In order to assist in addressing the risks to health posed by occupational exposure to WBV, the European Physical Agents (Vibration) Directive (PA(V)D) 7) specifies limits on daily occupational WBV exposure. The PA(V)D mandates application of ISO 2631-1 8) as the metrological framework for measurements of daily WBV exposure severity and the application of the appropriate frequency weightings 9) .Within the context of impact on health, the methods prescribed by ISO 2631-1 (1997) stipulate evaluation of WBV within the frequency range 0.5 Hz to 80 Hz.However, the standard also states that when assessing WBV in terms of impact on health "If it has been established that the frequency range below 1 Hz is not relevant nor important, a frequency range from 1 Hz to 80 Hz can be substituted". ISO 2631-1 does not give criteria by which in one can deem WBV components below 1 Hz as 'not relevant nor important'. One interpretation of the statement could be that if there exists negligible vibration energy below 1 Hz, then there is no need to measure vibration using instrumentation capable of measuring such low frequencies as it is 'not important' (although this would mean that the instrumentation would fail to meet requirements specified in ISO 8041 10) ). Another possible interpretation could be that if the vibration is operator-induced then it is 'not relevant' to an assessment of vibration emission, as it is not caused by the machine per se, but by the driver; an example of this could be an individual driving a machine with repeated acceleration and deceleration with a short cycle time. Energy from each braking/acceleration manoeuvre would constitute part of the measured acceleration signal and, if there are a high number of such manoeuvres, these could dominate the