Correlation between weighted acceleration, vibration dose value and exposure time on whole body vibration comfort levels evaluation

Abstract

Every environment offers stimuli to subjects. Some of these stimuli can be harmful to the human health, like vibration, depending on the intensity and/or exposure duration, among other factors. Even if the vibration is not harmful, it may cause discomfort. The ISO2631-1 (1997) Standard says that two exposures are equivalent when they have the same vibration energy. For that, it uses the exposure duration and the weighted acceleration or Vibration Dose Values (VDV) to calculate the equivalence, being those terms a power of 2 or 4, respectively, in the equivalence formula. Despite that, Annex C of the Standard states that there is no conclusive evidence to support a time dependency of vibration on comfort, reporting that some studies uses the frequency-weighted rms acceleration to calculate the dose of vibration received during an expected daily exposure (called eVDV – for Estimated). It should be expected that the same vibration energy would cause equivalent effect (on health or comfort). In order to verify this hypothesis, two frequency weighted acceleration values, measured according to ISO2631-1 (1997, 2010), were adopted, considering four different exposure durations in a way to reach three pre-established eVDV. The same frequency was considered for all studied situations to easy the comparison. To say that the time, the exposure duration or the VDV by itself are important parameters on the vibration influence can be naive and that was not confirmed in this study. The conclusion is that these variables superimpose themselves mutually, having different influences according to the other parameters involved.