Exposure to whole-body vibration (WBV) may cause health problems, e.g. lumbago. The risk will depend on intensity and duration. Exposure to WBV in vehicles varies due to several factors as the vehicle type, the terrain condition, the driver, the speed etc. To estimate the health risk, the measurement strategy has to consider this variation. Furthermore, to understand the importance of different preventive strategies, the cause of the variation has to be known. The objective of this study was to describe variation in exposure to seated WBV during occupational operation of forwarder vehicles and to investigate sources for variation. WBV was measured in 10 various terrain types for seven forwarders operated by 11 drivers. For each driver there were between four and 35 measurements. The measurement periods varied between 0.2 and 34 min. The vibration total value (a_v) and total vibration dose value (VDV_t) were determined. Results showed that WBV exposure varied considerably and that this variation could result in different conclusions regarding health risk assessments. The highest magnitudes were achieved during travelling activities. During travelling empty, variations in a_v were significantly dependent upon forwarder model and terrain type. No significant predictor for variation in VDV_t was however found for travelling empty. During travelling loaded the forwarder model and operator were the most important predictors for variation in a_v. Variation in VDV_t was also dependent on the forwarder model during travelling loaded.

Relevance to industry:​ To estimate the health risk from exposure to WBV in forwarders, the results suggests that exposure assessment strategies should include several measurements on the same forwarder and driver during various operational conditions. The results also indicate that both r.m.s.-magnitude and VDV shall be used for risk assessment, since they are influenced by various factors. Selecting another forwarder model can reduce the magnitude of WBV during travelling, suggesting opportunity for technical improvements. During travelling empty, WBV magnitude can be reduced by changing terrain type. During travelling loaded, the magnitude can be reduced by adjust the way the vehicle is driven.