Frequency weightings of hand-transmitted vibration for predicting vibration-induced white finger

Objective – To investigate the performance of four frequency weightings for hand-transmitted vibration to predict the incidence of vibration-induced white finger (VWF). Methods – In a longitudinal study of vibration-exposed forestry and stone workers (n=206), the incidence of VWF was related to measures of vibration exposure expressed in terms of 8-h frequency-weighted energy-equivalent r.m.s. acceleration magnitude (A(8)) and years of follow-up. To calculate A(8), the r.m.s. acceleration magnitudes of vibration were weighted by means of four frequency weightings: (i) Wh (the frequency weighting specified in ISO 5349-1:2001); (ii) Wh-bl (the band-limiting component of Wh); (iii) Whf (a frequency weighting based on finger vibration power absorption); and (iv) WhT (a frequency weighting based on a Japanese study of VWF prevalence). The relations of VWF to alternative measures of vibration exposure were assessed by the generalised estimating equations (GEE) method to account for the within-subject dependency of the observations over time. Results – Data analysis with a GEE logistic model and a measure of statistical fit suggested that A(8) calculated by weighting the tool r.m.s. accelerations with Wh-bl gave better predictions of the cumulative incidence of VWF than the other alternative measures of daily vibration exposure. Values of A(8) derived from the currently recommended ISO frequency weighting Wh produced less good predictions of the incidence of VWF than those obtained with frequency weightings Whf or WhT. Conclusions – This prospective cohort study suggests that measures of daily vibration exposure which give relatively more weight to intermediate and high frequency vibration are more appropriate for assessing the probability of VWF.