Foundations of hand-transmitted vibration standards.

Standards for hand-transmitted vibration predict dependent variables (e.g. finger blanching) from measurements of a few independent variables (e.g. vibration magnitude, vibration frequency, exposure duration). This paper illustrates the assumptions in the current International Standard guidelines for the evaluation of hand-transmitted vibration and compares research methods which may provide information to improve the guidance. Subjective assessments of vibration discomfort have influenced the frequency weighting used in current standards, but the data have been modified greatly for this purpose. Subjective and biodynamic data suggest that the severity of vibration may not be similar for vibration occurring in different axes. Physiological and pathological studies seek to uncover the mechanisms involved in the temporary and permanent changes caused by vibration, but they have yet to contribute to the guidance in standards. Future experimental studies in humans are unlikely to be sufficient to determine how injury depends on the characteristics of vibration exposures at work. Epidemiological studies are required to uncover the effects of occupational exposures, but the complexity of occupational exposures will prevent the formulation of standards based solely on the results of epidemiological studies. Standards for hand-transmitted vibration include unproven assumptions but, for those assessing the severity of occupational exposures, they offer the most reasonable method for predicting the likely effects of vibration. A combination of subjective, biodynamic, physiological, pathological and epidemiological studies is required to improve current guidance.