Habitually exposing the hands to vibrations may lead to recurring episodes of finger blanching and numbness, with reduction in manual dexterity, tactile sensitivity, and damage to soft tissue occurring in severe cases. By systematically analysing retrospective studies of workers occupationally exposed to vibration, it can be shown that the duration of employment (and hence exposure) determines, on the average, both the appearance of the initial vascular symptoms, and the transition from reversible to irreversible disorders in groups using similar tools. A power law relating vibration amplitude and duration of exposure can then be deduced for occupations involving near-daily exposure, provided an equinoxious contour is selected to frequency-weight vibration spectra. In this way both the appearance and progression of subjectivity reported symptoms can be related to the vibration experienced by the hands. If it is then assumed that an individual's susceptibility remains unchanged during the course of the disorders, tolerable vibration exposures for the whole population can be predicted. The vibration limits so derived compare favorably with those proposed for day-long exposure by the ISO.