Vibration exposure and vibration-induced white finger due to chain saw operation

A longitudinal study was undertaken to evaluate changes in the prevalence of vibration-induced white finger (VWF) during the period 1956 to 1980 among a population of Japanese state forestry workers. The vibration levels in the measurements occasionally exceeded the 30-minute line proposed by the Draft International Standard ISO/DIS 5349 in one-third octave bands mainly centered on 160 Hz, with 500 Hz in vertical, 400 Hz in sideways, and 250 Hz in back-and-forth sawing operations. The peak prevalence rate was 62.6%, found in the cohort beginning in 1958-1959. Beginning with the 1968-1969 cohort, the prevalence decreased significantly. During the study period, prevalence rates were approximately 10%, 15%, 20%, 25%, 30%, 35%, and 40% after 2, 3, 4, 5, 7, 9, and 12 years of exposure, respectively. The incidence rate increased gradually after 1960 and the peak value was reached in 1966. The peak value of the incidence rate by duration of exposure was about the same (8% to 10%) in the 1958, 1962, and 1966 cohorts; however, in later groups, the incidence rate decreased in the earlier stages of the exposure periods. The latent interval for the development of VWF was 6.4 +/- 3.7 years (6,000 to 7,000 hours) on average, with a 90% range of one to 14 years (700 to 16,000 hours). Of 452 study subjects with VWF (prevalence rate, 33.5%), 13.5% recovered within the exposure periods, 12.2% recovered within one year after the cessation of exposure, and 74.3% still had VWF more than two years after exposure had ended.(ABSTRACT TRUNCATED AT 250 WORDS)