VIBRATION EXPOSURE AND VIBRATION-INDUCED WHITE FINGER DUE TO CHAIN SAW OPERATION

Abstract

A longitudinal study was undertaken to evaluate changes in the prevalence of vibration-induced white finger (VWF) during 1956-1980 among a population of Japanese state forestry workers. The vibration levels in the measurements occasionally exceeded the 30 min line proposed by the Draft International Standard ISO/DIS 5349 in 1/3 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 .apprx. 10, 15, 20, 25, 30, 35 and 40% after 2, 3, 4, 5, 7, 9 and 12 yr 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 (8-10%) in the 1958, 1962 and 1966 cohorts; 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 yr (6000-7000 h) on average, with a 90% range of 1-14 yr (700-16,000 h). Of 452 study subjects with VWF (prevalence rate, 33.5%), 13.5% recovered within the exposure periods, 12.2% recovered within 1 yr after the cessation of exposure and 74.3% still had VWF > 2 yr after exposure had ended. Of 224 subjects (16.6%) with VWF in 1980, 93% had VWF 5 yr after exposure had ended, and 29% were still affected 10 yr afterward. The dose-effect relationship between the development of VWF and exposure components of vibration was estimated.