Abstract
Prevalence rates of vibration syndrome in two groups of forestry workers who were employed in private enterprises in Fukushima Prefecture and were operating chain saws not less than 25 days a year were evaluated in relation to the vibration acceleration levels of chain saws and the total working hours per year with the tools. The lst group consisted of 261 workers (mean age and SD: 46.2±11.0 yr) who had begun to operate the tools between 1965 and 1976 and were examined at least once in 1976 or 1977 and the 2nd group of 225 workers (46.1±11.0 yr) who were at work between 1976 and 1987 and examined at least once during 1983 to 1988. The following results were obtained:
1. It was estimated that the maximum acceleration levels of the chain saws used between 1965 and 1975, and between 1976 and 1988 ranged approximately from 2.5 G to 8 G (mean: 5.1 G) and from 1 G to 2.5 G (mean: 1.7 G) by the one-third octave band filters, respectively. The average intensity of vibration was thus reduced by 89% after 1976.
2. The number of working days per year and hours per day with the tools were 157±70 d (mean±SD) and 3.7±1.3 h (mean±SD) in the first group and 120±55d and 3.0±1.3 h in the second group, respectively. Therefore, the average total hours per year decreased by 38% after 1976.
3. Prevalence rates of typical symptoms due to vibration syndrome such as Raynaud's phenomenon, coldness of hands, numbness or paresthesia of hands, and pain in hands or arms decreased remarkably among workers of the second group in comparison with those of the first group (p<0.001, respectively). Regarding to Raynaud's phenomenon, prevalence rates according to years of work with the tools in the first group and second groups were 0% and 2.8% within 4 years, 11.1% and 5.0% from 4 to 6 years, 30.2% and 0% from 6 to 8 years and 32.3% and 3.7% from 8 to 12 years, respectively.
4. It is concluded that the remarkable reduction in the prevalence rates of vibration syndrome during the course of some 10 years from 1976 to 1988 was attributable, first of all, to the marked reduction of acceleration levels of chain saws after 1976 and secondarily to the decreased total hours per year during which the tools were used.
