Improvement of chain saw and changes of symptoms in the operators.

The average maximum acceleration levels of chain saws by the one-third octave band analyzer decreased considerably from 5.1 G (range: 2.5 to 8.0 G) during 1965-1975 to 1.7 G (range: 1.0 to 2.5 G) during 1976-1988. The effects of this reduced vibration level on the prevalence of vibration syndrome were studied by comparing two groups of male chain-saw workers: 285 who started to use chain saws before 1976 and were examined in 1975-1976; and 230 who started chain-saw work after 1976 and were examined during 1985 to 1988. As compared with the pre-1976 group, the prevalence of white fingers among the post-1976 group was one-seventh in chain-saw use of less than 5 years, about one-eighth in that from 5-9 years, and less than one-tenth in that of 10 or more years. Complaints of numbness or coldness in fingers or hands, and pain in hands or arms also decreased considerably from about one-fourth to less than one-tenth. This considerable reduction in the prevalence of vibration syndrome is attributable, above all, to a marked reduction in the acceleration levels of chain saws since about 1976, and secondarily to decreased total hours-per-year of vibration exposure due to improvements in general working conditions.