Suspected vibration magnitude on the body of chain saw users among National Forest workers in Kyusyu, from 1956 to 1984.

Chain saws were first used in Kyusyu in 1956 for cutting down trees and sawing timber in the national forests. In 1961, some workers complained of symptoms due to the vibrations, but countermeasures were not taken until later. The working system and payment system in those times were different from the systems, today. The magnitudes of the chain saw vibrations were very large and the chain saws were operated for many hours, each day. Workers with VWF (vibration induced white finger) had to continue to operate the chain saws without restriction. Vibration disease is related primarily to the vibration of the tools, but also to the transmission of the vibration to the workers. From the official data on chain saws used in national forests, vibration transmission to the body was determined for workers from 1956 to 1984 by comparing the vibration magnitude on the body during work with modern chain saws and during vibration loading tests with an electrodynamic shaker in the laboratory. The vibrations transmitted to the body in some rule in the observation. If the working posture of chain saw operator was the same as today, the vibration transmission was determined from the tool vibration, tool weight, joint fixation and orientation of the hands and the hands and the arms to the handle (joint elasticity). Older chain saws had 20 to 30 times larger vibration magnitudes than modern chain saws, and were also 2 to 3 times heavier. The vibrations transmitted to the foreheads of earlier workers were approximately the same magnitude as the vibrations at the back of the hands of present workers. Also the daily and annual hours of chain saw use were very long, and there were not sufficient measures to protect from the cold. The vibration in the former days led to more symptoms and lesions than in present times.