ちらつき値よりみた騒音に関する研究
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概要
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It has been shown that noise acts as a stressor on the human body. It may consequently be said that noise is one of the factors causing the so-called mental fatigue which proposes serious problems from the standpoint of industrial medicine. The author performed a study on the effects of noise in humans, using as standards of measurement flicker values which have been assumed to reflect fairly accurately the degree of mental fatigue. The experiments were conducted in 14 I. B. M. operators (all females in their twenties). The results obtained are summarized as follows: (1) The workers under investigation were divided into the following four groups according to the volume of work and the kind of job : punchers at peak stage, punchers at non-peak stage, non-punchers at peak stage and non-punchers at non-peak stage. Tests were conducted six times a day for three days in the period from Augsut to September, 1953 (autumn) in these four groups of workers exposed to the noise having a loudness level of 87 phons (mod.) with frequencies ranging from 500 cps to 4500 cps. Tests revealed that the flicker values measured after work showed decreases below the pre-work levels: 14.4 in punchers at peak stage, 12.5 in non-punchers at peak stage, 17.2 in punchers at non-peak stage and 18.7 in non-punchers at non-peak stage. Statistically there were no significant differences between these values with the level of significance of 0.05. Tests conducted in 7 office girls working in a quiet office (the control) four times a day for four days revealed that the flicker value measured after work was below pre-work level by 12.1. There were significant differences between the falls in flicker values of the control group and the I. B. M. groups with the level of significance of 0.05. Fluctuations of the flicker value of I. B. M. groups in one day, which were expressed in identical curves, were large, while those of the control group were small. The flicker value measured after work in those I. B. M. workers who commute by train fell by 15.2 from the pre-work level of 40.7, while the flicker value measured after work of those I.B.M. workers who come to the office on foot fell by 14.4 below the pre-work level of 39.2 There were no significant differences between these values with the level of significance of 0.05. According to Oshima, flicker values, which indicate the levels of excitation of the cerebrum, are generally high in the morning and low in the afternoon; they fall after an individual has been subjected to a strees, and rise after he has taken rest. It is the view of the author, therefore, that the fall in the flicker value of I. B. M. workers has been due not to the differences in the manner of trip to and from the office, the kind of job or the volume of work, but to noise which has acted as a stressor on them. (2) Some of the I. B. M. workers were provided with earplugs (selectone K.) so that they might be insulated from noise, and tests were conducted in a group of workers wearing earplugs and a group wearing no earplugs four times a day for four days in March, 1954 (spring). The flicker value of the group wearing earplugs fell by 3.1 below the pre-wrok level, while the flicker value of the group wearing no earplugs fell by 12.7 below the pre-work level. There was significant difference between these two values with the level of significance of 0.05. Fluctuation in the flicker value of the group wearing earplugs were larger than those of the group wearing no earplugs. This will indicate that the use of earplugs has been effective in preventing noise from exerting pressure on humans. (3) There has since the previous experiments been an improvement in the environmental condition of the I. B. M. workers, and the loudness level of the noise to which they are exposed has been reduced to 80 phons (mod.). Tests were conducted four times a day for four days in January, 1955 (winter). The fall in the flicker value was 14.5 in the group wearing earplugs, while it was 13.5 in the group wearing no earplugs. There was no significant difference between these values with the level of significance of 0.05. Fluctuations in the flicker value were identical in both groups. This will indicate that an improvement in environmental condition has reduced the influence of noise on humans, and the workers are subjected to the same amount of stress irrespective of whether their external auditory canals are closed with earplugs or not. (4) The group wearing earplugs and the group wearing no earplugs both working in the office where environment has been improved-were tested for flicker values four times a day for four days. The flicker value fell 5.3 in the group wearing no earplugs. There was no significant difference between the two, values with the level of significance of 0.05. Fluctuations of the flicker value were identical in both groups. This will show that the value of the reduction of noise level in preventing noise from exerting pressure on humans remains unchanged throughout the year. (5) The results of the present study described above have led the author to conclude that noise, which exerts pressure on humans, causes fluctuations of the flicker value to grow larger than normal, that reduction of noise level or the use of earplugs eliminates the pressure exerted on humans by noise, and that fluctuations of the flicker value are not influenced by the kind of job, the manner of trip to and from the offiice, or season.
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