Present paper deals with the problems of predicting temporary threshold shift (TTS) produced by intermittent noises of which off time is longer than two minutes. In the first experiment, to obtain the growth and recovery of TTS at 4 kc, three subjects with normal hearing acuity were exposed to 2000∼4000 cps octaveband noises at 90 db for durations from one minute to 35 minutes. (Figs.2 and 3) In the second experiment, six types of intermittent exposure to 2000∼4000 cpc noises 90 db shown in Fig.4 were used. TTS₂ (TTS two minutes after cessation of each exposure), residual TTS (TTS that exists just before the beginning of re-exposure) and TTS in recovery process after the intermittent exposure were measured on the same three subjects. The results of these experiments revealed that 1) the exposure-equivalent rule proposed by Ward etal. was valid in expeirmental conditions containing various off-times from four to 10 minutes, 2) TTS following the intermittent exposure could be predicted based on the exposure-equivalent rule and the equations of recovery process of TTS, and 3) recovery of TTS produced by the repeated exposure proceeded slightly slower than that of TTS produced by the continuous exposure.

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We notice a rapid innovation and rationalization of techniques as the recent feature of industrial advance in our country. Many laborers are found to work hard and are afflicted with mental stresses. Accordingly, new causes of labor accidents are expected to be brought about. In such circumstances, labor accidents must be analysed not only in respect to environmental conditions but also to human factors. Though we find accidents more frequently in certain types of jobs, it is important to notice that certain persons tend to get significantly more accidents than expected. Having chosen persons who had accidents above a certain frequency in a definite term from the field of labor by way of a practical method based on accidental reports recorded year by year, the author considered them accident-prone and made them the subjects of investigation. As a part of the screening study series for accident-proneness, the author made a research on the subjects by social status, biometry and CMI health questionnaire. The subjects were chosen among the workers of M-and H-Shipbuilding Yards. In M-Shipbuilding Yard, 26 persons who had accidents more than 3 times in six years from 1957 to 1962 were chosen as subjects of investigation and were classified as the accident-prone group. On the other hand, 23 persons with no or little record of accidents in the same period, who had the same type of jobs and were of the same ages, were selected and classified as the control group. In H-Shipbuilding Yard, those who caused accidents 7 times or more during ten years form 1954 to 1963 were classified as the accident-prone group. The control group was set up by the same method as described in the case of M-Shipbuilding Yard. The results were as follows: (1) The method of choosing persons who had accidents above a certain frequency in a definite term, considering the average frequency-rate and the average severity-rate of the subjects, can be used with ease in the actual field of labor. (2) In the accident-prone group, a tendency of low standard of education was observed. (3) Most of the persons in the accident-prone group were relatively advanced in age and poor in the visual acuity. (4) Comparing the health status of the accident-prone group with that of the control by means of CMI health questionnaire, the author found that the former had many chronic complaints, irritability, restlessness and quick-temper.

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