Abstract
The individual noise exposure for constant sound level conditions, and hence the noise injury risk, can be estimated by conventional measurement of sound intensity, frequency and duration of exposure. The durations of different intensity components of intermittent noise of known periodicity can be easily estimated from noise index calculations such as Swedish Standard SEN 590111. For intermittent exposure where the noise source varies in an uncontrolled manner, or when the exposed person moves between different noise zones, the total exposure can be recorded by the personal noise dosimeter which instantaneously integrates sound pressure and duration of exposure.
28 noise dosimeters type SRA 71 have been exposed to 100 dB “white noise” under standardized conditions. The results show good agreement between dosimeters and for the same dosimeter on different occasions. A nomogram has been prepared for converting the total noise dose to an equivalent sound level in dB(A).
The Swedish norms are based on tables where sound intensity and estimated exposure time are integrated, whereas the dosimeter integrates sound pressure and exact exposure time. This means that the present design of the dosimeter gives an average result 2—3 dB lower than the equivalent level according to the Swedish Standard (Q-value=3) for fluctuating noise. However, the dosimeter results agree approximately with the more liberal American norms (the Walsh Healey Act, Q-value = 6). The choice of most adequate method is still an open question. A possible solution may be given by investigation of a suitably composed group of subjects continuously exposed to varying types and levels of noise over a long period, using dosimetry combined with repeated hearing tests.