Impulse measurement considerations in setting occupational noise criteria

Résumé

The most common occupational noise limits are 85 dBA Leq and 140 dBZpeak for 100 impulses. Simple arithmetic shows that 100 high frequency pulses at 140 dBZ for 0.9 msec each will give 85 dBA (assuming the A-weighting has little effect due to the frequencies involved), i.e. in practical terms the Leq limit will usually be exceeded before the impulse limit. To check this in practice over 400 measurements were reviewed from a smelting and casting facility and from an ore milling operation. These measurements included impulse noise from jack hammers, pneumatic motors and exhausts, heavy scrap dropping into bins, etc. In no case was 140 dB exceeded, although 85 dBA was exceeded in many cases. More important, in every case the 85 dBA Leq limit would be exceeded well before the 140 dBZpeak limit. It is well known that noise dosimeters are unreliable in measuring impulse noise due to false impulses caused by rubbing the microphone and cable. As a result, routine assessment of impulse noise is much more difficult (expensive) than assessments using just Leq. It is concluded that in practice there is little advantage, and some decided disadvantages, to doing routine assessment (or regulation) of impulse noise exposure in industry.