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PDFWAC 296-307-63415

Use these equations when estimating full-day noise exposure from sound level measurements.

The employer must compute employee's full-day noise exposure by using the appropriate equations from Table 3 "Noise Dose Computation" when using a sound level meter to estimate noise dose.
Table 3
Noise Dose Computation
Compute the noise dose based on several time periods of constant noise during the shift
The total noise dose over the work day, as a percentage, is given by the following equation where Cn indicates the total time of exposure at a specific noise level, and Tn indicates the reference duration for that level.
D = 100*((C1/T1) + (C2/T2) + (C3/T3) + ... + (Cn/Tn))
The reference duration is equal to the time of exposure to continuous noise at a specific sound level that will result in a one hundred percent dose
The reference duration, T, for sound level, L, is given in hours by the equation:
T = 8/(2^((L - 90)/5))
Given a noise dose as a percentage, compute the equivalent eight-hour time weighted average noise level
The equivalent eight-hour time weighted average, TWA8, is computed from the dose, D, by the equation:
TWA8 = 16.61* Log10(D/100) + 90
[Statutory Authority: RCW 49.17.010, 49.17.040, 49.17.050, and 49.17.060. WSR 20-21-091, § 296-307-63415, filed 10/20/20, effective 11/20/20; WSR 05-01-166, § 296-307-63415, filed 12/21/04, effective 4/2/05.]
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