Code of Federal Regulations Title 29. Labor § 29.1926.52 Occupational noise exposure

(2)(i) When the daily noise exposure is composed of two or more periods of noise exposure of different levels, their combined effect should be considered, rather than the individual effect of each. Exposure to different levels for various periods of time shall be computed according to the formula set forth in paragraph (d)(2)(ii) of this section.

(ii) F_e = (T₁/L₁)+(T₂/L₂)+ ․․․ + (T_n/L_n)

Where:

F_e = The equivalent noise exposure factor.

T = The period of noise exposure at any essentially constant level.

L = The duration of the permissible noise exposure at the constant level (from Table D–2).

If the value of F_e exceeds unity (1) the exposure exceeds permissible levels.

(iii) A sample computation showing an application of the formula in paragraph (d)(2)(ii) of this section is as follows. An employee is exposed at these levels for these periods:

110 db A 1/4 hour.

100 db A 1/2 hour.

90 db A 1 1/2 hours.

F_e = ( 1/4 / 1/2 )+( 1/2 /2)+(1 1/2 /8)

F_e = 0.500+0.25+0.188

F_e = 0.938

Since the value of F_e does not exceed unity, the exposure is within permissible limits.