(d)

1. (1) In all cases where the sound levels exceed the values shown herein, a continuing, effective hearing conservation program shall be administered.

   Table D-2—Permissible Noise Exposures

   Duration per day, hours	Sound level dBA slow response
   8	90
   6	92
   4	95
   3	97
   2	100
   11⁄2	102
   1	105
   1⁄2	110
   1⁄4 or less	115

2. (2)

   1. (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.

   2. (ii) Fe = (T1/L1) + (T2/L2) + · · · + (Tn/Ln)

      Where: Fe = 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 Fe exceeds unity (1) the exposure exceeds permissible levels.

   3. (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. Fe = ( 1/4/ 1/2) + ( 1/2/2) + (1 1/2/8) Fe = 0.500 + 0.25 + 0.188 Fe = 0.938

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