This appendix is mandatory.
I. Computation of Employee Noise Exposure
A. Noise dose is computed using Table A-1 as follows:
1. When the sound level, L, is constant over the entire work day, the noise dose, D, in percent, is given by: D = 100 C/T, where C is the total length of the work day, in hours, and T is the duration permitted corresponding to the measured sound level, L, as given in Table A-1.
2. When the work day noise exposure is composed of two or more periods of noise at different levels, the total noise dose over the work day is given by:
D = 100 (C1/T1 + C2/T2 + . . . + Cn/Tn), where Cn indicates the total time of exposure at a specific noise level, and Tn indicates the duration permitted for that level as given by Table A-1.
B. The eight-hour TWA in dB may be computed from the dose, in percent, by means of the formula: TWA = 16.61 log10 (D/100) + 90. For an eight-hour work day with the noise level constant over the entire day, the TWA is equal to the measured sound level.
C. Exposure to impulsive or impact noise should not exceed 140 dB peak sound pressure level.
D. Any time that an employee spends deadheading shall be included in the calculation of the noise dose.
E. A table relating dose and TWA is given in Section II of this Appendix.
A-weighted sound level, L
(decibel)
| Duration
permitted
T
(hour)
|
|---|
| 80 | 32
|
| 81 | 27.9
|
| 82 | 24.3
|
| 83 | 21.1
|
| 84 | 18.4
|
| 85 | 16
|
| 86 | 13.9
|
| 87 | 12.1
|
| 88 | 10.6
|
| 89 | 9.2
|
| 90 | 8
|
| 91 | 7.0
|
| 92 | 6.1
|
| 93 | 5.3
|
| 94 | 4.6
|
| 95 | 4
|
| 96 | 3.5
|
| 97 | 3.0
|
| 98 | 2.6
|
| 99 | 2.3
|
| 100 | 2
|
| 101 | 1.7
|
| 102 | 1.5
|
| 103 | 1.3
|
| 104 | 1.1
|
| 105 | 1
|
| 106 | 0.87
|
| 107 | 0.76
|
| 108 | 0.66
|
| 109 | 0.57
|
| 110 | 0.5
|
| 111 | 0.44
|
| 112 | 0.38
|
| 113 | 0.33
|
| 114 | 0.29
|
| 115 | 0.25
|
| 116 | 0.22
|
| 117 | 0.19
|
| 118 | 0.16
|
| 119 | 0.14
|
| 120 | 0.125
|
| 121 | 0.11
|
| 122 | 0.095
|
| 123 | 0.082
|
| 124 | 0.072
|
| 125 | 0.063
|
| 126 | 0.054
|
| 127 | 0.047
|
| 128 | 0.041
|
| 129 | 0.036
|
| 130 | 0.031
|
| 140 | 0.078
|
In the above table the duration permitted, T, is computed by
where L is the measured A-weighted sound level.
II. Conversion Between “Dose” and “8-Hour Time-Weighted Average” Sound Level
A. Compliance with subpart B of part 227 is determined by the amount of exposure to noise in the workplace. The amount of such exposure is usually measured with a dosimeter which gives a readout in terms of “dose.” In order to better understand the requirements of the regulation, dosimeter readings can be converted to an “8-hour TWA.”
B. In order to convert the reading of a dosimeter into TWA, see Table A-2, below. This table applies to dosimeters that are set by the manufacturer to calculate dose or percent exposure according to the relationships in Table A-1. So, for example, a dose of 91 percent over an eight-hour day results in a TWA of 89.3 dB, and a dose of 50 percent corresponds to a TWA of 85 dB.
C. If the dose as read on the dosimeter is less than or greater than the values found in Table A-2, the TWA may be calculated by using the formula: TWA = 16.61 log10 (D/100) + 90 where TWA = 8-hour time-weighted average sound level and D = accumulated dose in percent exposure.
Table A-2—Conversion From “Percent Noise Exposure” or “Dose” to “8-Hour Time-Weighted Average Sound Level” (TWA)
Dose or percent noise
exposure
| TWA
|
|---|
| 10 | 73.4
|
| 15 | 76.3
|
| 20 | 78.4
|
| 25 | 80.0
|
| 30 | 81.3
|
| 35 | 82.4
|
| 40 | 83.4
|
| 45 | 84.2
|
| 50 | 85.0
|
| 55 | 85.7
|
| 60 | 86.3
|
| 65 | 86.9
|
| 70 | 87.4
|
| 75 | 87.9
|
| 80 | 88.4
|
| 81 | 88.5
|
| 82 | 88.6
|
| 83 | 88.7
|
| 84 | 88.7
|
| 85 | 88.8
|
| 86 | 88.9
|
| 87 | 89.0
|
| 88 | 89.1
|
| 89 | 89.2
|
| 90 | 89.2
|
| 91 | 89.3
|
| 92 | 89.4
|
| 93 | 89.5
|
| 94 | 89.6
|
| 95 | 89.6
|
| 96 | 89.7
|
| 97 | 89.8
|
| 98 | 89.9
|
| 99 | 89.9
|
| 100 | 90.0
|
| 101 | 90.1
|
| 102 | 90.1
|
| 103 | 90.2
|
| 104 | 90.3
|
| 105 | 90.4
|
| 106 | 90.4
|
| 107 | 90.5
|
| 108 | 90.6
|
| 109 | 90.6
|
| 110 | 90.7
|
| 111 | 90.8
|
| 112 | 90.8
|
| 113 | 90.9
|
| 114 | 90.9
|
| 115 | 91.1
|
| 116 | 91.1
|
| 117 | 91.1
|
| 118 | 91.2
|
| 119 | 91.3
|
| 120 | 91.3
|
| 125 | 91.6
|
| 130 | 91.9
|
| 135 | 92.2
|
| 140 | 92.4
|
| 145 | 92.7
|
| 150 | 92.9
|
| 155 | 93.2
|
| 160 | 93.4
|
| 165 | 93.6
|
| 170 | 93.8
|
| 175 | 94.0
|
| 180 | 94.2
|
| 185 | 94.4
|
| 190 | 94.6
|
| 195 | 94.8
|
| 200 | 95.0
|
| 210 | 95.4
|
| 220 | 95.7
|
| 230 | 96.0
|
| 240 | 96.3
|
| 250 | 96.6
|
| 260 | 96.9
|
| 270 | 97.2
|
| 280 | 97.4
|
| 290 | 97.7
|
| 300 | 97.9
|
| 310 | 98.2
|
| 320 | 98.4
|
| 330 | 98.6
|
| 340 | 98.8
|
| 350 | 99.0
|
| 360 | 99.2
|
| 370 | 99.4
|
| 380 | 99.6
|
| 390 | 99.8
|
| 400 | 100.0
|
| 410 | 100.2
|
| 420 | 100.4
|
| 430 | 100.5
|
| 440 | 100.7
|
| 450 | 100.8
|
| 460 | 101.0
|
| 470 | 101.2
|
| 480 | 101.3
|
| 490 | 101.5
|
| 500 | 101.6
|
| 510 | 101.8
|
| 520 | 101.9
|
| 530 | 102.0
|
| 540 | 102.2
|
| 550 | 102.3
|
| 560 | 102.4
|
| 570 | 102.6
|
| 580 | 102.7
|
| 590 | 102.8
|
| 600 | 102.9
|
| 610 | 103.0
|
| 620 | 103.2
|
| 630 | 103.3
|
| 640 | 103.4
|
| 650 | 103.5
|
| 660 | 103.6
|
| 670 | 103.7
|
| 680 | 103.8
|
| 690 | 103.9
|
| 700 | 104.0
|
| 710 | 104.1
|
| 720 | 104.2
|
| 730 | 104.3
|
| 740 | 104.4
|
| 750 | 104.5
|
| 760 | 104.6
|
| 770 | 104.7
|
| 780 | 104.8
|
| 790 | 104.9
|
| 800 | 105.0
|
| 810 | 105.1
|
| 820 | 105.2
|
| 830 | 105.3
|
| 840 | 105.4
|
| 850 | 105.4
|
| 860 | 105.5
|
| 870 | 105.6
|
| 880 | 105.7
|
| 890 | 105.8
|
| 900 | 105.8
|
| 910 | 105.9
|
| 920 | 106.0
|
| 930 | 106.1
|
| 940 | 106.2
|
| 950 | 106.2
|
| 960 | 106.3
|
| 970 | 106.4
|
| 980 | 106.5
|
| 990 | 106.5
|
| 999 | 106.6 |