49 CFR Part 227, Appendix A to Part 227 - Noise Exposure Computation

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View PDF at GPO Pt. 227, App. A
Appendix A to Part 227—Noise Exposure Computation
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.
Table A-1 1
A-weighted sound level, L(decibel) Durationpermitted T (hour)
1 Numbers above 115 dB(A) are italicized to indicate that they are noise levels that are not permitted. The italicized numbers are included only because they are sometimes necessary for the computation of noise dose.
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 noiseexposure 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

Title 49 published on 2014-10-01

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