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Subchapter 7. General Industry Safety Orders
Group 15. Occupational Noise
Article 105. Control of Noise Exposure

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Appendix A: Noise Exposure Computation


Noise Exposure Computation
I. Computation of Employee Noise Exposure
(a) Noise dose is computed using Table A-1 as follows: When the sound level, L, is constant over the entire work shift, 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 reference duration corresponding to the measured sound level, L, as given in Table A-1 or by the formula shown as a footnote to that table.
(b) When the workshift 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 reference duration for that level as given by Table A-1.
(c) The eight-hour time-weighted average sound level (TWA), in decibels, may be computed from the dose, in percent, by means of the formula: TWA = 16.61 log10 (D/100) + 90. For an eight-hour workshift with the noise level constant over the entire shift, the TWA is equal to the measured sound level.
(d) A table relating dose and TWA is given in Section II.
Table A-1
A-weighted
Reference
A-weighted
Reference
sound level,
Duration
sound level,
Duration
L (decibel)
T (hour)
L (decibel)
T (hour)
80
 
32
106
 
0.87
81
 
27.9
107
 
0.76
82
 
24.3
108
 
0.66
83
 
21.1
109
 
0.57
84
 
18.4
110
 
0.5
85
 
16
111
 
0.44
86
 
13.9
112
 
0.38
87
 
12.1
113
 
0.33
88
 
10.6
114
 
0.29
89
 
9.2
115
 
0.25
90
 
8
116
 
0.22
91
 
7.0
117
 
0.19
92
 
6.1
118
 
0.16
93
 
5.3
119
 
0.14
94
 
4.6
120
 
0.125
95
 
4
121
 
0.11
96
 
3.5
122
 
0.095
97
 
3.0
123
 
0.082
98
 
2.6
124
 
0.072
99
 
2.3
125
 
0.063
100
 
2
126
 
0.054
101
 
1.7
127
 
0.047
102
 
1.5
128
 
0.041
103
 
1.3
129
 
0.036
104
 
1.1
130
 
0.031
105
 
1
In the above table, the reference duration, T, is computed by
T = 8 / 2 (L-90)/5
where L is the measured A-weighted sound level.
II. Conversion Between “Dose” and “8-Hour Time-Weighted Average” Sound Level.
Noise exposure is usually measured with an audiodosimeter which gives a readout in terms of “dose.” Dosimeter readings can be converted to an 8-hour time-weighted average sound level (TWA).
In order to convert the reading of a dosimeter into TWA, use Table A-2. This table applies to dosimeters that are set 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.
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
TWA
Dose or
TWA
Dose or
TWA
Percent
Percent
Percent
Noise
Noise
Noise
Exposure
Exposure
Exposure
10
 
73.4
116
 
91.1
510
 
101.8
15
 
76.3
117
 
91.1
520
 
101.9
20
 
78.4
118
 
91.2
530
 
102.0
25
 
80.0
119
 
91.3
540
 
102.2
30
 
81.3
120
 
91.3
550
 
102.3
35
 
82.4
125
 
91.6
560
 
102.4
40
 
83.4
130
 
91.9
570
 
102.6
45
 
84.2
135
 
92.2
580
 
102.7
50
 
85.0
140
 
92.4
590
 
102.8
55
 
85.7
145
 
92.7
600
 
102.9
60
 
86.3
150
 
92.9
610
 
103.0
65
 
86.9
155
 
93.2
620
 
103.2
70
 
87.4
160
 
93.4
630
 
103.3
75
 
87.9
165
 
93.6
640
 
103.4
80
 
88.4
170
 
93.8
650
 
103.5
81
 
88.5
175
 
94.0
660
 
103.6
82
 
88.6
180
 
94.2
670
 
103.7
83
 
88.7
185
 
94.4
680
 
103.8
84
 
88.7
190
 
94.6
690
 
103.9
85
 
88.8
195
 
94.8
700
 
104.0
86
 
88.9
200
 
95.0
710
 
104.1
87
 
89.9
210
 
95.4
720
 
104.2
88
 
89.1
220
 
95.7
730
 
104.3
89
 
89.2
230
 
96.0
740
 
104.4
90
 
89.2
240
 
96.3
750
 
104.5
91
 
89.3
250
 
96.6
760
 
104.6
92
 
89.4
260
 
96.9
770
 
104.7
93
 
89.5
270
 
97.2
780
 
104.8
94
 
89.6
280
 
97.4
790
 
104.9
95
 
89.6
290
 
97.7
800
 
105.0
96
 
89.7
300
 
97.9
810
 
105.1
97
 
89.8
310
 
98.2
820
 
105.2
98
 
89.9
320
 
98.4
830
 
105.3
99
 
89.9
330
 
98.6
840
 
105.4
100
 
90.0
340
 
98.8
850
 
105.4
101
 
90.1
350
 
99.0
860
 
105.5
102
 
90.1
360
 
99.2
870
 
105.6
103
 
90.2
370
 
99.4
880
 
105.7
104
 
90.3
380
 
99.6
890
 
105.8
105
 
90.4
390
 
99.8
900
 
105.8
106
 
90.4
400
 
100.0
910
 
105.9
107
 
90.5
410
 
100.2
920
 
106.0
108
 
90.6
420
 
100.4
930
 
106.1
109
 
90.6
430
 
100.5
940
 
106.2
110
 
90.7
440
 
100.7
950
 
106.2
111
 
90.8
450
 
100.8
960
 
106.3
112
 
90.8
460
 
101.0
970
 
106.4
113
 
90.9
470
 
101.2
980
 
106.5
114
 
90.9
480
 
101.3
990
 
106.5
115
 
91.1
490
 
101.5
999
 
106.6
500
 
101.6
Note: Authority and reference cited: Section 142.3, Labor Code.
HISTORY
1. Editorial correction of Table A-1 filed 3-22-84; effective thirtieth day thereafter (Register 84, No. 12).
2. Amendment of Table A-1 filed 8-28-84; effective thirtieth day thereafter (Register 84, No. 35).
3. Change without regulatory effect amending Table A-2 filed 4-14-2009 pursuant to section 100, title 1, California Code of Regulations (Register 2009, No. 16).


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