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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

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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