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- QUESTION
Three workers (8-hour work shift) were monitored for work in different areas of a facility using calibrated noise dosimeters. The results are summarized in the following table.
Time for Monitoring Worker 1 Worker 2 Worker 3
3 hours 80.5 dBA 98.5 dBA 92.5 dBA
2 hours 81.0 dBA 86.5 dBA 85.0 dBA
2 hours 82.0 dBA 84.5 dBA 83.5 dBA
1 hour 95.0 dBA 83.5 dBA 80.0 dBAa. Calculate the 8-hour time-weighted average (TWA) noise exposure for each of the three workers.
b. Summarize which (one) of the exposures exceeds OSHA's permissible exposure limit (PEL) and/or action level for noise.
c. Discuss what factors about the noise monitoring may have affected the accuracy of the noise measurements.
Show your work for all mathematical calculations. Please refer to Appendix A to 29 CFR 1910.95 for assistance on how-to solve this problem.
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Answer
Industrial Hygiene Questions
TWA Calculation for the Workers
Worker 1:
The dose is calculated by the formula below:
Dose = 100 x (C1/T1 + C2/T2 + C3/T3 + ... + Cn/Tn)
Appendix A of Table G16-A outlines that:
80.5 dBA is equivalent to 81 or 27.9
81.0 dBA is equivalent to 81 or 27.9
82.0 dBA is equivalent to 82 or 24.3
95.0 dBA is equivalent to 95 or 4
Therefore;
Dose = 100 x (3/27.9 + 2/27.9 + 2/24.3 + 1/4) = 51.1516%
The formula for calculating TWA is 16.61 log(10)(D/100) + 90
Therefore, for Worker 1, TWA = 16.61 log(10)(51.1516/100) + 90 = 85.16415 = 85.1
Worker 1 TWA= 85.1 Dba
Worker 2:
The dose is calculated by the formula below:
Dose = 100 x (C1/T1 + C2/T2 + C3/T3 + ... + Cn/Tn)
Appendix A of Table G16-A outlines that:
98.5 dBA is equivalent to 99 which is equal to 2.3
86.5 dBA is equivalent to 87 which is equal to 12.1
84.5 dBA is equivalent to 85 which is equal to 16
83.5 dBA is equivalent to 84 which is equal to 18.4
Therefore;
Dose = 100 x (3/2.3 + 2/12.1 + 2/16 + 1/18.4) = 164.89849%
Worker 2’s TWA= 16.61 log(10)(164.89849/100) + 90 = 93.60797 = 93.6 dBA
Worker 3:
Appendix A of Table G16-A outlines that:
92.5 dBA is equivalent to 93 which is equal to 5.3
85.0 dBA is equivalent to 85 which is equal to 16
83.5 dBA is equivalent to 84 which is equal to 18.4
80.0 dBA is equivalent to 80 which is equal to 32
Therefore;
Dose = 100 x (3/5.3 + 2/16 + 2/18.4 + 1/32) = 83.09834%
Worker 3’s TWA= 16.61 log(10)(83.09834/100) + 90 = 88.66443 = 88.6 dBA
OSHA’s Permissible Limit
Worker 2’s exposure exceeds the set permissible limit by OSHA which is estimated at 90 dBA for an 8-hour period (Occupational Safety and Health Administration (OSHA), n.d). Worker 2’s TWA is 93.6 dBA. Therefore, the company should consider a hearing conservation program in the case of this worker to avoid potential damages. Hearing aids can be used to reduce sound levels and potential damage.
Factors Influencing the Accuracy of Noise Measurements
Temperature and background noise are some of the common factors which can influence the accuracy of noise measurement. Moreover, proximity to the noise source can also affect the derived figures. Therefore, the measuring equipment should always be calibrated prior and after the noise readings are taken. Also, the measuring equipment should be available at a shoulder level and within a distance of 2-feet from the person being monitored to prevent interferences from background noise (Canadian Centre for Occupational Health (CCOH), 2018).
References
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Canadian Centre for Occupational Health (CCOH). (2018, April 12). Noise - Measurement of Workplace Noise: OSH Answers. Retrieved from https://www.ccohs.ca/oshanswers/phys_agents/noise_measurement.html Occupational Safety and Health Administration (OSHA). (n.d.). 29 CFR § 1910.95 - Occupational noise exposure. Retrieved from https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=9735
Appendix
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