Tools › Mechanical Design › Acoustics › Noise Exposure › Example

OSHA Technical Manual noise dose: 95 dBA for 2 hours and 90 dBA for 3 hours, TWA, hearing-conservation action level and an NRR 29 protector

ToolNoise Exposure
SourceU.S. Department of Labor, Occupational Safety and Health Administration (2013). OSHA Technical Manual, Section III, Chapter 5: Noise. Appendix B.4 (adding exposure durations), B.5 (equivalent A-weighted level) and Appendix F (NRR derating); U.S. Department of Labor (2008). Occupational Noise Exposure. 29 CFR 1910.95, Appendix A.
LevelProfessional

Problem

A worker spends 2 hours at 95 dBA, 3 hours at 90 dBA and the remaining 3 hours of the shift in an office at 75 dBA. Find the OSHA noise dose and 8-hour TWA, whether the PEL and the hearing-conservation action level are met, the same day under the NIOSH 85 dBA / 3-dB criterion, the protected level with an NRR 29 earplug derated by OSHA's 50 % rule, and the A-weighted level of the manual's octave-band spectrum (94, 95, 92, 95, 97, 97, 102, 97, 92 dB from 31.5 Hz to 8 kHz).

Inputs to Enter

  • Criterion OSHA PEL (90 dBA, 5-dB exchange rate, 90 dBA threshold); segments 95 dBA 2:00, 90 dBA 3:00, 75 dBA 3:00
  • Protector NRR 29, derating OSHA 50 % of (NRR − 7)
  • Spectrum 94 95 92 95 97 97 102 97 92 dB (31.5 Hz to 8 kHz); attenuation data of 40 CFR 211.207 Figure 2 (125 Hz 21 ± 3.7 … 8000 Hz 36 ± 6.5 dB)
Open the Noise Exposure tool (loaded with this example)

Answers

  • Reference durations T = 8/2^((L−90)/5): 4 h at 95 dBA, 8 h at 90 dBA; the 75 dBA period is below the 90 dBA threshold
  • Dose D = 100 (2/4 + 3/8) = 87.5 % (manual: 7/8 of the PEL, not exceeded); TWA = 16.61 log10(0.875) + 90 = 89.0 dBA
  • Hearing-conservation dose (80 dBA threshold) 87.5 % ≥ 50 %: the action level of 85 dBA is exceeded (TWA 89.0 dBA), so a hearing conservation program is required; M.S. to the PEL +0.14, to the action level −0.43
  • NIOSH REL for the same day: T(95) = 48 min, T(90) = 2 h 31 min, dose 371 %, TWA 90.7 dBA; Leq 90.7 dBA
  • Protector: attenuation (29 − 7) × 50 % = 11 dB, protected level 78.0 dBA (manual's rule; Appendix F example 98 − (25 − 7) × 50 % = 89 dBA)
  • Spectrum: A-weighted sum 105.6 dBA with the IEC 61672 corrections (manual 105.5 with whole-decibel corrections), 105.9 dBC; long method 81.8 dBA protected; NRR of the Figure 2 data 19.8 dB, labelled 20

Notes

The tool's default inputs are this case; press Submit. Every printed number of Appendix A (Tables G-16, G-16a, A-1), the Technical Manual appendices, NIOSH 98-126 Tables 1-1 and 1-2 and 40 CFR 211.207 Figure 2 is checked in test_noise_exposure.php together with the numpy script References/Noise-Exposure/noise_check.py.