OSHA 29 CFR 1910.95 Appendix A — Noise Exposure Computation — Appendix A to OSHA 1910.95 provides the mathematical method for calculating noise dose and 8-hour time-weighted average (TWA) when a worker is exposed to different noise levels during different portions of their work shift. It is a non-mandatory appendix that documents the computation underlying OSHA's noise exposure assessment framework. This plain-language guide explains what Appendix A requires, what it means in practice for EHS managers, and how it connects to the broader OSHA 1910.95 hearing conservation program requirements. According to CDC/NIOSH, approximately 22 million U.S. workers are exposed to hazardous occupational noise annually.
Soundtrace delivers audiometric testing and noise monitoring that meets the technical requirements of all 1910.95 appendices — including ANSI S3.1 ambient noise validation per audiogram and ANSI S3.6 audiometer specifications.
The core formula from Appendix A is the noise dose calculation:
D = 100 × (C⊂1;/T⊂1; + C⊂2;/T⊂2; + … + C⊂n;/T⊂n;)
Where: D = noise dose (%), C = actual duration of exposure at a given noise level, T = permissible duration at that noise level per Table G-16.
A dose of 100% equals one full OSHA PEL (equivalent to 8 hours at 90 dBA).
Converting Dose to TWA
Once dose is calculated, the 8-hour TWA is determined by: TWA = 16.61 × log⊂10;(D/100) + 90
This converts percentage dose to the equivalent steady-state noise level that would produce the same dose over 8 hours.
Worked Example
| Noise Level | Actual Duration (C) | Permissible Duration (T) | C/T Ratio |
|---|---|---|---|
| 90 dBA | 4 hours | 8 hours | 0.50 |
| 95 dBA | 2 hours | 4 hours | 0.50 |
| 85 dBA | 2 hours | 16 hours | 0.125 |
Dose = 100 × (0.50 + 0.50 + 0.125) = 100 × 1.125 = 112.5%
TWA = 16.61 × log⊂10;(112.5/100) + 90 = 16.61 × 0.0512 + 90 = 90.85 dBA
This worker exceeds the PEL (TWA > 90 dBA) and exceeds 100% dose, triggering mandatory engineering controls assessment and HPD use, in addition to the full 6-element HCP (which was already triggered at ≥85 dBA).
Integration threshold: 80 dBA
Appendix A specifies that exposures below 80 dBA are excluded from the dose calculation. Noise at 79 dBA or below contributes zero to dose. This is the integration threshold, which is set at 80 dBA for OSHA compliance calculations.
How dosimeters implement Appendix A
Modern noise dosimeters perform the Appendix A calculation automatically when configured correctly. The key instrument settings that implement Appendix A: exchange rate 5 dB, criterion level 90 dBA, integration threshold 80 dBA, frequency weighting A, time response slow. A dosimeter configured with these settings outputs the Appendix A dose and TWA directly. See: noise dosimeter: OSHA requirements and settings guide.
OSHA 1910.95 compliant audiometric testing — every appendix requirement met
Soundtrace delivers audiometric testing that meets ANSI S3.1 test environment requirements (Appendix D), uses ANSI S3.6 calibrated audiometers, and is supervised by a licensed audiologist — fully compliant with every 1910.95 appendix requirement.
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