Calculate OSHA noise dose and 8-hour time-weighted average from multiple A-weighted, slow-response exposure periods.
OSHA Noise Dose and TWA Formulas
OSHA Appendix A assigns each A-weighted, slow-response sound level Li a permitted duration Ti = 8 / 2^((Li − 90)/5) hours. For several periods, dose is D = 100 × Σ(Ci/Ti). The corresponding 8-hour TWA is TWA = 16.61 log10(D/100) + 90.
A 50% dose corresponds to an 85 dBA TWA and triggers the general-industry hearing-conservation action level. A 100% dose corresponds to a 90 dBA 8-hour TWA. OSHA uses a 5 dB exchange rate; a NIOSH REL assessment uses a different 85 dBA criterion and 3 dB exchange rate and must not be substituted silently.
Measurement and Safety Limits
This calculator accepts only A-weighted, slow-response levels from 80 through 130 dBA, matching OSHA Appendix A’s table. It does not convert dBC or unweighted readings, evaluate impulse peaks, correct instrument error, establish representative exposure, or make a compliance determination. Levels above 115 dBA and impulsive noise need additional review.
Primary references: OSHA 1910.95 Appendix A, OSHA 1910.95, and NIOSH occupational noise REL.
