Noise dose and TWA arithmetic are useful only when the measurements behind them are valid. OSHA Appendix A gives formulas for computing dose and TWA from measured periods, and NIOSH publishes a more protective REL comparison, but neither source turns a local web form into a completed noise exposure assessment.
This guide explains how to use the ToolGrit noise-dose screen as a first-pass calculation while keeping the important boundaries visible: instrument calibration, dosimeter settings, representative sampling, worker movement, impulse/impact noise, state-plan rules, hearing protection, audiometry, employer program records, and qualified industrial-hygiene review.
OSHA and NIOSH Answer Different Questions
The local screen uses OSHA general-industry dose arithmetic with a 90 dBA criterion level, 8-hour criterion duration, and 5 dB exchange rate. A 50 percent OSHA dose corresponds to an 85 dBA TWA action-level screen, and a 100 percent OSHA dose corresponds to a 90 dBA TWA PEL screen.
The NIOSH comparison uses an 85 dBA criterion level and a 3 dB exchange rate. That is recommended health guidance, not an OSHA violation by itself. Employers may choose or be required by another authority to use more protective criteria, but the app keeps the OSHA and NIOSH labels separate.
An OSHA dose screen is not a citation, and a NIOSH REL screen is not an OSHA violation. Use current OSHA/state-plan text, employer policy, and qualified review before making program decisions.
Noise Dose & TWA Calculator
Calculate noise dose and time-weighted average per OSHA 29 CFR 1910.95 with NIOSH comparison.
Dose and TWA Arithmetic
For mixed exposures, the app sums each entered period as Ci/Ti, where C is the measured duration and T is the source formula reference duration for the measured level. OSHA Appendix A expresses the total dose as D = sum(Ci/Ti) x 100.
For the OSHA screen, T = 8 / 2(L-90)/5. For the NIOSH comparison, T = 8 / 2(L-85)/3. OSHA TWA from dose is TWA = 16.61 x log10(D/100) + 90. The ToolGrit app reports TWA as not available when the integrated dose is zero, rather than implying a 0 dBA exposure.
OSHA T = 8 / 2(L-90)/5
NIOSH T = 8 / 2(L-85)/3
Dose = sum(Ci/Ti) x 100
OSHA TWA = 16.61 x log10(D/100) + 90
Measurement Controls the Result
The numbers entered into a dose screen should come from a calibrated sound-level meter or personal dosimeter with documented settings. A-weighting, response, threshold, exchange rate, dose criterion, calibration checks, microphone position, worker movement, task timing, and exposure grouping can change the result.
Area readings, equipment nameplate levels, phone apps, and short spot checks can be useful for triage, but they are not a substitute for a representative occupational exposure assessment when program or compliance decisions are involved.
Without instrument records and a sampling strategy, a dose number is just arithmetic on assumed inputs.
Hearing Programs and Protection Need Separate Review
The app does not decide hearing-protection adequacy, audiometric testing status, standard threshold shift follow-up, training, recordkeeping, or medical referrals. Those depend on the full employer hearing-conservation program, measured exposure, worker records, device fit, NRR or fit-test attenuation, and current OSHA/state-plan requirements.
Use a dose screen to identify questions: Should monitoring be repeated? Are controls feasible? Do workers need program review? Is hearing protection fit and attenuation verified? Those questions still need qualified safety or industrial-hygiene review.
NRR, fit, dual protection, worker use, and audiometry are outside the local dose calculation.