Occupational noise assessment against OSHA, NIOSH, ACGIH, Australian, EU/UK, Canadian, and New Zealand standards
How to use
Select your jurisdiction, then add each noise source with its level (dBA) and duration. Sources can have any combination of levels and durations; they are combined into a single dose using the equal-energy rule. Press Calculate to see results.
Optionally enter a peak noise level (dBC) to check against the 140 dBC instantaneous limit. Enable the hearing protector section to assess whether an HPD (NRR or SLC80) provides adequate attenuation given the calculated dose.
Jurisdiction
Noise sources
Description
Level (dBA)
Hours
Minutes
Peak exposure
Hearing protector
Results
Source contribution to total noise energy
Understanding your results
Time-Weighted Average (TWA) is the equivalent continuous noise level over an 8-hour shift that produces the same dose as the actual mixture of levels and durations. It is the primary metric compared against regulatory limits. A TWA at or above the criterion level means the full 8-hour permissible dose has been reached.
Noise dose (%) is the fraction of the permissible daily exposure consumed. 100% dose = the criterion level held for 8 hours. Doses above 50% (OSHA action level) trigger hearing conservation program requirements; doses at or above 100% require engineering controls or HPD use. Doses can exceed 100%; this indicates the exposure is more than double the permissible limit in energy terms.
Standard differences: OSHA uses a 90 dBA criterion and 5 dB exchange rate, which is more permissive than NIOSH and ACGIH. NIOSH and ACGIH both use 85 dBA and a 3 dB exchange rate, which is based on equal-energy and is internationally recommended. Australia (HWSA 2022) aligns with NIOSH/ACGIH. Where standards disagree, the most protective standard (85 dBA, 3 dB ER) is the recommended engineering target.
Hearing protector adequacy: Adequate means the protected TWA is below the action level. Marginal means it is below the limit but above the action level; the HPD reduces exposure but does not fully control it. Inadequate means the HPD is insufficient even at its rated attenuation for the measured noise levels.