Key takeaway
A noise dose is a percentage of a specified exposure rule. OSHA-basis and NIOSH-basis percentages can differ for the same sound history without either calculation being a unit-conversion error.
Ask which rule makes the dose equal 100%
A noise-survey export contains a dose_percent column but loses the dosimeter profile. A receiving analyst cannot tell whether 100% refers to one exposure basis or another. The label percentage makes the values look directly comparable even though the reference duration at a given sound level may differ.
For its stated US general-industry context, OSHA’s mandatory Appendix A gives a 90 dBA, eight-hour reference and a five-decibel time tradeoff. NIOSH’s recommended limit uses 85 dBA over eight hours and a three-decibel exchange rate. These are different rule bases, not alternative units for one fixed dose. Applicability and workplace decisions require their own qualified review.
Compute two profiles for one fictional sound history
Hypothetical example: assume a constant A-weighted sound level for exactly eight hours, the declared profiles below and no measurement gaps. The scenario is a mathematical fixture; no worker or instrument was measured. It ignores hearing-protector attenuation and does not evaluate peak or impulsive noise.
At a constant 90 dBA, OSHA’s reference duration is eight hours, so dose is 100 × 8/8 = 100%. On the NIOSH basis, the reference duration is 8 / 2^((90 − 85)/3) = approximately 2.51984 hours. Eight hours therefore gives approximately 317.48%. At 85 dBA for eight hours, the corresponding example results are 50% on the OSHA basis and 100% on the NIOSH basis.
| Invented constant history | OSHA basis: 90 dBA / 5 dB | NIOSH basis: 85 dBA / 3 dB |
|---|---|---|
| 8 h at 85 dBA | 50% | 100% |
| 8 h at 90 dBA | 100% | 317.48% |
A percentage cannot reveal the lost profile
The completed fixture proves that unlike percentages should not be pooled under an unexplained common label. It does not provide a fixed conversion factor for arbitrary dose records. The ratio in the 85 dBA row differs from the ratio in the 90 dBA row. A varying sound history adds further dependence on the periods and settings that contributed to dose.
Keep the sound-level time history or the instrument’s relevant accumulated-exposure evidence where authorized. Store the criterion level, exchange rate, threshold, frequency weighting, response, measurement interval and projection settings beside the result. A profile name is useful only when its version and actual settings can be recovered. A later software default should not redefine old measurements.
Separate measured duration from projected full-shift exposure
Suppose a historical record contains only a short observation and a projected dose for a longer shift. Preserve both durations and the assumption that the observed conditions continued. Do not relabel the projection as a completed full-shift observation. If a worker changed tasks or moved areas, the extrapolation may no longer describe the stated history. Store whether the reported percentage was directly accumulated or extrapolated from a shorter interval.
NIOSH’s recommended settings include an 80 dBA threshold, A weighting and slow response, and its guidance calls for detailed task and measurement records. The threshold matters because it determines which levels contribute under the selected profile. A result missing that setting cannot be repaired by its percentage alone. Calibration checks and actual exposure coverage remain separate evidence questions.
Return a profile-specific record to the reviewer
For a mixed historical archive, retain separate profile-specific measures and an unresolved bucket for missing settings. The industrial hygiene reviewer can determine whether the original evidence permits recalculation and which rule applies. Do not interpret a lower percentage under one basis as evidence that exposure decreased between surveys conducted under different settings.
This review concerns the meaning of retained exposure records. It does not establish workplace compliance, a medical outcome or a safe work duration for anyone. Staff-linked surveys and health records can carry separate access restrictions. Describe the measurement and profile categories first; keep personal histories within their approved purpose while technical and disclosure questions are resolved.