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Every year, employers run annual audiograms and face the same set of questions: Does this result trigger an STS? Is it recordable? Do I need to notify the employee? Can I apply age correction? The answers depend on two distinct regulatory frameworks — 29 CFR 1910.95 (the hearing conservation standard) and 29 CFR 1904.10 (the recordkeeping rule for hearing loss) — which use different thresholds, different age-correction rules, and produce different obligations. This guide walks through both calculations step by step with worked examples.
Soundtrace automates both the STS calculation and 300 Log recordability determination from audiometric data, flagging results that require employer action and generating the documentation OSHA inspectors expect to see.
STS and 300 Log recordability are not the same calculation. A worker can have an STS without being recordable. A worker can be recordable without having a new STS this year. Age correction is permitted for one and prohibited for the other. These two frameworks must be evaluated independently every year.
When an annual audiogram is compared to a worker’s baseline, the result feeds into two separate regulatory analyses: STS determination under 29 CFR 1910.95 (did the threshold change from baseline by 10 dB or more?), and 300 Log recordability under 29 CFR 1904.10 (does the current audiogram show 25 dB or more total hearing level from audiometric zero, and is the loss work-related?). These evaluations use the same data but are otherwise independent.
An STS is triggered when the average of the shifts at 2000, 3000, and 4000 Hz (compared to baseline) equals or exceeds 10 dB in either ear. Steps: obtain annual audiogram thresholds; subtract baseline thresholds to get frequency-level shifts; optionally apply Appendix F age correction; average the three adjusted shifts; if ≥10 dB in either ear, STS has occurred.
Within 21 days: notify employee in writing; ensure HPDs are in use and refit/retrain if needed; refer for PLHCP evaluation at no cost if STS persists or no retest is conducted.
OSHA 1910.95 Appendix F age-correction tables are optional for STS calculation and can reduce or eliminate an apparent STS. Age correction is categorically prohibited for the 300 Log recordability determination under 29 CFR 1904.10(a). A worker whose age-corrected STS falls below 10 dB may still have current thresholds exceeding 25 dB from audiometric zero and qualify as a recordable case.
Applying age correction to the 300 Log recordability determination is a recordkeeping violation resulting in under-recording. OSHA inspectors specifically check for this error. The STS and recordability determinations must be documented separately.
When an STS is identified, the employer may retest within 30 days. If the retest no longer shows an STS, the employer may use the retest result for STS determination and is not required to notify the employee. The 30-day retest does not affect 300 Log recordability, which is evaluated on the current audiogram regardless of retest outcome.
Under 29 CFR 1904.10(a), a case is recordable when: (1) the current audiogram shows an average hearing level ≥25 dB at 2000/3000/4000 Hz from audiometric zero, without age correction; AND (2) the hearing loss is work-related per a PLHCP determination or OSHA’s default presumption.
OSHA’s rebuttable presumption: if work exposure caused, contributed to, or significantly aggravated the hearing loss, it is work-related. Without a PLHCP determination of non-work-relatedness, the employer must presume work-relatedness and record the case. A PLHCP may determine non-work-relatedness based on documented pre-existing non-occupational hearing loss, a diagnosed non-occupational condition, or presbycusis consistent with age and noise history. The employer cannot simply assert non-work-relatedness without professional support.
| Scenario | STS? | Recordable? | Action Required |
|---|---|---|---|
| 10 dB age-corrected shift; current avg 22 dB from zero | Yes | No (below 25 dB) | Notify, HPD refit, retraining. No 300 Log entry. |
| 8 dB age-corrected shift; current avg 30 dB from zero, work-related | No | Yes | 300 Log entry required. No STS notification. |
| 15 dB raw shift; current avg 35 dB from zero, PLHCP says not work-related | Yes | No (not work-related) | Notify, HPD refit. No 300 Log entry. Document PLHCP determination. |
Audiometric test records: duration of employment. Noise exposure measurement records: at least two years. OSHA 300 Logs, 300-A summaries, and 301 forms: five years from the end of the calendar year covered.
▶ Bottom line: STS and 300 Log recordability are parallel evaluations from the same data with different rules. Running only one is a compliance error. Document both evaluations, including whether age correction was applied and the work-relatedness determination.
Soundtrace performs both the STS calculation and 300 Log recordability determination from each annual audiogram, documents each evaluation separately, and generates audit-ready records.
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