A standard threshold shift (STS) is a change in hearing threshold, relative to a worker’s baseline audiogram, of an average of 10 dB or more at 2,000, 3,000 and 4,000 Hz in either ear. The definition comes from the US federal OSHA noise standard, 29 CFR 1910.95 (§1910.95(g)(10)(i)), where it triggers follow-up action in the hearing conservation program.
How an STS is identified
- Comparison with the baseline. Each annual audiogram is compared with the baseline to decide whether it is valid and whether an STS has occurred; a technician may do this (§1910.95(g)(7)(i)).
- Age correction. Allowance may be made for the contribution of aging (presbycusis), using the non-mandatory Appendix F (§1910.95(g)(10)(ii)).
- Retest. If the annual audiogram shows an STS, the employer may obtain a retest within 30 days and treat its results as the annual audiogram (§1910.95(g)(7)(ii)).
What the employer must do after an STS
The worker must be informed in writing within 21 days of the determination (§1910.95(g)(8)(i)). Unless a physician determines that the STS is not work related or aggravated by occupational noise exposure, the employer must ensure that (§1910.95(g)(8)(ii)):
- workers not using hearing protectors are fitted with them, trained in their use and care, and required to use them;
- workers already using hearing protectors are refitted and retrained, and given protectors with greater attenuation if necessary;
- the worker is referred for a clinical audiological evaluation or an otological examination, as appropriate, where additional testing is necessary or an ear pathology linked to hearing protectors is suspected;
- the worker is told of the need for an otological examination if an ear pathology unrelated to hearing protectors is suspected.
If the shift is persistent, an annual audiogram may become the new baseline (§1910.95(g)(9)).
When an STS goes on the OSHA 300 Log
Under 29 CFR 1904.10, an employer covered by OSHA’s recordkeeping rule must record the case on the OSHA 300 Log when a worker has a work-related STS in one or both ears and a total hearing level of 25 dB or more above audiometric zero (averaged at 2,000, 3,000 and 4,000 Hz) in the same ear(s) (§1904.10(a)). In practice:
- Age adjustment may be used to decide whether an STS occurred, but not for the 25 dB test (§1904.10(b)(3)).
- If a retest within 30 days does not confirm the recordable STS, the case need not be recorded; a confirmed case must be recorded within seven calendar days of the retest (§1904.10(b)(4)).
- A case need not be recorded if a physician or other licensed health care professional determines the hearing loss is not work-related or not significantly aggravated by occupational noise (§1904.10(b)(6)).
Recorded cases go in the 300 Log column for hearing loss (§1904.10(b)(7)).
In MyC’s health surveillance software, results from connected audiometers land straight in the record and can be compared against the worker’s own baseline, so a shift in hearing shows at the next exam.
Related terms
- Baseline audiogram: A baseline audiogram is the reference hearing test of a noise-exposed worker, against which later audiograms are compared to detect a shift in hearing.
- OSHA 300 Log: The OSHA 300 Log is the form on which US employers covered by 29 CFR Part 1904 record each work-related injury and illness that meets OSHA's recording criteria.
- Health surveillance: Health surveillance is a program of repeated health assessments for workers still exposed to a hazard after controls, to identify ill health caused by work.