OSHA Standard Threshold Shift Calculator
OSHA Standard Threshold Shift Calculator
The 2000, 3000 and 4000 Hz average shift from baseline that 29 CFR 1910.95(g)(10)(i) defines as a standard threshold shift, with the optional age correction shown separately and the 25 dB element of 29 CFR 1904.10 beside it.
Standard threshold shift
29 CFR 1910.95(g)(10)(i)Baseline average 12 dB HL, current average 26 dB HL, both over 2000, 3000 and 4000 Hz in one ear; Appendix F age correction 3 dB
Formula
- the criterion
- 29 CFR 1910.95(g)(10)(i): a standard threshold shift is “a change in hearing threshold relative to the baseline audiogram of an average of 10 dB or more at 2000, 3000, and 4000 Hz in either ear”. Either ear, so both are assessed separately and the worse one decides
- why two averages and not six thresholds
- the average of the three individual shifts is arithmetically identical to the difference between the two three-frequency averages, so entering the averages gives exactly the figure the regulation defines
- the age correction
- optional. 1910.95(g)(10)(ii) permits an “allowance … for the contribution of aging (presbycusis) to the change in hearing level” by correcting the annual audiogram “according to the procedure described in appendix F”, and paragraph (n)(2) makes Appendix F informational rather than mandatory. Appendix F is a lookup table by age, sex and frequency; it is not a formula and is not reproduced or approximated here
- the 25 dB element
- a SEPARATE test in a separate regulation. 29 CFR 1904.10 requires, for its own purposes, that “you must use the average hearing level at 2000, 3000, and 4000 Hz to determine whether or not the employee’s total hearing level is 25 dB or more”, and states that age adjustment may not be used for that determination. It is a level, not a shift
- the retest
- 1910.95(g)(7)(ii) allows the employer to “obtain a retest within 30 days and consider the results of the retest as the annual audiogram”, and 1904.10 provides that a retest within 30 days that does not confirm the shift removes the recording obligation
- the revised baseline
- 1910.95(g)(9) allows an annual audiogram to replace the baseline where the reviewing audiologist, otolaryngologist or physician determines that the shift is persistent, or that the annual audiogram shows significant improvement. Every later comparison then runs against the new baseline
- what this does not do
- determine recordability, work-relatedness, persistence, or any duty under the regulation. Those are determinations for the employer and the reviewing professional. This page computes the shift the regulation defines and prints the regulation’s own wording beside it
Worked example
Baseline average 12 dB HL, current average 26 dB HL, both over 2000, 3000 and 4000 Hz in one ear; Appendix F age correction 3 dB
Age-corrected current average = 26 − 3 = 23.0 dB HL
Shift = 23.0 − 12 = 11.0 dB, which is 10 dB or more and so meets the arithmetic of 1910.95(g)(10)(i)
Without the correction the shift is 26 − 12 = 14.0 dB. The 3 dB correction moved the answer but not across the criterion
Where the correction does decide it. With a baseline of 12 and a current average of 24, the uncorrected shift is 12.0 dB and the 3 dB corrected shift is 9.0 dB — one number read off a table deciding whether a criterion is met, which is why both figures are shown
Both sides of the criterion. A baseline of 15 with a current average of 25 and no correction gives exactly 10.0 dB, which meets it; 24.9 gives 9.9 dB, which does not
The 25 dB element, separately. The current average here is 26.0 dB HL unadjusted, which is 25 dB or more, so both of the arithmetic elements 1904.10 uses are present. Note that the age-adjusted average is 23.0 dB and would NOT reach 25 — and 1904.10 does not permit age adjustment for that element
An improvement comes out negative. Baseline 30, current 25, no correction: −5.0 dB. Small movements in either direction sit inside the plus or minus 5 dB uncertainty of a threshold measurement
Not the same question as ototoxicity monitoring. This average has no 500, 1000 or 6000 Hz in it. A 25 dB drop at 6000 Hz meets ASHA's single-frequency criterion and changes this figure not at all
Two different arithmetic tests in two different regulations
| Test | Regulation | Quantity | Age adjustment |
|---|---|---|---|
| Standard threshold shift | 29 CFR 1910.95(g)(10)(i) | An average CHANGE of 10 dB or more at 2000, 3000 and 4000 Hz, either ear, relative to the baseline | Permitted, via Appendix F, which (n)(2) makes informational |
| The 25 dB element | 29 CFR 1904.10 | A total hearing LEVEL of 25 dB or more on the average at 2000, 3000 and 4000 Hz | Expressly not permitted for this determination |
| Retest | 1910.95(g)(7)(ii) and 1904.10 | A retest within 30 days may be treated as the annual audiogram; a retest that does not confirm the shift removes the recording obligation | Not applicable |
| Revised baseline | 1910.95(g)(9) | The annual audiogram may replace the baseline where the professional reviewer finds the shift persistent, or finds significant improvement | Not applicable |
Three criteria for a changed audiogram, and they do not agree
| Criterion | Frequencies | Size | Written for |
|---|---|---|---|
| OSHA standard threshold shift | Average of 2000, 3000, 4000 Hz | 10 dB or more, either ear | Occupational noise surveillance |
| ASHA, single frequency | Any one test frequency, 0.25 to 20 kHz | 20 dB decrease | Cochleotoxic drug monitoring |
| ASHA, adjacent pair | Any two ADJACENT test frequencies | 10 dB decrease at both | Cochleotoxic drug monitoring |
| ASHA, loss of response | Three consecutive test frequencies | Response lost where previously obtained | Cochleotoxic drug monitoring |
A regulation’s arithmetic, and the table this engine cannot hold
OSHA’s standard threshold shift is one of the most consequential pieces of arithmetic in occupational health and one of the narrowest. 29 CFR 1910.95(g)(10)(i) defines it as a change from the baseline audiogram of an average of 10 dB or more at 2000, 3000 and 4000 Hz, in either ear. Three frequencies, one average, one comparison. There is no 500 Hz in it, no 1000 Hz, no 6000 or 8000 Hz, and the average is of the change rather than of the level.
Because the average of three shifts equals the shift of the two averages, the whole criterion can be computed from a baseline average and a current average, which is what this page does. The optional age correction is kept as a separate input for a reason. 1910.95(g)(10)(ii) permits an allowance for the contribution of ageing by correcting the annual audiogram according to Appendix F, and paragraph (n)(2) makes Appendix F informational rather than mandatory — so it is an option exercised rather than a step required, and whether it is applied can be what decides the answer. A 3 dB correction turns a 12 dB shift into a 9 dB one.
Appendix F is also a worked example of this engine’s limits, stated plainly rather than worked around. It is a lookup table by age, sex and frequency; there is no closed form for it, no interpolation is available here, and a curve fitted to it would be a plausible-looking number that is not the published correction. So the correction is taken from the reader, who has the table, exactly as a lung function page takes a predicted value from the report rather than reconstructing a reference equation.
One further distinction does real damage when it is missed. 29 CFR 1904.10 adds a second arithmetic element for its own purposes — a total hearing level of 25 dB or more on the same three-frequency average — and states that age adjustment may not be used for it. One of the two numbers is a change and may be age corrected; the other is a level and may not. This page shows both, separately, and renders no determination about either: the retest provision, the persistence of a shift, whether it is work-related and what has to be recorded are all decisions for the employer and the reviewing audiologist, otolaryngologist or physician under the regulation. Audiometric results are equipment- and calibration-dependent: the dB HL scale is defined against the reference equivalent threshold levels of the ISO 389 series for a particular transducer and coupler, so the same ear can read differently on two audiometers, and the BSA recommended procedure puts the uncertainty of any threshold measurement at no better than plus or minus 5 dB. Your own audiogram and the calibration standard it was recorded against govern, not this arithmetic.
Frequently asked questions
What is an OSHA standard threshold shift?
29 CFR 1910.95(g)(10)(i) defines it as a change in hearing threshold relative to the baseline audiogram of an average of 10 dB or more at 2000, 3000 and 4000 Hz in either ear. It is an average of the change at three frequencies, not a level, and the two ears are assessed separately.
How is the age correction applied?
Optionally, and from a table. 1910.95(g)(10)(ii) permits an allowance for the contribution of ageing by correcting the annual audiogram according to Appendix F, which is a lookup by age, sex and frequency, and paragraph (n)(2) makes Appendix F informational rather than mandatory. Read the 2000, 3000 and 4000 Hz corrections from Tables F-1 or F-2, average them, and enter that average.
Why does this calculator not include the Appendix F table?
Because the calculator engine has no table interpolation, and approximating a published correction table with a fitted curve would produce a plausible number that is not the regulation’s correction. The correction is therefore taken from the reader, who has the table, and shown as a separate input so its effect on the answer is visible.
What is the 25 dB rule, and is it the same as the shift?
No. 29 CFR 1904.10 adds a second element for its own purposes: a total hearing level of 25 dB or more on the average at 2000, 3000 and 4000 Hz. One is a change and the other is a level, they use the same three frequencies, and age adjustment is permitted for the shift but expressly not for the 25 dB determination.
Which frequencies are averaged, and why those?
2000, 3000 and 4000 Hz. They are the frequencies at which noise damage appears earliest and most consistently, which is why they were chosen for surveillance rather than the speech-frequency average. The consequence is that a loss at 6000 or 8000 Hz is invisible to this criterion however large it is.
Related calculators
References
- Occupational Safety and Health Administration. 29 CFR 1910.95 — Occupational noise exposure, paragraphs (g)(7) to (g)(10) and Appendix F. Washington, DC: US Department of Labor.
- Occupational Safety and Health Administration. 29 CFR 1904.10 — Recording criteria for cases involving occupational hearing loss. Washington, DC: US Department of Labor.
- American Speech-Language-Hearing Association. Guidelines for the Audiologic Management of Individuals Receiving Cochleotoxic Drug Therapy, GL1994-00003. Rockville, MD: ASHA, 1994.
- British Society of Audiology. Recommended Procedure: Surveillance Audiometry, OD104-65. Reading: BSA, 2017.
Not medical advice. For healthcare professionals and education. Reference intervals vary by laboratory and assay — always use your own laboratory's. Never base a dose or a treatment decision on this page alone. Full disclaimer at calcengines.com/disclaimer/