Recording Hearing Loss on the OSHA 300 Log: The 25 dB STS Rule, Explained

Most cases land on your OSHA 300 Log the same way: a worker gets hurt, the treatment goes beyond first aid or they miss work, and you record it. Hearing loss does not work like that. It has its own special recording rule with its own numeric thresholds, its own retest window, and its own column on the log. If you run a hearing conservation program — and you do if your workers are exposed to noise at or above an eight-hour average of 85 decibels — this is the recordability question you are most likely to get wrong.

The rule lives at 29 CFR 1904.10, and the heart of it is a two-part test built around a 25-decibel threshold. The mechanics are precise, and the precision is exactly where employers stumble. Let's walk through it.

Why Hearing Loss Has Its Own Rule

Occupational hearing loss is gradual. A worker does not lose their hearing in a single instantaneous event the way they break a finger. The damage accumulates over months and years of noise exposure, and the only way to detect it is to compare audiograms over time. Because the general recording criteria in 1904.7 — medical treatment, days away, restricted duty — do not map cleanly onto a condition you detect with a hearing test rather than a treatment decision, OSHA wrote a dedicated rule with a measurable, audiometric trigger.

That trigger is not a single number. It is two numbers that both have to be true.

The Two-Part Test

Under 29 CFR 1904.10(a), you must record a hearing loss case on the OSHA 300 Log when both of the following are true:

1. The employee has experienced a work-related Standard Threshold Shift (STS) in one or both ears, and
2. The employee's total hearing level is 25 decibels or more above audiometric zero, averaged at 2000, 3000, and 4000 Hz, in the same ear or ears as the STS.

Both conditions have to be met, in the same ear, before the case is recordable. An STS alone is not enough. A 25 dB hearing level alone is not enough. You need the shift and the threshold together.

This is the single most important thing to understand about hearing loss recordkeeping, because the two conditions are measured differently and use different reference points — and one of them allows an adjustment the other does not.

What a Standard Threshold Shift Actually Is

A Standard Threshold Shift is defined in the occupational noise exposure standard at 29 CFR 1910.95(g)(10)(i): a change in hearing threshold, relative to the employee's baseline audiogram, of an average of 10 decibels or more at 2000, 3000, and 4000 Hz in one or both ears.

The reference point here is the employee's own baseline — the audiogram you established when they entered the hearing conservation program. You are measuring change over time against that personal baseline, not against any fixed standard.

It is worth knowing that an STS triggers obligations under the noise standard regardless of whether the case ever becomes recordable. When a worker shows an STS, 1910.95 requires you to notify them in writing within 21 days and to take protective follow-up steps. That obligation is separate from the 300 Log. Recordability only enters the picture when the second condition — the 25 dB hearing level — is also met.

The 25 dB-From-Zero Check

The second condition uses a different reference point entirely. Instead of comparing against the employee's baseline, you look at their current audiogram and measure against audiometric zero — the standardized reference for normal hearing.

Using the current audiogram, average the hearing level at 2000, 3000, and 4000 Hz in the affected ear. If that average is 25 dB or more, the second condition is met.

This is where the reference points matter. The STS measures how much the employee's hearing has changed from their own baseline. The 25 dB check measures how much total hearing loss they have accumulated against the universal zero point. A worker can have a recordable-sized shift without yet reaching 25 dB total, and the case is not recordable until both are true.

Age Adjustment: Allowed for One, Not the Other

Here is the rule that catches even experienced safety managers. Hearing naturally declines with age, and OSHA lets you account for that — but only for one half of the test.

When you are determining whether an STS has occurred, you may age-adjust the employee's current audiogram using Tables F-1 (for males) or F-2 (for females) in Appendix F of 29 CFR 1910.95. This recognizes that some of the shift from baseline is ordinary aging rather than occupational noise.

When you are determining whether the employee's total hearing level is 25 dB or more above audiometric zero, you may not use an age adjustment. The 25 dB check is taken straight from the current audiogram, unadjusted.

Mixing these up is the most common technical error in hearing loss recordkeeping. Age adjustment can shrink a shift below the 10 dB STS threshold and legitimately keep a case off the log. It cannot be used to shrink the 25 dB total hearing level. Apply it to the first condition only.

A Worked Example

Consider a 47-year-old male production worker in a hearing conservation program. His baseline audiogram, averaged at 2000, 3000, and 4000 Hz in his right ear, was 12 dB. His current annual audiogram, same ear, same frequencies, averages 28 dB.

Step one — is there an STS? The raw shift is 28 minus 12, or 16 dB — above the 10 dB STS threshold. But you are allowed to age-adjust here. Using the male age-correction values in Table F-1, you subtract the age-related portion of the shift. Suppose the age correction reduces the shift to 13 dB. That is still 10 dB or more, so a work-related STS has occurred. (If the age adjustment had brought the shift below 10 dB, there would be no recordable STS and the analysis would stop.)

Step two — is the total hearing level 25 dB or more? Here you use the current audiogram with no age adjustment. The unadjusted average is 28 dB, which is above 25 dB. The second condition is met.

Step three — is it work-related? Apply the standard 1904.5 work-relatedness rules (covered below). If yes, both conditions are satisfied and the case is recordable.

Both thresholds met, same ear, work-related: this case goes on the 300 Log.

Work-Relatedness for Hearing Loss

Hearing loss uses the same work-relatedness analysis as every other case under 29 CFR 1904.5. If an event or exposure in the work environment either caused, contributed to, or significantly aggravated the hearing loss, it is work-related and presumed recordable once the audiometric thresholds are met.

The rule also gives you a specific off-ramp. Under 1904.10(b)(6), if a physician or other licensed health care professional determines that the hearing loss is not work-related — for example, because it stems from a non-occupational cause such as an inner-ear condition, a congenital factor, or a hobby like recreational shooting — you do not record the case. The audiologist who reviews your audiograms can help make the work-relatedness determination, though under the recordkeeping rule any licensed health care professional may do so.

Our decision tree for OSHA recordability walks through the general work-relatedness analysis that applies here.

The 30-Day Retest Window Most Employers Skip

This provision can save you from recording temporary or erroneous shifts, and many employers never use it.

Under 1904.10(b)(4), if you retest the employee's hearing within 30 days of the first test and the retest does not confirm the recordable STS, you are not required to record the case. Hearing thresholds can fluctuate — a worker who had a noisy weekend, an ear infection, or simply a bad test day can show an apparent shift that a clean retest does not confirm.

If the retest does confirm the recordable STS, you must record the case within seven calendar days of the retest.

There is also a back-end correction. If you record a case and later audiograms show the shift was not persistent — that the employee's hearing recovered — you may line out or erase the entry. This keeps temporary shifts from permanently inflating your injury and illness data.

Filling Out the 300 Log

When a hearing loss case is recordable, you check the dedicated hearing loss column on the OSHA 300 Log — it is one of the specific illness columns, separate from injuries and from "all other illnesses." You then classify the case by outcome. Most recordable hearing loss cases are "other recordable cases" because they do not involve days away from work or restricted duty, but you classify based on the actual outcome for that worker.

Because hearing loss is tracked in its own column, it also rolls up separately on your 300A annual summary. If you are working through the log mechanics, our step-by-step 300 Log guide covers each column, and the 300A annual summary guide covers how the column totals carry forward.

One edge case worth flagging: the construction industry is subject to the 1904.10 recordkeeping requirement even though the full hearing conservation program requirements of 1910.95 do not apply to construction in the same way. If you are a construction employer and you have audiometric data showing a recordable STS, you record it.

Why This Matters Beyond the Paperwork

Occupational hearing loss is one of the most common work-related illnesses in the United States. According to CDC and NIOSH surveillance data, about 11 percent of all workers report some hearing difficulty, and the rate is far higher among noise-exposed workers — roughly 23 percent, compared with about 7 percent of workers not exposed to occupational noise. It is also entirely preventable, which is why OSHA built a measurable, audiogram-based recording rule around it rather than folding it into the general criteria.

Accurate recording does two things for a small employer. It keeps you compliant with 1904.10, and it gives you the data to see whether your hearing conservation program is actually working. A pattern of recordable shifts in one work area is a signal worth acting on before it becomes a pattern of permanent loss.

The Bottom Line

When an audiogram comes back showing a possible shift, work through three questions in order. Is there a work-related Standard Threshold Shift — a 10 dB or greater average shift from baseline at 2000, 3000, and 4000 Hz, after any allowable age adjustment? Is the total hearing level 25 dB or more above audiometric zero on the current audiogram, with no age adjustment? And is the loss work-related under 1904.5? If all three are yes — in the same ear — check the hearing loss column on the 300 Log within seven days of a confirming retest.

Get the age-adjustment rule right, use the 30-day retest window when a shift looks questionable, and keep the two thresholds straight. Those three habits resolve nearly every hearing loss recordkeeping question a small employer will face.