A baseline audiogram is the first valid hearing test given to an employee enrolled in a hearing conservation program. It records the employee's hearing thresholds before significant workplace noise exposure, and every later annual audiogram is compared against it to detect work-related hearing loss.
OSHA's occupational noise standard, 29 CFR 1910.95, requires baseline and annual audiograms for employees whose noise exposure reaches the action level of 85 decibels (dBA) as an 8-hour time-weighted average.
What Is a Baseline Audiogram?
An audiogram measures the quietest sound a person can hear at several frequencies in each ear. Under 29 CFR 1910.95(g), testing must include at least 500, 1000, 2000, 3000, 4000 and 6000 Hz. The baseline captures that profile at the start of the program so later changes can be measured accurately.
Audiometric tests must be performed by a licensed or certified audiologist, otolaryngologist or other physician, or by a technician who is certified by the Council for Accreditation in Occupational Hearing Conservation (CAOHC) or has otherwise shown competence, working under the responsible professional's supervision.
Key OSHA Requirements
Timing
The baseline must be established within 6 months of an employee's first exposure at or above the action level. If a mobile test van is used, the employer has up to 1 year, provided the employee wears hearing protectors after the first 6 months until the baseline is done.
Quiet period
Testing must be preceded by at least 14 hours without exposure to workplace noise. Hearing protectors may be used to meet this requirement. Employees should also be told to avoid high levels of non-occupational noise during that period.
Annual comparison
At least annually after the baseline, a new audiogram is compared with the baseline to check for a standard threshold shift (STS): an average change of 10 dB or more at 2000, 3000 and 4000 Hz in either ear. Age correction may be applied using the standard's tables.
Follow-up
If an STS is found, the employer must notify the employee in writing within 21 days, fit or refit hearing protectors, train the employee in their use, and require them to be worn. The employer may obtain a retest within 30 days and use it as the annual audiogram. A persistent STS may in some cases replace the baseline as the new reference.
Recordkeeping
Audiometric test records must be retained for the duration of the affected employee's employment. Under 29 CFR 1904.10, a hearing loss case is recordable on the OSHA 300 Log when the employee has an STS and the total hearing level is 25 dB or more above audiometric zero, averaged at 2000, 3000 and 4000 Hz in the same ear.
How to Manage Baseline Audiograms Step by Step
- Identify exposed employees. Use noise monitoring to find everyone at or above 85 dBA as an 8-hour TWA.
- Schedule baselines promptly. Track each new hire or transfer's first exposure date so the 6-month window is not missed.
- Brief employees on the quiet period. Remind them to wear protectors and avoid loud noise for 14 hours beforehand.
- Test with qualified providers. Confirm technician certification and audiometer calibration.
- Compare annually and follow up. Review each annual test against the baseline and act on every STS.
- Keep records secure. Store results as confidential medical information for the length of employment.
Common Mistakes to Avoid
- Testing after a noisy shift, which can show a temporary threshold shift and produce a poor baseline.
- Missing the 6-month deadline for new or transferred employees.
- Losing the original baseline, which makes later comparisons unreliable.
- Failing to notify employees of an STS within 21 days.
How SMS360 Helps
SMS360's Compliance tools help teams track recurring requirements and due dates, such as baseline and annual audiogram deadlines, so they are visible before they are missed. Related records can be organized alongside training and incident data across sites.
Frequently Asked Questions
When is a baseline audiogram required?
OSHA requires a baseline audiogram within 6 months of an employee's first exposure at or above 85 dBA as an 8-hour time-weighted average. If a mobile test van is used, the deadline extends to 1 year, as long as the employee wears hearing protection after the first 6 months.
What is a standard threshold shift?
A standard threshold shift is an average change in hearing of 10 dB or more at 2000, 3000 and 4000 Hz in either ear, compared with the baseline audiogram. It triggers written notification, hearing protector fitting and training under 29 CFR 1910.95.
Can a baseline audiogram be replaced?
Yes, in limited cases. The standard allows a revised baseline when a standard threshold shift is persistent or when hearing thresholds show significant improvement. The audiologist or physician reviewing the results makes that determination.
