What should happen when an STS investigation finds that noise levels increased after the last monitoring survey?

Re-monitor immediately to establish current exposure levels, then review whether the hearing protection in use is adequate for current conditions. If not, evaluate engineering controls. OSHA requires feasible engineering or administrative controls before relying solely on HPE. A noise level increase from new equipment should trigger both re-monitoring and a control hierarchy review.

When Hearing Conservation Programs Stay Compliant but Fail

Q: What triggers OSHA's STS recordability requirement?

An STS becomes recordable when it is work-related and the worker's total hearing level is 25 dB HL or more above audiometric zero in the affected ear. Work-relatedness is determined by the employer with input from a reviewing professional, under 29 CFR 1904.10.

Q: How does NIOSH's recommended NRR derating work, and why does it matter?

Subtract 7 from the labeled NRR and divide by 2. For NRR 33, that yields 13 dB of estimated real-world attenuation. Workers with poor insertion technique may achieve considerably less. At high exposures, the difference between 8 dB and 13 dB of actual attenuation determines whether the effective dose stays within the permissible exposure limit.

Q: Is fit-testing worth implementing if it is not required by the standard?

For workers at high noise exposures, yes. Fit-testing determines whether a specific worker is achieving adequate attenuation from the device they use, which the NRR label cannot answer. NIOSH recommends it for all enrolled workers. Programs that have introduced fit-testing after STS investigations have consistently found workers with inadequate real-world attenuation despite program participation.

SITUATIONAL: Hearing Conservation Awareness

How Hearing Conservation Programs Stay Compliant While Workers Lose Their Hearing

OSHA’s occupational noise standard requires employers to monitor noise, enroll exposed workers, conduct annual audiograms, provide hearing protection, and train workers every year. These requirements are well-defined and most programs meet them on paper. What the standard does not require is proof that any of it is actually working. This article examines how that gap operates in practice, using documented patterns from OSHA enforcement data and published occupational health research.

How to Use This Article

This article draws on patterns documented in OSHA enforcement records, NIOSH field studies, and published occupational audiology research. Where specific numbers are cited, sources are linked. The program failures described are not hypothetical: they appear repeatedly across industries and facility sizes in the published literature on hearing conservation program effectiveness.

22M

US Workers Exposed to Hazardous Noise

OSHA estimates 22 million US workers face hazardous noise exposure at work each year. Occupational hearing loss costs more than $240 million annually in workers compensation alone.

Source: OSHA | Occupational Noise Exposure

~50%

Real-World NRR Loss

OSHA and NIOSH both recommend derating labeled NRR by 50 percent to estimate real-world attenuation. Workers who insert earplugs incorrectly achieve even less than the derated estimate.

Source: NIOSH | Noise and Hearing Loss Prevention

Most Common Recordable Illness

Hearing loss has been the most common occupational illness recorded on OSHA 300 logs for multiple consecutive years. It remains largely preventable with controls that are well understood and widely available.

Source: OSHA | 29 CFR 1910.95

The Compliance Gap the Standard Cannot Close

OSHA’s hearing conservation standard, 29 CFR 1910.95, is specific about what employers must do: monitor noise, enroll workers above 85 dBA, provide baseline and annual audiograms, supply hearing protection, and train workers on its use every year. A facility that checks all of those boxes is in compliance. What compliance does not require is verification that the hearing protection is actually working for the workers who are wearing it.

NIOSH field studies on hearing protector attenuation have consistently found that real-world attenuation falls well below labeled NRR values, often by 15 to 25 dB for foam earplugs. The main reason is insertion technique. Workers who receive a box of earplugs and a training presentation but have never had anyone watch them insert a plug and confirm the technique are, in many cases, receiving substantially less protection than the NRR label suggests. A program can complete 100 percent of its required activities and still not catch this.

Annual audiometric testing is where the gap eventually shows up. An STS, a standard threshold shift of 10 dB or more averaged at 2,000, 3,000, and 4,000 Hz compared to the baseline, is the signal. OSHA requires that confirmed STS cases be reported to workers within 21 days and that hearing protection be reviewed. What OSHA does not require is that the program investigate why the STS occurred. That investigation is left to the employer’s judgment, and published research on hearing conservation program effectiveness suggests it often does not happen.

What NIOSH Research Shows About Program Failure Patterns

NIOSH has published extensively on the gap between hearing conservation program compliance and hearing conservation program effectiveness. A 2011 NIOSH report on mining industry hearing loss found that workers in hearing conservation programs with high training completion rates and audiogram completion rates continued to show progressive hearing loss at rates inconsistent with adequate protection. The investigators found three common factors: noise monitoring that had not been updated after equipment changes, hearing protectors selected on labeled NRR without field verification of attenuation, and training that addressed program requirements without assessing whether workers could insert earplugs correctly.

Those three factors appear across industries. The pattern is not specific to mining. A 2014 study in the Journal of Occupational and Environmental Hygiene examined hearing conservation programs in manufacturing facilities and found that even in programs with full regulatory compliance, a substantial proportion of workers achieved personal attenuation ratings well below the levels needed to reduce their exposure to safe levels. The study concluded that fit-testing, which verifies the attenuation a specific worker achieves with a specific device, was the most reliable way to identify which workers were inadequately protected.

What Fit-Testing Shows That the NRR Label Does Not

A labeled NRR of 33 on a foam earplug represents attenuation measured in a laboratory with trained subjects achieving a perfect seal. OSHA’s recommended derating method divides the result by two after subtracting seven, giving an estimated real-world attenuation of roughly 13 dB. Field attenuation estimation systems measure the actual attenuation a specific worker achieves in real time, accounting for their ear canal anatomy, their insertion technique, and the specific device they are using.

In facilities where fit-testing has been introduced following STS investigations, it frequently identifies workers achieving personal attenuation ratings of 10 to 15 dB from earplugs rated at NRR 33. At noise exposures in the 95 to 100 dBA range, 10 to 15 dB of actual attenuation means the worker’s effective dose remains above the permissible exposure limit regardless of whether the program’s paperwork shows them as protected.

Source: NIOSH | Noise and Hearing Loss Prevention

The STS Trend Problem

OSHA requires STS cases to be reviewed for recordability each year. It does not require employers to compare STS rates across years or investigate whether the rate is increasing. Most programs review each year’s audiogram results independently, identify cases above the threshold, complete the required notifications and log entries, and file the results. The data that would reveal a worsening trend sits in three separate annual folders.

When OSHA inspects following a serious injury or illness, investigators frequently request multiple years of audiometric records and plot STS rates over time. What they find, according to OSHA enforcement summaries and industrial hygiene case literature, is that rising STS rates are common in facilities where the underlying causes have not been addressed. The year-over-year increase is visible in the data. It was never analyzed.

The implication for program management is practical: STS rate should be tracked as a rolling metric across years, broken down by work area and job classification. A single year’s rate has limited diagnostic value. Three years on one chart shows whether controls are working or whether something is eroding.

When Noise Monitoring Goes Stale

The standard requires re-monitoring when there is reason to believe exposure levels have changed. In practice, the trigger for re-monitoring is often the EHS manager’s memory of what changed, and that memory degrades over time. New equipment gets installed. A production shift gets added. A wall gets moved. The noise survey from four years ago no longer reflects what workers are exposed to.

OSHA enforcement records include numerous cases where the noise monitoring on file was several years old and the facility had made equipment changes since the survey. In those cases, workers were enrolled in the program based on exposure levels that no longer matched their actual work conditions, and their hearing protection was selected based on exposures that may have been significantly lower than what they were actually receiving. The program was compliant with the monitoring that existed. It was not protective against the noise that currently existed.

A practical approach: any time new noise-generating equipment is installed, treat that as a trigger for re-monitoring in the affected area before workers return to full production. Waiting for the next scheduled review cycle means operating with an unknown exposure for however long that cycle runs.

What Corrective Programs Actually Change

NIOSH guidance on restoring effectiveness to underperforming hearing conservation programs identifies several interventions that have demonstrated results in published follow-up studies. None of them are new requirements. They are existing program elements implemented with more rigor than the standard requires.

Intervention

What It Changes

Evidence

Fit-testing for workers at or above 90 dBA TWA

Identifies workers whose actual attenuation is below what their exposure requires; enables targeted retraining or device change

NIOSH recommends as best practice; multiple published studies show improved PAR after fit-test-informed retraining

Hands-on insertion training with observed competency check

Replaces awareness training with skill training; workers demonstrate correct technique before being marked complete

Consistent finding in occupational audiology literature: insertion technique errors are the primary cause of real-world NRR shortfall

Multi-year STS trend analysis in annual review

Makes rising STS rates visible before they cross a recordability threshold; enables earlier investigation

Standard practice in programs audited under CMS and MSHA requirements, both of which require trend analysis explicitly

Engineering control feasibility review tied to equipment changes

Ensures hierarchy of controls is applied when conditions change, not just at program inception

OSHA requires feasible engineering controls to be implemented; re-evaluating feasibility after equipment additions is consistent with that obligation

Source: NIOSH | Noise and Hearing Loss Prevention

Three Questions to Ask Your Own Program

Rather than running through a generic checklist, the following three questions tend to reveal whether a hearing conservation program is actually protecting workers or primarily generating documentation.

When was the last time anyone watched your workers insert earplugs, not to observe whether they were wearing them, but to confirm they were inserting them correctly? Annual training sign-in sheets do not answer this question. Fit-testing or observed insertion competency checks do.

If you plotted your STS cases from the past three years on a single chart, would the line be flat, declining, or rising? If the answer is rising, that trajectory is the finding that warrants investigation, not the individual cases that crossed a recordability threshold.

Has any noise-generating equipment been added or changed since the last noise monitoring survey? If the survey is more than two or three years old and the facility has changed, the exposure data the program is operating on may not reflect what workers are actually receiving.

Lessons from the Published Record

STS rate is the outcome metric. Everything else measures whether the program ran.

Training completion, audiogram scheduling, and earplug availability are activity metrics. They measure whether required program elements happened. STS rate measures whether those elements produced the result they were designed to produce. Programs that track only activity metrics can maintain spotless records while workers’ hearing progressively deteriorates. NIOSH has documented this pattern across multiple industries.

The audiogram is the early warning system. Acting on what it finds is the program.

Annual audiometric testing detects threshold shifts before workers experience noticeable hearing loss in daily life. The notification and log entry requirements that follow are not the response to a confirmed STS. They are the minimum regulatory requirements. The actual response is the investigation into why the shift occurred and what needs to change in the controls. That investigation is not required by the standard. It is what makes the standard worth following.

Prevention Checklist

Verify Protection Is Real

Fit-testing conducted for workers at 90 dBA TWA and above

Insertion technique observed and confirmed during training, not just sign-in completed

Multiple HPE types available; workers matched to device that achieves adequate PAR

Supervisor observation of HPE use during shifts documented periodically

Track Outcomes, Not Just Activities

STS rate tracked as a rolling metric across years, not just reviewed in isolation annually

STS cases mapped by work area and job classification to identify clustering

Year-over-year increase in STS rate triggers investigation before recordability threshold is crossed

STS rate included in regular EHS metrics, not buried in annual audiogram summaries

Keep Exposure Data Current

Noise monitoring repeated after new equipment installation or significant process changes

Engineering control feasibility reviewed whenever noise monitoring shows an increase

Noise survey reviewed at minimum every three years regardless of facility changes

Enrollment updated when re-monitoring changes which workers are above the action level

Key Takeaways

Compliance Does Not Require Proof That Protection Is Working

The standard’s requirements can all be met without anyone verifying that workers’ hearing protection is achieving the attenuation their exposure levels require. Fit-testing and observed insertion training fill that gap. Neither is mandated. Both are well-supported by NIOSH guidance and the published literature on what differentiates effective programs from compliant ones.

Rising STS Rates Rarely Appear Without an Identifiable Cause

When STS rates increase year over year in a facility with a functioning program, the cause is usually one of three things: noise levels have changed, hearing protection is being worn incorrectly, or a combination of both. A rising rate is a diagnostic signal. Finding what it is pointing to and fixing it is the work the standard does not require but effective programs do.

The Annual Audiogram Is Useful Only If Someone Acts on What It Shows

Annual audiometric testing is the most reliable tool a hearing conservation program has for detecting whether controls are protecting workers. What the standard requires to happen after a confirmed STS, notification and log review, is the minimum. Using STS findings to investigate program weaknesses, adjust controls, verify hearing protector fit, and track outcomes over time is what determines whether the audiogram produces any protective value beyond the data it generates.

Frequently Asked Questions

What triggers OSHA’s STS recordability requirement?
An STS becomes recordable on the OSHA 300 log when it is work-related and the worker’s total hearing level is 25 dB HL or more above audiometric zero in the same ear. Not every STS that shows up on an annual audiogram meets both criteria. The employer, with input from a reviewing professional, determines work-relatedness based on exposure history, non-occupational factors, and the pattern of the shift. OSHA provides guidance on the work-relatedness determination in its recordkeeping standard at 29 CFR 1904.10.

How does NIOSH’s recommended NRR derating work, and why does it matter for program management?
OSHA recommends subtracting 7 from the labeled NRR and dividing the result by 2 to estimate real-world attenuation. For a foam earplug rated NRR 33, this yields an estimated 13 dB of actual protection. Whether a worker achieves even 13 dB depends on insertion technique. Workers who cannot demonstrate correct insertion may be achieving considerably less. At exposures in the mid- to high-90 dBA range, the difference between 13 dB and 8 dB of actual attenuation is the difference between an effective dose that approaches or exceeds the permissible exposure limit and one that does not.

Is fit-testing worth implementing if it is not required by the standard?
For workers at high noise exposures, it is. The primary question fit-testing answers is whether a specific worker is actually achieving adequate attenuation from the device they are using, which the NRR label and the training sign-in sheet cannot answer. NIOSH recommends fit-testing for all workers enrolled in hearing conservation programs. Programs that have introduced fit-testing following STS investigations have consistently found workers whose actual attenuation fell well short of what their exposure required, in some cases across years of program participation.

What should happen when an investigation after a confirmed STS finds that noise levels increased after the last monitoring survey?
The immediate response is re-monitoring to establish current exposure levels, followed by a review of whether the hearing protection being used by affected workers is adequate for the actual current exposure. If current exposure levels require higher attenuation than the devices in use can reliably provide, engineering controls should be evaluated. OSHA requires feasible engineering or administrative controls to be used before relying solely on hearing protection equipment. A noise level increase caused by new equipment is exactly the type of change that should trigger both re-monitoring and a control hierarchy review.

Government and Regulatory Sources

Related VelSafe Articles

Using This in Your Program Review

The patterns described here, outdated noise monitoring, unverified hearing protector attenuation, STS data reviewed year by year without trend analysis, appear across industries and facility sizes in the published occupational health literature. They are not unusual. They persist because the standard does not require the practices that would catch them. Fit-testing, observed insertion training, and multi-year STS tracking are each straightforward to implement and well-supported by NIOSH guidance. None of them require a program overhaul. They require adding verification steps to activities the program is already running. Find more hearing conservation and worker safety resources at velsafe.com.