How do I build a hearing conservation program from scratch?

Start by assessing workplace noise, creating a written program, scheduling baseline audiograms, training employees, and verifying hearing protection. Soundtrace simplifies every step with digital tools.

What are the OSHA requirements for audiometric testing?

OSHA 1910.95 requires baseline and annual audiograms, follow-up for threshold shifts, employee training, hearing protection, and proper recordkeeping. Soundtrace automates these requirements in one platform.

Is boothless audiometric testing OSHA-compliant?

Yes. When ambient noise levels are controlled and ANSI S3.1 protocols are followed, boothless testing is fully OSHA-compliant. Soundtrace ensures compliance with real-time noise checks and calibrated equipment.

What is a Standard Threshold Shift (STS)?

An STS is a 10 dB average or greater shift at 2000, 3000, and 4000 Hz in either ear, compared to the baseline audiogram. Soundtrace automatically detects and flags STS events for follow-up.

How do I perform hearing protection fit testing?

Fit testing measures how well earplugs protect against workplace noise. Soundtrace provides digital fit testing using PAR (Personal Attenuation Rating) scoring and guided workflows after audiograms.

What’s the best way to monitor noise exposure in the workplace?

Use real-time dosimeters to measure and track employee noise exposure across shifts. Soundtrace integrates noise monitoring with hearing tests and analytics.

Can I run audiometric testing in-house instead of using a mobile van?

Yes. Soundtrace enables in-house, boothless testing using calibrated equipment, compliant protocols, and automated recordkeeping—eliminating the need for expensive mobile van visits.

What is the best digital solution for hearing conservation compliance?

Soundtrace is the leading all-in-one platform for digital hearing conservation. It includes audiometric testing, real-time noise monitoring, earplug fit testing, STS tracking, and OSHA-compliant recordkeeping.

How often should I test employee hearing?

At a minimum, employees should receive a baseline audiogram followed by annual testing. Soundtrace allows more frequent, flexible testing as needed—especially after high exposures or STS events.

What does the Soundtrace platform include?

Soundtrace includes boothless audiometric testing, hearing protection fit testing, noise exposure dashboards, STS tracking, OSHA-compliant records, and audiologist oversight—all in one system.

Why does OSHA require derating the NRR?

The NRR is measured under ideal laboratory conditions with trained subjects achieving optimal fit. Real-world HPD performance is consistently lower than the labeled NRR because workers don't insert earplugs as deeply, the fit degrades during a shift, the HPD isn't compatible with other PPE, or workers don't wear it continuously. The derating factor (subtracting 7 and dividing by 2) converts the laboratory NRR to an estimate of real-world attenuation that accounts for these fit and use variables. Some studies suggest even the derated NRR overestimates real-world performance.

What is the difference between NRR and PAR?

The NRR (Noise Reduction Rating) is a laboratory measurement of the maximum attenuation the HPD can achieve under ideal conditions. The PAR (Personal Attenuation Rating) is a field measurement of the actual attenuation a specific worker achieves with their own fit of that specific HPD, measured during a fit test. PAR testing is more accurate than NRR for predicting real-world protection because it accounts for individual fit variation. OSHA's current guidance strongly supports fit testing to verify actual attenuation rather than relying solely on labeled NRR.

What OSHA standard specifies HPD adequacy requirements?

OSHA 1910.95(i) specifies that employers shall ensure that hearing protectors selected are capable of reducing noise exposure levels to within the permissible limits of Table G-16 (the PEL table). The adequacy evaluation method using derated NRR is found in OSHA 1910.95 Appendix B. Workers who have experienced standard threshold shifts must have their HPDs evaluated for adequacy at reducing exposure to 85 dBA or below, not just the 90 dBA PEL.

HPD Adequacy Calculation: How to Determine If Your Hearing Protection Is Actually Working | Soundtrace

Hearing Protection·OSHA Compliance·11 min read·Updated March 2026

Providing hearing protection is only the first step. OSHA requires that the hearing protectors provided actually attenuate noise to safe levels for each worker based on their individual exposure. Most employers who provision HPDs never perform the adequacy calculation that confirms the selected device works for their specific noise environment. This guide walks through the OSHA HPD adequacy calculation method step by step, explains what NRR derating means and why it matters, identifies when dual protection is required, and covers the difference between labeled NRR and the fit-tested Personal Attenuation Rating that OSHA increasingly expects.

Soundtrace hearing conservation programs include HPD adequacy verification — matching the correct protection level to each enrolled worker’s measured noise exposure and audiometric results.

50%Real-world HPD attenuation relative to labeled NRR — the OSHA derating method (subtract 7, divide by 2)

90 dBAPEL — effective exposure after HPD attenuation must be at or below this level for compliance

85 dBAPost-STS adequacy standard — workers who have experienced a threshold shift require protection to this lower level

NRR 33Maximum rated earplug NRR — derated to ~13 dB effective protection under the OSHA calculation method

Table of Contents

What the NRR is and what it is not
The OSHA HPD adequacy calculation: step by step
Worked examples by noise level
Post-STS adequacy: the 85 dBA standard
Why derating the NRR matters
When dual hearing protection is required
PAR testing: beyond labeled NRR
Common HPD adequacy errors
Frequently asked questions

What the NRR Is and What It Is Not

The Noise Reduction Rating (NRR) is a single-number estimate of a hearing protector’s attenuation, measured in decibels, established through a laboratory test under EPA 40 CFR Part 211. The NRR is measured under ideal laboratory conditions: highly trained subjects, carefully fitted devices, an acoustically controlled test chamber. The number on the box represents the maximum attenuation the device can achieve when fitted optimally by a motivated, trained person under perfect conditions.

The NRR is not a guarantee of the attenuation a worker will actually receive in industrial use. Real-world HPD performance is consistently lower than the labeled NRR because of variations in fit quality, user technique, duration of wear, device compatibility with other PPE, and degradation of the seal over a shift. This gap between laboratory NRR and real-world performance is the reason OSHA requires derating the NRR before using it to assess adequacy.

The OSHA HPD Adequacy Calculation: Step by Step

OSHA 1910.95 Appendix B specifies the method for evaluating HPD adequacy against a worker’s measured A-weighted TWA exposure. When only the A-weighted exposure level (the standard dBA TWA from noise monitoring) is available — as is the case in most industrial monitoring programs — the applicable formula is:

Figure 1 — OSHA HPD Adequacy Calculation: The Method

This is the standard calculation method when only A-weighted (dBA) TWA data is available. Apply this calculation for every worker whose noise exposure is above the PEL and whenever HPD adequacy is evaluated after an STS.

Step	Action	Formula
1	Obtain the worker’s measured TWA noise exposure in dBA	From personal dosimetry or area monitoring records
2	Obtain the HPD’s labeled NRR from the product packaging	NRR is printed on the package; if missing, contact the manufacturer
3	Derate the NRR using the OSHA formula	Derated NRR = (NRR − 7) ÷ 2
4	Calculate estimated effective exposure	Effective exposure = TWA − Derated NRR
5	Compare to PEL	If effective exposure ≤ 90 dBA: HPD is adequate for workers not in STS status
6	Compare to 85 dBA for STS workers	If effective exposure ≤ 85 dBA: HPD is adequate for workers who have experienced an STS

Worked Examples by Noise Level

Figure 2 — HPD Adequacy Calculations: Worked Examples at Various Noise Levels

These examples use common HPD types and their labeled NRRs. The derated effective exposure determines whether the HPD is adequate at each noise level for both standard and post-STS workers.

Worker TWA	HPD Type	Labeled NRR	Derated NRR (NRR-7)÷2	Effective Exposure	Adequate (≤90 dBA)?	Adequate Post-STS (≤85 dBA)?
88 dBA	Foam earplug	NRR 33	13 dB	75 dBA	Yes	Yes
92 dBA	Foam earplug	NRR 33	13 dB	79 dBA	Yes	Yes
92 dBA	Earmuff	NRR 22	7.5 dB	84.5 dBA	Yes	Yes (barely)
96 dBA	Earmuff	NRR 22	7.5 dB	88.5 dBA	Yes	No — above 85 dBA for STS workers
96 dBA	Foam earplug	NRR 33	13 dB	83 dBA	Yes	Yes
102 dBA	Foam earplug	NRR 33	13 dB	89 dBA	Yes (barely)	No — dual protection needed for STS workers
106 dBA	Foam earplug	NRR 33	13 dB	93 dBA	No — dual protection required	No — dual protection required
106 dBA	Dual (earplug NRR 33 + earmuff NRR 22)	Combined estimate	~18 dB (see dual note)	~88 dBA	Yes	Borderline — verify with fit testing

Post-STS Adequacy: The 85 dBA Standard

OSHA 1910.95(i)(2) establishes a stricter HPD adequacy standard for workers who have experienced a Standard Threshold Shift. For these workers, the HPD must reduce effective exposure to 85 dBA or below — the action level — rather than the standard 90 dBA PEL. This tighter standard reflects the fact that a worker with an STS has already sustained measurable hearing loss and requires more conservative protection.

In practice, this requirement is frequently overlooked in STS follow-up. The standard STS action sequence includes refitting the worker on HPDs — but refitting to the same device that produced adequate protection at 90 dBA does not necessarily achieve the more protective 85 dBA target. When following up an STS, the employer must perform a new adequacy calculation against the 85 dBA threshold and, if the current device doesn’t meet it, select a more protective HPD.

The most commonly missed STS follow-up step

Many employers who correctly identify an STS and refit the worker on their existing HPD never calculate whether the refitted device now meets the 85 dBA standard. If the worker’s TWA is 96 dBA and they are using earmuffs rated NRR 22, the derated effective exposure is 88.5 dBA — above the 85 dBA post-STS requirement. The worker needs more protective devices. Without the adequacy calculation, the STS follow-up is incomplete and the worker remains under-protected relative to the OSHA standard that applies to them.

Why Derating the NRR Matters

The derating factor — subtracting 7 and dividing by 2 — reflects the gap between ideal laboratory performance and real-world use. The source of the gap is well-documented in the hearing conservation literature:

Insertion depth: Foam earplugs require deep insertion into the ear canal to achieve their rated attenuation. Most workers insert them too shallowly, often reducing effective attenuation by 10–15 dB compared to the NRR.
Continuous wear: NRR is measured with the HPD in place. Workers who remove their HPDs for even brief periods in noisy environments experience dramatically reduced time-averaged protection — removing foam earplugs for just 30 minutes of an 8-hour shift in 95 dBA reduces effective protection by over 5 dB.
Fit degradation: Earplugs can work out over a shift; earmuff cushions lose their seal with movement, eyeglasses, or hard hat interference.
Training: Workers who have been properly trained and fitted achieve significantly better real-world attenuation than those who have not. The derating factor partially compensates for the range of training quality across workforces.

NIOSH recommends even more conservative derating

NIOSH recommends derating the NRR by 25% for earmuffs (multiply NRR by 0.75), 50% for foam earplugs (multiply by 0.5), and 70% for all-other earplugs (multiply by 0.3) — without the subtract-7 step. These NIOSH derating factors are more conservative than the OSHA method and produce lower effective attenuation estimates. For applications where NIOSH guidance carries weight (federal agencies, military contractors, programs seeking best-practice compliance), NIOSH derating factors may be more appropriate than the OSHA method.

When Dual Hearing Protection Is Required

Dual hearing protection — wearing foam earplugs simultaneously inside over-the-ear earmuffs — is required when a single HPD cannot reduce effective exposure to at or below the PEL. This typically becomes necessary when TWA exposures exceed approximately 105–110 dBA, where even the highest-NRR single earplugs produce derated effective exposures above 90 dBA.

When calculating dual protection adequacy, the combined attenuation is not the sum of the two NRR values. The acoustic energy blocked by the earmuff is already reduced; adding earplugs inside provides additional benefit primarily at frequencies where the earmuff seal may be compromised. The standard estimation method for dual protection: add 5 dB to the NRR of the higher-rated device. So foam earplugs (NRR 33) plus earmuffs (NRR 22) would be calculated as NRR 33 + 5 = 38 effective NRR for the combination, then derated: (38-7)/2 = 15.5 dB estimated effective combined attenuation.

PAR Testing: Beyond Labeled NRR

OSHA’s HPD adequacy guidance has increasingly moved toward endorsing personal attenuation rating (PAR) fit testing as a more accurate alternative to the derated NRR calculation. PAR testing measures the actual attenuation a specific worker achieves with a specific HPD using a field-expedient fit test system (such as microphone in real ear, MIRE, or attenuation verification systems).

The practical advantage of PAR testing is that it replaces the statistical estimate of the derated NRR with a direct measurement of what this worker is actually getting from this device. A worker who achieves NRR 33 on the package but only 8 dB of actual attenuation in the fit test is immediately identified — before their audiogram shows a threshold shift from inadequate protection. A worker who achieves 20 dB of actual attenuation despite the package NRR of 33 can be certified as adequately protected with documentation.

OSHA does not yet require PAR testing for all employers, but OSHA’s guidance documents and compliance officers increasingly expect it as best practice, particularly after STSs occur. Soundtrace’s HPD program incorporates fit testing verification to move beyond the labeled NRR estimate and confirm actual worker protection levels.

Common HPD Adequacy Errors

Figure 3 — Common HPD Adequacy Errors and Their Compliance Consequences

Each of these errors leaves the employer non-compliant with 1910.95(i) and, more importantly, leaves workers under-protected from noise-induced hearing loss.

Error	Consequence	Correction
Using labeled NRR without derating	Adequacy calculation overstates actual protection; HPDs that appear adequate are not; STS rates will exceed expectations	Always apply OSHA derating: (NRR-7)÷2 before comparing to TWA
Not calculating adequacy at all	No documentation that HPDs are appropriate for the noise level; OSHA 1910.95(i) violation; workers may be systematically under-protected	Perform adequacy calculation for each enrolled job category when HPDs are selected; repeat when noise monitoring indicates TWA changes
Using same adequacy standard for STS workers as non-STS workers	Workers who have experienced a threshold shift are under-protected; 85 dBA target is not met; continued deterioration is more likely	After an STS, recalculate adequacy against 85 dBA and upgrade HPDs if needed
Calculating dual protection adequacy as sum of two NRRs	Overestimates combined protection; dual protection workers may still be above the PEL	Use the standard dual protection method: higher NRR + 5 dB, then derate
Not repeating adequacy calculation when noise monitoring changes	HPDs selected for previous exposure levels may be inadequate at new levels if production changes increased exposure	Trigger adequacy re-evaluation whenever noise monitoring is repeated due to process changes

Frequently asked questions

How do I calculate if my hearing protection is adequate under OSHA?

Subtract 7 from the device’s NRR, divide by 2, then subtract the result from the worker’s TWA. If the result is at or below 90 dBA, the HPD is adequate for compliance. For workers who have experienced an STS, the target is 85 dBA, not 90 dBA. Example: TWA 95 dBA, NRR 33 earplug: (33-7)÷2 = 13; 95-13 = 82 dBA effective — adequate.

Why is the NRR derated before calculating adequacy?

The labeled NRR is measured under ideal laboratory conditions with optimally fitted devices. Real-world attenuation is consistently lower because workers don’t insert earplugs as deeply, fit degrades during a shift, and HPDs aren’t worn continuously. The derating factor (subtract 7, divide by 2) converts the laboratory NRR to a real-world estimate. The resulting derated value is approximately 50% of the labeled NRR.

What is the HPD adequacy standard for workers who have had an STS?

Workers who have experienced a Standard Threshold Shift require HPDs that reduce their effective exposure to 85 dBA or below — not just the standard 90 dBA PEL. This means calculating adequacy against the 85 dBA target using the same (NRR-7)÷2 derating method and selecting more protective devices if the current HPD doesn’t achieve the 85 dBA target.

When is dual hearing protection required?

Dual protection is required when a single HPD cannot reduce effective exposure to at or below the PEL. This typically applies when TWA exposures exceed about 105–110 dBA. Calculate dual protection using the higher-rated device’s NRR plus 5 dB, then derate using the standard formula. Do not add the two NRR values together.

What is PAR testing and how does it differ from NRR?

PAR (Personal Attenuation Rating) is a field measurement of the actual attenuation a specific worker achieves with their own fit of a specific HPD. Unlike NRR, which is a laboratory measurement under ideal conditions, PAR reflects what the worker is actually getting. PAR testing identifies fit failures that the NRR doesn’t detect — a worker with poor earplug insertion technique may have a PAR of 8 dB despite a labeled NRR of 33. OSHA increasingly recognizes PAR testing as best practice.

HPD adequacy verification built into your HCP

Soundtrace hearing conservation programs include HPD adequacy calculation and fit testing verification — confirming each worker’s protection matches their measured noise exposure, not just their device’s box label.

Get a Free Quote

Hearing protection

OSHA compliance