The Noise Reduction Rating on a package is a laboratory average. It tells you what trained subjects achieved with expert insertion in a calibrated booth — not what your workers receive in the field. NIOSH research consistently shows average foam earplug users achieving 10–15 dB of real-world attenuation against a labeled NRR of 28–33 dB. In January 2025, NIOSH formalized what the research has long shown: individual, quantitative fit testing is now the recommended standard for evaluating HPD attenuation, replacing the NRR derating approach that has been the default since 1998. HPD fit testing — measuring the actual attenuation a specific worker achieves with a specific device — is the only method that closes this gap at the individual level, and it is the most defensible documentation of OSHA 1910.95(i) compliance.
Soundtrace HPD fit testing uses a REAT-based system to generate a Personal Attenuation Rating for each worker, linked to their audiometric testing history and noise exposure data in one unified profile — part of a complete OSHA 1910.95 hearing conservation program.
A worker in a 100 dBA environment wearing NRR-33 earplugs may be receiving only 10–15 dB of protection — leaving them at an effective exposure of 85–90 dBA — if insertion is poor. The audiogram will eventually detect this. Fit testing detects it before the threshold shifts.
- NIOSH 2025: individual fit testing is now the recommended standard
- Why the NRR fails in the field
- OSHA HPD requirements under 1910.95
- How OSHA calculates HPD adequacy
- PAR adequacy calculator
- What HPD fit testing measures
- REAT vs. MIRE: the two methods
- Reading PAR results and fit tiers
- The post-STS HPD obligation
- Setting up an in-house fit testing program
- When fit testing must be repeated
- Dual hearing protection
- Frequently asked questions
NIOSH 2025: Individual Fit Testing Is Now the Recommended Standard
In January 2025, NIOSH issued a Science Policy Update formally superseding the NRR derating guidance from its 1998 Criteria for a Recommended Standard — Occupational Noise Exposure. The update is direct: NIOSH now recommends employers use individual, quantitative fit testing to evaluate the attenuation received by workers from their hearing protection devices in place of the NRR derating scheme.
The 1998 document had acknowledged that individual fit testing was ideally what employers should do, but commercially available fit-test systems did not exist at the time. As of 2025, with multiple compliant systems available under ANSI S12.71-2018, NIOSH has removed that caveat. The update explicitly states that fit testing provides a Personal Attenuation Rating that accurately reflects the level of sound reduction an individual worker receives while wearing a specific hearing protector.
NIOSH does not favor a specific method. Any system that computes a PAR per the current ANSI S12.71 standard satisfies the recommendation. The update does not change OSHA enforcement authority — OSHA 1910.95 remains the enforceable standard — but it signals where regulatory expectations are heading. See: OSHA 1910.95 hearing conservation program requirements.
▶ Bottom line: NRR derating is no longer the NIOSH-recommended approach. Employers who continue to rely solely on label math without fit testing are operating below the current NIOSH guidance standard — which matters for both compliance posture and workers’ compensation exposure.
Why the NRR Fails in the Field
The Noise Reduction Rating is determined under ANSI S12.6 laboratory conditions. Subjects are coached by audiologists, insert devices with professional guidance, and are tested in ideal acoustic environments. The NRR represents 98th-percentile laboratory performance. Real workplace conditions are not laboratory conditions. Workers insert foam earplugs in seconds without supervision, often without rolling the foam tightly enough, inserting it deeply enough, or allowing sufficient expansion time. Studies by NIOSH and independent researchers consistently show average real-world earplug insertion providing 10–15 dB of attenuation against labeled NRRs of 28–33 dB. See: NIOSH vs. OSHA noise exposure limits.
Foam earplugs show the largest NRR-to-field gap because attenuation depends entirely on insertion technique. NIOSH recommends derating all foam earplug NRR values by 50% for field use — and as of 2025, recommends individual fit testing entirely in place of derating.
OSHA HPD Requirements Under 1910.95
OSHA 1910.95(i) requires employers to provide hearing protection devices at no cost to all enrolled employees. The requirement has three tiers:
- Action level (85 dBA TWA): HPD must be made available. Use is voluntary unless mandatory use applies.
- PEL (90 dBA TWA): HPD use is mandatory. Device must attenuate TWA to 90 dBA or below.
- Post-STS: HPD use mandatory. Device must attenuate TWA to 85 dBA or below — a tighter standard than the PEL.
OSHA requires a variety of HPD options — not a single model. Workers must choose from different types. Under 1910.95(i)(4), HPDs must be properly fitted and employees instructed in their use and care. Fit testing documentation directly supports this obligation. See: OSHA 1910.95 complete employer guide.
Simply providing an HPD does not satisfy 1910.95(i). The HPD must actually attenuate noise to safe levels for each enrolled worker. Individual fit testing using the PAR method provides a worker-specific demonstration that this obligation has been met — and is now what NIOSH recommends.
How OSHA Calculates HPD Adequacy
OSHA Appendix B provides two methods for calculating whether an HPD adequately protects a worker at a given TWA. Both use the labeled NRR:
Method A (subtract 7, divide by 2): For a 95 dBA TWA worker using an NRR-33 earplug: (33 − 7) ÷ 2 = 13 dBA protection. Protected exposure = 82 dBA. Passes standard PEL compliance.
Method B (NIOSH 50% derating): NRR-33 derated to 16.5 dB. Protected exposure = 78.5 dBA. More conservative — but NIOSH now recommends replacing this calculation with a directly measured PAR.
| Worker TWA | NRR 33 (Method A) | NRR 33 (50% derate) | PAR 22 (fit tested) | Post-STS (≤85 dBA)? |
|---|---|---|---|---|
| 88 dBA | 75 dBA ✓ | 71.5 dBA ✓ | 66 dBA ✓ | ✓ All pass |
| 94 dBA | 81 dBA ✓ | 77.5 dBA ✓ | 72 dBA ✓ | ✓ All pass |
| 100 dBA | 87 dBA ✓ (PEL only) | 83.5 dBA ✓ | 78 dBA ✓ | ✗ Method A fails (87>85) |
| 105 dBA | 92 dBA ✗ | 88.5 dBA ✗ | 83 dBA ✓ | ✗ Only fit-tested PAR passes |
PAR Adequacy Calculator
Enter a worker’s measured TWA and their fit-tested PAR to see whether the device is adequate — under both the standard and post-STS thresholds.
What HPD Fit Testing Measures
Fit testing measures the Personal Attenuation Rating — the actual attenuation a specific worker achieves with a specific HPD on a specific date, using their normal insertion technique. Two distinctions from the NRR:
- Individual vs. population: NRR reflects a population of trained laboratory subjects. PAR reflects this worker’s actual technique with this device today.
- Habitual vs. coached: Workers should insert earplugs as they would on the production floor — not coached to achieve optimal insertion before the test.
Run the test with habitual insertion to capture actual field performance. If the worker fails, coach on correct technique and retest — documenting both the pre-coaching and post-coaching PAR. This captures the protection gap, provides the training, and creates the complete compliance record in one session.
REAT vs. MIRE: The Two Recognized Methods
| Feature | REAT (Real-Ear Attenuation at Threshold) | MIRE / F-MIRE (Microphone in Real Ear) |
|---|---|---|
| How it works | Measures hearing thresholds with and without HPD. Threshold shift = PAR. | Probe microphone at ear canal measures sound level inside vs. outside HPD simultaneously. |
| Equipment | Calibrated audiometer — same hardware as annual audiogram | Dedicated probe microphone system. Separate from audiometric hardware. |
| Test time | 8–12 min; runs after audiogram in same session | 3–5 min; standalone session |
| Gold standard | ✓ Directly measures auditory benefit at threshold | Physical measurement; good correlation for most device types |
| ANSI S12.71 compliant | ✓ Yes | ✓ Yes |
| Used by Soundtrace | ✓ Yes | — |
REAT uses the same audiometric hardware already in place for the annual audiogram. Open-ear thresholds from the audiogram serve as the REAT baseline — occluded thresholds are measured immediately after with the HPD inserted. One session, two compliance records, no additional equipment teardown.
Reading PAR Results and Fit Quality Tiers
A PAR must be interpreted against the worker’s noise exposure. The adequacy formula: Worker TWA − PAR = protected exposure. Standard threshold: ≤90 dBA. Post-STS threshold: ≤85 dBA.
PAR brings protected exposure to or below the required level. Strong margin (≥5 dB) preferred. Document, schedule annual retest.
PAR meets minimum adequacy but with narrow margin (<5 dB). Retraining on insertion technique recommended before next cycle.
PAR fails to bring protected exposure to required level. Retrain and retest immediately. Device change if PAR remains inadequate.
The Post-STS HPD Obligation
A confirmed Standard Threshold Shift triggers a specific HPD response under 1910.95(g)(8)(ii): refit the worker on HPD or provide a more protective device if the current device is inadequate. The post-STS adequacy standard tightens from 90 dBA to 85 dBA under 1910.95(i)(3). A device that passed the standard adequacy calculation may no longer be adequate after an STS.
Refitting a worker after an STS without documenting that the new HPD achieves the 85 dBA adequacy threshold is a citable gap under 1910.95(g)(8)(ii) and (i)(3). A PAR result from a fit test is the exact documentation OSHA looks for on inspection. See: OSHA hearing conservation violations and penalties: 2026.
▶ Bottom line: After a confirmed STS, fit testing the new HPD produces a dated, worker-specific PAR that proves the upgraded device meets the 85 dBA post-STS adequacy threshold.
Setting Up an In-House HPD Fit Testing Program
Soundtrace handles the full fit testing workflow as a managed service, but for employers who want to run in-house testing, the setup requirements are straightforward. ANSI S12.71 specifies what systems must do; NIOSH 2025-104 confirms that any compliant system satisfies the federal recommendation.
The fit-test system must compute a PAR per the current ASA/ANSI S12.71-2018 (R2022) standard. This is the compliance threshold NIOSH 2025-104 references. Both REAT and MIRE systems qualify if they meet the standard.
A licensed audiologist or physician must be designated as Professional Supervisor under 1910.95(g)(3). The PS must be available for clinical review of flagged results, STS determinations, and medical referrals. Soundtrace provides PS coverage as part of its managed service.
For REAT, the ambient noise level must meet ANSI S3.1 limits at the test frequencies — the same requirement as the annual audiogram. See: ambient noise compliance and audiometric testing protocol.
Operators must understand how to instruct workers to insert HPD without coaching for optimal fit, how to administer the test, interpret PAR results against the worker’s TWA, and conduct retraining when a worker fails.
PAR adequacy can only be determined against a known TWA. If noise monitoring data is not current for all enrolled workers, prioritize completing those assessments before or alongside fit testing. See: noise monitoring and recordkeeping: OSHA requirements.
Each fit test record must include: employee name and job classification, test date, HPD make and model, PAR result, adequacy determination, any retest results, and actions taken. Under 1910.95(m)(2), records must be retained for the duration of employment. See: audiometric records security: HIPAA and SOC 2 compliance.
Fit testing is most efficient when timed with the annual audiogram. Workers complete the audiogram first (establishing open-ear thresholds for REAT), immediately followed by HPD insertion and the fit test. Both records are generated in a single session.
When Fit Testing Must Be Repeated
A PAR is valid for a specific worker, device, and date. Repeat testing is required when:
- Annual cycle — timed with the audiogram; technique degrades and workers substitute HPD brands without reporting it.
- Confirmed STS — required under 1910.95(g)(8)(ii) when refitting; must use the 85 dBA post-STS adequacy standard.
- HPD change — any change in device type, brand, or size; PAR results do not transfer between devices.
- Declining audiogram trend — if a worker shows progressive threshold shifts despite apparent HPD compliance, a fit test may reveal technique degradation.
- Significant physical change — weight change, ear surgery, or scarring can alter canal geometry and invalidate a prior PAR.
Many programs run fit testing at onboarding and never repeat it. A worker who passed at hire may have developed technique degradation, switched to a brand from the supply cabinet, or experienced physical changes. Annual testing catches this before the next STS.
Dual Hearing Protection
At exposures above 100–105 dBA TWA, or for post-STS workers in high-exposure environments, a single HPD may not provide adequate attenuation. Dual protection — simultaneous earplugs and earmuffs — adds attenuation, but not by the sum of both NRR values. NIOSH estimates the combined protection at approximately the higher NRR plus 5 dB, because bone conduction caps achievable attenuation. Fit testing should be conducted with the combined system if dual protection is designated.
Frequently Asked Questions
OSHA 1910.95 does not mandate individual fit testing, but NIOSH’s 2025 Science Policy Update (Publication No. 2025-104) now recommends individual, quantitative fit testing as the preferred approach in place of NRR derating. After a confirmed STS, 1910.95(g)(8)(ii) requires refit and adequacy verification. Fit testing is the most defensible method to document that obligation at the individual level.
NIOSH Publication No. 2025-104, issued January 2025, supersedes the NRR derating guidance from the 1998 Criteria for a Recommended Standard. NIOSH now recommends individual, quantitative fit testing as the preferred method for evaluating HPD attenuation. The update does not change OSHA enforcement authority, but reflects the current best-practice standard.
A PAR is the actual measured attenuation a specific worker achieves with a specific HPD using their normal insertion technique. Unlike the NRR — a population average from lab testing — the PAR reflects real-world field performance for that individual. Protected exposure = TWA minus PAR. Generated by REAT or MIRE fit testing methods compliant with ANSI S12.71.
The NRR is a laboratory average measured under ideal conditions with trained subjects. NIOSH recommends derating foam earplug NRR by 50% for field use. The PAR is measured on a specific worker using REAT or MIRE — it reflects that individual’s actual protection with habitual insertion. No derating is applied to the PAR because field performance is directly measured.
Immediate retraining on insertion technique and retest in the same session. If PAR remains inadequate, try a different device size, type, or model. Persistent failures may indicate anatomical incompatibility — custom-molded earplugs or earmuffs should be considered. All attempts, results, and actions must be documented.
Annual fit testing timed with the audiogram is best practice. Fit testing is also required following any confirmed STS under 1910.95(g)(8)(ii). Any change in HPD type, brand, or size requires a new fit test — PAR results do not transfer between devices.
REAT (Real-Ear Attenuation at Threshold) measures hearing thresholds at specific frequencies with and without the HPD in place. The difference is the PAR. REAT uses the same audiometric equipment as the annual hearing test — Soundtrace runs fit testing immediately after the audiogram in the same session.
After a confirmed STS, OSHA 1910.95(i)(3) requires HPD that reduces the worker’s exposure to 85 dBA TWA or below — stricter than the standard 90 dBA threshold. Fit testing confirms the upgraded device meets this enhanced requirement for that specific worker at their specific TWA.
HPD fit testing + audiometry + noise monitoring — one session, one profile
Soundtrace REAT-based fit testing runs immediately after the annual audiogram, generating a PAR linked to noise exposure data and audiometric history in a unified cloud record — meeting the new NIOSH 2025 recommendation.
Schedule a Demo Get a quote for your facility →- OSHA Hearing Conservation Program: The Complete Guide
- Audiometric Testing for Employers: Complete OSHA Guide
- Standard Threshold Shift: Employer Action Guide
- OSHA 1910.95: Complete Employer Guide
- Noise Monitoring & Recordkeeping Under OSHA 1910.95
- NIOSH vs. OSHA Noise Exposure Limits Compared
- OSHA Hearing Conservation Violations & Penalties: 2026
- Workers’ Compensation for Occupational Hearing Loss: 50-State Guide
- Audiometric Records Security: HIPAA & SOC 2 Compliance