How to Conduct a Noise Risk Assessment and Select Hearing Protection That Actually Works
Noise-induced hearing loss is one of the most widespread occupational illnesses, and it’s irreversible. But it’s also preventable—if you’re using the right strategy. Too many organizations focus only on measuring noise and handing out earplugs. The real value comes from using data to make smart decisions about inclusion in a Hearing Conservation Program (HCP) and matching protection to risk.
Here’s how to do it the right way.
Move Beyond the TWA: Use Dose-Based Data for Decision Making
OSHA’s noise standard sets an action level at 85 dBA (8-hour TWA), but relying solely on TWA can mask the true risk. For example, short bursts of high-level noise may not push the TWA over 85, but still result in harmful exposures.
To properly determine if someone belongs in the HCP, don’t just record one reading. Instead, take multiple measurements across different days and similar exposure groups (SEGs). Then, apply statistical analysis to the results. The American Industrial Hygiene Association (AIHA) recommends converting sound level data to percent dose for evaluation, especially if you're using Bayesian Decision Analysis (BDA).
Using Bayesian Decision Analysis to Classify Risk
BDA allows you to make informed decisions even when sample sizes are small. It categorizes exposure into four tiers:
Category 1: Very likely not overexposed
Category 2: Unlikely, but uncertain
Category 3: Likely overexposed
Category 4: Very likely overexposed
To use BDA properly, you must express your noise data as a percentage of the allowable dose, not just the dBA TWA. Tools like IHSTAT, expostats, or OEMetrics can help perform this analysis, offering confidence intervals, exceedance probabilities, and upper confidence limits (UCLs).
If a SEG falls in Category 3 or 4, they should be enrolled in the HCP, even if the average TWA looks borderline.
Once You Know the Risk, Match the Right Protection
With the statistical evidence in hand, the next step is selecting appropriate hearing protection. This isn’t a one-size-fits-all process.
Here are key considerations:
1. Actual Exposure Levels
Use the estimated percent dose or confidence interval from your statistical model. Don’t just assume “everyone gets the same plugs.”
2. Type of Noise
Continuous noise, intermittent bursts, or impact noise each pose different challenges. Match HPD types accordingly.
3. Compatibility with Other PPE
Hard hats, safety glasses, respirators—each one can interfere with proper fit.
4. Worker Fit and Preference
Comfort drives compliance. If it's not worn correctly, it’s not working.
Understanding the NRR—and Adjusting for Reality
The Noise Reduction Rating (NRR) printed on hearing protection is based on ideal lab conditions. Real-world protection is lower.
OSHA's Recommended Field Adjustment:
Adjusted NRR = (NRR-7) * 0.5
Then subtract the adjusted NRR from the A-weighted exposure
More Protective Derating:
Formable Foam earplugs: Adjusted NRR = (NRR-7) * 0.5
Pre-molded plugs: Adjusted NRR = (NRR-7) * 0.25
Earmuffs: Adjusted NRR = (NRR-7) * 0.75
Dual protection: Add 5 dB to the higher-rated protector
Note: Many safety professionals still quote outdated or overly generous reductions. Make sure your derating practices reflect real-world performance.
Don’t Skip Fit Testing
Even the best earplug won’t help if it’s worn incorrectly. Fit testing is the only way to verify the protection each worker actually receives.
Options include:
3M E-A-Rfit Dual-Ear Validation System
Honeywell VeriPRO
FitCheck Solo by Michael & Associates
Fit testing also creates teachable moments during annual training. Workers see the impact of correct insertion firsthand.
Final Thoughts
Protecting hearing starts with the right data. That means measuring noise exposure across SEGs, analyzing dose-based risk using statistical tools, and only then deciding who goes into the HCP. From there, tailor protection using real-world NRR adjustments and validate with fit testing.
Smart hearing conservation is a process, not a handout.
