Every hearing protector sold comes with a number printed on the packet, and that number is the single most misread figure in personal protective equipment. People treat it like a speed limit sign. A plug says 33, the machine is loud, 33 sounds like a lot, so the plug goes in and everyone moves on. Then the annual audiometry comes back with a notch at 4 kHz and nobody can explain it, because on paper the worker was protected.
The rating is real. It is just not a measurement of what happens inside your workers’ ears.
Where the numbers come from
The two rating systems you will meet most often are the Noise Reduction Rating used in the United States and the Single Number Rating used in Europe.
The NRR is required on protectors sold in the US under Environmental Protection Agency labelling rules. It comes from laboratory testing on a small panel of subjects, with the protector fitted under ideal conditions, often by the experimenter rather than the wearer. The SNR comes from testing to EN ISO 4869 and appears on protectors certified to the EN 352 series. European packaging often also gives H, M and L values, which describe performance against high, medium and low frequency noise, and those three numbers are more useful than the headline figure if you know the character of your noise.
Both systems share the same weakness. They describe what a protector can do in a lab with careful fitting and short wear time. They do not describe a tired operator on a night shift who rolled a foam plug with dirty fingers and pushed it halfway in.
Why the label overstates protection
Field studies have repeatedly found that real world attenuation falls well short of the labelled figure, and that the gap is largest for earplugs. The reasons are mundane. Plugs are not inserted deeply enough. Earmuff seals are broken by spectacle arms, hair, hood edges and hard hat brims. Protectors get lifted for conversation and not put back. Foam plugs get reused until they no longer expand properly.
For that reason, regulators and safety bodies apply a derating. Practices differ, which is worth knowing if you read guidance from more than one country.
- OSHA guidance for the US says that when noise has been measured in dBA, you subtract 7 dB from the NRR before applying it, and its technical guidance further suggests halving the result to allow for real world fit.
- NIOSH has recommended derating by protector type, with larger deratings for plugs than for muffs, reflecting how much more fit dependent plugs are.
- The UK Health and Safety Executive suggests subtracting 4 dB from the predicted protection to allow for real world factors when using SNR or HML calculations.
The exact method matters less than the habit. Never use the printed number straight. If your selection only works with the full label value, it does not work.
The limits you are trying to meet
The legal framework sets what “enough” means, and again it differs across the Atlantic.
In the European Union, the noise directive sets a lower exposure action value of 80 dB(A) daily exposure, an upper exposure action value of 85 dB(A), and an exposure limit value of 87 dB(A). The limit value is the only one assessed taking hearing protection into account. Peak values are set at 135, 137 and 140 dB(C) respectively. At the lower action value, hearing protection must be made available. At the upper action value, it must be worn and the area marked as a hearing protection zone.
In the United States, OSHA sets a permissible exposure limit of 90 dBA as an eight hour time weighted average using a 5 dB exchange rate, and requires a hearing conservation programme at an action level of 85 dBA. NIOSH recommends a stricter limit of 85 dBA with a 3 dB exchange rate. The exchange rate is the quiet difference that catches people out. Under a 3 dB rule, every 3 dB increase halves the permitted time. Under OSHA’s 5 dB rule, it takes a 5 dB increase. A process that looks acceptable under one method can be well over under the other. The OSHA occupational noise exposure pages set out the US requirements in full.
Too much protection is a real problem
This is the part buyers rarely believe. More attenuation is not always better. A worker wearing a high rated plug in a moderately noisy area may not hear a reversing alarm, a shouted warning or the change in pitch that tells an experienced fitter that a bearing is going. Feeling isolated, they lift the protector to hear, and then they are unprotected.
The HSE advises aiming for a level at the ear of between 70 and 80 dB, and avoiding protectors that take the level below 70 dB. In practice, for a shop floor running in the mid to high 80s dB(A), a modest protector worn all the time beats a high rated one that comes out every twenty minutes.
Where noise is genuinely extreme, dual protection with plugs under muffs is used. Do not add the two ratings together. The combined protection is only a few dB better than the better of the two on its own, because sound also reaches the inner ear through bone conduction. US guidance commonly suggests adding about 5 dB to the higher rated protector as an estimate.
| Situation | What usually goes wrong | Practical response |
|---|---|---|
| Foam plugs issued from a dispenser | Shallow insertion, dirty hands, reuse | Train the roll, pull and hold method and check it on the floor |
| Earmuffs with safety glasses | Arms break the seal | Thin arm frames, gel cushions, or switch to plugs |
| Muffs on hard hats | Poor clamping force, cups not over the ear | Confirm the muff is approved for that helmet model |
| Intermittent noise areas | Protector removed and not replaced | Banded plugs or level dependent muffs |
Making the rating mean something on your floor
The only way to know what a person is getting from a protector is to measure it on that person. Individual fit testing systems for earplugs are now widely available and give a personal attenuation rating in a few minutes. I have watched a worker go from single digit attenuation to well over twenty dB with nothing more than a demonstration of how to pull the ear back while inserting the plug. That one session did more than a year of toolbox talks.
If fit testing is not available, do the simple checks. A properly inserted foam plug should barely be visible from the front. Your own voice should sound louder and hollow when the plugs are in, which tells you the seal is good. Muff cushions should be soft and unbroken, and hardened or split cushions should be replaced without discussion.
Choosing for the person and the task
Selection starts with your noise survey, preferably with octave band data if you want to use HML properly. Then look at the people. Comfort for an eight hour shift, heat, compatibility with other PPE, the need to communicate, and whether the protector can be inserted with gloved or dirty hands. Offer more than one type, because ear canals are not standard sizes and a protector that hurts will not be worn.
Finally, remember where this sits. Hearing protection is the last control, not the first. Quieter machines, enclosures, isolation mounts, maintenance of worn bearings and moving people away from the source all reduce exposure for everyone in the area, protected or not. A proper risk assessment and your local regulation decide the final answer, and the audiometry results will tell you, eventually, whether the programme is working.
