Comparing methods for selecting hearing protection - SNR, HML and Octave Bands.
For compliance with the Control of Noise at Work Regulations 2005 it is important that hearing protection is assessed as suitable for this. There are three methods for achieving this.
Key points: Three methods for choosing hearing protection
The three methods are SNR, HML and Octave Band.
The simplest method is to use the SNR route, a single number of how many decibels a protector reduces noise by.
HML breaks the noise into three frequency ranges, while Octave Band splits it down even further.
SNR is good enough for most places and is compliant with the Control of Noise at Work Regulations 2005.
HML and Octave Band are useful for more specific noise risks.
This dedicated page on choosing the correct hearing protection allows you to enter your noise level and it will give you a list of suitable hearing protectors.
A need for hearing protection is a common outcome of a noise assessment or a noise survey. Although it is technically at the bottom of the ‘hierarchy of controls’ whereby companies need to eliminate noise risk first, then control it by some other organisational means if possible, often hearing protection is either the only practical outcome, is needed as a temporary interim measure or is needed alongside other controls for any residual risk.
Hearing protection needs to be ‘just right’, so not too weak meaning people are still at risk, but also not too strong so people become isolated.
Link: More detail on the issues with over-protection
How to check hearing protection is suitable for the noise risk - the possible methods
Employers have to make sure hearing protection is correct for their noise risk and the HSE give three ways to do this:
Using SNR is the simplest method.
A little more complex is called the HML method.
The most complex is the Octave Band route.
(As an aside, our American brethren use NRR, not SNR and the two are not the same - you cannot used NRR here in the UK, if you see anything saying NRR, ignore it).
SNR: The easy way to assess hearing protection suitability
SNR Means the Single Number Rating, a single number of decibels which a hearing protector has been proven to reduce external noise by.
The ideal range for what you want someone to hear under the protector is in the region of 70 to 78 dB(A). (The HSE say a little higher as well but that’s getting too close to the limits for comfort for me).
The simplest way to use the SNR route is to go to this page on choosing the right hearing protection. That page has a few free tools, including ones where:
You can enter a protector’s SNR and it will tell you what noise level it is good for.
A tool where you can enter both an SNR and your noise level and it will tell you if that SNR is good.
And the best one, a tool where you can enter your noise level and it will list loads of hearing protectors which are suitable.
You can also calculate SNR manually
To calculate it manually, all you need to do is take the average dB(C) noise level which your noise assessment should give you, and subtract the hearing protector’s SNR from it. Then, add 4 back to it to allow for some slightly incorrect use, and the answer is the sound level people should be experiencing under the hearing protection.
As an example:
A Laser Lite plug has an SNR of 35. (And appalling spelling).
The dB(C) result in the noise assessment for the job is 95 dB(C).
The calculation is 95-35, giving 60dB.
Add 4dB to account for real-world usage so we get a result of 64dB, that’s what people experience at the ear under the protection.
Don’t use peak dB(C)
Do not use the peak dB(C) figure as that almost always comes out as the hearing protection being insufficient, you want the average dB(C) level. A noise assessment done by a good professional should have given you that figure.
If you don’t have it you could use the average dB(A) figure but that is generating room for error and is best avoided as average dB(A) and dB(C) are often not the same. As noise gets into the important levels which concern us though they are however often fairly close. It’s not an ideal route but better than nothing.
HML: a slightly more complicated route
When you buy hearing protection, alongside the SNR number on the pack you will usually see values called HML, each with their own decibel rating. These are:
H: High frequency noise reduction
M: Mid range noise reduction
L: Low frequency noise reduction
Where SNR gives you one number for the hearing protection, HML gives you those three for how many decibels the protector reduces noise by in each of those frequency ranges.
To use it, the HSE have a workbook which has a download with an HML tab you can use.
Octave Band: The most complex route
This is effectively an extension of HML and breaks the noise down into a larger number of smaller frequency bands, with a number of decibels for each of how much noise reduction the protector gives for that band.
A reason for this one is that almost all hearing protection is most effective at specific types of frequency so for some very specific circumstances, you can use Octave Bands to ensure the hearing protection is a match for the noise source in terms of frequencies. For example, if your noise is very high frequency but the hearing protector is most effective at low frequencies then the level of overall reduction may not quite be as much as you may think.
Again, that link to the HSE above includes a tab for using Octave Band data.
Example manufacturer performance data
This is for the E-A-R Classic ear plugs and shows the SNR, the HML figures and all the Octave Band data.
If using Octave Bands, use the APVf line as that is the decibels of noise reduction at each frequency.
E-A-R Classic noise attenuation performance data
Which route should you use to assess hearing protection?
For 99% of cases, use SNR. The HSE list it as a suitable option, it is simple, and it works. And most of the time the result of a calculation by SNR is the same as the other two methods as well.
If you have a very specific type of noise risk then the other two may be more suitable.
What is a good noise level under the hearing protection?
You should aim for around 70 to 78 dB under the protector - that’s the noise people actually hear.
81 to 84 dB is a level I don’t personally like hearing protection as that is far too close to the limits for my liking - if there are no better options then OK, but I would avoid it unless you have absolutely no other options.
79 to 80 dB is technically OK and is within what the HSE say is suitable, but I would steer clear of that personally as it is getting too close to the upper noise limit where hearing starts to be damaged - someone wearing it slightly incorrectly could easily then be at risk.
65 to 69 dB is again OK. The HSE class that as a little too strong but if it is good for other risks within the company then it is fine. As a guide, this is about the noise level of an office so not horrendously quiet - your production staff would just be a the same noise level as your office staff.
64 dB and below is too strong and should be avoided. People tend to not put plugs in properly or off-set ear muffs to let more noise through as they can’t hear what’s going on. They are then at risk and the employer is wasting money on hearing protection that’s not actually doing a lot.
Link: HSE on hearing protection should not reduce noise levels below 70 dB(A).
Extract from L108: HSE statement on noise levels under hearing protection
Make sure the hearing protection is properly certified
As a related issue, this means making sure it is certified to EN 352: 2020.
A lot of listings for no-brand protection on places like Amazon do fudge this so these are best avoided. If it only says ‘workplace noise’ in a listing without giving any proof of certification to EN352, avoid it.
There is more information on standards for hearing protection here.
FAQ: Choosing the right hearing protection
Can we play it safe and just buy the strongest hearing protection?
No, hearing protection which is too strong introduces its own risks, hearing protection needs to be strong enough but not too much.
Can we use NRR to check if hearing protection is good enough?
No. I am talking about the UK here so the Control of Noise at Work Regulations 2005 and the HSE’s L108, Controlling Noise at Work (Third Edition) document, and these require the use of SNR, HML or Octave Bands. NRR has no application here. NRR and SNR are not synonymous and the numbers are not interchangeable.
There is a bewildering array of hearing protection on the market, can you recommend some specific types?
Yes, and they are listed on the hearing protection advice page for you.
More information on hearing protection in the workplace
Article last reviewed and updated: June 2026
