SNR stands for Single Number Rating. It is a single figure, in decibels, for how much a hearing protector reduces noise, measured in a laboratory to EN ISO 4869. Every ear plug and ear defender sold in the UK carries one. As a rough guide, subtracting the SNR from the noise level gives an estimate of the level at the wearer’s ear.
What the law requires
- At a daily exposure of 80 dB(A), the lower exposure action value, employers must make hearing protection available and provide information and training.
- At 85 dB(A), the upper exposure action value, hearing protection is compulsory, and hearing protection zones must be marked.
- The exposure limit of 87 dB(A) applies at the ear, taking the hearing protection into account, and must not be exceeded.
- These come from the Control of Noise at Work Regulations 2005. Hearing protection is the last resort: reduce the noise at source first.
How much SNR do you need?
HSE gives this table as a guide, based on the noise level during the task rather than the daily exposure:
| Noise level, dB(A) | Select a protector with SNR of |
|---|---|
| 85 to 90 | 20 or less |
| 90 to 95 | 20 to 30 |
| 95 to 100 | 25 to 35 |
| 100 to 105 | 30 or more |
Use the lower end of each SNR range when the noise is at the lower end of its band. The table is not suitable for noise with a lot of low-frequency content — press shops, generators, plant rooms and boiler houses, for example — where the more detailed HML or octave-band methods should be used.
Why more is not always better
HSE advises avoiding protectors that bring the level at the ear below 70 dB. Over-protected workers can miss warning signals and struggle to talk to each other, so they tend to lift a defender or pull a plug out — and protection only works while it is worn. A protector removed for even a short part of a shift gives far less protection over the day than its SNR suggests.
Allow for the real world
Laboratory ratings assume a perfect fit. HSE recommends allowing 4 dB for real-world factors such as fit and wear. For example, at 94 dB(C), a protector with an SNR of 27 gives an estimated 67 dB(A) at the ear; adding the 4 dB allowance gives 71 dB(A) — inside the 70 to 80 dB target.
Ear plugs or ear defenders?
- Ear plugs are cooler and more comfortable in heat, and sit easily alongside other PPE. Foam plugs must be rolled down and fitted properly to reach their SNR.
- Ear defenders suit intermittent noise, where people take protection on and off, and are easier to check at a glance.
- If your team wears helmets, helmet-mounted defenders keep both together — check the attachment matches your helmet.
- In food and pharmaceutical production, use metal-detectable plugs.
This is general guidance. Base your selection on a noise assessment, and see HSE’s guidance on noise at work for the full methods.
Frequently asked questions
- What does SNR mean on hearing protection?
- SNR is the Single Number Rating: one figure, in decibels, for how much the protector reduces noise in laboratory tests.
- What SNR do I need for 90 dB?
- HSE’s guide suggests an SNR of 20 to 30 for noise of 90 to 95 dB(A), and 20 or less for 85 to 90 dB(A).
- Is a higher SNR always better?
- No. HSE advises avoiding protectors that bring the level at the ear below 70 dB, because over-protected workers miss warnings and tend to remove their protection.
- When must hearing protection be worn at work?
- Under the Control of Noise at Work Regulations 2005, hearing protection must be made available at 80 dB(A) daily exposure and is compulsory at 85 dB(A).