Workplace Noise Compliance & Hearing Protection Standards

SNR stands for Single Number Rating. It is the simplified attenuation value used throughout Europe to indicate the overall level of noise reduction provided by a hearing protector.

For example:

• An earplug with an SNR of 30 dB is designed to reduce noise exposure by approximately 30 dB when fitted correctly
• A workplace noise level of 100 dB may therefore be reduced to approximately 70 dB at the ear

SNR values are determined through laboratory testing as part of EN352 certification and provide a simple way of comparing different hearing protection products.

While SNR is useful as a general guide, workplace noise is rarely uniform across all frequencies. Different environments produce different sound profiles, meaning two workplaces with the same dB level may require completely different hearing protection solutions.

This is where HML and full octave band data become important.

HML values provide a more detailed breakdown of hearing protector performance across different sound frequencies.

HML stands for:

• H = High frequency attenuation
• M = Medium frequency attenuation
• L = Low frequency attenuation

These values help determine how effectively a hearing protector reduces different types of noise.

High Frequency Noise (H)

High frequency noise includes sounds such as:

• Grinding
• Cutting
• Air release systems
• High-speed machinery
• Metal-on-metal impact

Medium Frequency Noise (M)

Medium frequency noise is commonly associated with:

• General manufacturing
• Mechanical equipment
• Production lines
• Industrial processing

Low Frequency Noise (L)

Low frequency noise may include:

• Heavy engines
• Compressors
• Turbines
• HVAC systems
• Large industrial plant equipment

Different hearing protectors may perform very differently across these frequency ranges, even if their SNR values appear similar.

For example:

• Two earplugs may both carry an SNR of 30 dB
• One may provide stronger low-frequency attenuation
• Another may perform better against high-frequency noise

This is why relying solely on SNR can sometimes lead to incorrect hearing protection selection.

Selecting suitable hearing protection is about achieving the correct level of attenuation for the specific workplace environment. The objective is to reduce noise exposure to a safe level without causing overprotection, communication difficulties, or reduced situational awareness.

There are three recognised methods used to assess hearing protection performance:

• The SNR Method
• The HML Method
• The Octave Band Method

Each method requires different levels of noise measurement data and provides different levels of accuracy.

The SNR (Single Number Rating) method is the simplest and most commonly used approach.

This method estimates the protected noise level at the ear by subtracting the hearing protector’s SNR value from the measured workplace noise level.

Data Required

To use the SNR method, you need:

• The workplace C-weighted noise level (dB(C))
• The hearing protector’s SNR value

Example

• Workplace Noise Level - 98 dB(C)
• Hearing Protector SNR - 25 dB
• Estimated In-Ear Exposure - 73 dB

The aim is typically to achieve a protected noise level of approximately:

• 70 to 75 dB at the ear

When Is the SNR Method Suitable?

The SNR method is generally suitable where:

• Noise exposure is relatively consistent
• The noise is not heavily tonal
• There are no dominant low-frequency sounds
• A simple assessment is sufficient

Limitations

SNR provides a single overall attenuation figure and does not consider the frequency characteristics of the workplace noise. As a result, it is the least precise of the three methods.

The HML method provides a more accurate assessment because it considers the frequency profile of the workplace noise.

HML stands for:

• H = High frequency attenuation
• M = Medium frequency attenuation
• L = Low frequency attenuation

Different hearing protectors perform differently across frequency ranges, meaning two products with identical SNR values may perform very differently in real-world environments.

Data Required

To use the HML method, you need:

• The workplace A-weighted noise level (dB(A))
• The workplace C-weighted noise level (dB(C))
• The hearing protector’s H, M, and L attenuation values

These HML values should be provided in the hearing protector’s technical data or certification documentation.

When Is the HML Method Suitable?

The HML method is recommended where:

• Noise contains varying frequencies
• There is some low-frequency noise present
• Greater accuracy is required
• Communication and awareness remain important

This method provides a more realistic prediction of hearing protector performance than SNR alone.

The Octave Band Method is the most accurate method of selecting hearing protection.

Rather than using overall averages, this approach analyses noise levels across individual frequency bands and compares them against the hearing protector’s attenuation performance at each frequency.

Data Required

To use the Octave Band Method, you need:

• Workplace noise measurements across octave band frequencies
• A sound level meter capable of octave band analysis
• The hearing protector’s octave band attenuation or APV (Assumed Protection Value) data

When Is the Octave Band Method Suitable?

The octave band method is typically used where:

• Noise levels are very high
• Noise is heavily tonal
• Significant low-frequency noise is present
• Multiple complex noise sources exist
• Maximum accuracy is required

Because it evaluates the actual frequency content of the workplace noise, the octave band method provides the most precise prediction of protected in-ear exposure.