All About Noise Reduction Rating (NRR)

All About Noise Reduction Rating (NRR)


The danger of exposure to high noise levels is real. If you find yourself in a noisy environment, you can take the right measures to protect your hearing.

What should I know about hearing protection devices?

Workers in an environment where the sound or noise level exceeds 85 decibels (dBA) should wear hearing protection. This helps minimize the risk of hearing loss and reduce the noise exposure level.

Whenever hearing protection is required, you should put in place a complete hearing conservation program that covers:

  • Noise assessment
  • Employee training
  • Audiometric testing
  • Record keeping
  • Hearing protector selection and maintenance

Keep in mind that the efficiency of hearing protection devices decreases when removed (even for a short period), if it is worn only from time to time, and if it doesn’t fit properly.

What are the types of hearing protectors available?

  • Earplugs: inserted in the ear canal and can be pre-molded or moldable. 3M offers a wide variety of disposable, reusable, and custom-made earplugs.
  • Semi-insert earplugs: two earplugs retained over the ends of the ear canal by a rigid headband.
  • Earmuffs: ear cushions made of sound-attenuating materials that fit over the ear, held together by a headband. 3M Ear muffs are offered in various positions: over the head, behind the head, and cap attached.

What is Noise Reduction Rating? (NRR)

Noise Reduction Rating (NRR) is a system used to determine the effectiveness of hearing protectors to reduce sound exposure. This unit of measurement is powerful since it easily indicates the functionality of a device and its ability to protect the worker.

Values range from 0 to approximately 35. The higher the rating on the hearing protector label, the greater it will reduce noise exposure.

Is the NRR accurate?

The short answer is… no. NRR is a bit optimistic, and the actual protection of a device is usually lower than what is stated.

The NRR is a laboratory test and is conducted in highly controlled facilities. The real-world results are different because of poor fit, lack of proper training on the hearing protection device, and enforcement.

How can I get a good protection number?

To get a realistic value, it is recommended that the noise reduction rating be derated to better estimate your hearing device protection.

To approximate an NRR, a little math is needed. This is a simplified version, and you can get all the information on the NRR derating plan in the CSA Z94.2-14 Hearing Protection Devices Standard.

  • Take the NRR rating indicated (in decibels) on the label and subtract seven.
  • Divide the result by two.
  • Subtract the result from the noise exposure level (in decibels) of your environment.

Let’s put it in action:

Let’s say you’re exposed to a noise level of 100 dBA. You have earmuffs with an NRR of 30.

  • Subtract 7 from 30 = 23.
  • Divide this result by two = 11.5.
  • Subtract the result (11.5) from the noise exposure level of your environment (100) = 88.5.

This means that you would be exposed to 88.5 dBA and not 70 dBA, as you may believe.

To get optimal protection, hearing protection devices are indispensable in any noisy work environment. With the help of NRR labels, you can better understand noise exposure levels and get an approximate idea of how much a specific hearing protection device truly protects your workers.

Learn more on the 3MTM PeltorTM product line here.