What is NRR?

Hearing Loss

Workers have been using hearing protection devices (HPD) since the 1960's to protect themselves from high levels of noise. Approximately 30 million workers in the United States are occupationally exposed to hazardous noises each year. 10 million of those workers suffer from noise-induced hearing loss (NIHL) according to NIOSH. For more than 25 years hearing loss has been listed as one of the most prevalent occupational health concerns. Permanent hearing loss can occur when exposed to high levels of noise. Repeated exposure to high levels of noise can cause tinnitus (ringing in the ears). Other issues related to loud noise at work are physical and psychological stress, reduction in concentration and communication, loss of productivity, and increased probability of work-related accidents.

With radically smart products, the right education, and a structured hearing conservation program noise-induced hearing loss is 100% preventable.


Hearing and Noise Reduction Overview

According to the World Health Organization noise-induced hearing loss (NIHL) is the most common, permanent, and preventable occupational injury in the world.

Noise damage is different from most other occupational injuries. It causes no pain or visible trauma, the ears do not bleed when hearing is being damaged, it leaves no visible scars, it is unnoticeable in its earliest stages, it accumulates with each over-exposure, and it generally takes years to diagnose.

Damage occurs as sound waves from high noise levels enter your ear canal and cause the eardrum to vibrate. Small bones behind your eardrum transmit these vibrations to the cochlea. Receptor cells in the cochlea convert these vibrations into electrical impulses and send them to your brain. These vibrations are then interpreted as sound. When high noise levels damage your hearing it does not damage the eardrum or bones. Loud noise damages the receptor cells in the cochlea overtime. Unlike other cells in your body that can regenerate, nerve cells in the cochlea, once damaged, are gone forever.

So if somebody has hearing loss, how can we tell whether it is caused by noise? Here are the five common indicators of noise-induced hearing loss:
  1. The amount of time exposed to loud noise. There is no delayed effect in regards to noise damage.
  2. It is almost always a high-frequency hearing loss.
  3. It is usually bilateral (affects both ears equally). There are some exceptions to this but for employees who are on their feet during the workday; the hearing loss is usually in both ears equally.
  4. Gradual progression. We don’t measure hearing loss due to noise in terms of days or weeks. It usually takes us years to notice the permanent change in hearing.
  5. Appropriate symptoms. If a worker says he has pain in his ears or drainage this is probably not due to high noise levels. Ringing in the ears, tinnitus is a common symptom that is linked to noise-induced hearing loss.

Basically, If you experience ringing or humming in the ears after work, inability to communicate with a co-worker when only an arm's length away, and/or temporary hearing loss at any time the background noise is most likely hazardous.


ANSI Hearing Protection Standards

The American National Standard Institute (ANSI S12.6) entitled, Methods for Measuring the Real-Ear Attenuation of Hearing Protection, specifies laboratory-based procedures for measuring, analyzing and reporting the passive noise-reducing capabilities of hearing protection devices (HPD). The actual effectiveness of any individual protector cannot be determined under workplace conditions. OSHA’s noise standards requires that personal hearing protection be worn to attenuate the occupational high noise exposure of employees and the National Institute for Occupational Safety and Health(NIOSH) recommends that all workers exposures to noise should be controlled below a level equivalent to 85dBA for eight hours to minimize occupational noise-induced hearing loss.

A dB (Decibel) is the unit used to express the intensity of sound. The decibel scale is a logarithmic scale in which 0 dB approximates the threshold of hearing in the mid frequencies for young adults and in which the threshold of discomfort is between 85 and 95 dB. The threshold for pain is between 120 and 140 dB. Again the decibel scale is a logarithmic scale, not a linear scale. Similar to the Richter earthquake rating scale, small numbers represent enormous changes. Sound energy that is twice the level of 83 dB is not 166 dB, but rather 86 dB.

Damage from noise exposure depends on the loudness and length of exposure. Habitual exposure to noise above 85 dB will cause gradual hearing loss. HPD's are required when noise averages more than 90 dB during an 8-hour workday. For unprotected ears, the allowed exposure time decreases by one-half for each 5 dB increase in the average noise level. The table below shows noise levels and how long a person can be exposed without hearing protection before there is damage to the ear.

Noise Level Allowable Exposure Time:

Continuous dB Permissible Exposure Time
85dB 8 hours
90dB 4 hours
100dB 1 hour
105dB 30 minutes
110dB 15 minutes
115dB 0 minutes


The two most common methods for monitoring noise levels are area sampling with a sound level meter or personal sampling with a noise dosimeter. The sound level meter reads the instantaneous noise level in a specific working environment and is accurate only when noise levels are constant in the area. For non-static workers with fluctuating noise exposures, the noise dosimeter gives a more accurate measure of the exposure to noise. Both of these methods measure the unprotected exposure and then an estimate must be made for the protected exposure.




NRR Stands For Noise Reduction Rating

NRR (noise reduction rating) is a single number rating method that describes a hearing protection device (HPD) based on how much the overall noise level is reduced by the HPD. Most noise measurements in the industry are derived from the A-weighting scale. The A-scale is simply a filter applied to microphones on noise measurement devices that replicates the response of the human ear to sound. Hearing sensitivity in both low and high frequencies falls off in the human ear as it is not the perfect microphone. To account for this reduction in the low and high frequencies manufacturers of noise measurement devices include an A-weighting filter so that measurements are similar to what the human ear actually hears. The NRR theoretically provides an estimate of the protection that should be met or exceeded by 98% of the wearers of a given HPD.

The EPA has created a label and requires that all HPD’s have this label on its packaging. The number in the top right of the label is the NRR.

Wearing time is often overlooked by HPD buyers who select devices based on maximum ratings (highest NRR) without enough attention given to comfort or the potential noise in a given environment. NRR is also affected by employees who remove HPD’s to communicate. This obviously reduces the effectiveness of the hearing protection device. When hearing protectors are not worn 100% of the time protection drops to less than half the stated protection level after only 30 minutes during eight hours of noise exposure.