Hearing Conservation in 2012: Focus on NRR
The best way to use the time while we await the new labeling regulation is to train users to fit protectors correctly and use fit testing to document the protection provided by a given protector.
- By Theresa Y. Schulz
- Mar 01, 2012
Noise in the workplace and hearing conservation will continue to be an issue in 2012. Although regulatory changes seem stalled, significant attention is being given to noise hazards.
After serving their country in the U.S. armed forces, many veterans are returning to the workplace. Unfortunately, a significant number now suffer from hearing loss, as noise-induced hearing loss and tinnitus rank as the top injuries of soldiers returning from active combat. Managing these and other employees who have existing hearing loss is a challenge for hearing conservation program managers.
Noise is one of OSHA's priorities for 2012 -– and with good reason. Noise-induced hearing loss (NIHL) is one of the most prevalent preventable injuries/illnesses both in the United States and worldwide. During an "OSHA Listens" meeting in November 2011, OSHA leaders clearly conveyed their intent to continue to make noise a priority.
Don't wait for an OSHA citation to make sure your hearing conservation program is effective. Leading companies are realizing that a personal approach is a best practice and leads to more-effective hearing conservation. Shaw Industries was recognized in 2011 with the Safe-in-Sound Award for lowered noise levels and increased assurance of hearing protector effectiveness. (For more information on this model hearing conservation program, go to http://www.hearforever.org or http://www.safeinsound.us.)
EPA's final rule regarding hearing protection labeling is still pending. But in the meantime, we need to educate ourselves as consumers of hearing protection. What new information will these labels include, and how can we use it?
The proposed rule changes the very heart of the Noise Reduction Rating (NRR). The new NRR will be a range that is reported from very different testing methods than the old (current) NRR.
The Current Method
Hearing protectors are tested in a laboratory sound room that is intended to simulate a typical noisy setting in industry. Ten human test subjects take traditional hearing tests (audiometric threshold testing) with ears open (no hearing protectors) and occluded (with hearing protectors fit for them by the experimenter). This process is repeated three times for each subject. The differences between those measurements are "attenuation measurements."
The attenuation measurements for all subjects are then input into a formula (the measurements are logarithmically added, two standard deviations are subtracted to account for variability between all the subject's results, and 3 dB is subtracted to account for the different noise spectrums in industry). This process is called Real Ear Attenuation at Threshold (REAT). The result is a single number, the Noise Reduction Rating.
The Proposed Method
The proposed rule is very similar but with critical changes in the process. Under the proposed rule, the subjects will be trained to fit the hearing protector and will fit it themselves. Due to the inherent variability of ear plug fit, testing of ear plugs will require 20 subjects; ear muffs still will require 10 subjects. Sample attenuation measurements are shown in Figure 2. The results will no longer be a single number but will be a range of numbers, still called the Noise Reduction Rating, determined by the distribution of attenuation measurements.
The range that is shown on the label was proposed to be the minimum amount of attenuation that 80 percent of trained users achieved and what the top 20 percent of trained users achieved. Which percentiles will be required on the new labels are not final yet, but certainly more information about the potential capability of a given hearing protector will be available with this new label.
Comparison of characteristics of current EPA labeling to proposed EPA labeling:
Description of Rating:
- Current: A single-number estimate of protection
- Proposed: A high/low range of estimated protection
- Current: Estimates the 98th percentile of protection obtained by users when properly fitted
- Proposed: Esimates the 80th and 20th percentile of protection obtained by users
- Current: ANSI S.3.19-1974 (Experimenter Fit), 10 subjects for ear plugs and ear muffs, HPDs fit by experimenter
- Proposed: ANSI S12.6-2008 Method A (Supervised Subject-Fit), 20 subjects (for ear plugs) or 10 subjects (for ear muffs), HPDs fit by subject after brief training
- Current: Intended for use with dBC noise measurements. Requires a 7 dB correction for use with dBA measurements.
- Proposed: Can be applied directly to dBA noise measurements.
- Current: Various de-rating schemes promulgated by various organizations (including OSHA)
- Proposed: Designed to be used with no required de-rating
- Current: Currently, no retestng of HPDs required
- Proposed: Periodic retesting of HPDs required every five years
The proposed EPA regulation addresses for the first time the rating of non-standard hearing protectors (such as Active Noise Reduction, ANR, including noise cancellation headsets used during travel, for example) and level-dependent (or impact noise) protectors (such as Impact Sport-styled ear muffs). Under the old labeling requirements, these specialized protectors were rated with a low NRR simply because they were not tested in the higher noise ranges where their noise reduction capability is activated. EPA has included these types of hearing protectors in its new labeling regulation so purchasers can make informed choices.
The labels for passive HPDs will include a statement such as "This protector was not tested for impulse noise." That certainly does not mean that the protector is not effective against impulse noise. In fact, maximum protection from impulse noise can be achieved with a well-fit, deeply inserted foam ear plug. So even though passive hearing protection (regular ear plugs and ear muffs) are not "tested" for impulse noise for labeling purposes, they are an effective choice that will protect from hazardous impulse noise.
Hearing protectors that are specifically designed to be used around impulse noise allow low-level ambient sounds in or even amplify them until an impulse noise "shuts down" the hearing protector. The proposed labeling will include two ranges; one will be the results of the new passive testing procedure discussed above and the other the results of the new procedure to test HPDs that are specifically for protection against impulse noise. The label will identify the protector’s intended function (Passive, Active, or Impulsive) and provide the respective range(s) of effectiveness afforded by the product. EPA uses the following definitions:
- Passive Noise Reduction. The reduction of sound transmission based solely on the use of materials and/or structural elements.
- Active Noise Reduction. The reduction of sound transmission based on the use of electronic elements (e.g., circuits and transducers) to produce acoustic signals of approximately equal and opposite phase and amplitude to reduce the transmitted sound.
- Impulsive Noise Reduction. The reduction of peak impulse sound transmission based upon the single or combined use of passive and/or active noise reduction elements.
Stress Correct Fit and Fit Testing
New methods are proposed so that active noise reduction devices are tested to show their benefits, including noise reduction in the intended operational mode. Currently, these devices must be tested in passive mode because that was the only recognized mode at the time the 1979 EPA regulation was promulgated. An ANR device uses electronic circuitry to sample an external sound signal, analyzes the principal acoustic component(s), and then generates a signal that is 180 degrees out of phase that is played into the space under the protector, effectively canceling the external signal that is under the protector. When tested in passive mode with the electronics turned on, the traditional passive, human threshold based tests described above (REAT) are contaminated by the electronics. The proposed alternate method uses a microphone to measure the signal rather than a human subject and is called Microphone in Real Ear (MIRE). Hearing protectors designed to protect primarily against impulse noise also will use the MIRE method in order that human test subjects are not exposed to unoccluded (unprotected) hazardous impulse noise.
These proposed labels do provide more information for the consumer but might also lead to some confusion. Knowing what kind of hearing protectors are best for a given situation will help understand the information provided on the new labels. Remember: Even though passive hearing protectors are not required to be tested for impulse noise, they are still very effective protection against impulse noise when worn correctly.
The proposed method for labeling hearing protector includes the obvious but often misunderstood concept that "The sound pressure level at the user's ears will depend upon the fit of the protector." The best way to use the time while we're awaiting the new regulation on labeling of hearing protectors is to train users to fit the protector correctly and to use fit testing to document the protection provided by a given hearing protector.
This article originally appeared in the March 2012 issue of Occupational Health & Safety.