January 16, 2003
Editor's Note: This article is based on the 1998 Criteria for a Recommended Standard: Occupational Noise Exposurepublished by the National Institute of Occupational Safety and Health (NIOSH).
No, this "I can't hear you" isn't the bark of a marine drill sergeant. It's the lament of a worker exposed to hazardous noise without using proper hearing protection.
Noise in the workplace has been a constant threat since the industrial revolution. Too much noise exposure can cause a temporary change in hearing (your ears may feel stuffed up) or a temporary ringing in your ears (tinnitis). These short-term problems usually go away within a few minutes or hours after leaving the noise. Repeated exposures to loud noise can lead to permanent, incurable hearing loss or tinnitis.
The National Institute of Occupational Safety and Health (NIOSH) released its Criteria for a Recommended Standard: Occupational Noise Exposure in 1998. The publication is a revision of the organization's 1972 publication Criteria for a Recommended Standard: Occupational Exposure to Noise. The recommendations in the 1998 criteria go beyond attempting to conserve hearing by focusing on preventing occupational noise-induced hearing loss (NIHL).
The 1998 study reevaluated and reaffirmed the recommended exposure limit (REL) for occupational noise exposure established by NIOSH in 1972: 85 decibels, A-weighted (decibel, A-weighted is the unit representing the sound level measured with the A-weighting network on a sound level meter), as an 8-hr. time-weighted average (85dBA as an 8-hr. TWA). Exposures at or above this level are hazardous.
By incorporating the 4000-Hz audiometric frequency into the definition of hearing impairment in the risk assessment, NIOSH found an 8% excess risk of developing occupational noise-induced hearing loss (NIHL) during a 40-year lifetime exposure at the 85-dBA REL.
The noise level of the average ringing telephone is 80dB. A power lawn mower has a noise level of 90dB. The REL for occupational noise exposure is 85dB—halfway between the telephone and power mower noise levels. For workers whose noise exposures equal or exceed 85dBA, NIOSH recommends a hearing loss prevention program (HLPP) that includes exposure assessment, engineering and administrative controls, proper use of hearing protectors, audiometric evaluation, education and motivation, record keeping, and program audits and evaluations.
Ideally, the most effective way to prevent NIHL is to remove the hazardous noise from the workplace or to remove the worker from the hazardous noise. Hearing protectors should be used when engineering controls and work practices are not feasible for reducing noise exposures to safe levels.
A hearing protector is any device designed to reduce the level of sound reaching the eardrum. The main types of hearing protectors are earmuffs, earplugs, and ear canal caps (also called semi-inserts). Each of these categories includes a wide range of devices. For example, earplugs may be subcategorized into foam, user-formable (such as silicon or spun mineral fiber), premolded, and custom-molded earplugs. Some types of helmets also function as hearing protectors.
Items not specifically designed to serve as hearing protectors (e.g., cigarette filters, cotton, and .38-caliber shells) should not be used in place of hearing protectors. Likewise, devices such as hearing aid ear molds, swim molds, and personal stereo earphones must never be considered as being hearing protective.
When a worker's time-weighted noise exposure exceeds 100dBA, both earplugs and earmuffs should be worn. It is important to note that using such double protection will add only 5 to 10dB of attenuation. Given the real-world performance of hearing protectors, NIOSH cautions that even double protection is inadequate when TWA exposures exceed 105dBA.
How much attenuation a hearing protector provides depends on its characteristics and how the worker wears it. The selected hearing protector must be capable of keeping the noise exposure at the ear below 85dBA. Because a worker may not know how long a given noise exposure will last or what additional noise exposure he or she may incur later in the day, it may be prudent to wear hearing protectors whenever working in hazardous noise. Workers and supervisors should ensure periodically that the hearing protectors are worn correctly, are fitted properly, and are appropriate for the noise in which they are worn.
Historically, emphasis has been placed on a hearing protector's attenuation characteristics -- almost to the exclusion of other qualities necessary for it to be effective. Although those who select hearing protectors should consider the noise in which they will be worn, they also must consider the workers who will be wearing them, the need for compatibility with other safety equipment, and workplace conditions such as temperature, humidity, and atmospheric pressure.
A variety of styles should be provided so that workers may select a hearing protector on the basis of comfort, ease of use and handling, and impact on communication. Each worker should receive individual training in the selection, fitting, use, repair, and replacement of the hearing protector. What is the best hearing protector for some workers may not be the best for others. The most common excuses reported by workers for not wearing hearing protectors include discomfort, interference with hearing speech and warning signals, and the belief that workers have no control over an inevitable process that culminates in hearing loss. Fortunately, none of these reasons present insurmountable barriers. Given adequate education and training, each can be successfully addressed.
Workers and management must recognize the crucial importance of wearing hearing protectors correctly. Intermittent wear will reduce their effective protection dramatically. For example, a hearing protector that could optimally provide 30dB of attenuation for an 8-hr exposure would provide effectively only 15dB if the worker removed the device for a cumulative 30 min. during an 8-hr. day. The best hearing protector is the one that the worker will wear.
The NIOSH document contains detailed descriptions of methods used for estimating the amount of sound attenuation a hearing protector provides. In the U.S., the noise reduction rating (NRR) is required by law to be shown on the label of each hearing protector sold. Both NRR and other hearing protector ratings are based on data obtained under laboratory conditions in which experimenters fit hearing protectors on trained listeners. As such, these rating may differ markedly from the noise reduction that a worker would experience in the real world. Studies have repeatedly demonstrated that real-world protection is substantially less than noise attenuation values derived from experimenter-fit, laboratory-based methods.
In general, the data gathered from testing show that earmuffs provide the highest real-world noise attenuation values, followed by foam earplugs; all other insert-type devices provide the least attenuation. The results also conclude that ideally, workers should be individually fit-tested for hearting protectors.