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| A Brief Background
One in 10 Americans has a hearing loss that affects his or her ability to understand normal speech. Excessive noise exposure is the most common cause of hearing loss. Noise, or unwanted sound, is one of the most common health problems in American workplaces. The National Institute for Occupational Safety and Health (NIOSH) estimates that 30 million workers in the U.S. are exposed to hazardous noise. Exposure to high levels of noise may cause hearing loss, create physical and psychological stress, reduce productivity, interfere with communication, and contribute to accidents and injuries by making it difficult to hear warning signals. The damage caused by noise, called sensorineural hearing loss or nerve deafness, can be caused by several factors other than noise, but noise-induced hearing loss is different in one important way: it can be reduced or prevented altogether by using protective ear plugs. The following OSHA links provide extensive information related to the origins of noise and its impact on our ability to hear: Physics of Sound Anatomy and Physiology of the Ear Effects of Excessive Exposure Ultrasonics Specific Requirements for Hearing Protection OSHA requires employers to determine if workers are exposed to excessive noise in the workplace. If so, the employers must implement feasible engineering or administrative controls to eliminate or reduce hazardous levels of noise. Where controls are not sufficient, employers must implement an effective hearing conservation program. Section 5(a)(1) of the OSH Act, often referred to as the General Duty Clause, requires employers to "furnish to each of his employees employment and a place of employment which are free from recognized hazards that are causing or are likely to cause death or serious physical harm to his employees". Section 5(a)(2) requires employers to "comply with occupational safety and health standards promulgated under this Act". Some states have slightly different requirements. If you are unsure, the following link provides information about states with alternative plans: OSHA-approved State Plans Links to Other Standards and Guidance The American Conference of Governmental Industrial Hygienists (ACGIH) has established exposure guidelines for occupational exposure to noise in their Threshold Limit Values (TLVs). The National Institute for Occupational Safety and Health (NIOSH) recommends using the Criteria for a Recommended Standard: Occupational Noise Exposure -- Revised Criteria. NIOSH (1998) Publication No. 98-126 Department of Defense (DOD) DOD Hearing Conservation Program (HCP). DOD Instruction 6055.12 (1996, April). Department of Transportation (DOT)/Federal Motor Carrier Safety Administration Code of Federal Regulations. Vehicle Interior Noise Levels, 49 CFR 393.94. Environmental Protection Agency (EPA) Product Noise Labeling. EPA Regulation 40 CFR Part 211 (1979). Federal Railroad Administration (FRA) Code of Federal Regulations. Locomotive Cab Noise, 49 CFR 229.121. Mine Safety and Health Administration (MSHA) Health Standards for Occupational Noise Exposure The hearing damage criteria established by the OSHA noise regulation takes into consideration the noise level and the exposure time. An exposure to 90 dB for 8 hours is considered to be safe by OSHA, but it is recommended that you always use hearing protection when exposed to 100dB or more, even if the exposure is short. The exposure is doubled for every increase of 5 dB, as defined by OSHA. (Physically the sound pressure level doubles every 3 dB). The table below explains the relationship between noise level and exposure time.
What Kind of Noises Are We Talking About, Anyway? Below is a list of noise levels for sounds and equipment that you may be familiar with. Many of the examples are from the NIOSH website, but other references have also been used. It is important to keep in mind that you should really be concerned with the noise level at the ear, instead of the noise that is actually produced by the equipment.
How Am I supposed to Measure a Noise? The first step toward solving any noise problem is to define it. To understand what requirements must be implemented according to OSHA's noise standard(s), it is necessary to determine exposure levels. There are various factors that may indicate noise is a problem in the workplace or at home. While people react differently to noise, subjective responses should not be ignored because they may provide warnings that noise may be at unacceptable levels. Noisy conditions can make normal conversation difficult.
You need to know the approximate noise level of the environment you are seeking protection against. The decibel (dB) level can be measured with a sound-level meter. This works fine in professional environments, but homeowners and consumers can use estimates and common sense. Most equipment and machinery used by homeowners, such as lawn mowers, chain saws, line trimmers and similar devices do not produce sounds in excess of 100dB. In addition the exposure time is usually limited to a couple of hours. If you use a tool that produces 100 dB, and plan to use it for an hour or two, and you use an average hearing protector with a 25 dB Noise Reduction Rating, you will be more than adequately protected. Of course, if you also are exposed to noise at work, you must take this into consideration, since it is your total daily dose that matters. To calculate your exposure the Environmental Protection Agency’s noise regulation advises that you deduct the NRR from the noise level. (*Example, the tool and hearing protector discussed above: 100 dB - 25dB = 75 dB at the ear.) For professional applications, when the noise level is known in dB(A), OSHA advises that the NRR be reduced by 7 dB: (*Example: 100dB(A) - (25 - 7)dB = 82dB at the ear.) OSHA may also require a 50% reduction of the NRR after the above reduction: (*Example: 100dB - (25 - 7) x 0.5 = 91dB at the ear.) What is NRR (Noise Reduction Rating)? It is an attempt to summarize a hearing protectors performance in a simple manner, by processing all the test data in accordance with an established formula. The NRR rating is widely and most commonly used. The NRR is a single-number rating that is required by law to be shown on the label of each hearing protector sold in the United States. The values of sound attenuation used for calculation of the NRR are determined in accordance with ANSI S3.19-1974, "American National Standard for the Measurement of Real-Ear Hearing Protector Attenuation and Physical Attenuation of Earmuffs." Click here to find out how to calculate NRR (NIOSH) |
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