About Metalworking Machine Noise Levels
In the metalworking industry, there is a significant amount of hearing loss created by a significant amount of noise. There are a variety of sources for this noise, from dropping tools to machines. These devices necessitate that metalworkers protect their hearing. Available devices for hearing protection include ear plugs, ear muffs, and active noise reducers.
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Noisy Machines
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Each activity in metalworking creates noise, which is typically measured in decibels. Even with metalworking fluids cutting down on the vibration created by the machines, there is still a great amount from the cutting activities and the machines themselves. According to a study by J. Granneman available at www.peutz.fr, noises on a job site such as grinding, welding, cleaning with compressed air, and punching each create 90 to 100 decibels of noise. Noise above 85 decibels is considered dangerous to hearing if you are exposed to it in a job, especially if the shift is more than eight hours, according to the U.S. Occupational Safety and Health Administration (OSHA). The noise must be measured from the location of the person hearing it (including passersby).
In addition, some localities have laws regulating the amount of noise allowed. Even if a casual visitor (who may leave if the noise is uncomfortable) might not receive damage until the decibel level is 125 decibels (which is considered painful), the noise pollution may require protection as a precaution against potential liability (more information is available in Resources).
Ultrasonic Waves
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Ultrasonic waves also have documented medical effects that can disrupt body function. Even though these waves are so low in frequency that they are not heard, they still may pose a significant danger to hearing, though experts have had difficulty studying ultrasonic effects because in the real world, they are not separable from the effects of audible noise on hearing, according to Occupational Audiometery (see Resources). Reports in medical journals have discussed the ability of these waves to concentrate chemicals in certain parts of the body. In fact, the military has experimented with these waves as a nonlethal form of crowd control.
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Hearing Protection
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Ear plugs, ear muffs and active noise reducers all protect hearing at work. Ear plugs are inserted into the ear to passively block sound to the ear canal by providing a barrier. They are usually available as foam, though they come in other materials such as plastic, thick wax, and sometimes a wad of toilet paper. These are often combined with other means (ear muffs). To estimate the hearing protection obtained from combined sources, add a 5-decibel advantage to the higher protection number of the two devices. Ear plugs are used to block out all sound, making communication difficult, though it is better to be able to hear later than never again.
Ear Muffs
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Ear muffs passively deny sound by a barrier that cups over the ear to muffle (hence the word muff) sound. The ear muff does not discriminate between sounds and blocks all sound that it encounters. These are sometimes uncomfortable and not always worn when they should be due to extreme discomfort in hot climates or in situations where communication is vital during the loud work being done.
Active Noise Reduction
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Objections to muffs (and earplugs for that matter) are partially overcome with the latest generation of hearing protection. A review by Cody Alderson on bowhunting.net evaluates a device that cancels out the loud noises while giving a boost to quieter sounds. It resembles ear muffs but has a volume control on the side of one of the headphones. If effective, this would make the device especially useful In metalworking machine shops, since it allows for communication but limits noises louder than 85 decibels. Instead of cutting out all noise once the noise surpasses 80 decibels, as many other noise canceling headphones do, this device only cuts out specific noises that have reached a certain level, according the evaluation. This would have exciting implications in the workplace, where communication is critical.
Sound Mats
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Metalworking machine noise levels are further reduced by adding noise-absorptive layers sometimes called "sound mats." These layers can be made of anything that absorbs the sound. A layer of compacted fiberglass insulation (covered in plastic of course) or "egg carton" foam will muffle some of the noises in a machine shop if they are merely hung about in strategic locations around the shop. One such place would be the outer panel of a machine (so long as it does not get in the way of other safety features, the function or the safe operation of the machine). Pads may also be made from moving blankets to cover walls or ceilings. Just keep in mind that whatever is used, it should be in a layer of plastic since it needs to be cleaned from time to time.
OSHA
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OSHA requires that work environments with more than 85 decibels for eight hours have a hearing-protection program in place for their workers. This means that the worker has to have a baseline hearing test and a test every year after that as long as he is working in a noisy environment (even if it is only above 85 decibels for a day). Noncompliance may lead to fines and vulnerability to litigation. OSHA can be contacted to determine your organization's compliance to improve worker safety at osha.gov or by calling the OSHA office in your state.
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