Noise is a given on most construction sites. Protecting your workers' hearing from excessive noise is not only required by OSHA but is the right thing to do. But what's excessive noise and how can you best take care of your workers? Let's look at noise, hearing protection, and new blade technology that is reducing the noise generated during concrete cutting.
What is noise dose?
Sound waves can generate enough power to damage human ears, which contain many tiny sensitive parts. Noise is measured as a “dose” that is calculated as a combination of the noise level and duration of the noise. The level is measured using the decibels scale, which is abbreviated as dB. This scale is a logarithmic scale meaning the noise level doubles with each 10 dB increase—at a level of 80 dB normal conversation is possible, while at 90 dB you would have to shout to be heard.
The National Institute for Occupational Safety and Health (NIOSH) has set a Recommended Exposure Limit of 85 dB for eight hours a day. Noise exposure at or above that level is considered dangerous. Employers are required to keep their workers' exposure level below the limit by changing processes or by using hearing protection devices.
For louder noises, though, the allowable duration quickly gets shorter. At 90 dB, the exposure duration must be less than 2 hours and 31 minutes; at 100 dB the duration drops to 15 minutes, at 110 dB it drops to 1 minute and 11 seconds.
Also you need to consider the total daily noise dose, which is a summation of all the various noise levels and durations.
In the end, if you have a noisy site or if you are at all concerned about noise levels, it's best to call in a professional. Noise monitoring is quite technical and the rules for protecting workers are long and involved. To get NIOSH's Occupational Noise Exposure Standard, go to www.cdc.gov/niosh/docs/98-126. You should get annual hearing tests for all workers who are in areas with noise exceeding 80 dB (about the noise level of a vacuum cleaner). Once you've established a Hearing Loss Prevention Program, the exposure monitoring and medical monitoring records must be retained for 30 years.
There are four basic types of hearing protectors: formable foam plugs, premolded plugs, semi-insert devices, and earmuffs. Each will have a noise reduction rating, ranging from 20 to 35 dB. In practice the actual noise reduction is closer to 10 to 20 dB, mostly depending on fit. To check to see if you are getting the expected hearing protection, cup your hands over your ears while listening to a steady noise—if the plugs are fitting properly, there should be no change in noise level.
To insert an ear plug—whether a foam plug, a premolded plug, or a semi-insert device—reach over the top of your head to the opposite ear and pull your ear up to open the ear canal. With foam plugs, you should roll the plug between your fingers to compress the foam and then insert it into your ear—one size fits all. The foam will expand and fill the ear canal.
Molded plugs come in various sizes and styles, so experiment until you find one that is comfortable and works. Semi-insert devices are on a band that hangs below your chin. This device does not provide as much protection as plugs or earmuffs, but is easy to take on and off, and is good for intermittent loud work, such as using a concrete saw or drill.
Earmuffs provide the greatest protection but make sure the cushion fits tightly against your head and that hair, caps, and glasses aren't preventing a good fit. When working around really loud noise (more than 100 dB or about the level of a chain saw), dual protection of plugs and muffs may be necessary and can reduce the noise level another 5 to 10 dB.
For a good primer on hearing protection, visit Indianapolis-based Aearo's Web site at www.e-a-r.com/hearingconservation to download An Earful of Sound Advice, which is also an excellent training resource.