Dru Sahai, ROH, M.Sc.(A), Project Coordinator Construction Safety Association of Ontario How to prevent noise-induced hearing loss in construction Introduction Noise exposure is one of the most widespread health hazards in construction. Each year in Ontario there are about 300 new compensation claims for noise-induced hearing loss (NIHL) in the industry. NIHL can and should be prevented. Prolonged exposure to noise over the years generally causes permanent damage to the inner ear that can't be repaired medically or surgically. Because NIHL is usually gradual, impairment isn't noticed until a substantial degree of hearing loss has already occurred. The occupational and personal consequences are significant:
This article documents the noise levels found on construction sites, indicates the extent of hearing loss among construction workers, and recommends how the industry can help prevent NIHL. Sound and HearingSound stimulates tiny hair-like cells in your inner ear. These vibrate and send auditory messages to your brain. But too much noise for too long can damage the cells. When they no longer send signals to the brain, hearing is lost. Damage often occurs slowly over a number of years and may go unobserved until too late. Most of the workplace sounds that cause permanent damage occur over a long time (for example, about 8 hours per workday over 10 years or more). Sound is defined by strength, frequency (pitch), and duration. Decibel (dB) is the unit used to measure a sound's strength. The decibel scale is not linear but logarithmic. This means that noise levels can't be added directly like other numbers. For example, a backhoe and a compressor each producing 90 dB have a combined output of 93 dB, not 180. But 93 dB is still twice as much noise as 90 dB. In other words, sound intensity doubles every 3 dB. Sounds must also be specified in terms of frequency or pitch. Most workplace noises include a wide band of frequencies and are measured through the "A" filter in sound-level meters. The noise level is therefore expressed in decibels (dB) on the "A" scale, or dB(A). Duration of exposure is equally important. Duration is typically measured over a workday and accumulated through many years. NoiseA noise level of 85 dB(A) over an 8-hour workday is potentially damaging. The louder the noise, the faster the damage. Remember that sound intensity doubles every 3 dB. So for each 3 dB increase in sound level, potential damage to the ear doubles. Noise exposure must be controlled accordingly.
These guidelines are legislated in some jurisdictions across North America. But there are no standards for noise on construction sites in Ontario. When considering sounds that can damage hearing, keep one important point in mind. What matters is the energy of the sound reaching the ear, not its source. In other words, it makes no difference whether the sound is made by a bulldozer or an orchestra. Construction NoiseBy conducting sound surveys, CSAO has identified the construction trades and activities most likely to expose workers to hazardous noise. Most trades are typically exposed to noise levels greater than 85 dB(A) averaged over an 8-hour shift. Graph 1 summarizes sound levels for the noisiest trades and work environments. With average exposures over 95 dB(A), boilermakers, sheet metal workers, and ironworkers are at significant risk of NIHL if not properly protected. Table
1 shows noise levels measured for various types of tools and equipment
found on construction sites. Audiometric Testing Hearing loss is measured by determining the lowest level at which a person can hear at various frequencies. The first audiometric sign of NIHL is usually a loss of sensitivity in the higher frequencies from 3,000 Hz through 6,000 Hz. Permanent hearing loss results if exposure continues on a regular basis. As hearing loss spreads to higher frequencies, important speech information can become muffled and difficult to understand. Audiometric testing has shown significant NIHL in 49% of British Columbia construction workers tested and 50% of Alberta boilermakers with 20 or more years' experience. PreventionA hearing conservation program for construction must include the following components:
To identify a noise problem and determine whether a sound survey is necessary, some basic questions need to be answered.
If it's decided that a sound survey is necessary, ensure that the person conducting the assessment is thoroughly familiar with the operation, calibration, and limitations of the meters used. Administrative controls may include the following measures.
Engineered noise controls include
Training helps to ensure that the risks of noise exposure are understood and that exposed workers are not only instructed but also motivated to use hearing protectors conscientiously. Personal hearing protectors are barriers that reduce the amount of noise entering the ear. The devices are either insert or muff types. The insert type attenuates noise by plugging the ear canal. The muff type covers the external ear and provides an "acoustical seal." The Noise Reduction Rate (NNR) for a particular device is identified on its packaging. The NNR is an important consideration in choosing hearing protectors. To attain maximum rated protection, devices must be worn according to manufacturers' instructions. Again, training is essential. For exposure levels over 105 dB(A), double protection may be required, that is, earmuffs and earplugs. At the other extreme, it's important to avoid overprotection. Using more protection than necessary can make workers feel isolated from their work environment. Take care to select protectors with sufficient, but not excessive, attenuation to keep noise below the safe limit of 85 dB(A). Individuals exposed to noise in excess of 85 dB(A) averaged over an 8-hour shift should undergo periodic audiometric testing to determine whether they are developing NIHL. Anyone showing a significant deterioration in hearing compared to previous tests should be referred for a thorough medical examination.
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