Sound & Noise
Sound is caused by pressure variation in an elastic medium, usually air, with characteristics of frequency measured in cycles/second or Hertz (Hz, perceived as pitch), and intensity measured in decibels (perceived as loudness). Noise is considered to be unwanted sound. While the human ear can hear from about 50-20,000 Hz, the speech range is between 1000 and 3000 Hz. Noise induced hearing loss typically occurs at about 4000 Hz, but with continued exposure spreads above and below. The bulk of hearing loss resulting from noise occurs in the first decade of exposure.

Other characteristics may influence the effects of sound. Noise can be continuous, intermittent, impulse or impact and may be for a short or long duration. Temporary hearing loss may follow a noise exposure. If exposure is continued, permanent loss may result.

Experience has shown that exposure to 80 dB of sound causes no significant hearing deficits except in sound-sensitive individuals. At 85 dB however, more and more people may have injury. If you need to shout to communicate at 2-3 feet, you are probably exposed to injurious sound. Prolonged exposure may cause hearing loss that is essentially permanent and non-treatable. Initially higher frequency consonants are lost or confused making for example “bark” sound like “shark” or “ark”. As hearing loss continues, vowels begin to be confused as well. Sometimes hearing loss is accompanied by just the opposite - Tinnitus - or hearing sounds, ringing, chirping that is not really there. This is subjective and so not measurable, but can be very distracting and irritating.

Regulations
The Occupational Safety and Health Administration (OSHA) and the Mine Safety Health Administration (MSHA) have regulations concerning noise exposure in industry, construction, and mining. The Federal Railroad Administration (FRA) and Federal Aviation Administration (FAA) define hearing criteria for engineers, and pilots. For more information on the regulations concerning your job, please speak with your company safety officer.

Audiogram Testing
Audiogram testing is a screening method that tests pure sounds with an arbitrary zero reference level. If you can hear these tones up to 25 dB, your hearing is considered to be normal. This testing does not discriminate between causes of loss, and if your levels are significantly above 25 dB, or one ear is significantly worse than the other, you may be referred to a specialist to determine other causes of hearing loss or ear disease. Alaska Occupational Health does hearing testing using a standard technique to help to get the best test available and allows comparison of your tests year to year to eliminate errors. Our technicians are certified by the Council For Accreditation In Occupational Hearing Conservation (CAOHC), our equipment is approved by the National Institute for Occupational Safety and Health (NIOSH), and our booth is OSHA certified. To avoid any effects of temporary hearing loss, we suggest that you precede your testing with a 14 hour noise free period, and avoid testing when you have recently traveled or had a head cold. Your ears will be examined to detect wax buildup and other diseases and you will be asked to complete a hearing questionnaire so we can interpret your audiogram more accurately.

Hearing Protectors
Hearing protection is optional for an employee exposed to noise levels below 90 dB, but you might want to consider using protection anyway if you perceive your work area as loud. Employees must use hearing protection if they are exposed to levels greater than 90 dB or they have been shown to have a loss of hearing with annual surveillance. Although hearing protection can reduce noise exposure, they can also interfere with hearing ability and communication needs. Equipment should be compatible with other safety equipment, comfortable, and used and cared for properly. Various types of hearing protection include earplugs, canal caps, ear muffs, non-linear protectors, and noise cancellation devices. Look for the Noise Reduction Rating (NRR) of your selected hearing protection. This is the amount of noise reduction in ideal circumstances. To determine “real world values”, we recommend you divide the number by 2. For example, if you are in an environment with 90 dB ambient noise exposure and you are wearing ear plugs with an NRR of 16, your exposure is 90 - 8 = 82 dB. If you wear a second type of hearing protection, for instance earplugs + muffs, you should divide the NRR of the higher device by 2, then add 5 for the second device. (Two are not twice as good.) The best hearing protector is one that is used consistently.

Non-Occupational Exposure
Non-occupational noise exposure can also lead to hearing loss. Saws, snow-machines, loud vacuum cleaners, power tools, etc. may all contribute to your hearing loss.

OSHA regulation (opens in new window):

http://www.osha-slc.gov/OshStd_data/1910_0095.html

CAOHC (opens in new window):

http://www.caohc.org/