Noise Exposure/Hearing Conservation
Hearing conservation programsare designed to prevent noise induced hearing loss. A written hearing conservation program is required by the Occupational Safety and Health Administration (OSHA) “whenever employee noise exposures equal or exceed an 8-hour time-weighted average sound level (TWA) of 85 decibels measured on the A scale (slow response) or, equivalently, a dose of fifty percent.” This 8-hour time-weighted average is known as an exposure action value. While the Mine Safety and Health Administration (MSHA) also requires a hearing conservation program, MSHA does not require a written hearing conservation program. MSHA’s hearing conservation program has almost the same exact requirements as the OSHA hearing conservation program requirements.
Noise, or unwanted sound, is one of the most pervasive occupational health problems. It is a by-product of many industrial processes. Sound consists of pressure changes in a medium (usually air), caused by vibration or turbulence. These pressure changes produce waves emanating away from the turbulent or vibrating source. Exposure to high levels of noise causes hearing loss and may cause other harmful health effects as well. The extent of damage depends primarily on the intensity of the noise and the duration of the exposure. Noise-induced hearing loss can be temporary or permanent. Temporary hearing loss results from short-term exposures to noise, with normal hearing returning after period of rest. Generally, prolonged exposure to high noise
levels over a period of time gradually causes permanent damage. OSHA’s hearing conservation program is designed to protect workers with significant occupational noise exposures
from hearing impairment even if they are subject to such noise exposures over their entire working lifetimes.
Proper training and education of those exposed to noise is the key to preventing noise-induced hearing loss. If employees are properly trained on how to follow a hearing conservation program, then the risk of noise-induced hearing loss is reduced. OSHA requires said training to be completed on an annual basis. Proper training is imperative since “even with a very modest amount of instruction attenuation performance can be significantly improved
What can be done to reduce the hazard from noise?
Noise controls are the first line of defense against excessive noise exposure. The use of these controls should aim to reduce the hazardous exposure to the point where the risk to hearing is eliminated or minimized. With the reduction of even a few decibels, the hazard to hearing is reduced, communication is improved, and noise-related annoyance is reduced. There are several ways to control and reduce worker exposure to noise in a workplace.
Engineering controlsthat reduce sound exposure levels are available and technologically feasible for most noise sources. Engineering controls involve modifying or replacing equipment, or making related physical changes at the noise source or along the transmission path to reduce the noise level at the worker’s ear. In some instances the application of a relatively simple engineering noise control solution reduces the noise hazard to the extent that further requirements of the OSHA Noise standard (e.g., audiometric testing (hearing tests), hearing conservation program, provision of hearing protectors, etc.…) are not necessary. Examples of inexpensive, effective engineering controls include some of the following:
- Choose low-noise tools and machinery
- Maintain and lubricate machinery and equipment (e.g., oil bearings).
- Place a barrier between the noise source and employee (e.g., sound walls or curtains).
- Enclose or isolate the noise source.
Administrative controlsare changes in the workplace that reduce or eliminate the worker exposure to noise. Examples include:
- Operating noisy machines during shifts when fewer people are exposed.
- Limiting the amount of time a person spends at a noise source.
- Providing quiet areas where workers can gain relief from hazardous noise sources (e.g., construct a sound proof room where workers’ hearing can recover – depending upon their individual noise level and duration of exposure, and time spent in the quiet area).
- Restricting worker presence to a suitable distance away from noisy equipment.Controlling noise exposure through distance is often an effective, yet simple and inexpensive administrative control. This control may be applicable when workers are present but are not actually working with a noise source or equipment. Increasing the distance between the noise source and the worker, reduces their exposure. In open space, for every doubling of the distance between the source of noise and the worker, the noise is decreased by 6 dBA.
Hearing protection devices (HPDs), such as earmuffs and plugs, are considered an acceptable but less desirable option to control exposures to noise and are generally used during the time necessary to implement engineering or administrative controls, when such controls are not feasible.
Where engineering and administrative controls are not successful in lowering noise exposure, hearing protection devices must be used. OSHA requires that employees be offered a variety of hearing protection devices, including ear muffs and ear plugs. Noise exposure may be continuous, intermittent or impulsive (less than one second in duration with a delay of more than one second).
Types of Hearing Protectors
There’s a wide variety of types of hearing protectors available, including ear muffs, foam and preformed ear plugs, and canal caps. Selection is based upon several factors, as described below.
Ear Muffs– These devices fit against the head and enclose the entire external ears. The inside of the muff cup is lined with acoustic foam which can reduce noise by as much as 15 to 30 decibels. Ear muffs are often used in conjunction with ear plugs to protect the employee from extremely load noises, usually at or above 105 decibels.
Ear Plugs– Preformed ear plugs come in different sizes to fit different sizes of ear canals. Formable or foam ear plugs, if placed in the ear correctly, will expand to fill the ear canal and seal against the walls. This allows foam ear plugs to fit ear canals of different sizes.
Choosing a Hearing Protector
Choosing the right hearing protector depends upon several factors:
- Good seal: sound reduction is dependent upon blocking any air leakage which will allow sound to bypass the hearing protector and enter the ear. For this reason, the hearing protector must fit properly whether over the ear or in the ear
- Comfort: Both comfort and convenience is important if the device is to be used consistently. The ease of placing and removing the device, as well as environmental factors such as the presence of dirt or chemicals must be considered
- Communication: Hearing protectors often make communication difficult by reducing and distorting sounds. Employees who are hearing-impaired who must receive detailed face to face instruction may prefer ear muffs so that they can lift up the muffs to hear speech.
Correctly Fitting the Device
Ear Plugs – Remember to use the opposite hand to open the ear canal. This is done by grasping the top of the ear and gently pulling upwards. The plug, having been compressed, is placed into the ear canal and held in place for about 10 seconds to allow for expansion of the ear plug.
Ear Muffs – The ear muff cushion must form a seal against the head all around the ear and not rest against any part of the outer ear.
Maintaining a Hearing Protector
Ear plugs must be replaced on a daily basis or whenever they become soiled. Using an unclean ear plug may lead to an ear infection. Employees should be issued their own ear muffs, however, if ear muffs are used by more than one employee, the ear muffs should be cleaned frequently. Ear muffs should be wiped off with soap and water. Ear muffs should be inspected regularly for signs of wear and tear, and should defects appear, the device should be replaced.