This article of Hearing Conservation is a reference tool that you can use to reinforce your understanding of how noise can affect your hearing and what you can do to minimize the effects of high noise levels.
When your job requires you to be exposed to high noise levels, it is essential for you to take steps to protect your hearing. Infrequent exposure to loud noises may not be hazardous, but prolonged exposures to these noises can cause irreversible hearing loss.
Hearing Conservation is divided into three parts:
- Hazardous Noise Levels
- OSHA Standard
- Hearing Protection Equipment
“Hazardous Noise Levels” explains what hazardous noise levels are, defines applicable terms, and identifies and describes properties of sound waves.
“OSHA Standard” describes the OSHA occupational noise exposure standard.
“Hearing Protection Equipment” explains how ear plugs and ear muffs provide hearing protection.
Hazardous Noise Levels
In most cases, short, infrequent exposure to loud noise is not harmful. However, prolonged exposure to loud noise can cause irreversible hearing loss. This part explains what hazardous noise levels are and how they can affect a person’s hearing.
In some jobs, workers experience loud noise levels during their entire workday. Other jobs involve exposure to loud noises, but only for short periods of time. It is not always easy to tell when a noise is too loud or when exposure to loud noises has gone on long enough to be harmful.
When people talk about noise, they are generally referring to any unwanted sound. To better understand noise and the effects of noise, it is first necessary to discuss sound and sound waves.
Sound and Sound Waves
Sound is any pressure variation that the human ear can detect. Sound waves are a series of pressure vibrations that move through a medium such as air or water.
The Hearing Process
The hearing process begins at the outer section of the ear. Sound waves enter the ear and cause the eardrum to vibrate.
The vibration of the eardrum moves three tiny bones inside the middle ear: the hammer, the anvil, and the stirrup. The movement of the bones in the middle ear transfers the vibrations of the eardrum to the inner ear.
The inner ear is filled with a fluid and houses a very sensitive membrane containing thousands of hair like nerve endings called cilia. The cilia convert the movement of the fluid into nerve impulses. The nerve impulses are then carried to the brain, where they are converted into what is perceived as sound.
Two important properties of sound waves are intensity and frequency.
Intensity is the loudness of a sound, and it is measured in units called decibels (dB). A typical decibel scale ranges from 0 dB, which indicates a sound barely perceptible to the human ear, to levels of 130 dB or higher, which are sounds that can cause pain. A jet engine or a gunshot is an example of a sound in the 130+ range.
Frequency is the pitch of a sound, and it is measured in units called hertz. The human ear can hear sounds between 20 hertz and 20,000 hertz, but a person’s hearing is most sensitive to sounds between 1,000 and 5,000 hertz. The majority of industrial sounds have frequencies greater than 1,000 hertz.
In general, high intensity, high frequency sounds are the most damaging to a person’s hearing.
The OSHA standard defines the action level as the level at which some form of hearing protection is required on the job. Without this protection, prolonged exposure to noise that is at or above this level can result in hearing loss.
The action level at which a hearing conservation program must be put into place is 85 dB, as measured on an 8-hour, time-weighted average.
A time-weighted average is a standardized method of reporting the sound levels averaged over an 8-hour period. Using an average helps to account for noise levels that may be higher or lower than the action level during an employee’s work shift.
This part describes the OSHA regulation for hearing conservation.
Occupational Noise Exposure Standard
To deal with the issues of noise exposure on the job, the Occupational Safety and Health Administration (OSHA) developed the occupational noise exposure standard.
Anyone whose job involves working around loud noises for any length of time should be aware of the OSHA standard. The OSHA standard should be posted, in full, in a conspicuous location at each facility.
Hearing Conservation Program
The OSHA occupational noise exposure standard requires companies to meet certain guidelines to guard employees against hearing loss. Among them are guidelines for establishing a hearing conservation program.
The OSHA standard describes exactly what the hearing conservation program must cover. In general, the program is designed to identify and monitor high noise areas, provide workers in those areas with hearing protection and training, monitor the workers’ hearing levels with regular testing, and maintain and provide access to the results of hearing tests.
Identifying High Noise Areas
The first step in initiating a hearing conservation program is to use sound level detection equipment to determine which areas exceed the limits of the OSHA standard. These areas should then be documented and designated as high noise areas by warning signs or some other warning method.
Any time there is a change to a high noise area, such as replacing process equipment, that may affect noise levels, monitoring is repeated. Employees working in such a high noise area should be notified of the change by their employer.
Hearing Protection and Training
The OSHA standard states that employees exposed to hazardous noise levels must be given the opportunity to select hearing protection. The employees must also be properly trained in the use of the hearing protection.
The training program, which should be repeated annually, should include information on the effects of noise on hearing, the purpose of hearing tests, and the purpose of hearing protection.
Hearing tests are an important part of a company’shearing conservation program. A hearing, or audio metric, test measures the ear’s ability to detect sound at specific frequencies or tones.
Audio metric tests should be performed by certified personnel on any employee who is included in the hearing conservation program.
To effectively determine potential hearing loss, OSHA has identified three mid-level frequency ranges – 2,000hertz, 3,000 hertz, and 4,000 hertz – where changes in hearing are measured against a previously established initial, or baseline, test.
Baseline tests are usually performed within 6 months ofan employee’s first exposure to noise levels at or above 85 decibels. Then, employees are retested each year to track any significant changes.
Any changes may signal a decrease in an employee’sability to hear tones at the specified test frequencies.
Standard Threshold Shift
An employee who experiences a change in hearing threshold relative to his or her baseline test that averages 10 decibels or more at 2,000, 3,000, and 4,000 hertz in either ear is said to have undergone a standard threshold shift.
If a standard threshold shift is detected, the OSHA standard requires that the affected employee be notified, in writing, within 21 days of that determination. Then, if necessary, that employee may undergo further testing or evaluation to determine the proper course of action.
Course of Action
For example, if the employee is not presently wearing hearing protection, he or she may be required to do so. Employees who are already wearing hearing protection may need to be fitted for additional equipment or have their existing hearing protection refitted or supplemented.
The results of hearing tests, as well as any information about the noise levels in a facility, must be made available to the affected employees.
Any employee who has questions about the hearing conservation program in his or her company should ask the person in charge of the program. Employees who do not know who is in charge of the program should ask a supervisor.
Employees who are included in the hearing conservation program should make sure that their hearing is tested at least annually and that they understand the results of the tests.
Hearing Protection Equipment
This part describes how ear plugs and ear muffs provide hearing protection.
Although companies are responsible for maintaining hearing conservation programs, ultimately it is up to each employee to protect himself or herself from hearing loss or injury. On the job, that protection is provided by hearing protection equipment.
Hearing Protection Devices
Hearing protection devices come in several forms. The type of protection that an employee uses depends largely on personal preference and on the equipment provided by the employer.
The two most common types of hearing protection are ear plugs and ear muffs.
Ear plugs come in a variety of shapes and sizes. They are generally made from flexible foam rubber, silicone, vinyl, or plastic.
Ear plugs work to block out sound by conforming to the shape of the ear canal.
One of the most important factors in using ear plugs is proper insertion. If an ear plug does not conform properly to the ear canal, it will not provide protection.
Inserting an Ear Plug
One common type of ear plug is made of disposable, expandable foam. The first step in inserting this type of ear plug is to compress the ear plug by rolling it between your thumb and forefinger. Then, with your other hand, reach over your head and pull the top of your ear. This straightens your ear canal. Then insert the ear plug.
If the ear plugs do not feel right, remove them and try another pair. If you are still not comfortable, consult your supervisor. You might have to consider a different form of protection.
Not all ear plugs are inserted the same way, so it is important to read the directions carefully.
Levels of Protection
In general, ear plugs provide greater protection than ear muffs, because ear plugs fit inside the ear canal. However, wearing a combination of ear plugs and ear muffs provides the greatest level of protection.
Like ear plugs, ear muffs are available in a variety of shapes and sizes, and they can provide varying levels of protection.
Ear muffs are made up of three parts: the headband, the ear cushions, and the ear cups.
For proper fit, the headband should be adjusted so that the ear cushions create a tight, noise-reducing seal around the ears.
The ear cushions should be inspected regularly. Perspiration can deteriorate the ear cushions and limit their effectiveness.
Noise Reduction Rating
One way to determine the effectiveness of a hearing protection device is to check the device’s noise reduction rating (NRR). The NRR is a measure of the approximate number of decibels that the device attenuates, or reduces.
Manufacturers of hearing protection devices are required to test their products and assign them an NRR. Before choosing hearing protection, workers should know the minimum NRR required for hearing protection in their work area. Workers who are not sure what the NRR is should check with a supervisor.
For whatever type of hearing protection an employee chooses, the employer should provide training on how to properly use the equipment.
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