Course 159 Hearing Protection: Basic

Noise and the Basics of Hearing Loss

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Sound and Noise – What’s the Difference?

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.

Noise - is nothing more than unwanted sound. Noise is one of the most widespread occupational health problems. It is a by-product of many industrial processes.

Check out this short audio clip by Dan Clark of that gives a quick overview of nature of sound, noise, and ways to prevent hearing loss in the workplace.

How is Sound Measured?

Sound is measured in two ways: decibels and frequency.

Decibels measure the pressure of sound. Frequency is related to a sound’s pitch and is measured in units called hertz (Hz), or cycles per second. The pitch of a sound — how high or low it seems — is how you perceive its frequency; the higher the pitch, the higher the frequency. High-frequency sounds are generally more annoying than low-frequency sounds and can be more harmful to hearing.

Human hearing is most sensitive to frequencies between 3,000 and 4,000 Hz. That’s why people with damaged hearing have difficulty understanding higher-pitched voices and other sounds in the 3,000 to 4,000 Hz range.

Check out the CDC Noise Meter page to get a better idea how "loud" is loud.

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1. Noise is nothing more than _____.

a. sound that vibrates
b. loud sound
c. non-sinusoidal waves
d. unwanted sound

How Does the Ear Work?

The outer ear consists of the pinna, the ear canal, and the eardrum. When sound waves enter the outer ear, the vibrations impact the ear drum and are transmitted to the middle and inner ear.

The middle ear consists of the ossicles (malleus, incus, stapes) and the ear drum. In the middle ear three small bones called the malleus (or hammer), the incus (or anvil), and the stapes (or stirrup) amplify and transmit the vibrations generated by the sound to the inner ear.

The inner ear consists of the cochlea, the auditory (hearing) nerve, and the brain. The inner ear contains a snail-like structure called the cochlea which is filled with fluid and lined with cells with very fine hairs. These microscopic hairs move with the vibrations and convert the sound waves into nerve impulses–the result is the sound we hear. Exposure to loud noise can destroy these hair cells and cause hearing loss!

2. In which part of the ear does injury occur due to excessive workplace noise?

a. Ear drum
b. Cochlea
c. Incus
d. Semicircular ducts

The Perils of Exposure

As mentioned earlier, very loud sounds can damage the sensitive hair cells in your inner ear. Hair cells are the foot soldiers for your hearing. As the number of damaged hair cells increases, your brain receives fewer impulses to interpret as sound. When you damage hair cells, you damage hearing.

Exposure to high levels of noise may cause other harmful health effects as well as hearing loss. The extent of damage to the ear mostly depends on the intensity of the noise and the duration of the exposure. Hearing loss caused by noise can be temporary or permanent.

  • Temporary hearing loss results from short-term exposures to noise, with normal hearing returning after a period of rest.
  • Prolonged exposure to high noise levels over a period of time gradually causes permanent damage.

Loud noise can also create physical and psychological stress, reduce productivity, interfere with communication and concentration, and contribute to workplace accidents and injuries by making it difficult to hear warning signals.

Noise-induced hearing loss limits your ability to hear high frequency sounds, understand speech, and seriously impairs your ability to communicate.

The effects of hearing loss can be profound as hearing loss can interfere with your ability to enjoy socializing with friends, playing with your children or grandchildren, or participating in other social activities you enjoy, and can lead to psychological and social isolation.

3. The extent of damage to the ear from excessive noise mostly depends on the _____ and the _____.

a. dBA rating; distance from the noise source
b. frequency of the sound; direction of exposure
c. intensity of the noise; duration of the exposure
d. rate of vibration; length of noise level

Temporary and Permanent Hearing Loss

Damaged earhair cells.
Repeated exposures to loud noise can damage hair cells to the point that they won't recover.

While a single exposure to loud noise can damage your hair cells, it probably won't destroy them. You may experience ringing in your ears and some sounds may be muffled, but your hair cells will recover and so will your hearing. This is called a temporary threshold shift.

Repeated exposures to loud noise can damage hair cells to the point that they won't recover. Because the damage is permanent, the result is called a permanent threshold shift. No treatment will restore it. When you destroy hair cells, you destroy hearing.

Exposure to Chemicals

No longer is noise considered to be the only source of hearing loss associated with work. Exposure to chemicals, like aromatic solvents, and metals, such as lead, arsenic, and mercury, can result in hearing loss.

Combined exposures to noise and chemicals can cause more hearing loss than exposure to either agent alone. Vibration and extreme heat are also potentially harmful to hearing when combined with noise.

4. Permanent hearing loss is usually the result of _____.

a. repeated exposure to excessive noise
b. an exposure to high-impact noise
c. a combination of variable-impact noises
d. numerous exposures to various noises

How to Know if Your Hearing is Damaged

Hearing loss is painless and gradual. It usually develops over several years — you might not even notice the loss during those years.

Sometimes, overexposure to loud noise can trigger ringing or other sounds in your ears, called Tinnitus. While tinnitus may be a symptom of damaged hearing, it can also be caused by infections, medications, and earwax.

The only way to know for sure if noise has damaged your hearing is to have a hearing examination by a certified audiometric technician, audiologist, otolaryngologist, or physician.

If you answer "yes" to any of the following questions, your hearing may be at risk:

  • Do you frequently ask people to repeat sentences?
  • Do you feel your hearing is not as good as it was 10 years ago?
  • Have family members noticed a problem with your hearing?
  • Are you exposed to loud noise without hearing protection where you work?
  • Do you have to shout to a co-worker because of the noise around you?
  • Are you exposed to noise from firearms, motorcycles, snowmobiles, power tools, or loud music without hearing protection?

5. What is the symptom called that causes ringing or other sounds in your ears due to overexposure to noise?

a. Vertigo
b. Otitis
c. Tinnitus
d. Otosclerosis

Warning Signs of Hazardous Workplace Noise

Damaged earhair cells.
How loud is your environment?

There are various factors that may indicate noise is a problem in the workplace. While people react differently to noise, subjective responses should not be ignored because they may provide warnings that noise may be at unacceptable levels.

Noisy conditions can make normal conversation difficult. As a general guideline, the work area is too noisy if a worker cannot make himself understood without raising his or her voice while talking to a co-worker 3 feet away. Other clues that it's too loud include:

  • When noise levels are above 80 decibels (dB), people have to speak very loudly.
  • When noise levels are between 85 and 90 dB, people have to shout.
  • When noise levels are greater than 95 dB, people have to move close together to hear each other at all.

Noise-induced hearing loss can develop rapidly in workers exposed to relatively high noise levels on a daily basis.

When It's Too Loud in the Workplace

OSHA requires that employees be placed in a hearing conservation program if they are exposed to average noise levels of 85 dB (called the "action level") or greater during an 8 hour workday. In order to determine if exposures are at or above the action level, it may be necessary to measure or monitor the actual noise levels in the workplace and to estimate the noise exposure or "dose" received by employees during the workday.

6. You can be pretty sure there is too much noise in your workplace when _____.

a. you must shout at a co-worker 3 feet away to be heard
b. the dust vibrates on the top of work surfaces
c. others can't hear you from the next work station
d. the music in your earphones makes it hard to hear

How to Evaluate Noise Exposure

The first step toward solving any noise problem is to define it. To understand what requirements must be implemented according to OSHA's noise standard, it is necessary to determine exposure levels. The following sections provide information about evaluating noise exposure levels:

  • Walk-around Survey
  • Work-shift Sampling
  • Instruments Used to Conduct a Noise Survey
Tour the facility and develop a detailed understanding of potential noise sources.
Tour the facility and develop a detailed understanding of potential noise sources.

Walk Around Survey

A walk around survey should be performed to screen for noise exposures and to determine if additional monitoring is necessary. When screening for noise exposures, sound level meter measurements and estimates of the duration of exposure are sufficient. The resulting spot readings can be used to determine the need for a more thorough evaluation.

If the results of the walk around survey indicate time-weighted average (TWA) exposures of 80 dBA or more, then additional noise monitoring should be performed.

7. After you conduct a walk-around survey for noise levels, you determine the average noise level in a work area is 83 dBA. What should be your next action?

a. Nothing, because noise levels are below the action level
b. Immediately develop a hearing conservation program
c. Conduct additional noise monitoring
d. Hand out hearing protection to everyone in the area

Work-shift Sampling

When the results of the walk around survey indicate that the noise levels may exceed those outlined in OSHA's noise standard, additional monitoring is necessary. Establish a sampling protocol for your workplace. A general protocol is provided as an example below.

  1. Inform the employee being monitored that the dosimeter (noise sampling equipment) should not interfere with his/her normal duties, and emphasize that the employee should continue to work as usual.
  2. Explain the purpose of the dosimeter to each employee being sampled and emphasize that the dosimeter is not a speech recording device.
  3. Instruct the employee being sampled not to remove the dosimeter unless absolutely necessary and not to cover the microphone with a coat or outer garment or move it from its installed position. Inform the employee when and where the dosimeter will be removed.
  4. Check the dosimeter periodically to ensure the microphone is properly oriented.
  5. Obtain and note sound level meter readings during different phases of work the employee performs during the shift.
  6. Record the information required on the OSHA-92 Noise Survey Report.

Personal and Area Monitoring

Personal monitoring: A sound level meter can also be positioned within the immediate vicinity of the exposed worker to obtain an individual exposure estimate.

Area monitoring: This method can be used to estimate noise exposure when the noise levels are relatively constant and employees are not mobile. In workplaces where employees move about in different areas or where the noise intensity tends to fluctuate over time, noise exposure is generally more accurately estimated by the personal monitoring approach.

8. Which type of monitoring process may be best to estimate noise exposure when noise levels are constant and employees are not mobile?

a. Personal monitoring
b. Area monitoring
c. Long-term monitoring
d. Position monitoring

Noise Survey Instruments

Damaged earhair cells.
Industrial hygienist using a sound level meter.

Basically, there are two different instruments to measure noise exposures: the sound level meter and the dosimeter.

Sound Level Meter (SLM)

A sound level meter is a device that measures the intensity of sound at a given moment. Since sound level meters provide a measure of sound intensity at only one point in time, it is generally necessary to take a number of measurements at different times during the day to estimate noise exposure over a workday. If noise levels fluctuate, the amount of time noise remains at each of the various measured levels must be determined.

Sound level meters can be used to:

  • Spot-check noise dosimeter performance.
  • Determine the employee's noise dose whenever use of a noise dosimeter is unavailable or inappropriate.
  • Identify and evaluate individual noise sources for abatement purposes.
  • Aid in determining the feasibility of engineering controls for individual noise sources.
  • Evaluate hearing protectors.

9. Which type of measurement instrument measures sound intensity at a given moment?

a. Audio meter
b. Dosimeter
c. Noise detector
d. Sound level meter

Noise Survey Instruments (Continued)

Damaged earhair cells.
Noise dosimeter attached to a worker.

Noise Dosimeter

A dosimeter is like a sound level meter except that it stores sound level measurements and integrates these measurements over time, providing an average noise exposure reading for a given period of time, such as an 8-hour workday.

Dosimeters can be used to:

  • Make compliance measurements according to OSHA's noise standard.
  • Measure the employee's exposure to noise and automatically compute the necessary noise dose calculations.

With a dosimeter, a microphone is attached to the employee's clothing and the exposure measurement is simply read at the end of the desired time period. A reader may be used to read-out the dosimeter's measurements. Since the dosimeter is worn by the employee, it measures noise levels in those locations in which the employee travels.

10. Which type of measurement instrument provides an average noise exposure reading for a given period of time?

a. Audio meter
b. Sound detector
c. Noise dosimeter
d. Sound level meter

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