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This material is for training purposes only. Its purpose is to inform employers and employees of best practices in occupational safety and health and general OSHA compliance requirements. This material is not a substitute for any provision of the Occupational Safety and Health Act or any standards issued by OSHA.
MODULE 7: HEARING PROTECTION

What's the noise all about?

Most of us take hearing for granted. When we go home at the end of a workday and when we get up in the morning, we expect to hear well. Human hearing is amazingly sensitive. Our ears can distinguish 400,000 different sounds and can detect sounds so quiet that they cause the eardrum to vibrate less than 1/80,000,000th of an inch. But that remarkable sensitivity doesn't have a lifetime guarantee — to maintain it, you have to care for it. In our society, noise is as much a part of our lives as the air we breathe. We're exposed to noise in our workplaces, at home, and during our recreational activities. Yet our ability to hear well offers few clues when we put it at risk.

Noise-induced hearing loss is the term for hearing damaged by exposure to excessive noise. The damage to hearing caused by excessive noise at work and play may not be apparent for years. Hearing loss can't be treated or cured, but it can be prevented.

Sound and Noise

Sound is what you hear. Of course, a dog can hear sounds that you can't, and you can feel the sound of a jet as it prepares to take off. However, most of us relate sound — our sensation of very small, rapid changes in air pressure — with things we hear.

Noise is any sound that you don't want to hear. Although one person’s noise may be another person’s music, there’s a point at which sound becomes a problem for all of us: when it’s so loud that it destroys our ability to hear the sounds we want to hear.

How is sound measured?

Sound is measured in two ways: decibels and frequency.
  • Decibels indicate the pressure of sound. Sound waves transfer that pressure from place to place and are expressed in units on a logarithmic scale.

  • 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 a sound’s pitch the higher its 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 3,000-4,000 Hz. That’s why people with damaged hearing have difficulty understanding higher-pitched voices and other sounds in the 3,000-4,000 Hz range.

Children usually have the best hearing and can often distinguish frequencies ranging from the lowest note on a pipe organ (about 20 Hz), to the trill of a dog whistle (20,000 Hz).

When is workplace noise dangerous?

There’s only one way to know: Have the noise evaluated by someone trained to conduct a sound survey. Anyone trained to use a sound-level meter and a dosimeter and evaluate the data should be able to do the survey.

There are three types of surveys:
  1. Basic survey (area monitoring). Use a sound-level meter to identify areas in the workplace that may put workers’ hearing at risk.
  2. Detailed survey (personal monitoring). Use a sound-level meter and a dosimeter to monitor and estimate an individual’s daily noise exposure.
  3. Engineering survey. Measure noise levels produced by machinery in different operating modes to find ways to eliminate or control the noise.
An effective noise survey should give you enough information to understand a noise problem — to identify it and to determine how to control it. It’s important to narrow the survey’s focus, however, so that you aren't overwhelmed with more information than you need to make a good decision.

"Yeah, that machine used to be noisy...but it's not so loud any more."

Think about it this way: You can walk across a grassy yard a couple of times every day without causing any damage to the grass. However, if you continually walk back and forth, you eventually beat down the grass, forming a path. The grass loses its ability to spring back. It just lays down and eventually dies. In a similar manner, continual loud noise beats down the hair cells in your the cochlea of your inner ear. Eventually, they lose the ability to spring back. The big difference, however, is that while grass can grow back, those hair cells in your ear won't. When you consider that you've only got around 16,000 hair cells in each ear, and they are thinning out from the day you are born, it's important to take good care of them.

When employees Need Protection

Your workplace must have a hearing-conservation program when employees are exposed to noise levels that are equal to or greater than 85 dBA averaged over an eight-hour period. And, if your workplace has noise levels that are greater than those shown in the table below, you must use engineering or administrative controls to reduce employee exposures. If these controls aren't effective, employees must also use hearing protectors to reduce exposures to safe levels. 
 
          PERMISSIBLE NOISE EXPOSURES*
 ______________________________________________________________
                             
    Duration per day, hours  | Sound level dBA slow response
 ______________________________________________________________
                             
 8...........................                    90
 6...........................                    92
 4...........................                    95
 3...........................                    97
 2...........................                   100
 1 1/2 ......................                   102
 1...........................                   105
 1/2 ........................                   110
 1/4  or less................                   115
 ____________________________________________________________
* When the daily noise exposure is composed of two or more periods of noise exposure of different levels, their combined effect should be considered, rather than the individual effect of each. If the sum of the following fractions: C(1)/T(1) + C(2)/T(2) C(n)/T(n) exceeds unity, then, the mixed exposure should be considered to exceed the limit value. Cn indicates the total time of exposure at a specified noise level, and Tn indicates the total time of exposure permitted at that level. Exposure to impulsive or impact noise should not exceed 140 dB peak sound pressure level.

Engineering and Management Controls

Engineering controls are most effective. Basically, all we're talking about is attempting to eliminate or reduce the noise level by redesigning, replacing or enclosing noisy equipment. When you replace a noisy machine with a quiet one, modify it to make it quieter, or change the sound path so that the noise never reaches the listener, you are using an engineering control. For example, if you have an old, noisy electric hand drill, you can replace it with a newer, quieter one. If you have a large noisy chipper/shredder, however, replacing it may not be practical. Instead, you might enclose the shredder to isolate the noise.

Management (Work Practice/Administrative) Controls attempt to limit exposure by reducing the duration of exposure to the noise. Examples include:
  • Reduce the time employees spend working in noisy areas; rotate two or more employees so that each is exposed to noise less than 85 decibels, averaged over an eight-hour day.
  • Shut down noisy equipment when it’s not needed for production.
  • Ensure that employees maintain equipment so that it runs smoothly and quietly.
  • Ensure that employees know how to perform their tasks and operate equipment at safe noise levels.
  • Use warning signs to identify work areas where noise exceeds safe levels.
  • Encourage employees to report noise hazards to supervisors.

Hearing Conservation Program

I'm not going to talk at length about the hearing conservation program because we're trying to focus in on the actual hearing protection (PPE) itself in this module. Elements of a hearing conservation program Your workplace must have a hearing conservation program if employees are exposed to noise levels that are equal to or greater than 85 dBA averaged over an eight-hour period. The program’s critical elements include exposure monitoring, audiometric testing, hearing protector use, employee training, access to information, and recordkeeping.

Hearing Protectors

As you are probably well aware, there are basically four types of hearing protectors.
  • Molded earplugs
  • Custom-molded earplugs
  • Self-molded earplugs, and
  • Ear muffs

Molded earplugs are usually made of plastic or silicone rubber. They are available in a variety of shapes and sizes and are usually characterized by one or more ribs or contours. They are considered multiple use; therefore, they must be cleaned and properly stored after each use.

Custom molded plugs are generally made of plastic and are designed from a molded wax insert of the wearer's ears. They are considered multiple use but cannot be switched ear to ear.

Self-molded earplugs are generally made of mineral down or plastic foam and are molded or formed by the wearer. Generally one size fits all and they may be either single or multiple use.

Earmuffs are designed to be multiple use and may be designed to be worn with the harness over or behind the head, or below the chin. They are generally more comfortable, but usually provide less noise reduction, thus less protection, than ear plugs.

More Employer Responsibilities

Employers must make sure that hearing protectors are worn:

  1. By all employees who are required by the PPE standard to wear personal protective equipment; and
  2. By all employees who are exposed to an 8-hour time-weighted average of 85 decibels or greater, and who:
  • Have not yet had a baseline audiogram
  • Have experienced a standard threshold shift.

The intent of the law is that employers make hearing protectors available to all employees that meet the criteria above at no cost to employees. Also, hearing protectors must be replaced as necessary. And, employees must be given the opportunity to select their hearing protectors from a variety of suitable hearing protectors provided by the employer. The employer must also make sure that hearing protectors fit properly at the initial fitting and then supervise their correct use. One effective way to make sure employees are involved in this process is to ask your PPE supplier account representative to display a range of products to the employees.

Education and Training

The employer must provide training in the use and care of all hearing protectors provided to employees who are exposed to noise at or above an 8-hour time-weighted average of 85 decibels, and must make sure employees participate in the program. Although the standard only requires "training," make sure your PPE training (or any safety training for that matter) includes "educating" the employee as to the importance of the correct use of their PPE. As we talked about in Module 3, education tells employees the "why" which increases understanding. Understanding affects attitude which, in turn, influences behavior. The goal is to get employees to "want to" use their PPE correctly. The educational component of this training includes information on:
  • The effects of noise on hearing
  • The purpose of hearing protectors
  • The advantages, disadvantages
  • Attenuation of various types
  • The purpose of audiometric testing, and an explanation of the test procedures.
The employer must also make sure that each employee demonstrates the ability to use and care for the PPE they are using.

Last words.

Well, it's time to take your module quiz. It's been a long seven modules, but you did it! Answer the questions on the following review quiz.



Take the Review Quiz

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