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 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.
Sound is measured in two ways: decibels and 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).
There's only one way to know: Have the noise evaluated by someone trained to conduct a sound survey (e.g., a person trained to use a sound-level meter and a dosimeter and that has the ability to evaluate the data).
Below is a list of three different types of surveys:
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 is 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 lies down and eventually dies. In a similar manner, continuous loud noise beats down the hair cells in 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 only have 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.
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 in more than 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.
|Duration Per Day (Hrs)||Sound Level dBA Slow Response|
|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.
To control noise hazards, a hierarchy of controls has been used as a means of determining how to implement feasible and effective controls. ANSI Z10-2012, Occupational Health and Safety Management Systems, encourages employers to use the following hierarchy of hazard control strategies shown below.
Elimination and substitution, while most effective at reducing hazards, also tend to be the most difficult to implement in an existing process. If the process is still at the design or development stage, elimination and substitution of hazards may be inexpensive and simple to implement. For an existing process, major changes in equipment and procedures may be required to eliminate or substitute for a hazard.
These strategies are considered first because they have the potential to completely eliminate the hazard, thus greatly reducing the probability of an accident.
Basically, all we're talking about is attempting to eliminate or reduce the noise level by redesigning the noisy equipment. When you modify a machine to make it quieter, or change the sound path so that the noise never reaches the listener, you are using engineering controls. For instance, you might enclose a shredder to isolate the noise.
Although ANSI gives this strategy its own category, OSHA considers warning signs and other devices as administrative controls. They help to protect only by warning employees about the noise hazard and to wear hearing protection.
Administrative controls attempt to limit exposure by reducing the duration of exposure to the noise. Below is a list of examples:
Of course, we're talking about hearing protection here. However, if you can eliminate or reduce noise levels so that you don't need earplugs or muffs, it is well worth the money spent in the long term. It can be quite a challenge to supervise proper wearing of hearing protection all the time.
We're 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. Your workplace must have a hearing conservation program if employees are exposed to noise levels that are equal to or greater than 85 dBA average over an eight-hour period (called the 8-Hour Time Weighted Average). Check out Course 751 Hearing Conservation Program Management for more in-depth information regarding hearing conservation.
The critical elements of an effective Hearing Conservation Program include:
Click here for a sample Hearing Conservation Program.
As you are probably well aware, there are basically four types of hearing protectors.
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 may not provide as much protection because they only sit over the ears, rather than directly in the ear canal.
Click here to see how to insert earplugs!
Employers must make sure that hearing protectors are worn:
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.
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.
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 employer must also make sure that each employee demonstrates the ability to use and care for the PPE they are using.