April 1, 2008
Hearing protection devices (HPDs) come in many shapes and sizes, and there is no such thing as “one size fits all.” It seems that there are as many types of hearing protection devices as there are sources of noise, making the selection process a labyrinth to navigate.
Choosing the right type of hearing protection is based as much on art as it is on science. Unfortunately, many employers leave the selection process up to their purchasing department, which may make decisions based on cost rather than suitability. In fact, the selection process is far more complicated. Selection decisions should be based on the requirements of the job, comfort and durability.
Earplugs and earmuffs
Hearing protection devices are pieces of personal protective equipment (PPE) used to protect the ears from noise-induced hearing loss. HPDs fall under one of two categories: earplugs or earmuffs. Earplugs are inserted into the ear, and earmuffs fit over and around the external ear. So, how do you choose between these two types of HPDs?
You should base your selection of earplugs or earmuffs on the pros and cons of each device. For example, earplugs are generally preferable for longer use, whereas earmuffs may be more appropriate for operations that require donning and doffing hearing protection many times per day. Earplug effectiveness is highly dependent on the individual’s ability to insert the plug properly in the ear, as opposed to earmuffs, which require less training and skill to don properly.
You should also consider the working environment when selecting between earplugs and earmuffs. Because earplugs fit inside of the ear, they may be more appropriate for tight spaces than the more cumbersome earmuffs. Furthermore, earplugs may be more suitable for cold environments as they can be worn under caps. And earplugs tend to be more comfortable in hot environments than earmuffs, which can produce sweat under the cup.
Finally, when deciding between earplugs and earmuffs, examine employee practices and health. Long hair, glasses and other safety gear can interfere with the earmuffs’ seal against the head, making earplugs more appropriate for these situations. Conversely, if an employee has an inner ear infection, excess buildup of wax, or other ear canal conditions, then earmuffs should be selected in place of earplugs.
What is the NRR?
The NRR, or noise reduction rating, is one of the most important indicators of how effective HPDs will be. The NRR is a numerical rating required by law to be shown on the label of each HPD sold in the United States. It provides users with information on how many decibels the product can be expected to reduce noise when used properly.
While the NRR is widely used, it is poorly understood. One of the most common misconceptions of the NRR is that the HPD actually protects to that number. The key to the NRR is that the hearing protection must be used and worn perfectly in order to provide the level of protection indicated. Because people are far from perfect, OSHA has required that a correction factor be calculated in order to account for these imperfections, which may include air leaks and vibration in the ear, as well as vibration of the device itself.
For example, when you order earplugs (or earmuffs) that have a NRR of 29 decibels, you cannot assume they will reduce noise exposures by 29 dB. In fact, OSHA requires that you employ the following calculation:
protected dBA = unprotected dBA – (NRR – 7)
This equation suggests that hearing protection with a 29 dB NRR may actually only provide 22 dB of noise reduction. NIOSH takes this equation one step further by derating the NRR by 50 percent for foam plugs (75 percent for earmuffs):
protected dBA = unprotected dBA – (NRR – 7)/2
So now the NRR has been reduced from 29 decibels to only 11 decibels. The important thing to remember here is that you need to know the sound levels in the work environment in order to determine whether the selected hearing protection is providing adequate protection to the employee.
Another pitfall of the NRR is that employers often use the highest NRR product they can find rather than provide employees with hearing protection that is appropriate for the work environment. This often leads to misuse, and in many circumstances leads to employees not wearing hearing protection. For example, a lift truck driver operating a lift in a 92 dBA environment would benefit from having low NRR plugs or musician’s plugs (which intentionally permit some noise to pass) rather than having greater NRR plugs, which could hamper communication.
One of the most important steps in protecting employees from noise-induced hearing loss is to train them on how to properly insert and wear HPDs. Unfortunately, many hearing conservation programs fall short when it comes to training employees in the use of HPDs. Small group training or one-on-one coaching is most effective. Provide employees with several types of hearing protective devices so each individual can select the type of earplug that is most comfortable for them. This will increase the likelihood of the employee’s continued use of hearing protection.
One of the most important aspects of employee training is that employees be instructed on how to properly wear HPDs. For example, earplugs may be properly inserted by pulling the pinna (the upper skin of the outer ear) outward and upward while inserting the earplug into the ear canal. Earmuffs should lay flat against the face, and should not be impeded by hair, eyeglasses, jewelry or other PPE. Finally, like all equipment that comes into contact with both the work environment and the body, hearing protection should be well maintained and cleaned in order to prevent infections and irritation.
Do your homework
While it may seem that protecting employees from noise exposure is as simple as buying earplugs, there really is more to it than meets the eye. Remember, the effectiveness of your hearing protection program is only as good as the time that is invested in researching hearing protection devices and selecting the right type for your employees and your facility.
When selecting HPDs for your worksite, consider whether the environment and work conditions are better for earplugs or earmuffs, don’t always go for the highest NRR, and keep in mind that training is key to protecting workers from noise exposure. Investing a little time on the front end of the selection process will likely yield good employee practices and healthier ears.
SIDEBAR: Walk-around survey
- Tour your facility and develop a detailed understanding of operations and potential noise sources. Look for indications that noise may be a problem.
- Use a sound level meter to take spot readings of operations that are in question. Make notes regarding what equipment is on or off.
- Estimate exposures by identifying workers and their locations and estimate the length of time they spend in different areas or how long they operate particular equipment or tools.
- If the results of your walk-around survey indicate time-weighted average (TWA) exposures of 80 dBA or more, then additional noise monitoring should be performed.