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Saturday, May 7, 2011

QuickFitWeb Hearing Protection Test

Approximately 30 million workers are exposed to hazardous noise on the job. While we would prefer to eliminate noise through engineering controls or reduce exposure to noise through administrative controls, hearing protectors are critical when noise is unavoidable. 

Hearing protectors only work if they fit your ears and you wear them properly.  An earplug that doesn't quite fill your ear canal or an earmuff with a small crack in the padding will let lots of noise into the ears through any gaps, even tiny ones.

For best results, conduct this test in a quiet room (background noises can interfere with the test sounds). You can listen through speakers or headphones connected to your computer. Speakers will work with either earmuffs or earplugs. Headphones can be used with earplugs and should be the full-sized "circumaural" type that covers the entire ear and does not press on the inserted earplug.Click "1. Without hearing protection" in the sound player display above and adjust the volume so the sound is barely audible. (You may need to use the controls on your computer along with the on-screen slider.)Put on your hearing protection. If using soft foam earplugs, we recommend the NIOSH Roll-Pull-Hold method. Click "2. With hearing protection" and listen for the test sound. You should not be able to hear the test sound if your hearing protection is fitted properly. If you can hear this track, re-fit your hearing protection and repeat this step.

To help you get the most from your hearing protectors, researchers at the National Institute for Occupational Safety and Health's (NIOSH) Pittsburgh Research Laboratory developed QuickFitWeb, an online tool to check your hearing protection in a minute or less.

Studies of hearing protector users have shown repeatedly that average protection values in the real world are much lower than the labeled Noise Reduction Ratings (NRR) determined in laboratories with trained and motivated subjects. Even worse, many hearing protector users get virtually no protection at all because of poor fit. It's hard to tell if your hearing protectors are working well just by looking at them. A more accurate approach is to check how much they block or "attenuate" noise. Hearing protectors vary in their attenuation characteristics, with most providing a maximum of 20 to 35 decibels of noise reduction when worn correctly. Any hearing protector that's suitable for use in noisy settings will attenuate noise by at least 15 decibels.

The NIOSH QuickFitWeb helps you determine if your hearing protection is giving you at least 15 decibels of attenuation by comparing two "threshold" tests—one without hearing protection and one with the devices on or in your ears. To use QuickFitWeb, play the test sound (a pulsing random noise that sounds like "wooshing" to most people) from the website. As you listen to the sound, adjust the volume on your computer until the sound is right on the edge between audible and too quiet to hear. That sound level is your "threshold of hearing." Then put on your hearing protectors and play the next test sound. The second sound is exactly the same as the first except that it's 15 decibels louder. If you can hear the louder sound through your hearing protection, the devices are attenuating sound by less than 15 decibels and are not protecting you adequately. You need to correct the problem by trying hearing protectors that fit you better or correcting the way you put them on. Then you can try the test again until you get a good fit.

The QuickFitWeb is a highly simplified variation of standard hearing protector evaluations. The QuickFitWeb tests only one octave band centered at 1000 Hz. That is, we filtered a sample of random noise to have maximum energy at 1000 Hz and with energy dropping to zero at 500 Hz and 2000 Hz. Using just a single test frequency saves time and serves the purpose of checking for adequate fit since well-fit hearing protectors will have good attenuation on all frequencies. The QuickFitWeb also streamlines testing by checking for just one attenuation value: 15 decibels. If a protector is poorly fitted, it will usually provide far less than 15 decibels of attenuation. Protectors suitable for noisy environments are generally rated to provide at least 20 decibels of attenuation so they should completely block a sound that's just 15 decibels over the user's hearing threshold.

Quickfit deviceQuickFitWeb is a spinoff from the NIOSH QuickFit standalone device. QuickFit is a small, self-contained device that looks like one side of a set of earmuffs and allows the user to play test sounds, adjust the threshold,and check for at least 15 decibels of protection. It was designed to use inexpensive off-the-shelf circuits and parts so that it could be produced at very low cost. Ideally, it could be placed affordably near any noisy worksite so workers could check their earplugs every time they put them in. Prototypes of the QuickFit device started a series of field evaluations in February 2008.

Portable digital audio player and headphonesAnother related product is QuickFitMP3—a set of digital sound files in the popular MP3 format that can be played on almost any computer or music player. By playing the sounds in sequence, users can test whether their hearing protectors are attenuating noise by at least 15 decibels. These MP3 files are downloadable now from the QuickFitWeb page. A future enhancement of this approach will be to provide a sequence of MP3 "tracks" that vary by 5 decibels to allow users to assess approximately how much attenuation they are getting from their hearing protectors. They will also use the separation possible with stereo headphones to permit testing earplugs inserted in right versus left ears independently. These added sound files will allow some additional training and evaluation scenarios that are beyond the scope of the current QuickFit products.

Noise-induced hearing loss is 100 percent preventable but once acquired it is permanent and life-altering.  The QuickFit products are tool for workers to ensure that their hearing protection is actually working and preventing hearing loss. 

—Robert F. Randolph, M.S.
The author is the Manager of the Hearing Interventions Team at NIOSH's Pittsburgh Research Laboratory

More information on work-related hearing loss is available on the Noise and Hearing Loss Prevention page on the NIOSH website.

Posted 5/12/08 at 12:08 pm


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