For this blog entry we will discuss how we can know if a worker with hearing impairment can hear alarms.
The question:

I have an employee that has moderately-severe hearing loss bilaterally in the high frequencies, moderate low frequency loss in the right ear, and mild low frequency loss in the left.  I have requested information about the sound levels of alarms in the area he will be working in, but I was curious as to how to calculate if he will be able to hear the alarms once he is wearing hearing protection.  My instinct is the level of the alarm, minus the NRR rating, and if it is greater than his loss levels, he should be able to hear it?

There are a lot of variables in this question. So let’s fill in the blanks for one scenario.

1. Let’s look at the sound frequency of the alarm system. Frequencies below 1,000 Hz are masked easier by low frequency noise; frequencies greater than 2,000 Hz need louder volume levels to be heard due to the employee’s hearing loss.

2. We don’t know the type signal the alarm is using.  It could be pulsed, like horn beeps or a continuous steady state tone.  Intermittent sounds are more recognizable than steady state tones.

3. We don’t know the background noise level in the work area. A comfortable listening level would be 6 dBA above background noise levels. Since this is an alarm, I would think it would need to be 10-12 dBA or greater to be recognized as such. But the signal should not be so loud as to elicit a startle effect, thereby increasing heart rate, blood pressure, and stress in general.

4. We do know the employee has a hearing loss.
So let’s go at it this way. Since the most comfortable listening level is 6 dBA above background noise, and we suspect that 10 dBA would be sufficiently loud enough to be a good warning alarm, then the attenuation of the hearing protector (HP) would lower both the warning alarm and background noise about the same. So one method of calculating the attenuation of the hearing protector is to subtract 7 from the NRR, and then divide by two (in case of loose fit). To apply, say the work area is 90 dBA and the hearing protector has a NRR of 31.  90 dBA less HP attenuation (31-7=24/2=12), and (90-12=78).  With HP inserted 78 dBA would be the loudness level of the background noise at the eardrum. The warning signal would be presented at 88 dBA if the signal to noise ratio was 10, or the alarm was 10 dB greater than the background noise (90-12+10=88).  Since we suspect the employee will be able to hear an 88 dBA signal level, it should work.

Of course a cheap shot is to put the hearing protection on the employee and ask them if they can hear the alarm system and if it is sufficient to alert them to danger.

Courtesy of George Cook, Au.D., Occupational Audiologist

Elizabeth Masterson, PhD, CPH, COHC

Greetings from the National Institute for Occupational Safety and Health (NIOSH)! Some new and exciting public health surveillance efforts for occupational hearing loss (OHL) have been underway and we would like to share our progress, future plans and the results from our first study. The NIOSH OHL Surveillance Project began in 2009 to establish a national repository for occupational hearing loss data and to conduct surveillance and research of this common occupational illness.

During this project we have partnered with 14 audiometric service providers (which we will refer to as providers) and collected nearly nine million audiograms, many of which were conducted before 2000, allowing for historical trends to be examined. None of the audiograms contain personal identifying information. We also developed quality assurance methods to identify and remove from analyses audiograms with quality deficiencies or hearing loss consistent with non-occupational exposures. These characteristics included unlikely threshold values, negative slope indicating excessive background noise during testing, and large inter-aural differences (>40 dB). The North American Industry Classification System (NAICS) was used to identify the industry, and a NAICS code was assigned to each audiogram (U.S. Census Bureau, 2012). NAICS codes can range from two-digit to six-digit numbers, and industry specificity increases with each digit.

Rest of article: http://www.caohc.org/updatearticles/fall2012/first-results.php

 The National Hearing Conservation Association’s 2013 annual conference will take place February 21-23 at the Hilton St. Petersburg Bayfront in St. Petersburg, Florida.  The meeting, which attracts about 300 audiologists, occupational health nurses, and researchers, will feature workshops and poster presentations on hearing loss prevention.  The slate of speakers and sessions can be viewed at www.hearingconservation.org.

Attendees who are interested in learning about the latest products and technology in hearing loss prevention can peruse displays of new earplugs, headphones and other hearing conservation devices in the exhibit hall.

In addition to the educational events, the meeting will include several social events.  Participants will be able to enjoy an art auction, silent auction and scavenger hunt.  A networking social will take place at the Dali Museum across the street from the Hilton.

To register, go to www.hearingconservation.org and click on the annual conference link.