Monthly Archives: September 2015

Question Behind Noise

September 22, 2015
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Perhaps the Reason We Haven’t Solved the Noise Induced Hearing Loss Problem is Because We’re Not Asking the Right Questions

By Jeffery M. Goldberg, Protectear.com

“Calling noise a nuisance is like calling smog an inconvenience. Noise must be considered a hazard to the health of people everywhere”- Former U.S. Surgeon General William Stuart

People have known this about noise and its effects on hearing for decades and yet Noise-Induced Hearing Loss (NIHL) remains epidemic in the workplaces of America. Why? Maybe as Bertrand Russell once noted,

“In all affairs, it’s a healthy thing now and then to hang a question mark on the things you have long taken for granted.”

While examining why we haven’t made more progress eliminating Noise Induced Hearing Loss (NIHL) I look to our neighbours, the United States, because their development path is well defined. As early as the beginning of the last century, noise was recognized as being an industrial hazard.

Because it was difficult to measure noise at the time, NIHL was recognized but not quantified nor were any limits on exposure set. After a series of studies by the military and military sponsorship of civilian laboratories after World War II through the mid-1960s, 90 dBA was determined to definitely be a level above which actions to limit exposures were necessary. Therefore, 90 dBA was written into the U.S. Occupational Noise Standard in 1969 as part of the legislation as the Permissible Exposure Limit (PEL). The Occupational Safety and Health Administration (OSHA) was directed to develop the rest of the regulation picking up from paragraph (c) of the legislation to define the steps necessary to form an effective hearing conservation program.

It is recognized that about one quarter of workers whose LEX,8h is above 90 dBA will develop NIHL. Albeit the National Institute for Occupational Safety and Health (NIOSH) revised its own Recommended Exposure Limit (REL) down from 90 dBA to 85 dBA and further recommended a 3-dB exchange rate instead of the earlier 5-dB exchange rate in the legislation, today the 90 dBA PEL (Permissible Exposure Limit) remains in the U.S. OSHA regulation.

OSHA set an action level of 85 dBA that includes exposed workers in a hearing conservation program and the use of hearing protection devices (HPDs) for those workers who had shown a change in hearing that could be attributed to noise exposure.

There is more to the history of NIHL regulation in North America. In 1979 the U.S. EPA issued a regulation that required HPD attenuation value be placed on the packaging of all HPDs sold in the United States (this means the same information appears in Canada as the product sold in Canada is mainly the US product). This “required HPD attenuation” is the Noise Reduction Rating (NRR) that was to be used by Audiologists and Industrial Hygienists to determine if the HPD’s noise reduction would be adequate to reduce protected exposure levels to below the PEL.

Noise Reduction Rating (NRR)

The problem was that, although Audiologists and industrial hygienists now had this new NRR for selecting HPDs matched to noise exposures, workers still continued to lose their hearing. Study after study comparing NRRs to attenuation actually achieved by those wearing the protection yielded considerable discrepancies. Finally, in 1994, a study published by Berger (Aearo, now 3M), Franks (NIOSH ret), and Lindgren (GN Netcom) compiled the data from 22 previous studies from the prior 20 years and conclusively showed that there was hardly any relation between the NRR and the protection workers actually received.1 Further, studies of the HPD-using noise-exposed workers found that they continued to get NIHL. The OSHA directed programs were merely documenting the development of NIHL, not preventing it. One union official referred to this asaudiometric voyeurism.

There was a wide discrepancy between what laboratories determined for the NRR as the attenuation potential of a hearing protector and what users were achieving in practice. Why?

Set aside, the consideration of whether the PEL/exchange-rate should be 90 dBA/5 dB or 85 dBA/3 dB. For years the most prevalent thinking concerning the ineffectiveness of HPDs has been the problem of matching earplugs and earmuffs with a particular wearer’s ears. Once the best match HPDs had been selected, a wearer needed to be taught how to fit them properly. The Industry began Fit Testing with the development of Fit Check in 1995.2 Three decades of pursuing this course has had relatively little effect on the problem. In fact, Dr. Peter Rabinowitz, an associate professor in the Department of Environment and Occupational Health at the University of Washington, has studied one of the leading users of Fit Testing systems, Alcoa, for years. Dr. Rabinowitz saw no change in outcomes of Alcoa’s hearing conservation program as a result of Fit Testing. Maybe fitting the protector is not entire problem.

Unpublished research conducted by a branch of the U.S. Military has shown an inability to trigger preliminary hearing loss with even a minuscule amount of hearing protection. What does that mean? It might mean the weight we have been placing on matching attenuation to noise exposure is less important than we thought in preventing NIHL. Is it possible we’ve been asking ourselves the wrong question?

Instead of asking ourselves, How do we get people to wear their hearing protection?” we should be asking,“Why aren’t people using their hearing protection to greatest effect?” Sadly, a panel of experts at the recent National Hearing Conservation Association (NHCA) conference observed that they were not aware of any research into the topic of the causes of NIHL either ongoing or planned.

In trying to puzzle out this conundrum, I recalled a speech given by Dr. Barry Blesser to the NHCA in 2011 on the reason people play their music players at the volumes they do. Dr. Blesser cited the primacy of hearing in the ordering of our senses. As Dr. Blesser pointed out

  • Hearing is the only fully formed sense we are born with
  • It operates 24/7/365 – we have no ear lids
  • It acts to warn us of danger before any other sense because it works around corners in 360 degrees.

Is it possible that what prevents us from using Hearing Protection Devices (HPDs) correctly is the protection itself? Unlike any other PPE, HPDs typically work by partially disabling the sense it seeks to protect. By disconnecting us from our surroundings, reducing or eliminating the effectiveness of our hearing in a noisy, dangerous, environment, we create a situation the human may be “hard wired” to perceive as unsafe.

The deck of an aircraft carrier during flight operations is one of the noisiest places on earth. Sound levels can reach 150 dB. Flight crews exposed to those levels are mandated to wear earplugs, inside an earmuff, inside a helmet (the helmet is not impact protection. It reduces “bone conduction”; the tendency of the bones of the skull to conduct sound to the ears). It is well known that workers in high noise are easier to protect than workers in moderate noise; they seem to take noise more seriously. But, given this dangerously noisy environment, why do airmen sometimes leave out their earplugs. Anecdotally, the expression used by flight crews to explain their actions “deaf is better than dead” implies that sense of life-threatening danger outweighs the sense to protect one’s hearing. Could this be a more prevalent than we have heretofore imagined?

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Is it possible we have undervalued our need to hear when safety is at issue?

Let’s presume, for a moment, that we have. What would hearing protection that allowed us to hear safety be? We know that most industrial noise is in certain frequency ranges. If these are not the same frequencies humans’ use for speech, then we should be able to create hearing protection that passes “speech frequencies” and blocks noise. In this way we could control the loudness with which our ear perceives our environment and set a separate level for interpersonal communication. As well, we could facilitate other forms of communication through use of radios, like 2-way or cell phones, while still keeping industrial noise at a safe level. Would this make a difference as to how users wore their hearing protection?

I’d like to quote Sir Arthur Conan Doyle’s protagonist Dr. Watson in his Sherlock Holmes novels. Dr. Watson was fond of saying,

“When you have eliminated all which is impossible, then whatever remains,

however improbable, must be the truth.”

We take intelligent individuals, teach them to operate sophisticated machinery, and they create precision parts repeatedly to exacting tolerances. Why would these same individuals not be able to master the process of inserting and earplug or wearing an earmuff correctly? In an article in the Journal of Applied Psychology in 2002, Dov Zohar of the Technion – Israel institute of Technology showed how interventions by supervisors, managers, and even executives did modify workers behavior to improve hearing protection use (and thereby Hearing Loss Prevention program outcomes).3

We can improve hearing loss prevention program outcomes. It requires the commitment of the organization to change behaviour. It starts with removing as much of the noise as possible and protecting against the rest. It requires facilitating functional hearing protection options. And it requires persistence and perseverance but it can be done. I know. I’ve seen it work.

References

  1. Berger EH, Franks JR, and Lindgren FL.  International review of field studies of hearing protector attenuation. Presented at the 5th International Conference on the Effects of Noise on Hearing, Gothenburg, Sweden, May 1994.
  2. Developed by Dr. Kevin Michael of Michael and Associates www.michaelassociates.com.
  3. Zohar D. Modifying supervisory practices to improve subunit safety: A leadership-based intervention model. J Appl Psychol 2002;87(1)156–63.

Read Full Article 

Can Hockey Playoffs Harm your Hearing?

Excessive exposure to loud sounds is the leading cause of preventable hearing loss, and most cases of noise induced hearing loss are due to occupational exposure. The importance of hearing protection in the workplace is now well recognized, and most industries in North America have programs and regulations in place to ensure the hearing health of their workers. Far less attention has been paid to auditory damage caused by noise outside of work. With the popularity of loud devices, such as MP3 players and cellular telephones, and noisy activities, such as rock concerts and sporting events, everyday life is increasingly hazardous to hearing for all members of society. Therefore, there is a growing need to increase awareness of potential sources of damaging sounds and education about the use of hearing protection during leisure pursuits.

get Loud

Report – Can Hockey Playoffs Harm your Hearing?

This report illustrates the impact that even brief exposure to leisure noise can have on an individual’s hearing, through the example of a Stanley Cup final hockey game. The success that the Edmonton Oilers enjoyed during the 2006 Stanley Cup playoffs electrified the city. It was suggested in the media that the arena used by the team was one of the loudest buildings in the National Hockey League, and the Canadian Broadcasting Corporation demonstrated noise levels at certain times during broadcasts with the use of a sound level meter. Although measuring sound levels at key points is informative, what matters most is the exposure of a given individual over the course of the entire game and the effects of that exposure on the person’s  hearing.
To measure cumulative sound exposure, the second author wore a noise dosimeter to games 3, 4 and 6 of the 2006 Stanley Cup finals between the Edmonton Oilers and Carolina Hurricanes. The effect on the hearing function of the second author and his wife was measured by audiological testing immediately before and after game 3.

oilers

Noise measurement

A data-logging noise dosimeter was set to sample the noise level near the second author’s ear every second for the entire game. Thus, no matter where he was in the building, the dosimeter sampled his noise exposure.

Audiometric tests

Two audiometric tests were used for the pre and postgame measures: pure tone audiometry and otoacoustic emissions. Both tests were performed in a double walled audiometric booth by a licensed audiologist using

Go to: calibrated equipment. For the puretone audiometry test, we measured the softest pure tone that could be detected (threshold) at the following frequencies: 250, 500, 1000, 2000, 4000 and 8000 Hz. The distortion production otoacoustic emissions test assesses the integrity of the outer hair cells of the inner ear. The outer hair cells are important for detecting soft sounds and allow tolerance of a wide range of input intensities. Unfortunately, outer hair cells are usually the first structures to be damaged by exposure to loud noise.

Results

Noise data

During game 3 of the series, the scoring of goals led to fairly obvious spikes in the noise level (Fig. 1). A level of 120 dB A is roughly equivalent to the sound level of a jet taking flight. (Aweighting
is a filtering function applied to the noise dosimeter so that it is sensitive to input frequencies in the same way as the typical adult ear is.) The intermissions offered a temporary reprieve for the ears, but even during those interludes, the noise level was such that in an equivalent 8 h/day workplace environment, hearing protection would be required by law.
Fig. 1: Noise exposure level for the duration of game 3 of the 2006 Stanley Cup finals. Key points of interest are indicated. The red line at 90 dB indicates a derived “safe” level of this 3hour game. Sounds above the line have the potential …

The average exposure levels for each game (> 3 hours) were 104.1, 100.7 and 103.1 dB. Standards have been defined for maximum allowable daily noise doses, and an average level of 85 dB A for 8 hours is generally considered the maximum allowable daily noise dose. Stated differently, this means that there is a risk of hearing damage if you experience that level of noise for more than 8 hours. For each 3 dB increase in average noise level, the time you can safely stay at a level is halved. Thus, at 88 dB, it would take only 4 hours to reach the maximum allowable daily noise dose, at 91 dB it would take only 2 hours, and so on. For the levels experienced in game 3 of the series, the time to reach the maximum allowable daily noise dose was less than 6 minutes. In terms of
projected noise dose, each person in the arena not wearing hearing protection received about 8100% of their daily allowable noise dose. Given that most fans do not wear hearing protection during hockey games, thousands are at risk for hearing damage.

Audiometric data

Puretone audiometric data indicated that the hearing thresholds of both subjects deteriorated by 5 to 10 dB for most frequencies. The biggest changes occurred at 4000 Hz (the frequency known to be most susceptible to noise damage), where subject 2 experienced a temporary threshold shift in one ear of 20 dB. Whereas 5 to 10 dB may be within the test–retest confidence limits of puretone audiometry, 20 dB represents a real change in hearing status. It is important to note that this temporary threshold shift usually disappears in a day or two. However, if the ears are subjected to further noise exposure before full recovery, the temporary threshold shift may become
permanent. According to the oto acoustic emissions data, subject 1 experienced a decrease in the strength of the outer hair cell responses. Consistent with the puretone results, the decrease was more pronounced at higher frequencies. For subject 2, the otoacoustic emissions were so strong both before and after the game that any decrease in emissions might have been masked by an equipment ceiling effect. Both subjects described the world as sounding muffled
after the games, and both experienced mild ringing tinnitus.

Interpretation

Most people do not consider the risk of excessive noise exposure when participating in leisure activities. However, as this brief report shows, leisure noise over a period of a few hours can be harmful if precautions are not taken. The risk of hearing loss for those who attend hockey games frequently (e.g., season ticket holders, arena workers and the hockey players themselves) warrants serious consideration. Even the cheapest foam earplugs will attenuate sounds by about 25 to 30 dB. At the levels experienced during these hockey games, such earplugs would drop the average sound exposure to below 80 dB, where no hearing damage is likely to occur (even if the game were to go into quadruple overtime). And, contrary to popular belief, communication in noisy environments is actually easier with earplugs than without. The 2 most common symptoms of excessive noise exposure are hearing loss and tinnitus, both of which can have a substantial negative impact on quality of life. We live in an increasingly clamorous world, and many of our occupations and leisure activities are potentially hazardous to hearing. More than ever before, there is a need to
broaden awareness and better educate everyone about the need to protect hearing, both at work and at play.

Read Full Article.

By William E. Hodgetts and Richard Liu
From the Departments of Speech Pathology and Audiology (Hodgetts) and of Otolaryngology (Liu), University of Alberta, Edmonton, Alta.; and the Craniofacial Osseointegration and Maxillofacial Prosthetic Rehabilitation Unit (COMPRU), Caritas Health Group (Hodgetts), Edmonton, Alta.

Copyright © 2006 CMA Media Inc. or its licensors. This article has been cited by other articles in PMC.