How is it possible for young adults to incur noise-induced hearing loss? A review of what the scientific literature suggests relative to the possible noise exposure durations and levels for a typical young adult (eg, late teens or early 20s).

   
Vishakha W. Rawool, PhD, is a member of the faculty in the Department of Speech Pathology and Audiology at West Virginia University, Morgantown, WVa.

It has been reported that 20% of the workforce between the ages of 17 and 25 years entering industries already have notches consistent with noise exposure.1 The following review, in the form of the sound-exposure diary of a hypothetical high school graduate waiting to enter college during the fall semester, along with relevant research findings, may shed some light on why 1 out of every 5 individuals may have noise-induced hearing loss at an early age.

However, before looking at the sound-exposure diary, let’s review a few of the basics related to noise and noise exposure.

Measurement of noise in dBA. The loudness of sound is usually expressed in A-weighted sound level or decibels (dBA). The dBA scale attempts to mimic the sensitivity of the human ear at different frequencies, by de-emphasizing sounds at frequencies where the ear is less sensitive. More specifically, it de-emphasizes sounds by about 4 dB at 500 Hz, 11 dB at 200 Hz, 19 dB at 100 Hz, and 30 dB at 50 Hz. Thus, dBA measurements minimize these low frequencies compared to a noise reading in dB Sound Pressure Level (SPL), which includes the low frequencies.

Measurement of noise exposure using the time weighted average. For some studies included in this review, exposure levels are expressed in terms of time weighted average (TWA). For most individuals, noise exposure varies during the day. For example, a person may be in a relatively quiet environment for most of the day, but be exposed to moderate noise for a couple of hours and very loud noise for 20 to 30 minutes. To assess this person’s vulnerability to noise-induced hearing loss, both the noise levels and the amount of time spent in each noise level are taken into account. A formula is used to calculate the consequential noise exposure during the period of a workday and the result is referred to as TWA. With reference to occupational noise, the term TWA generally refers to the time weighted average noise exposure level over the period of 8 hours.

Maximum permissible noise exposure for protecting hearing. Average noise exposure levels of less than or equal to 85 dBA for an 8-hour day are recommended to prevent hearing loss in noisy work environments.2 With each 3 dB increase in the noise exposure level, the recommended number of hours is reduced in half. Thus, if the exposure levels are 88 dBA, the maximum recommended exposure time is 4 hours. The maximum recommended exposure levels for a variety of exposure durations mentioned in this review, using the recommendations of the National Institute for Occupational Safety and Health (NIOSH), are displayed in Table 1.

According to the Occupational Safety and Health Administration (OSHA), unprotected exposure to continuous noise above 115 dBA of any duration is not permitted.3 It should be noted that these exposure limits are for occupational noise exposure, and some investigators have suggested that the allowable exposure limits are probably higher for music. (The March 2007 and March 2006 special editions of HR address some of the specifics related to occupational hearing loss standards and hearing protection for musicians, respectively.)

A few studies included in this review note temporary threshold shifts (TTS), a measure of temporary decrease in auditory sensitivity following exposure to loud sounds. In animals, repeated exposure to sounds that cause TTS can lead to permanent hearing loss over time.4

Sound-exposure Diary: Friday

Sound exposure on Friday 6:30 am. Woke up with the music alarm on my clock. I like it loud; if it is soft, I have a tendency to sleep through it. I kept the music on while getting ready to go to work.

Friday 7:30 am to 8 am. Drove for half an hour to work, listened to loud music on the car stereo while driving.

The sound levels in car audio systems can be as high as 154.7 dBA.5

Most of us have experienced the vibrations from another car as the car with a blaring sound is waiting at the red light, suggesting use of extremely loud levels.

Friday 8 am to 12 Noon. Worked at construction site without hearing protection.

In the United States, among male youths who are 18 years old, construction labor is the second most common occupation during the school year and the most common summer occupation.6

According to a survey, 29% (69/238) of the college freshmen may be exposed to occupational noise and only 15% (10/69) of those who work in noisy environments may be using hearing protection devices (HPDs).7

Noise exposure for workers in the construction industry can be expected to range from 90 to 130 dBA because of the use of heavy machinery and equipment, transport vehicles, and noise producing tools.8,9 Noise exposure for construction workers may occur from the use of their own equipment and activities, and from the events that occur in the surrounding area.10,11

A study conducted in a Mideastern state in the United States found hearing loss in the 4 kHz and 6 kHz regions in 60% of the operating engineers who use heavy construction machinery. The workers reported using HPDs only 48% of the time they were supposed to use them.12

Friday 12:30 pm to 1 pm. I listened to my iPod through earbuds during lunch-break for about 30 minutes to help myself relax. I had to turn the volume all the way up in order to drown out surrounding noise.

A-weighted noise exposure levels

Maximum permissible exposure duration

85 dBA

8 hours

88 dBA

4 hours

91 dBA

2 hours

94 dBA

1 hour

97 dBA

30 minutes

100 dBA

15 minutes

103 dBA

7.5 minutes

106 dBA

3.75 minutes

110 dBA

1 minute 29 seconds

115 dBA

28 seconds

TABLE 1. NIOSH-established maximum recommended noise exposure sound and duration levels.

According to a survey, 51% of the high school students had experienced at least 1 of 4 symptoms of hearing loss.13 A total of 43% of the students in this survey reported that they listened to their MP3 players at loud volume levels.

Williams14 measured sound exposure from personal stereo systems under noisy listening conditions. A total of 13 of the 55 personal stereo system users in the study exceeded the 8-hour 85 dBA TWA and 2 users exceeded 100 dBA TWA.

Mori15 divided shipyard workers into two groups: those who listened to recorded music regularly and those who did not. The shipyard workers who listened to recorded music showed a higher prevalence of hearing loss compared to those who did not listen to the music. This study highlights the effect of recreational noise on those who are subjected to high levels of noise in the work environment.

Apple has applied for a patent that describes a software-based iPod hearing protection technology that can limit the iPod user’s exposure to loud music. The technology is designed to track the person’s sound exposure over time and impose recovery periods during which the volume is reduced so that the ears have a chance to recover after being exposed to loud segments.

The ZEN MP3 and portable media players by Creative have an audio setting called “Restrict Volume” that allows users to specify a maximum volume. These products come packaged with guidelines on safe listening practices.

Friday 1 pm to 5 pm. Resumed construction work without ear protection.

Friday 5 pm to 5:30 pm. While driving back, listened to my car stereo. The volume had to be turned up from where it was in the morning.

Having to turn up the volume suggests a temporary threshold shift.

Friday 6:30 pm to 7 pm. I drove to a concert arena while listening to my car stereo.

Friday 7 pm to 11 pm. Attended a concert without ear protection. I sat near the loudspeaker during the concert.

At rock concerts the audience can be routinely exposed to sound levels of 120-140 dBA,16 with peaks up to around 150 dB.17 A recent study7 found that 18% of college freshmen prefer to sit near the loudspeaker during concerts, where the sound pressure levels are higher.

Clark and Bohne18 documented the auditory thresholds of 6 volunteers before and after a rock concert that lasted for 4 hours. The average exposure was 100 dBA. Five of the volunteers experienced TTS of greater than 50 dB, predominantly in the 4 kHz region.

Yassi et al19 determined the auditory thresholds of 22 individuals before and after attendance at rock concerts. A total of 17 of the 22 attendees experienced a TTS of 10 dB or greater at 4 kHz.

Bogoch et al20 examined the perceptions of rock concert attendees about risk of noise-induced hearing loss and use of hearing protection at a busy rock concert venue. There were a total of 204 respondents with a mean age of 20.6 years. Approximately 40% of the attendees thought that it was very likely that noise levels at the concert could damage their hearing and 34% thought that it was somewhat likely. However, 80% admitted to never wearing HPDs at such events. Hanson and Fearn21 found significant hearing losses in those college students who admitted frequent attendance at pop-music entertainment compared to a control group.

Lebo and Oliphant22 pointed out that, by the nature of its acoustic properties, amplified pop music may be particularly traumatic because of the presence of high-level sound pressure peaks, the low frequency emphasis of pop compared to orchestral music, and continuity of the sound from the addition of amplified and re-amplified reverberation during concerts.

West and Evans23 noted that the absence of hearing disturbances following pop-music exposure should not necessarily be taken as complete absence of risk and that the potentially deleterious effects of pop music could be virtually eliminated not by banning it but simply by limiting amplification to more reasonable levels.

Friday 11 pm to 11:30 pm. Listened to my car stereo while driving back.

Friday 12 Midnight to 12:30 am. Turned my sleep music alarm on to help drown the ringing in my ears.

Ringing indicates damage to hearing.

Sound-exposure Diary: Saturday

Saturday 10:30 am to 12:30 pm. Using a gas-powered lawn mower, mowed grass without ear protection.

The noise levels of gas-powered lawn mowers range from 80 to 95 dBA.24 Electric-powered lawn mowers are about 10-20 dB quieter. A poll published in the May 2008 edition of Consumer Reports indicates that 79% of people who mow their lawns rarely or never use hearing protection.

During winter, the use of snowblowers can also lead to excessive sound exposure.

Saturday 1 pm to 2 pm. Did woodwork in the garage without ear protection.

Noise levels from home power tools vary from 65 to 115 dBA depending on the tool. Our measurements in a metal and wood workshop showed peak measurements as high as 128 dBA from a power activated nailer.

Individuals who do woodwork are 30% more likely to have a hearing loss than those who never do such work.25

Saturday 2:30 pm to 3:15 pm. Used the vacuum cleaner without ear protection.

The noise levels in vacuum cleaners can range from 60 to 90 dBA. Some vacuum cleaners provide the option of selecting strong or weak mode, with comparatively higher noise levels associated with the strong mode. Noise is not always related to efficiency. A vacuum cleaner can be designed in such a way that it has better suction power without producing too much noise.

Saturday 4 pm to 6 pm. Attended a charity showcase sports event.

Stadiums have very high noise levels and the levels can be higher in domed stadiums.

In a recent study, noise levels were measured at three hockey games. The average levels ranged from 100 to 103 dBA with peaks measured at 120 dBA.26

Professional football players often use earplugs to reduce the distracting crowd noise and the earplugs are often equipped with filtered CFA adapters to improve the ability to hear team members.27

Saturday 7 pm to 12 Midnight. Went to a live music club and then to a dance studio.

Gunderson et al28 measured the sound levels in eight live-music clubs in New York. The average sound levels during performances ranged from 94.9 to 106.7 dBA.

Fifteen percent of children in the age range of 10 and 17 years may be attending clubs at least once a week. It has been suggested that an upper limit of 95 dBA should be enforced in clubs and that this limit would reduce the incidence of hearing loss greater than 10 dB from 10%-20% to 1%.29,30

Meecham and Hume31 showed that the attendance of university students in noisy nightclubs is high, and there is a significant association between the attendance and the duration of tinnitus. The authors suggested that attendance at nightclubs may increase the perception of tinnitus in susceptible ears.

Tomasevic et al32 measured auditory thresholds and distortion product oto-acoustic emissions (DPOAEs) of 22 attendees at a nightclub and found that 59% of the subjects had a TTS of 10 dB or greater and 36% showed a 6 dB or greater reduction in DPOAE amplitudes, suggesting trauma to cochlear structures.

Sound-exposure Diary: Sunday

Sunday 1 pm to 2 pm. Hung out and played games at an electronic arcade.

Noise levels of 88 to 90 dBA have been reported in arcade game centers. With less than 1-hour exposure, such levels have the potential to cause a 4 to 8 dB TTS at 4 kHz in some individuals.33

Sunday 2:30 pm to 3:30 pm. Did recreational shooting without ear protection.

Hearing is known to be significantly worse among sports hunters compared to a control group and the majority of sports hunters do not wear HPDs.34 Nondahl et al35 found that men who had regularly engaged in target shooting or who had done so in the past year were more likely to have a marked high-frequency hearing loss than those who had not. In addition, 38% of the target shooters and 95% of the hunters reported never wearing hearing protection while shooting in the previous year.

Our own inquiries suggest that hunters are often concerned about not being able to hear warnings or signals from hunting partners while using HPDs, and their primary concern is not being able to hear the approaching prey. However, some well-fitted, level-dependent earplugs allow good speech communication at a distance of up to 63 meters, at least under laboratory conditions.36,37

The amount of attenuation provided by level-dependent hearing protectors depends on the sound level in the environment. Such protectors are designed to attenuate high-level sounds such as gunshot noise while allowing low and moderate levels of sounds such as speech to enter the ear naturally. For example, the Combat Arms Earplugs is a level-dependent earplug that begins reducing noise-exposure at 110 dBP, and at 190 dBP provides an overall noise reduction of about 25 dB.

Sunday 4:30 pm to 6 pm. Watched a movie in a theater.

The sound levels in movie theaters can vary widely depending on the particular theater, the particular movie, and the particular segment of the movie. According to a noise survey conducted by CBS News in 2003, the average noise levels during five different movies at five different theaters varied from 70 to 78 dBA, but maximum levels varied from 85 dBA to 95 dBA.

Sunday 7 pm to 8 pm. Talked with a friend on my mobile phone. The volume had to be turned up all the way for easier communication.

The fact that the volume had to be turned up all the way suggests the occurrence of a TTS.

During exposure to pulsed mobile phone radiations, some individuals show a 1 dB reduction in distortion product oto-acoustic emissions, which is a measure of cochlear function.38 Although there is no substantial risk of tumors of the 8th or auditory nerve in the first decade after initiating the use of a mobile phone, the risk may increase after long-term use.39

Sunday 9 pm to 12 Midnight. I practiced with my rock-band in the basement without ear protection.

Steel drum players can produce average sound levels of about 110 dBA with their drums.40,41 Some classical musicians sitting close to the bass drum, snare drum, and tympani during a performance can be exposed to levels exceeding 137 dBA.42 (For a comprehensive list of musical instruments and their approximate sound levels in dBA and peak dB SPL, see the table in Marshall Chasin’s article, “Hearing Aids for Musicians,” in the March 2006 HR.)

The noise levels in untreated small basements can be high due to relatively long reverberation times allowing reflections of sounds to persist over a longer period. The reflections mix with the original sounds occurring later in time and can increase the sound levels.17

The March 2006 HR is devoted to musicians and hearing issues, and the March 2007 and September 1999 editions of HR are devoted to occupational hearing protection issues.

Kahari et al43 found hearing disorders in 74% of the rock/jazz musicians. Hearing disorders included hearing loss, tinnitus, hyperacusis (hypersensitivity to the loudness of sounds), or distortion and/or diplacusis (distorted pitch perception or a sudden change of pitch with a change in loudness). The sound levels measured in this study at the musician’s position were high; the safe exposure time was exceeded after 1 to 45 minutes in the different measurements. All maximum dBA measurements exceeded safe limits, suggesting pronounced risk of damage to the inner ear.

Schmuziger et al44 compared the hearing of non-professional pop-rock musicians who had experienced repeated exposures to intense sound levels during at least 5 years of musical activity to a control group. The musicians had significantly worse hearing than the control group within the frequency range of 3 to 8 kHz. However, hearing loss was minimal in those musicians who always wore hearing protection.

The ER-15 earplug manufactured by Etymotic Research provides 15 dB of attenuation throughout the frequency range and thus may provide sufficient protection for some musicians.45 However, the ER-25 may be more appropriate for drummers who may need up to 25 dB attenuation. The ER-20 is a lower-cost alternative that is designed to match the fundamental and harmonic structure of music at the ear, providing 20 dB attenuation.46 There is a slight high-frequency roll-off in the ER-20, which may help to minimize damage that may occur from high-hat cymbals (see Patty Niquette’s article, “Hearing Protection for Musicians,” in the March 2006 HR.)

Other Potential Hearing Threats

Obviously, this diary is only an example of some activities in which a student or young adult might encounter high sound levels. There are many others. For example, Mirbod et al47 measured noise levels during aerobic sessions in three aerobic studios. The highest noise levels were in the range of 93-96 dBA and occurred during the peak exercise period. Yaremchuk and Kaczor16 reported a range of 78 to 106 dBA in aerobics classes, with 79% of the readings reaching 90 dBA or more. Aerobics instructors in this study reported that, after class, they received complaints of fluctuating hearing loss and tinnitus 50% of the time. Nassar48 recorded a range of 89-96 dB(A) in aerobics centers in England. A significant temporary threshold shift was found in all the individuals attending these classes 2 minutes after attendance, and half of the participants reported tinnitus following the exposure.

The repeated exposure to loud sounds some youths may be receiving can partially explain why 1 out of every 5 youths appears to have a noise-induced notch at a very young age. In this context it is important to note that there is a great variation in individual susceptibility to noise-induced hearing loss. The TTS and permanent threshold shifts can vary between 30 dB and 50 dB among individuals.4 Thus, not all youths may suffer from the same degree of loss with the same exposure.

Proper education of youths and their parents/caregivers about hearing loss occurring from exposure to loud sounds may be useful in minimizing the sound exposure and promoting the use of HPDs during loud occupational and non-occupational activities.

Conclusions

An admittedly extreme example of potential sound exposure is presented in this article. Although not all individuals will follow this type of behavioral pattern, the current hypothetical diary suggests that some teenagers may be exposed to potentially harmful, cumulative sound exposure that can lead to hearing loss. Previous studies have also suggested a critical need for promoting healthy hearing behaviors among young individuals.7

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Correspondence can be addressed to hearingreview@allied360.com or to Vishakha Rawool, PhD, at .