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Figure 3. Normal voice sentence intelligibility as a function of the steady background sound level in an indoor situation. At the typical conversational distance of 1 meter using normal speech volumes, people with normal hearing require 45 dB(A) ambient noise for 100% speech comprehension. Speech comprehension decreases noticeably at approximately 70 dB(A) ambient-noise levels and reaches zero at 75 dB(A). From EPA, 1974, Figure D-1.
From a public health perspective, the NIOSH noise criteria (1998) allow an 8% excess risk of hearing loss after 40 years of occupational noise exposure. This means that workers exposed to 85 dB(A) at work have an 8% increased risk of hearing loss compared with a similar population not exposed to occupational noise. The concept of excess risk is problem- atic because it assumes that hearing loss is part of normal aging, which is probably not true (Fink, 2017c) and an 8% risk of injury is not acceptable for the public. The difference between occupational and public noise exposure standards was discussed in a NIOSH Science Blog post (Kardous et al., 2016). However, the principles of occupational noise control (Murphy, 2016) can be applied to the public.
Seventy to Seventy-Five A-Weighted Decibel Ambient
Noise Interferes with Speech Comprehension in Those with Normal Hearing
Ambient noise also interferes with speech comprehension for those with normal hearing. This has been known since 1974, when the EPA published the graph in Figure 3. The text states that the maximum sound level that will permit relaxed con- versation with 100% sentence intelligibility is 45 dB, but the decrement in speech intelligibility does not become mean-
ingful for most listeners with normal hearing until ambient noise reaches 65-70 dB.
Eighty-Five A-Weighted Decibels Are an Occupational
Noise Exposure Standard
The National Institute on Deafness and Other Communica- tion Disorders (NIDCD; 2017) states that “long or repeated exposure to sound at or above 85 decibels can cause hearing loss.” This statement is accurate but misleading. Eighty-five decibels or A-weighted decibels without a time limit is not a safe noise exposure level (Fink, 2017a). The auditory injury threshold is 75-78 dB(A) (Mills et al., 1981; Flamme et al., 2012) and may be as low as the effective quiet level, the sound pressure level required to recover from noise-induced tem- porary threshold shift, which is only 55 dB(A) (Kryter, 1994).
Unfortunately, in the absence of any federal guideline, stan- dard, or regulation for nonoccupational noise exposure, the 85 dB sound level of the NIDCD has become the de facto fed- eral safe noise exposure level. It is often cited as a safe volume level or as the sound pressure level at which hearing loss begins, without exposure time, by audiology experts in media reports; it is mentioned in educational materials such as the Dangerous Decibels program (bit.ly/28W7TA4) and in mate- rials provided by the American Speech-Hearing-Language Association (ASHA) and the American Academy of Audiol- ogy and is used as a volume limit for headphones marketed as “safe” for hearing in children as young as 3 years, without specifying a time limit for exposure (Saint Louis, 2016).
At an 85 dB(A) occupational exposure, an employer must implement a hearing conservation program (OSHA, 2002). Elements of a hearing conservation program include baseline audiograms, education about noise protection, provision of hearing protection devices, annual audiograms, and metic- ulous record keeping. Obviously, the public has no such protections.
One Hour at Eighty-Five A-Weighted Decibels Can Cause Hearing Loss
WHO recommends only 1 hour of exposure at 85 dB(A) [LAeq(1)] daily for the public to prevent hearing loss (Berglund et al., 1999). An occupational noise exposure calculator will show that after only a 1-hour exposure, it is impossible for the listener to achieve the 70 dB average daily noise exposure level to prevent hearing loss. This means that noise levels in many restaurants are high enough to cause hearing loss during a typical meal lasting 1-2 hours.
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