Dunn Lecture Addresses Hazards of Impulse Noise

By Ed Rutkowski

Pennsylvania Convention Center, Philadelphia (May 22, 2018)—Elliott Berger, a scientist with 3M’s Personal Safety Division, delivered the 2018 Derek Dunn Invited Noise Lecture at AIHce EXP 2018 yesterday. Berger’s thorough address recounted current research on the hazards of impulse noise and recommended approaches to protecting the hearing of exposed workers, particularly military personnel.

Impulse noise is created by the compression of gas from a chemical combustion, Berger explained. The sound wave generated by an impulse noise is characterized by rapid onset to a peak level, followed by a decay. Common impulse sounds include the firings of rifles and handguns, which range from 140 to 175 A-weighted decibels. Military weapons such as howitzers can be as loud as 190 dBA. Even a balloon pop can be as loud as 150 dBA. Prolonged exposure to noise at 85 dBA can lead to hearing loss.

Because impulse sounds can exceed a critical level that causes immediate, permanent damage to the ear, impulse noise is “arguably the most dangerous type of noise to which we're exposed,” Berger said. A single, high-level impulse noise can cause permanent hearing loss and permanent tinnitus.

Many factors make impulse noise difficult to measure, Berger explained. He referred to a paper published by the National Hearing Conservation Association, which showed that the accuracy of sound level meters declines with increasing noise levels and may underestimate noise hazards at peak sound pressure levels of more than 150 dB. Above that level, laboratory-grade instrumentation is needed for accurate measurement.

But a full characterization of such high levels of noise isn’t necessary to confirm that workers who are exposed to impulse noise need hearing protection. Berger offered guidance on several varieties of hearing protection devices. Traditional HPDs such as ear muffs and ear plugs “block sound much like room walls block sound from adjacent space,” Berger said. These devices, when properly sized and properly worn, can achieve up to thirty decibels of noise reduction and, according to Berger, provide the greatest protection possible for both steady-state and impulse noise.

More complex HPDs include electronic hearing protection, which behaves like a hearing aid to amplify low sounds. At high sound levels, the circuitry in the device shuts down and protects the user in a similar manner to traditional HPDs, by creating a seal against the ear to attenuate noise. While such devices are useful, Berger warned that “more complicated products are not more protective.” For maximum noise protection, Berger recommended dual protection—ear muffs worn in combination with ear plugs. “You can probably get all the gains you need by wearing an electronic ear plug under a passive muff,” Berger said.

A Fellow of AIHA and the Acoustical Society of America, Berger has received many honors for his work on noise, including the National Hearing Conservation Association’s lifetime achievement award in 2013. He was the lead editor on two editions of AIHA’s Noise Manual and has authored 17 textbook chapters and more than 80 published articles. He currently chairs the American National Standards Institute’s working group on hearing protector attenuation.

Ed Rutkowski is editor in chief of The Synergist.

View more Synergist coverage of the conference on the AIHce Daily page.