02/14/2007

An airbag might save your life in a car accident, but it could also cost you your hearing.

A researcher at a national hearing conference says 17 percent of people exposed to deployed airbags in American cars will suffer from permanent hearing loss. His findings also show, contrary to what experts have previously thought, airbag deployment is more hazardous to the ear when a car's windows are rolled down.

Dr. G. Richard Price presented his findings this week at the National Hearing Conservation Association's 32nd annual hearing conference. Price, who is a consultant at Auditory Hazard Analysis in Charlestown, Md., focused his invited presentation on the hidden auditory danger posed by everyday "impulse" noises.

An impulse noise is a brief burst of sound like a shotgun blast, as opposed to a continuous noise like the droning of a washing machine. Price said in addition to the well-known dangers of impulse noises like gunfire, minor events like a hammer hitting a nail or even the sound of a baby's rattle can produce hearing loss.

"The good news is almost all of this hearing loss is preventable," Price said. "Wearing hearing protection, designing equipment better, and being aware of the problem can all contribute to preservation of hearing, our very precious resource."

In Price's study of car airbag deployment, he sought to determine whether the auditory danger was greatest in cars with the windows down or the windows up. Previously, experts thought rolled-up windows were more dangerous because they allow for higher pressure to be created inside the cabin.

The research concludes that having car windows rolled up when airbags are deployed is actually less hazardous to the ear than rolled-down windows. This is because the higher pressure generated in the closed cabin actually prevents greater damage to the ear.

The pressure causes a displacement in the middle ear that stiffens the stapes, a small bone outside the inner ear. This stiffening limits the transmission of energy to the inner ear, where hearing damage takes place. In airbag experiments where the cabin is completely sealed and pressure is even higher, hearing damage is reduced even further.

Price's study only included cars sold in the United States with front and side airbags. Under U.S. regulations, American cars must have larger, more powerful airbags than cars sold in places like Europe. Cars with smaller airbags sold in other parts of the world would likely pose less auditory danger when tested under identical circumstances, Price said.