"Although one movie viewing was not enough to cause permanent hearing loss alone ... repetitive temporary threshold shifts may ultimately cause permanent hearing deficits," says study researcher William Thane Hancock, MD, a family practice resident at the University of Hawaii Family Practice and Community Health Residency Program in Mililani, Hawaii.
Hancock, who presented the study of movie sound levels at the American Academy of Pediatrics 2004 National Conference & Exhibition, used sound meters positioned centrally in the theater to collect data on 23 movies at eight different theater complexes in Hawaii.
The good news, Hancock tells WebMD, is that none of the films surpassed the limit of 140 decibels set by the Occupational Safety and Health Administration (OSHA). The peak sound level (during onscreen explosions, gunshots, and car chases) reached 130 decibels, which he says is similar to standing 100 meters from a jet during takeoff.
But the OSHA standard is probably not a perfect measure of the risk of hearing loss in children, says Dennis R. Durbin, MD, of the Children's Hospital of Philadelphia.
"There is no standard for entertainment exposure levels," says Durbin, who was not involved in the study.
And the movie sound level is actually higher than the limits that OSHA sets for sound exposure on the job, where OSHA regulations stipulate that workers should not be subjected to more than 85 decibels over a period of eight hours. For every three decibels over 85, the time is cut in half. So the agency would not allow more than a 15-minute exposure to 100 decibels.
The highest sound dose recorded by Hancock and colleagues was an action movie that registered more than 96 percent of the maximum allowed sound exposure.
"Surprisingly the children's movies sampled had average exposures similar to those of action movies," Hancock says. Documentaries were easiest on the ears, with sound at about 65 percent of the OSHA maximum decibel level.
And for moviegoers who like those big new theaters with stadium seats, Hancock says the sound in those theaters is more likely to spike near the OSHA maximum ranges. And movies are getting noisier, he says, noting that new releases were consistently louder than re-releases.
Hancock says an estimated 12 percent of children in the U.S. aged 6 to 19 have noise-induced hearing loss. Noise is second only to age as a cause of hearing loss, and an accumulation of noise-induced hearing loss may be responsible for some of the age-related effects.
Hancock, who discussed his study at a news conference, says he plans to collect more data to determine if any of the effects are significant to hearing loss in children.
For now, he recommends that parents have children follow up movies with quiet activities to "give their ears a break after a loud movie."
SOURCES: American Academy of Pediatrics 2004 National Conference & Exhibition, San Francisco, Oct. 9-13, 2004. William Hancock, MD, University of Hawaii. Dennis R. Durbin, MD, Children's Hospital of Philadelphia, Pa.
By Peggy Peck
Reviewed by Michael W. Smith, MD
© 2004, WebMD Inc. All rights reserved