Study recommends ear plugs for frequent mass transit users
Last Updated: Friday, June 19, 2009 | 4:12 PM ET
CBC News
People who use mass transit frequently would be well advised to wear ear plugs next time they take a ride — or risk irreversible hearing loss, a new study says.
The study, published Thursday in the American Journal of Public Health, measured noise levels on New York City's transit system.
Researchers from Columbia University and the University of Washington found that subways in New York had average noise levels of 80.4 decibels. Roughly half of the maximum levels observed on subway platforms were over the 90 decibel threshold.
Suburban trains, meanwhile, averaged 79.4 decibels, and tramways 77.0 decibels. Underground trains were significantly noisier than those than ran above ground. Major hubs were noisier than local stations.
Decibels are a logarithmic unit of measurement, so a noise level of 80 decibels is 10 times as intense as a 70 decibel reading and 100 times as intense as a 60 decibel level. Normal conversation typically hovers around 60-65 decibels.
There is no known risk to hearing loss at sound levels below 70 decibels, according to Health Canada. The World Health Organization recommends daily exposures of no more than 70 decibels for a 24 hour average.
Sustained exposure to noise levels above 85 decibels can pose a hearing loss risk.
To counter elevated noise levels, like those found in the New York transit system, the researchers recommend people who use transit frequently use ear plugs while riding.
Highest readings comparable to rock concert
The two highest readings were observed on a subway platform (102.1 decibels) and at a bus stop (101.6 decibels). Noise at those levels would be comparable to what someone at a rock concert or who uses a chainsaw might experience. Two minutes of exposure to these levels each day would be enough to cause hearing loss in some frequent riders, the study authors say.
Noises at those levels aren't typical in the transit system, but the researchers say that other factors can contribute to an elevated risk of irreversible hearing loss.
For example, riders who travel on transit systems listening to MP3 players at high volumes to drown out the background noise can compound the problem.
"Transit-related noise levels are high enough to potentially present a risk of noise-induced hearing loss to some frequent transit riders, and this risk could increase substantially when we account for riders' other noise exposures from work and recreational activities," said Dr. Robyn Gershon, one of the study authors.
