Noise from public transportation, especially subways, may be loud enough to harm some passengers’ hearing, a new study suggests.

The study, which measured noise levels in New York City’s subways, buses, ferries and commuter trains, found that decibel levels on subway platforms reached as high as 102.1 - louder than the noise level of a chain saw.

Overall, the study found, subway platforms were the loudest mass-transit sites - registering at about 81 decibels, on average, while noise levels inside subway cars were somewhat lower, at just over 79 decibels.

Noise levels of about 80 decibels or higher are considered potentially hazardous to hearing, depending on how long and how often a person is exposed. Experts generally recommend that people average no more than 2.7 hours per day around 80-decibel noise levels, and no more than 15 minutes of exposure to 90 decibels.

The current findings suggest that people who only occasionally use mass transit have “little to no risk” of noise-induced hearing loss, lead researcher Richard Neitzel told Reuters Health.

“However, for people who ride mass transit daily, and for long periods of time each day, transit noise levels are high enough to present a risk of noise-induced hearing loss over time,” said Neitzel, a research scientist at the University of Washington in Seattle.

Subway riders are not the only mass-transit users potentially at risk, according to the study, which is published in the American Journal of Public Health.

On average, the researchers found, noise levels inside ferries were nearly 78 decibels, while on buses that figure was about 75. On the commuter trains that connect the city with surrounding suburbs, the average decibel level ranged from roughly 71 to 76.

In general, train platforms and bus terminals had somewhat higher noise levels than the trains and buses themselves. Ferries, on the other hand, were noisier than their terminals.

Neitzel recommends that people who frequent mass transit consider wearing protective gear; even inexpensive foam earplugs are helpful if worn properly, he noted.

The researcher also stressed that while many riders like to use MP3 players, standard headphones do not block out external noise - and people may further their risk of hearing damage by turning the music volume up to drown out environmental noise.

He recommends that MP3 users try special noise-blocking headphones so they can keep their music at a safe volume.

While the study looked only at New York City’s more than 100-year-old transit system, Neitzel said that the subway findings are likely relevant to other systems of a similar age.

The results may not, however, be generalizable to newer subway systems - like Washington, D.C.‘s Metro and San Francisco’s BART, both of which began operating in the 1970s.

In general, newer or better-maintained machinery - whether a subway car or a lawnmower - is less noisy than older or poorly maintained versions, Neitzel noted.

SOURCE: American Journal of Public Health, August 2009.