July 9, 2009
Got ear plugs? You may want to sport them on the subway, researchers say
By Mary Guiden
News & Community Relations
Seattle doesn’t have a subway, but that doesn’t stop research scientist Rick Neitzel from doing his work. Neitzel, UW Department of Environmental and Occupational Health Sciences, and colleagues from Columbia University Mailman School of Public Health recently collaborated on a mass transit study in New York City.
The team found that Metropolitan Transit Authority (MTA) subways had the highest average noise levels of all mass transit in New York City, with levels high enough to potentially increase the risk of noise-induced hearing loss. Findings from the study were published online last month in the American Journal of Public Health and will appear in the August 2009 issue.
Researchers studied the risk of excessive exposure to noise related to mass transit ridership, conducting an extensive set of noise measurements of New York City mass transit systems.
“Transit-related noise levels are high enough to potentially present a risk of noise-induced hearing loss to some frequent transit riders,” said Neitzel, lead author. “This risk could increase substantially when we account for riders’ other noise exposures from work and recreational activities.”
Noise induced hearing loss, a permanent, irreversible health problem, is estimated to affect more than 30 million people worldwide, and as many as 10 million in the U.S. alone.
Using sensitive noise-measuring instruments called dosimeters, Neitzel and co-authors, including Robyn Gershon, an environmental and occupational health scientist and faculty member at Columbia University, measured levels at platforms and stations, as well as inside vehicles on New York City subways, buses, ferries, commuter railways and the Roosevelt Island tramway.
The research team found that, on average, MTA subways had the highest average noise levels, at 80.4 decibels (dBA). The highest individual measurements in the study were found on an MTA subway platform (102.1dBA) and at a bus stop (101.6 dBA). In contrast, the noise level of a whisper is 30 dBA, normal conversation is 60 to 70 dBA, a chainsaw is 100 dBA, and gunfire is 140 dBA.
The U.S. Environmental Protection Agency and the World Health Organization recommend daily exposures of no more than 70 dBA for a 24-hour average. Noises that register below 70 dBA generally have no impact on hearing health and don’t cause people to exceed the daily recommendations.
Neitzel said he’s not aware of noise level surveys for Seattle-area transit systems. “That highlights a pretty glaring hole on noise levels associated with transit systems in general,” he said.
But that doesn’t mean Seattle transit riders all need to start wearing ear plugs on buses, trains and ferries. “I would expect people are not exposed as long to transit noise in Seattle. The risk of hearing loss among bus riders here would be less than in New York because people aren’t spending as much time on the bus.”
For those with longer commutes, Neitzel said he recommends spending a few dollars on a set of foam earplugs that you can purchase at a drugstore. Make sure you wear them correctly, since most people don’t roll them down properly before inserting the plug into the ear.
And don’t even think about just cranking up the volume on your iPod or other MP3 player. Neitzel said turning up the volume of your music actually exposes your ears to even more noise. “People will often increase the volume by four or six decibels to hear over the background noise,” he said. “And the more noise we add, the more worried we get about hearing loss. A better solution is to invest in noise-blocking or sound-isolating headphones or ear buds, which do a better job of keeping the outside noise out.”
The research team is following up this study with a large, community-based study of noise exposures from multiple sources to develop even more accurate predictions of noise-induced hearing loss in urban populations. Neitzel said he’s curious about the Washington state ferry system as a possible subject, in addition to other transit. Staten Island ferry noise was the second highest noise level found, he noted.
The study “Noise Levels Associated with New York City’s Mass Transit Systems” was funded by the National Institute of Environmental Health Sciences. Co-authors include Columbia University’s Marina Zeltser, Allison Canton and Dr. Muhammad Akram.
