SSS 2009-06-22（在线收听）

This is Scientific American’s 60-Second Science, I’m Steve Mirsky. Got a minute?

“Stand clear of the closing doors, please.” Definitely keep your arms and legs away from the closing doors on the subway. But there’s a potentially more insidious danger to your health - the noise.

Mass transit is generally a safe way to travel, one reason why 33 million Americans use it every weekday. But a study that compared the various modes of mass transit in New York City found that the subways topped all other transit types for average noise, at a grinding 80 decibels. The din was sometimes worse on the platforms, topping out at 102 decibels. Commuter trains were much quieter, at about 75 decibels. Remember, that’s on a log scale, so, for example, 80 is actually 10 times noisier than 70—and about three times louder than 75. Normal conversation is between 60 and 70 decibels. The study is in the American Journal of Public Health.

The EPA and the World Health Organization recommend daily averages of no more than 70 decibels to protect your hearing. So earplugs may be in order if your particular commute is literally deafening.