When audiologist Brian Fligor of Boston Children's Hospital first caught word of an upcoming attempt by Seattle Seahawks fans to set the Guinness World Record for the loudest crowd roar at a sports stadium, he scratched his head.
"Oh boy," he said. "Pack people in nice and tight, all screaming at about 115 decibels, and yeah, I could imagine peak sound might hit 132 decibels."
"I'm a football fan," Fligor added. "But I'm not a big fan of that."
The current crowd noise record is 131.76 decibels, set at a Turkish soccer arena in 2011. At that level, people can suffer immediate and permanent hearing damage, Fligor and other experts warned. In a society filled with iPods, rock concerts, subways and battlefields, loud noise is often overlooked as an environmental health hazard, they said.
Sporting events aren't typically high on the loud list, but Seahawks fans also don't see themselves as typical. CenturyLink Field has earned a reputation around the NFL for its opponent-distracting noise, a result of the stadium's acoustical design and the lungs of some 60,000 screaming fans, often known as the team's "12th man."
The loudest official recording during a Seahawks game is 112 decibels. Fans and the organizing group of this Sunday's crowd roar, Volume 12, believe they have a good chance at the Guinness World Record.
Joe Tafoya, co-owner of Volume 12 and a former Seahawks defensive end, is well acquainted with the Seattle stadium's noise. He recalled one particular moment during the 2005 NFC Championship game there -- a victory that led the team to its first Super Bowl.
"I had to stop and look around the stadium in sheer amazement of the level of noise, the passion the fans were pouring into it," he said. "That stuck with me."
The idea that such noise could be in any way a health risk never crossed his mind. But now, he said, he sees hearing loss as a "public health issue."
In addition to going for the crowd roar record at this week's Seahawks match-up against the San Francisco 49ers, Volume 12 is working with Seattle's hearing-impaired community to raise awareness of noise-induced hearing loss. Volunteers will be handing out 30,000 ear plugs attached to informational cards to fans at the game.
Standard foam ear plugs are designed to drop noise levels entering the ear by around 30 decibels, but that may not be enough to safely stifle the crowd noise on Sunday.
"In the real world, it's probably more like 20 or 25 decibels," said Dr. Jay Rubinstein, director of the University of Washington's Virginia Merrill Bloedel Hearing Research Center. "That would be adequate if you're trying to reduce levels that start at 100 or 110 decibels. If you're going to be around something noisier, you need a greater level of hearing protection."
Rubinstein noted that hearing loss is the result of both a sound's intensity and its duration. The U.S. Occupational Safety and Health Administration limits the amount of time a worker can be exposed to noise levels of 85 decibels and higher to 8 hours a day. For every additional 5 decibel increase, the maximum time is cut in half. At 115 decibels, for example, the limit is just 15 minutes.
By the time noise levels reach 130 decibels, "it's really unsafe to be listening to the noise for any period of time," said Troy Cascia, an audiologist at the University of California, San Francisco Medical Center.
Of course, football fans aren't the only ones at risk of noise-induced hearing loss. Certain occupations can be dangerously loud, such as construction work and military service.
One in three U.S. soldiers returning from the Middle East reports hearing loss, making it the most common injury sustained by troops -- ahead of post-traumatic stress disorder and traumatic brain injury. Ringing in the ears (tinnitus) is No. 2 on the list.
Then there are those notoriously noisy rock concerts and iPod earphones.
"If you go to a concert one time, that's not a big deal. But if you go to three concerts a year from age 15 to 55, then your hearing when you're 55 may actually look more like the hearing of a 75-year-old," said Fligor, noting that just 4 percent of concert-goers wear earplugs. "Without hearing protection, you've essentially prematurely aged your ear."
Some everyday exposures to noise are less avoidable, such as the passing of an express subway car or firetruck. In those cases, experts suggest sticking a finger in each ear may be the best defense.
"We live in a noisy world," said Fligor, "and we are living longer."
More years means more exposure, and a greater likelihood that earlier exposures will manifest as hearing damage. That damage can be subtle, such as a diminished ability for the ear to detect the high pitch notes of speech, said Cascia, who emphasized the importance of protecting children's hearing. "It can make it sound like people are mumbling," he added.
Experts' best advice: seek hearing protection anytime you expect sounds to exceed about the level of a shout, and eat a healthy diet and get regular exercise. Poor circulation caused by conditions like type 2 diabetes or smoking can make the ear more susceptible to damage.
For those fans attending the game in Seattle on Sunday, they recommend wearing ear plugs, perhaps even with ear muffs on top, and limiting the time they're in the packed stands.
"Take a break and go out for 15 minutes," said Cascia, who happens to be a 49ers fan.