What if I told you there was an invisible, tasteless, odorless chemical to which virtually all Americans are exposed every single day, and that this particular hazard has been associated with things like heart attacks, and hypertension, and cognitive impacts, and depression. Is also been associated with hearing loss, and tinnitus or ringing in your ears. Would you believe me? Well, I hope you do because it's true. We're going to spend the rest of this module talking about noise or unwanted sound. Many of you will already be familiar with the auditory or hearing impacts of noise. So you may know that too much noise exposure will cause permanent, irreversible, incurable noise-induced hearing loss. Now, that loss can happen one of two ways. The first is if you have chronic exposures to relatively high levels of noise, this ends up causing basically metabolic damage in your inner ear and subsequent hearing loss. But it's also possible to get something called acoustic trauma which occurs as a result of a very brief but extremely intense exposure for example, to an explosion. In this case, we're not worried about long-term metabolic loss, we're worried about for example shredding of your eardrum, or disruption of your middle ear bones, or damage to your inner ear. Either way, you get it. Noise-induced hearing loss has profound social, occupational, and psychological impacts. The prevailing theory is that hearing loss basically occurs after a series of small temporary and reversible hearing losses that then add up to a permanent damage. So if you imagine, every time you do something excessively loud, you might suffer a temporary hearing loss. If your hearing recovers, but it only recovers 99.99 percent after each one of those events, well if you have a number of those events in a row, you're going to slowly start to accrue a permanent, irreversible hearing loss. You can actually give yourself a hearing test. So if you know you're going go do something noisy, maybe going to a concert or to a show and you're riding in a car there, when you're in the car, turn on some talk radio and turn it down so you can just barely hear it. Now get out of the car, go do the noisy thing and if when you get back in the car, you can't hear the radio anymore, you've had yourself a temporary hearing loss. I can virtually assure you that if you then spend some time out of noise, maybe sleeping overnight and get back in the car later, you will be able to hear the radio again. So again, most of us are familiar with hearing loss from noise, but what about these non-auditory impacts? It turns out there's a whole host of non-auditory impacts that are now pretty strongly linked to noise in the workplace or in the community. These include things like hypertension, ischemic heart disease, heart attacks for example, Stroke, sleep disturbance, psychological effects, cognitive effects, occupational injuries, annoyance, list goes on. There's a couple of complimentary pathways that the noise may take to cause these health outcomes. So one is, noise is annoying and it's generally stressing on your system. So if you're constantly annoyed and stressed, that basically puts you into the fight or flight mode and causes a hormone cascade that can lead to things like high blood pressure and heart attacks. But we also know that if you're trying to sleep in noise, your sleep is disturbed by that noise and disturbed sleep can lead to all of these impacts and then some. How do we go about assessing this incredibly common exposure? Well, we can do it in a couple of different ways. We could think about area or activity-based measurements. So you can see in the lower left here a map of New York City, and this is basically a map that's showing different noise levels across the city. For those of you who have traveled to New York, you may recognize the flight patterns for Newark and LaGuardia and JFK airports. Those are the bright red and blue areas there. We could also think about making personal measurements. So we might put what's called a dosimeter on someone. This device that they can actually wear around that measures the noise next to their ear. Or we can take again an activity-based measurement where we take a sound level meter that's pictured in the middle image here, we go out and we measure different types of activities or sources. We can also create models, so we could use a combination of measurements from a sound level meter with a map to create a noise map like the one you see pictured here. Finally, you may have an app to measure noise on your smartphone. These apps often don't make very accurate measurements, but it's certainly a place to start to figure out if you have a potentially high noise exposure. There are standards out there to protect us against noise. So in the workplace, the Occupational Safety and Health Administration has a legally enforceable permissible exposure limit that basically says a worker can be exposed to 90-A weighted decibels or dBA on average over an eight-hour shift. That's about as loud as standing right next to a gas-powered lawn mower. This is a permissible limits, so this is the legally enforceable limit. But even OSHA will acknowledge that if you're right at this upper end of the safe limit, about one in four workers are going to have a substantial and serious hearing loss after 40 years. We also have exposure recommendations for communities again designed to protect against noise-induced hearing loss. So both the Environmental Protection Agency and the World Health Organization recommend a limit not for eight hours, but for 24 hours, and that limit is a 24-hour average exposure of 70 dBA or less, that's about as loud as a reasonably quiet vacuum cleaner. This level is designed to protect anyone from getting any hearing loss in the community, even the most vulnerable or susceptible individual. There are other limits out there that are designed to protect against annoyance or disturbed communication, those tend to be much quieter down around 35 to 55 decibels. By comparison, a normal conversation with someone at arm's length is going to be about 60 decibels. Let's think about your daily life. Where might you be exposed to noise? Well, you may have a noisy job, the way you get back and forth to your job or school, the transportation method of car, bus, mass transit, maybe you take an airplane. All of those things can add noise, and of course, your recreational activities going to concerts or sporting events. All of these things are contributing noise. Maybe you watch TV at home at a high volume, maybe you listen to music very loud, maybe you live right next door to a construction site or in an industrial facility, maybe you shoot guns which actually is a relatively brief exposure but incredibly intense. What does the research show on noise in daily life? I did a study with colleagues at Columbia University, where we looked at about 4,500 people who lived and worked in New York City. We surveyed them to figure out where they were spending their time, and then we surveyed them to figure out where their exposure to noise was coming from. So on the left here, you can see a pie chart showing that the average participants spend about 73 percent of their time either at home, or running errands, and shopping. They spent about 16 percent of their time at work, spent about four percent of their time writing transit, and only about one percent of their time at these noisy non occupational or recreational activities, and about six percent of their time listening to music. On the right-hand side, you can see where they actually got their exposure from. So the shocking finding here was that for just about half of our subjects, the primary source of exposure for them was not the workplace which I was trained to expect as an industrial hygienist, but rather listening to music. So the primary risk of noise-induced hearing loss for the average person in this study was not going to concerts or riding mass transit. It was actually listening to music. So finally, what can we do to reduce noise exposure? We've talked in other modules about the hierarchy of controls and we can absolutely apply that to noise as well. So we can think about substituting or eliminating a noise source, so we can get rid of the noise altogether. If we can't do that, we can think about engineering controls changing the source in some way to reduce the noise level. The NASA image you see on the right here describes a couple of different changes that are being evaluated for jet engines. So in the 1960s and '70s, the American public got quite upset about all this new jet engine noise from commercial airliner activities, and the government basically said to the airline manufacturers, "We don't care how you do it, but you are going to make jet engines quieter." After a lot of complaining that they were going to be put out of business and it was going to raise the cost of airplanes too much, they did it. So now airplanes are substantially quieter than they were even in the early 1980s, to the point where we've now had about a 90 percent reduction in how many people are exposed to excessive levels of airline noise. If we can't do engineering controls, we can think about administrative controls, limiting the length of time that we're exposed. Finally, last and least, we could consider personal protective equipment. So this would be wearing ear plugs or earmuffs to reduce our exposure. That's not to say these things can't be effective when they're used correctly, but they do require the user to know how to use them, how to use them correctly, and when to use them. So hopefully now, you have a better sense of this very under-recognized environmental health hazard, how we go about measuring it, and most importantly, how we can actually reduce exposures to keep the public healthy.
