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[dupe] 13-Year-Old Scientist's Research Shows Hand Dryers Can Hurt Kids' Ears (npr.org)
170 points by Osiris30 9 months ago | hide | past | web | favorite | 63 comments

Relevant thread on the same subject from two weeks ago:


Hand dryers need to die.

Their primary benefit is lower cost of operation for the facility, but other than that, their environmental impact is at best marginally better than paper towels, and worst is their hygienic aspect.

Various studies have found up to a two-fold increase in bacteria count on users' hands, as well as a risk of contaminating the surrounding area with bacteria blown off of the user's skin:

"In 2009 a published study was conducted by the University of Westminster to compare the levels of hygiene offered by paper towels, warm air hand dryers and the more modern jet-air hand dryers. It found that after washing and drying hands with the warm air dryer, the total number of bacteria was found to increase on average on the finger pads by 194% and on the palms by 254%; drying with the jet air dryer resulted in an increase on average of the total number of bacteria on the finger pads by 42% and on the palms by 15%; and after washing and drying hands with a paper towel, the total number of bacteria was reduced on average on the finger pads by up to 76% and on the palms by up to 77%." [1]

The noise aspect discussed in this article is yet another reason air dryers need to die. I hadn't even considered the effect they might have on kid's ears, and I'd imagine most adults probably haven't thought about it either. I find them positively annoying, but having your ears at the same height as these monstrosities must be horrible.

Kudos to Miss Keegan for her wonderful research!

1: https://en.wikipedia.org/wiki/Hand_dryer

> Various studies have found up to a two-fold increase in bacteria count on users' hands,

I take issue with the nature of that statistic.

What does a 'two-fold increase' actually mean? Is it two hundred bacteria, instead of one hundred, when pre-hand-wash, I have millions?

Is it double the bacteria after use, compared to before use? If so, how many bacteria do I even have, after washing my hands?

What is the quantifiable harm of this 'double'? Double times 'next to nothing' is still 'next to nothing'.

(I despise hand-dryers, but I also take issue with these sorts of claims.)

Not that I want extra bacteria, but I wonder how significant that increase is practically, or what the baseline is. I'll sometimes shake a dozen peoples' hands in a row if I'm at a party, or hold onto public transport rails... Can it be much worse than that?

Well, one of the reasons for washing and drying ones hands is to reduce the amount of bacteria exposure. I don't have the same expectation when shaking a dozen peoples' hands at a party.

It’s to reduce specific types of bad bacteria that you might have contaminated yourself with when you went to the toilet.

I don’t think anyone can expect that washing your hands will eliminate all bacteria- including those in the air.

That said, I still hate hand dryers and still refuse to use them.

I don't know enough to be informed but I'm naturally skeptical about this idea that germs == bad. Maybe a washroom is an autoimmune proving ground for my body.

I think what might help is some better sense about what the pros and cons are to exposure. Are there some germ sources you want to avoid while others you can probably be fine with? Should my kid really wash his hands after visiting a playground?

At the moment all I see is that germs are lumped into one category and treated as a quantity to eradicate 99.9% of with lysol.

Or put simply, why should any of the numbers in your comment be seen as a bad thing?

I’m personally against over-sanitization and think exposure to a moderate amount of ‘germs’, especially during developmental years, is healthy. However, a public restroom isn’t really the place I want to get my daily dose. I’m definitely no infectious disease expert, but traces of excrement and grime from hundreds of strangers definitely sounds like something I’d like to avoid.

Probiotic foods and exposure to my family’s germs, on the other hand, I am okay with.

I don't know if the numbers are a bad thing or not, but when making evolutionary arguments, consider that in the environment of evolutionary adaptedness, humans would have been regularly exposed to germs from a much smaller number of humans than modern humans are in a crowded city (and that small group would mostly have been exposed to germs from each other, not strangers with access to modern transport).

My intuition tells me that exposure to all the germs is bad, but exposure to none of the germs is bad too. I think there's some sort of healthy middle. I feel let down by the various actors that fail to help find and promote wherever that middle is.

I want a resource that says, "okay so bathrooms have very dangerous bacteria because of feces. But your playground will generally be fine for a little autoimmune exercise. Go let your kid get a cold or two." My physician just hummed and hawed about this. And parenting resources are full of people freaking out over sanitizing everything.

Regardless of the research, I think what’s not discussed is how the choices around these devices are typically made by a single owner of a business. As the population continues to increase, and people generally become more educated and these types of experiences have more value, how could we come up with either solutions to the core issue, or solutions to give more funds to a business owner who would gladly install a better solution if those funds were available?

Taking a sample of a hundred random people, especially in a larger city, their values (however ranked) are wildly different, yet one person likely made the decision on the dryer, dependent still on the strengths of the local paper (janitorial supplies) company’s salesperson.

Currently, there isn’t a micro donation or registry (wedding registry) type framework where people can influence these decisions. Something similar could be in store?

Even Kickstarter, while it allows popular ideas to move forward, doesn’t allow these types of decisions to be influenced.

If your question is how to fix negative externalities, the answer is "regulation".

Otherwise... you can't make people care about every little thing in their lives. Sure we can solve this hand dryer problem with an awareness campaign or microdonations or whatever. But what do we do for the other hundred thousand issues like this?

Nobody has that much attention to spare on non crucial things. That's why we elect people to make these decisions for us.

Many things are going to suck as long as our elections remain broken. That is a much harder problem to fix, but there is no way around it.

Unregulated markets, no matter how innovative, do not always produce perfect outcomes. Basic conditions for and solutions to market failure have been known for more than a hundred years. It's not rocket science.

Micro donations? I think this is implemented by the legislature in the building code. If you’d like to run a restaurant, you must have restrooms with N urinals and M stalls per space of occupancy. Each restroom must contain K sinks per facility. You must provide drying apparatus.

Once the towel-squeezers were legal; now they’re not. Dyson next.

I agree with you. That’s why I mentioned solving it at the core first or creating a new type of framework that enabled influencing these decisions at a local level, if the former (your point) fails.

I’d also like to point out that the hostility on choice and applicable laws still fallback to a single Jill or Jack, when 100k people may end up using their bathroom. It’s the current reality, laws don’t exist at this detail, except for extremes.

> marginally better than paper towels

Of which you need only one to dry your hands:


There are tons of hand dryers in hospitals. Completely self-defeating, facepalm-worthy infrastructure.

> In response to these results, Dyson confirmed to NPR in an email that an acoustics engineer would be meeting with Nora to discuss her research.

You go girl. Rock on! No matter what happens, what an awesome response from Dyson to look at this girl's well thought out research and go, "Huh. Yeah, we should probably give that a second pass."

It can be made into a positive thing: e.g. hand dryers with attention paid towards being comfortable for childrens' ears, marketed especially toward early education institutions and the like.

Seconded! Very well done.

I don't understand why they have to be so loud.

I recently bought a Miele vacuum cleaner, and compared to other cheap vacuums I've had before. It's significantly quieter whilst still having effective suction.

Is it cost cutting or is this the best kind of motors possible for hand dryers?

As a side note: I wonder what the testing conditions are like for these dryers. Like there's one of the Xcellerator driers at my local bouldering place's toilet.

It's a very small tilled room. I went once and the sound caused my ears to ring for hours.

I don't go in without my noise cancelling headphones now haha.

But I imagine if the room was a lot bigger that would not be an issue.

Wild speculation: I wonder whether loudness is actually a design goal, to make the dryer appear more powerful. A sizable number of people are skeptical of electric vehicles, because they perceive an earth-shaking vroooom to be an essential part of the driving experience. Could someone with industry experience chime in?

There are car makers who now use DSPs to process exhaust noise to play INTO the interior of the car to make people feel like they're driving! I drive a turboed car, turbos are naturally sound dampening, I'm totally fine with it being quieter as long as its actually faster.

To the speed point though, I'd probably drive a P100D because they're ridiculously fast...

VW even did this mechanically before switching to an electronic version. At least that means it's easier to shut it up: https://www.carworklog.com/2016/07/02/guide-disableturn-down...

I didn't know about the tube, I def would've plugged that. I have a MKIIV Golf-R and you can absolutely hear the "Soundaktor in action, its so goofy...

This, frankly, is my favorite sound mod -> https://www.youtube.com/watch?v=g_owsz8Za_Y

Same here, it's a beast. I've done a slew of other VCDS mods if you're interested. 5 brake lights instead of 3, tighter lane keep (tesla-like), power windows after door open engine off, enable menus while driving, rest-of-world dynamic headlights, brighter blind spot indicators, hazards on skid, no seatbelt chime, the list goes on and on. And open that center console if it doesn't open!

Non-commercial vacuum cleaners are acoustically engineered to be loud for this reason. Other examples of intentional loudening include the opening of car doors and aluminum beverage cans.

I suspect that the loud "powerful" noise level was selected to be in line with Dyson's brand image.

One good thing the EU did was to end this pointless rat race with anti-noise and efficiency legislation. No single vendor could have done it, because consumers equal loudness with effectiveness in a vacuum cleaner.

> consumers equal loudness with effectiveness in a vacuum cleaner.

I wonder how many consumers believe this versus how many actively seek out quieter vacuums.

Loud machines are loud because loud is the easiest. It takes serious analysis and engineering to discover exactly where the noise comes from and/or is amplified and fix that. Sometimes you can cut a machine's noise level in half just by tightening a few screws or replacing some raster by a different material, but you don't know which one until you detect where the noise comes from.

Your Miele is less noisy because they (and their suppliers) invested lots of engineer hours in making it less noisy, both at the motor level and at the level of the entire vacuum cleaner.

I am pretty sure it is just cost; after all, places install them to save on consumables cost and staff to periodically refill towels and empty the trash.

A few days ago someone posted on hackernews about about noise canceling shapes I wonder if that can be used to muffle such sounds. Using architecture to expand or muffle sounds has been used for centuries but sadly we have stopped using them much because of easy availability of electronics.

I read the previous post on this that appeared on HN a couple of weeks back. https://news.ycombinator.com/item?id=20282837

My 3 year old used to close her ears anyways when near any of these hand dryers but now i warn her when one is about to turn on.

“In response to these results, Dyson confirmed to NPR in an email that an acoustics engineer would be meeting with Nora to discuss her research. “

Good for them. And good for her. My son (4) hates these things. He dries his hands on his shirt instead.

My 4.5 year old son will not let me use them. He'll throw an absolute fit if I try. I have a lot more sympathy for that now!

My son, now five, has hated them for years. He dries his hands on my shirt instead...

Mine too.

I’ve been suspicious of this for years. These things are incredibly loud and they’re right at ear level for kids.

My 11yr old son has been complaining about them being way to loud for him for years as well... I think I own him an apology for not taking the complaint more seriously.

The modern world is full of loud noises that damage our hearing prematurely.

Probably the worst culprits are headphones with the volume too high, and overly amplified concerts.

Everyone should be using musician style earplugs at concerts. They're designed to as best uniformly attenuate the volume to safe levels.

And in my opinion, a good pair always makes the music sound better.

And I never leave with ringing in my ears Because it's no longer just a wall of noise.

> And in my opinion, a good pair always makes the music sound better.

Yes. I can’t understand the thinking that goes into such extreme levels of amplification. It sounds horrible, like my ears are clipping the waveform before my brain gets the audio signal.

Is there a sound engineer out there brave enough to set the levels to a “reasonable” 95dB or what?

Sound engineer here. My goal is always to keep things as quiet as possible. It can be really hard to do so. The louder the mix, the more control you have because you have a larger ratio of PA sound to stage sound up front, and a larger ratio of PA sound to audience/bar noise in the back. The quieter the mix, the more the audience near the front gets overwhelmed with drums and whatever else on stage is naturally loud, and the more the audience in the back gets overwhelmed with the drunk people nearby.

Basically, the necessary mix volume is established by getting the vocals to sit sufficiently above those uncontrollable things, and everything else falls into place.

That said, plenty of engineers do mix too damn loud. They might have a good reason (and would compromise the mix by lowering it), but they might not (and are hurting people's ears unnecessarily).

So the loud music + ear plugs combination might actually be optimal, because the net effect is to reduce the volume of all the nonmusic noise.

Given the circumstances, sure. If you'd rather have conversations than shut them out, not so optimal.

Thanks. So what OscarCunningham said in sibling comment:

Ambient and unwanted noise might be at 90dB. You need at least 20dB of headroom to get a good sound and range, so the PA might be (for an arbitrary attendee) at 110dB.

Then I use my fancy flat-curve earplugs to chop 20dB off of everything, resulting in 90dB music and 70dB (and still drowned-out) unwanted noises.

My numbers might not be right, but general idea, right?

Absolutely. But even the flattest earplugs aren't flat because not all the sound goes through the canal they plug up. Bass conducts through your whole body so you end up with 110dB of bass, 90dB mids/highs, 70dB noise. The unattenuated bass isn't damaging your ears, but it makes a non-flat experience.

This is why I recommended some -12dB earplugs in another comment.

Do you have any purchase advice/recommendations?

I've used two primarily:

Alpine MusicSafe Pro

Etymotic Research ER20

I'd say both are comparable. Though the Alpines come with three filters allowing you to select the level of attenuation.

The Etymotics are bit longer so stick out your ear a bit funny looking, but they're more cone shaped and are easier to put into your ear.

The Alpines come with a little tool that helps inserting it into your ear.

To be honest they're both quite cheap so try both and not break the bank.

If you want to go higher end you can get ones where you can get a custom mold to your ear canal. But I don't have a recommendation there.

I got a pair of Etymotic’s ER20 ear plugs after seeing a few recommendations here on HN. I’ve worn them at concerts, at loud events, in a hotel next to the freeway, and even in the car when the driver had the radio too loud for me. Highly recommend them. I have small ear canals and the foam earplugs never worked, but Etymotic’s “standard” fits me fine, and also works for another friend with normal ears.



I personally use squishy foam-type ones at concerts (and when I played in a band) and find they make music sound better by isolating the individual components of the band. They are far from fancy, but I have not had ringing in my ears after a show since I started using them. I wish I had been smarter as a teen.

See: https://www.amazon.com/Macks-Ultra-Soft-Foam-Earplugs/dp/B00...

A lot of concert venues have these: https://www.amazon.com/Howard-Leight-Honeywell-Disposable-LP...

They're comfy and they sound pretty good. Unlike some others, they only reduce by about 12dB, which brings a concert into the safe zone while retaining good clarity. The more reduction you have, the more bass-heavy the resulting curve is, which doesn't sound too good.

I mean, these things hurt MY ears too and I'm 30. I will frequently just dry my hands on my pants. She did a great job!

Some air dryers start with a motion detector and and it was impossible to get most of the kids to even enter the toilet because they were afraid that it would start the dryer accidentally. I myself was confused why their reaction was so extreme but didn't think that the noise is much louder at their height and that their ears are more sensitive to loud noise too.

Interesting that it needs a kid scientist to take this on them because adults with their height bias didn't measure at those spots.

I wonder how sanitary they are, considering that they are basically using a bunch of bathroom air blasted at your previously-clean hands, too.

I would hate those things even if they were silent.

You're also breathing bathroom air though?

Sure, but blasting a large volume of it at my wet hands I imagine would concentrate a lot more of the contents of the air on the surface of my hands than I am breathing.

My 3 year old covers his ears in any public bathroom regardless of whether anyone is even in there.

Hand dryers are one item but there are some toilets that are also excessively loud as well.

I honestly hate hand dryers, half the time I end up drying my hands on the sides of my pants if I'm wearing jeans... My kid hates the sound of them too so it totally makes sense that they're actually bad.

I have never understood hand dryers. I mean how lazy one can be that they need a machine to blow hot air instead of wiping their hands.

They're not for the benefit of people who use them. They're supposedly cheaper than paper towels for the owner, and there may be some environmental benefit. I haven't seen research into either claim though.

Kudos to the author!

My toddler son is always scared by the hand dryers. He refused and tried to escape from bathrooms with hand dryers.

Just wipe your hands on your pants after shaking them in the air for a bit.

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