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%." 
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!
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.)
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 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?
Probiotic foods and exposure to my family’s germs, on the other hand, I am okay with.
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.
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.
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.
Once the towel-squeezers were legal; now they’re not. Dyson next.
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.
Of which you need only one to dry your hands:
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."
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.
To the speed point though, I'd probably drive a P100D because they're ridiculously fast...
This, frankly, is my favorite sound mod -> https://www.youtube.com/watch?v=g_owsz8Za_Y
I suspect that the loud "powerful" noise level was selected to be in line with Dyson's brand image.
I wonder how many consumers believe this versus how many actively seek out quieter vacuums.
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.
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.
Good for them. And good for her. My son (4) hates these things. He dries his hands on his shirt instead.
Probably the worst culprits are headphones with the volume too high, and overly amplified concerts.
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.
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?
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).
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?
This is why I recommended some -12dB earplugs in another comment.
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.
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.
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 would hate those things even if they were silent.
Hand dryers are one item but there are some toilets that are also excessively loud as well.
My toddler son is always scared by the hand dryers. He refused and tried to escape from bathrooms with hand dryers.