May
12
2014

Sound shock vs hygiene – high speed hand dryers

hand dryerHigh-speed hand dryers are an engineering success story, chiming with the prevailing agenda of austerity and sustainability, but what is the trade off? As someone with normal hearing, Dr. John Drever found the new generation of power hand dryers in WC’s intrusive. On becoming a father he became aware of how the sudden triggering of aggressive sound in a quiet space can panic children and others sensitive to noise – prompting his investigation of the issue.

Back in July 2013, I was vexed by the Daily Mail’s spin on my research when they announced: “Super fast hand dryers may be loud enough to damage people’s hearing”. This was never a conclusion of my research – to inflict permanent damage on your hearing you would need to spend an excessive amount of time in the presence of a non-stop high-speed hand dryer in a WC. Frustratingly, this caption obfuscated the subjective and more subtle message of product sound design I was keen to impart. While arguably not as serious as hearing loss, I was being educated by a wide range of users about pain, fear, discomfort, anxiety, sensory shutdown, social exclusion and the onset of phobia that was coming about due to the quality and level of sound generated by high-speed hand dryers within the highly reflective acoustic of the WC.

Public toilets are already a complex and challenging space for many. What the users I was hearing about have in common is what we could categorise as sensitive hearing, a condition that the standard A-weighted decibel used in most acoustic standards does not account for, leaving them vulnerable.

Beyond my own family, I have been informed by many parents that their children are terrified by the sound of high-speed hand dryers, and as all caring parents of young children will know, the last thing you want to instil is a link between discomfort and toilets. Toilets offer an unusually quiet zone within the urban setting (with sound levels as low as 45 dB LAeq), so accidental triggering of a high-speed hand dryer (which is easily done by some brands in cramped conditions) marks an immediate shift in the room’s sound pressure (80 to 95dB LAeq), which will quite naturally elicit a flight-or-fright response in not only kids, but I would say most users.

It is well documented that children’s hearing is much more acute than adults’ particularly at the higher region of the audible spectrum, and as the high-speed dryer generates a lot of high-frequency sound due to air turbulence, the problem for kids is compounded. Moreover it is a major challenge to vocally reassure your child due to the devastating impact on speech intelligibility.

It is not just children who have sensitive hearing. I found particular complaints among the following groups – visually impaired; hearing aid users; Alzheimer’s disease; Ménière’s disease; cerebral palsy and, most significantly, hyperacusis (sensitive hearing) sufferers, and hyperacute hearing in autism and Asperger syndrome. Here is a typical comment (From an ASD chat room) from someone with hyperacute hearing:

“I can’t stand those hand dryers and it amazes me whenever I see people nonchalantly using them like the sound is nothing. It’s very painful for me. I won’t go in restrooms that have them unless it’s absolutely necessary and if someone uses the dryer while I’m in there, I plug my ears. I don’t care if I look like an idiot.”

While high-speed hand dryers have been an engineering success story, chiming with the prevailing agenda of austerity and sustainability, but what is the trade off? The rule of thumb is, the faster the hand drying cycle the louder the noise! The notion of ‘noise as power’ is a feature that has been actively marketed – just look at the product names: Airblade; Airforce; Air Fury; G-Force; Hurricane; Rafale; Jet Towel; Tornado; Typhoon. These names denote muscularity, anger, violence, extreme weather and militarisation, and to be fair there are many sensory seekers who enjoy the visceral power of high-speed hand drying.

There is, however, some good news for those who do not, with encouraging technological developments in new range dryers consciously designed for slower, yet quieter operating levels, such as the Airdri Classic+ MkII. The challenge of reducing noise, however, is not solely for the product maker. The planner, the architect and, most importantly building acousticians all have a role to play. WCs can be very small (e.g. 20m3), are often rectangular, surrounded by hard surfaces with very low absorption coefficients across the spectrum, resulting in an ultra-reflective space with high frequency room modes. Basically, they are the most problematic space, acoustically speaking, in which to install a high-speed hand dryer. My studies have shown hand dryer sound levels multiplied more than 10 times due to reflection. This is not a new problem, as we nostalgically remember the thunderbox.

So, in conclusion, please don’t stop drying your hands as it is a essential part of good hygiene. However, it is evident, even from this initial study, that there is a major issue when considering the impact on sensitive hearers to high-speed hand dryers, which in the most extreme case could result in exclusion from public space, the workplace and education. This is not a call for silent loos either, as shared toilet provision requires a certain level of background noise for acoustic privacy. This is necessary to address other common health issues like paruresis (shy bladder) and parcopresis (shy bowel).

However, from my preliminary field tests I have in situ acoustic readings from power hand dryers that are akin to the sound levels of a road drill! While allowable by law, as it won’t damage hearing if experienced in short bursts, the stress response affecting many from this noise is undeniable.

As an afterword, I would like to remind us of a rose-tinted pre-War generation who were cognisant of the issues of product noise. On the 31st May 1935, The Anti-Noise League launched an exhibition on noise abatement at the Science Museum in London. In the forward to their publication Lord Horder wrote:

“The principle that noise is a nuisance and a disturber of human happiness has been generally accepted. The result is that needless noise (and there is a great deal more preventable noise than we imagine) is being suppressed wherever possible… Manufacturers are almost one hundred per cent amenable to good sense and to the good of the community.”

 

Dr John Drever PhD, FRGS, FRSA, AoU, MIOA
Head of the Unit for Sound Practice Research, Goldsmiths University

8 Comments + Add Comment

  • Anyone who needs some assistance in choosing a hand dryer for a school, one that considers noise, hygiene and high speed, please read…https://www.blowmotion.co.uk/a-guide-to-selecting-hand-dryers-for-schools/

    It’s an updated article I wrote that discusses these issues.

  • Thanks for your work on this. I have become increasingly offended by these hand dryers in recent years and months, especially since having a child who like most children I have seen becomes very agitated and stressed at the noise level, particularly in busy service stations or shopping centres where there might be several going off at once. Furthermore, these areas are now so loud that pleasantries and small talk are impossible and where it is no longer possible to just take a 5 minute break from the world, but more of a toileting conveyor belt. These spaces hace become dehumanised.

  • I work in a primary school and I have found that since installing new high speed hand dryers, the noise levels have increased dramatically.

    It’s not quite at the level to startle the kids when they walk past but you can hear when they are in use all the way down the hall as the doors are very thin.

    Granted, they work extremely well but the constant on/off noise is distracting.

  • Fortunately there are now many quieter high speed hand dryers on the market that effectively dry hands, but do so at a very low noise level. They are perfect for environments with small children and those who are sensitive to the loud noise emitted by other hand dryer units. Models such as the Xlerator XL can be modified with a Noise Reduction Nozzle, while others, including the Excel Dryer Cast Hands Off dryer and Palmer Fixture’s EcoStorm provide exceptionally quiet operation. More options are now available for those with sensitive hearing so they can benefit from the efficiency and ease of operation of modern high speed hand dryers! Learn more at http://www.handdryersupply.com

    • Very helpful! I’ve been pushing to have EcoStorm installed and have met resistance about noise levels. Will be using your comment and this article to try and make the switch happen faster.

  • Typical of The Daily Mail to put a spin on your research. That’s subjective journalism for you. Shame on them.

    Thanks for sharing, Dr Drever.

  • We look forward to further investigations with Dr Drever into the subtly of sound composition to allow us to offer even more in depth information on the noise output of the hand dryers we provide. We have begun the process of including independent test results showing the amplification from the manufacturer’s stated noise specifications when tested in a normal room with hands placed in or under the dryer to give customers a more realistic view of the sound levels than typically provided.

  • HI Dr. Drever,

    My name is Kritika Vayur, and I am studying Acoustics as a graduate student.

    I find your view to be true, in my case. My trip to the public restroom is what initiated my investigation of the overtly annoying noise that they produce. I am looking at the SPL produced by original hand dryers as well as any new ones (such as the dyson’s). Jeff Fullerton’s article in 159th ASA meeting analyzed the SPL, in dBA, of the then current hand dryers in public restrooms, which solidified my thoughts on the piercing sound of the driers.

    I would be honored to discuss my thoughts with you on this subject. I hope to speak with you soon.

    Thank you.

    Kritika Vayur

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