Blown away by scientific proof?
April 1st 2009

Dyson has dismissed the paper industry-funded study into towels versus dyers reported last issue as 'scientifically flawed, insignificant and sensationalist'. Gerardine Coyne spoke with Dyson microbiologist Toby Saville at the firm's Chippenham HQ

Unsurprisingly, the recent University of Westminster study, A comparative study of three different hand drying methods: paper towel, warm air dryer, Dyson Airblade dryer, funded by the European Tissue Symposium (ETS) and covered in last month's CM raised eyebrows at Dyson.The company is concerned that the Westminster study could undermine perceptions of the product using statistics and statements that as far as Dyson is concerned, are neither legitimate nor based on scientific fact.

"Firstly the Westminster study has not been peer reviewed," says Toby Saville."It is a client-based study that has only been published on a website and not in a scientific journal.As a scientist I am disappointed by the flaws in the method and at the way conclusions have been drawn from results without a true explanation of the context." He says Dyson's approach to Airblade development was precisely the opposite."We went to great lengths to verify the Airbade's hygiene and safety credentials, with independent testing, peer review and certification." The Westminster University study found that bacteria increased greatly on hands after washing and drying hands with a standard warm air dryer, increased slightly using the Airblade and decreased using paper towels.However Saville points out that testing was done on the hands before washing and after drying.He says this makes it impossible to tell whether bacteria growth is from washing hands or drying them.

Saville says the hands should have been sampled for bacteria after washing with soap and water to quantify the amount of bacteria present.For example if hands were washed poorly,bacteria could still be left on the hands, or it could have been transferred from the taps or sink. Saville argues that the hands should then have been tested after drying with the three methods to see if bacteria that was present after handwashing increased or decreased with each drying method.

In Dyson's own tests, it was found that rubbing hands together during drying may release bacteria under the skin's surface, i.e. the body's 'natural' bacteria.As the bacteria in the Westminster study was categorised as 'general, gut and skin bacteria', Saville says rubbing could have caused the sensational increase in bacteria the University claimed resulted from the warm air dryers tested.

Saville theorises that the increase in bacteria using the Dyson Airblade may be due to the hand washing – either improperly washed hands or possibly rubbing."The air blown from the Airblade is HEPA filtered, so it can't be the air that is adding bacteria," says Saville."If the hands had been tested after washing, it could be verified what was on them before the drying process.As it is, there is no explanation as to where the bacteria growth has come from." Saville does not contest the study findings that paper towels decreased bacteria on hands.However, if a person was to touch the dispenser or the inside of it, in his opinion there was a chance for contamination. Saville claims an in-house study for Dyson found that after sterilising a paper towel dispenser, when a person with wet hands detached a towel, bacteria was deposited onto the surface of the dispenser where hands had made contact.

Defining antimicrobial

Dyson's main concern is the Westminster study claim that the Airblade causes cross-contamination and is therefore unsuitable for areas with strict hygiene requirements such as hospitals or food preparation plants.

"Every component of the Airblade is antimicrobial,"explains Saville. "Ours is silver-based. But let's define what antimicrobial means. Antimicrobial does not mean that a surface is kept sterile. It means that when bacteria comes physically into contact with that surface it cannot grow or replicate and is killed within 24 hours to a 99.9% efficiency.The antimicrobial surface limits bacteria.We don't say to the end user that it's self-cleaning,we tell them it needs wiping down with a damp cloth.Think of it like a sink – you wouldn't leave a sink uncleaned in a washroom.The bacteria has to touch the surface of the Airblade for the antimicrobial effect to work, if it's on top of a layer of skin or soap, then it won't be effective. It needs a contact time." The Westminster study results showed that on tests at a London railway station bacteria had gathered in the slits and bottom of the Airblade."That is as intended!"says Saville."Any bacteria in water left on hands after washing – and commuters are probably not using the hospital standard 60 second washing procedure – is stripped off the hands by the dryer, onto the antimicrobial surface where it cannot grow and is killed."

If hands did touch a surface where there was bacteria – in the Westminster study it was at the bottom of the dryer where water collected – Saville said transferring may be possible."Users may touch the bottom, but if there is any water there, and their hands get wet, they will dry them again, blowing off the water containing bacteria.The dryer is not growing or colonising bacteria, it is what is coming off people's hands, stripped off by the Airblade. " But what about the Westminster claims that water droplets and therefore bacteria were found a couple of metres away from the Airblade after drying? "We are aware that with some ways of drying the hands, small droplets will spread up to two metres to the side of the dryer.We stipulate that in food plants, food preparation surfaces must be two metres away.

However it's not as cut and dried as that. "The Westminster study did not put the results in a meaningful context.The scientist used a solution of water and yeast on the subject's hands that contained hundreds of millions, if not billions of yeast cells.The fact that 76.2 colonies were found a quarter of a metre away, and 1.2 colonies were found two metres away, out of millions is like a drop of water in a swimming pool.

"You could easily find these amounts of bacteria on any surface you care to test in a washroom,which we all touch when completing the rest of the hand hygiene process – taps, soap dispensers or even paper towel dispenser openings.When given some context, and knowing how unrealistic the test set up was, the numbers reported are pretty insignificant. I think the conclusions drawn have been sensationalised."

Food for thought

Dyson has had research carried out by Campden BRI – the biggest member-based food research company in Europe."All the big food brands are members and they look to Campden for advice on technology," says Saville. "Campden came to us as its members were interested in using the technology and Campden wanted to test it.

"We didn't know what the results were going to be. If the product had aerosolised bacteria,we would have had to say,'this is not suitable for the food market'and gone away and redesigned the product if we'd still wanted to enter that market.As it turns out the aerosolised bacteria count using the Airblade was barely any different from the background 'clean environment' count, eight bacteria on average as opposed to five bacteria without the dryer– so of no consequence.

Will there ever be a truly bacteria free solution? "In hospitals you strive for that, purely because you don't know what you're moving around, whether it's good or bad bacteria.

You have to eliminate everything," states Saville."But we wouldn't even bother with the healthcare market if we thought there was a risk of an infection being traced back to the product.That would send us under.Hospital infection control departments and microbiologists wouldn't take it on if they thought there were risks.They do their own tests and check our research before they're happy to use it.

"There are areas we wouldn't expect to use it because of the noise – you wouldn't want it on a ward in the middle of a night for example.We are very realistic about where we want it.We know it will go into A&E, public areas and back of house staff areas.The healthcare sector will not consider you until they are happy on the hygiene front," says Saville.The Westminister University study has now been removed from the university website.

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