Scientists at the University of Leeds investigated the hypothesis that forced air hand dryers, touted for their greenness, might spread bacteria due to aerosolization of contaminated particles. E.L.Best, et.al., recently published a study in the Journal of Hospital infection comparing the propensity of three common hand drying techniques to contaminate the environment, users, and bystanders.
Coating hands with lactobacilli as a surrogate for poorly washed hands, they sampled the air both close and at a distance (one meter) away from the source after the hands were dried using jet dryers, warm air dryers, and paper towels. They also used a separate test using colored paint hand coatings to simulate droplet scatter.
The air bacterial colony forming units (CFUs) of jet driers at close range were 70.7, or 4.5 times higher than warm air driers (15.7 CFUs), and 27 times higher than paper towel drying (2.6 CFUs). There was a similar trend at one meter away. Colored air droplet patterns were also of similar trend, as were persistent airborne CFUs after 15 minutes (14 vs 4 vs < 1 CFU).
Among the conclusions was the suggestion that air dryers may be unsuitable for use in healthcare settings.
BUT WAIT! There’s more!
Reported in Huffington Post is the fact that the research was commissioned by the paper towel industry… as was pointed out by a spokesperson for Dyson – an air hand dryer maker.
I love this stuff!
And then of course you need to apply one of my favorite formulas in physics when you are standing near someone else using the air driers. The cube of the distance. Stand back. You will be exposed to 1/9 as many particles if you are three feet away compared to being one foot away, and a whopping 1/216 at six feet away (not compensating for gravity, subtended angle, air resistance, and other factors).
Green or clean or both! Wash your hands well to begin with (generally poorly done) and the point may be moot.
Marshall Kubota, MD