This is more microbiology than chemistry but it has been a subject that fascinated me. Electric hand dryers in public toilets have long been touted as more hygienic than paper towel.
Not so, it seems.
[Wikipedia] In 2008, a study was conducted by the University of Westminster, London, to compare the levels of hygiene offered by paper towels, warm air hand dryers and the more modern jet-air hand dryers .
The key findings were:
- 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%
- 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 scientists also carried out tests to establish whether there was the potential for cross contamination of other washroom users and the washroom environment as a result of each type of drying method. They found that:
- the jet air dryer, which blows air out of the unit at claimed speeds of 400 mph, was capable of blowing micro-organisms from the hands and the unit and potentially contaminating other washroom users and the washroom environment up to 2 metres away
- use of a warm air hand dryer spread micro-organisms up to 0.25 metres from the dryer
- paper towels showed no significant spread of micro-organisms.