Credit: Jason Nichol
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You're in a public bathroom with clean, dripping hands, standing in front of an electric hand dryer and a paper towel dispenser. What do you do?
There's a huge range of hand dryers on the market, but in all of them the heating element is the main power-sucking culprit - the element in a 2450W hand-dryer, for example, uses 2200W of its power.
Ninety-eight per cent of the global warming potential of an electric dryer and 65 per cent of resource depletion comes from the electricity use during its lifetime.
Short of running tests each time you visit a public toilet, it's difficult to tell which models are using the most energy. Real boffins will even tell you it depends on whether the nozzle spins upwards to dry wet hair!
But on average, the typical public bathroom contains a dryer that uses 0.02 to 0.08 kWh, producing 21 to 85 g of CO2. Hit the button twice and you'll double that.
A tale of two towels
Most of the studies that have been done on this dilemma came out in favour of electric dryers, finding that paper towels use up to 10 times more energy. But then, they were commissioned by electric dryer companies.
They assumed people use two paper towels after they wash their hands. When in actual fact, on average, for both men and women, 1.5 paper towels are used per bathroom visit, according to Jim Bowyer, a professor of bioproduct and bioprocess engineering at the University of Minnesota.
The studies also assumed that paper towels weighs 2.8 to 3.8 g, when most paper towels are actually between 1.97 g and 2.12 g.
When this variation is accounted for, and using energy figures from BuildingGreen, an independent building advisory company, the energy needed to harvest and manufacture a paper towel is 0.07 kWh if the paper is made form virgin fibre, or 0.04 kWh if the towel has recycled content.
So, in fact, the energy use per bathroom visit is about the same no matter which option you choose.
Recycling dead end
Don't be fooled by the utilitarian appearance of paper towels - most aren't made from recycled paper. Office supply company Corporate Express, which sells office and bathroom products to 45,000 clients in Australia and New Zealand, carries only two types of recycled paper towels in the 11 varieties it stocks.
Even if you do use paper towels with recycled content the recycling loop ends after we dry our mitts on them; recycling companies class discarded paper towels as 'contaminated' and add them to general waste.
It seems counterintuitive, but hand dryers have more recycling potential than paper towels. "You could absolutely recycle a hand dryer," says Chris Fisher from metal recycling company CMA. "You'd just take it to a scrap yard."
Constantly re-stocking dispensers with fresh wads of paper towels also takes a significant environment toll, according to The Climate Co2nservancy. It creates emissions through making garbage bags (0.3 g of CO2 per use), transportation (5.3 g per use), paper-waste disposal in landfill (24.7 g per use) and garbage-bag waste (0.2 g per use). In total, there are an additional 30.5 g of CO2 emissions associated with paper towel use.
Paper towels start to take the upper hand again when it comes to manufacture. Paper towels are made from trees, a renewable resource, whereas hand dryers are made from metals and plastic. Ores and oil are not renewable resources.
One way to determine the impact of a material is to look at the embodied energy. This is all the energy consumed from the mining and processing of natural resources to manufacturing, transport and delivery.
For a hand dryer in Melbourne (for example), the embodied energy contained in three kilograms of steel, 1.7 kg of aluminium, 231 g of copper, and 64 g of plastic, plus another kilogram of other materials adds up to 96.4 kWh. If the dryer lasts 10 years in a moderately busy bathroom, then this works out to be 0.004 kWh per use, which is nothing compared to energy use of the dryer.
But the emissions during manufacture are also serious. To make steel, iron ore is burnt with coal. And the mining and manufacture of aluminium is responsible for the emission of powerful greenhouse gases called perfluorcarbons.
But pulp and paper manufacture have serious environmental impacts as well, such as the creation of chemical pollutants. Sulphur compounds, dioxins and organochlorines are just three of the nasty by-products.
Organochlorines and sulphur can be persistent, toxic and accumulate in the environment while dioxins cause cancer.
Water use and deforestation are also big issues. The estimated annual water use of the proposed Gunns pulp mill in Tasmania is 26 billion litres. Deforestation is estimated to create 58.9 million tonnes of CO2 emissions in Australia per year, or the equivalent of driving 14.4 million cars for a year.
In reality, neither option is good for the environment. If possible, use the excess water to fix up your hair or let your hands dry naturally. Otherwise, electric hand dryers have a slight advantage because they can run on green power and they are recycled.
There is also more hope for greener hand dryers in the future. Over the last 60 years or so the technology of electric hand dryers had not changed. But recent developments from vacuum manufacturer Dyson include taking the heating element out and reducing drying time to 10 seconds instead of 30 or 40 seconds.