It's the age-old question that continues to baffle many of us in the bathroom: when you come to drying your hands, should you reach for the paper towel, or the electric dryer?
For some, this decision might be related to hygiene, and for others, drying performance. For many, environmental concerns are also an important consideration, no doubt motivated by the fact that our daily activities contribute to the complex web of growing sustainability pressures facing the planet.
So how might we decide which of the two most common methods of drying our hands - paper towel or an electric dryer - is the most effective, and environmentally friendly, without resorting to the convenient wipe on the trousers?
Life cycle analysis is a method long used to identify life cycle environmental impacts of products and services, including materials, manufacturing, transport, use, and end of life (e.g. disposal).
Using this analysis, we can search out "hot spots" - those parts of the life cycle which have higher impacts - to identify the most important aspects for our analysis.
The heat on hand-dryers
So let's cut to the chase: what are the hot spots for the most common hand drying systems?
Life cycle research consistently shows that the environmental impacts of the electricity and towels used at the point when we dry our hands dwarf the impacts throughout the rest of the life cycle. These include the materials, manufacturing, and disposal of hand-dryers and towel dispensers.
This is because we use dryers and dispensers many times before they are replaced. But every time we dry our hands we consume resources, either paper or electricity.
The environmental impact of hand drying is therefore most significantly affected by how much and what type of paper towel we use, or how much energy is consumed by the electric hand dryer.
Paper v. air
Research comparing these two methods of drying concluded that both the conventional hand dryer and the paper towel performed roughly the same, environmentally speaking.
Each method, however, gained a small advantage over the other depending on changes to critical factors such as:
weight and number of paper towels used per dry (the average is two)
proportion of recycled paper
power rating and length of time for drying using an electric dryer
other regional electricity impacts
So in some contexts a paper towel is the slightly better option, and in others, the conventional electrical hand dryer. This depends largely on how the electricity is generated, and how the towels are produced and disposed of.
A new contender?
You might have noticed a proliferation of fancy new dryers in bathrooms in recent years. While conventional dryers use a combination of warmth and air flow to evaporate and blow water off your hands, these newer dryers use a non-heated rapid air stream to simply strip the water off. Do they make the grade?
Several recent studies independently peer reviewed by experts have compared several high speed dryers to paper towels and conventional electrical hand dryers.
At first glance, the two high speed dryers investigated - namely, the XLERATOR and Dyson Airblade - already have an advantage over conventional electric dryers. They have a much shorter drying time (between 12 and 20 seconds, compared with 20-40 seconds for conventional dryers) and a lower power rating (around 1.5 kilowatts, compared with 2.4kW). The studies mentioned above have confirmed this advantage, even when potentially lower energy consumption by the conventional dryer is considered.
The researchers also compared the impacts associated with generating and using electricity for the dryer with the impacts and emissions related to paper production, manufacturing, and disposal.
And, again, the high speed dryers came out on top. This result held even when fewer than two towels per dry were used, and when the paper was 100% recycled, both in manufacturing and disposal.
Overall, these life cycle studies found that using a high speed dryer reduced environmental impacts markedly. This included global warming potential, land use, water use, solid waste, ecosystem quality, and embodied energy, when compared with conventional dryers and paper towels.
The final verdict
It seems a compelling argument can be made that, when faced with the choice, we should reach for the high speed electrical dryer over the conventional dryer, and even the humble paper towel.
As electrical grids become less greenhouse intensive the environmental benefits of high speed electrical dryers over paper towels may even increase.
However, this trend could change in the future: towels may become lighter and smaller; social marketing campaigns may highlight how towels can be better used and reused; new technologies may surpass the benefits of high speed drying.
Regardless, the key point here is that products, such as those for hand drying, should be considered within the broader context in which they occur; that is, across the entire life cycle from cradle to grave.
Only once we take into account the whole system can we make informed decisions that can secure better environmental outcomes now and into the future.
And at least we can now feel a little less anxious the next time we're faced with this drying dilemma.
Simon Lockrey is a Research Fellow at RMIT University in Melbourne.