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A comparative life cycle assessment of conventional hand dryer and roll paper towel as hand drying


Science of the Total Environment 515–516 (2015) 109–117

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Science of the Total Environment
journal homepage: www.elsevier.com/locate/scitotenv

A comparative life cycle assessment of conventional hand dryer and roll paper towel as hand drying methods
Tijo Joseph a, Kelly Baah a, Ali Jahanfar a, Brajesh Dubey a,b,?
a b

School of Engineering, University of Guelph, 50 Stone Road East, Guelph, Ontario N1G2W1, Canada Department of Civil Engineering, Indian Institute of Technology - Kharagpur, Kharagpur, India 721302

H I G H L I G H T S ? Comparative life cycle assessment of two prevalent hand drying methods was conducted. ? Two methods, warm air hand dryer use and paper towel use, assessed. ? Towel material and manufacturing and dryer electricity use major impact contributors.

a r t i c l e

i n f o

a b s t r a c t
A comparative life cycle assessment, under a cradle to gate scope, was carried out between two hand drying methods namely conventional hand dryer use and dispenser issued roll paper towel use. The inventory analysis for this study was aided by the deconstruction of a hand dryer and dispenser unit besides additional data provided by the Physical Resources department, from the product system manufacturers and information from literature. The LCA software SimaPro, supported by the ecoinvent and US-EI databases, was used towards establishing the environmental impacts associated with the lifecycle stages of both the compared product systems. The Impact 2002+ method was used for classi?cation and characterization of these environmental impacts. An uncertainty analysis addressing key input data and assumptions made, a sensitivity analysis covering the use intensity of the product systems and a scenario analysis looking at a US based use phase for the hand dryer were also conducted. Per functional unit, which is to achieve a pair of dried hands, the dispenser product system has a greater life cycle impact than the dryer product system across three of four endpoint impact categories. The use group of lifecycle stages for the dispenser product system, which represents the cradle to gate lifecycle stages associated with the paper towels, constitutes the major portion of this impact. For the dryer product system, the use group of lifecycle stages, which essentially covers the electricity consumption during dryer operation, constitutes the major stake in the impact categories. It is evident from the results of this study that per dry, for a use phase supplied by Ontario's grid (2010 grid mix scenario) and a United States based manufacturing scenario, the use of a conventional hand dryer (rated at 1800 W and under a 30 s use intensity) has a lesser environmental impact than with using two paper towels (100% recycled content, unbleached and weighing 4 g) issued from a roll dispenser. ? 2015 Elsevier B.V. All rights reserved.

Article history: Received 20 October 2014 Received in revised form 15 December 2014 Accepted 3 January 2015 Available online 18 February 2015 Editor: D. Barcelo Keywords: Hand dryer Paper towel Life cycle assessment IMPACT 2002+ Uncertainty analysis

1. Introduction Since the middle of the 19th century, it has been identi?ed that hand hygiene is very important in reducing the possibility of infection from disease causing microbes (Best and Neuhauser, 2004). Several scienti?c studies have been published since that time on hand hygiene and its effectiveness in curbing the spread of infectious diseases (Aiello et al., 2008; Das et al., 2008; Han and Hlaing, 1989). Bloom?eld et al. (2007) suggested hands as the most signi?cant entry point for microbial ingress
? Corresponding author at: Department of Civil Engineering, Indian Institute of Technology - Kharagpur, Kharagpur, India 721302. E-mail address: bdubey@uoguelph.ca (B. Dubey).

to the human body and highlighted the relevance of hand hygiene procedures in controlling pathogen spread. The Centers for Disease Control and Prevention in the United States recommends drying hands after hand washing because wet hands can take in and transmit much more germs than if they were dry (Centers for Disease Control and Prevention, 2013). Therefore, in public settings in particular, hand drying is an important closing procedure after hand washing. In general, there are three different means of hand drying and these are through using paper towels, using cloth towels and using a hand dryer. All these three methods involve the manufacture, use and disposal or recycling of products which can ultimately affect the natural environment (Finnveden et al., 2009). Growing public awareness on hygiene and rising hygiene standards is increasing the demand for hand dryers and tissue products for use in

http://dx.doi.org/10.1016/j.scitotenv.2015.01.112 0048-9697/? 2015 Elsevier B.V. All rights reserved.

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public restrooms and in institutional, commercial and industrial settings. The global tissue market, a signi?cant percentage of that being paper towel products, registered a consumption of 31.5 million tonnes in 2012 (UUtela, 2013). As far as this global market, North America has the highest per capita consumption. On the other hand, around 2 million units of hand dryers were shipped out in 2013 (TMR, 2014). Market research forecasts continued growth in both the tissue and hand dryer segments. At the present time, paper towels dominate the hand drying market. According to a 2009 media report quoting a hand dryer manufacturer, the share of paper towels in the drying market was around 90% at that time (Sterrett, 2009). However, hand dryers are making an increasing foray into the drying market. In order to assess the environmental impact of products and services, the most widely used tool is Life Cycle Analysis (LCA) otherwise known as Life Cycle Assessment (Guinée, 2001). Using LCA, all material demand, energy requirements and environmental emissions associated with the manufacture, use, transport and disposal phases of a product, through its life cycle, are identi?ed (Guinee et al., 2010; Joshi, 1999). A LCA study can thus be used to compare products and processes so as to identify the better option in terms of environmental performance and thus make better informed decisions (Finnveden et al., 2009; Montalbo et al., 2011). There is concern that trees have to be felled to produce paper towels leading to a common perception that hand dryers are more ecofriendly. A review of literature shows that only a handful of LCA studies, comparing paper towel and electric hand dryer as hand drying methods, have been published to date (Budisulistiorini, 2007; Dettling and Margni, 2009; Environmental Resources Management, 2001; Montalbo et al., 2011). However, the results from these studies do not allow for a consistent conclusion to be derived as to whether dryer use or paper towel use has a greater life cycle environmental impact. Further, majority of these LCA studies were commissioned by dryer manufacturers and none looked at a product use scenario based in Canada. This paper seeks to add to the existing study base through a comparative LCA case study of two hand drying methods in a university campus setting in Canada and in process, providing an independent assessment of the better method solely from an environmental sustainability point of view. 2. Methodology LCAs typically include a goal and scope de?nition, inventory analysis, life cycle impact assessment and an interpretation phase (ISO, 2006a,b). An LCA methodology, in line with ISO14040:2006 and ISO 14044:2006, is adopted in this study. This LCA is carried out using the proprietary LCA software SimaPro? 7 with database support from ecoinvent v2 & US-EI databases available in SimaPro. 2.1. Goal and scope The goal of this LCA study is to assess and compare the life cycle environmental impact of using either paper towels or a warm air hand dryer which are two available hand drying methods at the University of Guelph (UoG) campus located in Ontario, Canada. For the purposes of this paper, the product system consisting of paper towels and its dispenser unit is termed the dispenser product system. The product system associated with the hand dryer is termed the dryer product system. The scope of this LCA is a cradle to gate system boundary and is applied to the different life cycle stages of the two product systems, right from material and manufacturing, transport of ?nished products and ?nally its use on campus at UoG. The end of life disposal and recycling scenarios are excluded under the scope of this study. 2.2. Case study scenario A hands-under type warm air hand dryer, rated at 1800 watts (W), is compared to a controlled roll paper towel dispensing unit

that issues paper towels made from 100% recycled paper. The case study is based on a United States (US) manufacturing scenario for the hand dryer unit, the paper towel dispensing unit, the paper towel rolls as well as for all associated packaging for both the product systems. The electricity grid source mix powering the hand dryer unit during its use phase is based on the 2012 grid scenario in Ontario. 2.3. System boundary The system boundaries selected in this study are presented in Fig. 1. Under the framed system boundaries, the analysis covers raw material extraction & re?ning, manufacturing of semi-?nished components for the hand dryer as well as for the dispenser unit, manufacturing of the paper product and corrugated board packaging, assembly of the components into the ?nal ?nished product systems, transportation of product systems to the university campus and lastly, their use phase on campus. 2.4. List of assumptions The following summarises the key assumptions and scenarios considered in this study: ? Washroom users will not avail of both hand drying methods at the same time. ? Paper towel use intensity is 2 sheets per dry and hand dryer usage is 30 s per dry. ? A ?ve year product lifetime is considered for both the hand dryer and dispenser units during which time there is no deterioration in their operation or any requirement of maintenance. ? Over the considered lifetime of both the hand dryer and dispenser unit, the per annum washroom footfall remains a constant. ? Only one type (100% recycled content, unbleached) of roll paper towel is used as a dispenser consumable. ? Annual consumption of paper towel rolls at UoG translates to consumption with no carry-over inventory, no stub roll waste and no stock damage. ? A simple supply chain scenario is considered without distribution or warehousing hubs. ? Semi-?nished products (e.g., machined aluminium die-castings, copper windings) manufactured by sub-suppliers using extracted and re?ned raw materials, are fed to two assembly plants (one assembly plant for the dispenser product system and another assembly plant for the dryer product system) where they are ?rst converted to ?nished product components (e.g., electric motor) from which the ?nal products (hand dryer, dispenser unit and paper towel rolls) are assembled and packaged for onward shipment. All the sub-suppliers are assumed to be located within a 250 km radius of the two main assembly plants. ? The entire hand dryer and dispenser installation demand on campus is met using only two delivery runs. ? A single shipment from the assembly factory to UoG provides for an entire ?ve year paper towel demand.

2.5. Functional unit The functional unit quali?es and quanti?es the obligatory properties and performance output that should be associated with the product system under study and is also the central reference unit to which all the other data is normalised (Cooper, 2003; ISO, 2006a,b). The primary goal of both the hand drying systems under study here is to assist washroom users at UoG in achieving a pair of dry hands before leaving the restroom. On this basis, the functional unit for this study is de?ned as

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Fig. 1. Selected system boundaries & life cycle stages for the dryer & dispenser product systems.

‘a pair of dry hands’. In de?ning the functional unit, the required dryness level is not quanti?ed. To the knowledge of the authors, there are no standards available, common to both drying methods, which would otherwise have allowed for a common basis in establishing dryness requirements. Paper towels typically, can achieve a dryness ef?ciency of above 90% (Redway and Fawdar, 2008). Warm air hand dryers too can achieve a similar performance, but subject to the drying time. For the purpose of this study, it is hypothesized that both product systems, subject to their typical use intensities, provide a satisfactory and comparable dryness level to washroom users. Within the goal and scope of this

study, no other properties or technical details for both the product systems are considered relevant. 2.6. Reference ?ow & allocation of life cycle stages The reference ?ow quanti?es the material and energy ?ows that are required to achieve the functional unit (Cooper, 2003). Along with the functional unit, the reference ?ow allows for deriving a common basis when conducting LCA studies of comparable product systems. Fig. 1 also illustrates the life cycle stages associated with the functional unit. This

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begins with the extraction and re?ning of raw materials like trees, ores and crude oil to yield outputs like paper, metals and plastics. Subjecting these outputs to different semi-?nishing operations, e.g., injection moulding (plastics) and corrugation (paper) yields sub-components. These sub-components go into building the ?nal product systems. For the dispenser product system, used paper towels generated during its use phase go into a steel bin lined inside with a compostable grade liner. At the end-of-life, the compostable liner and the used paper towels undergo composting, while the dispenser unit is dismantled with its subparts going into a land?ll. The dryer unit, at its end-of-life, is also disassembled and its sub-parts are either recycled or land?lled. The material and energy ?ows required to achieve the life cycle stages associated with the product systems delivering a pair of dry hands form the basis of the reference ?ow. However, both the dispenser and hand dryer units can achieve the functional unit, a pair of dry hands, many times over during their respective lifetimes. Thus in this case, only a portion of the life cycle stages of the hand dryer and dispenser unit can be allocated when assigning the reference ?ow. The applicable allocation is derived as follows: Amount of roll paper towel use at UoG per annum based on 873 sheets per 800 ft roll — 7,327,962 sheets/annum (R. Watson, personal communication, March 2013) Estimated number of washroom users at UoG per annum based on assigning a use intensity of two paper towels per washroom user — 3,663,981 washroom users/annum Estimated number of washroom users over the lifetime of both the hand dryer and dispenser units (lifetime for both the hand dryer unit and dispenser unit taken as ?ve years) — 18,319,905 washroom users Calculated allocation based on an estimated installation ?gure of 500 hand dryers/dispenser units on campus — 2.73 × 10? 5. 3. Life cycle inventory (LCI) analysis Inventory analysis is carried out in order to quantify the inputs and outputs (energy, materials, wastes etc.) associated with the life cycle stages of both the dryer and dispenser product systems (De Smet and

Table 1 Lifecycle stages of dryer & dispenser product systems. Dryer product system Material & manufacturing Production of hand dryer components (ore mining → material re?ning → semi-?nished product forms) Production of corrugated board packaging Assembly of hand dryer from components Shipment of hand dryer components from sub-suppliers to the dryer assembly plant (within US) Shipment of the assembled hand dryers from the factory in US to UoG campus in Canada Electricity consumption during hand dryer use (use phase is based in Ontario, Canada)

Stalmans, 1996). The relevant life cycle stages for both the product systems, considering the scope of this study, were grouped under three main headers — material and manufacturing, transport and use. The groups and details of their stage components are further elaborated in Table 1. Note should be made here that the use group for the dispenser product system includes the production of paper towel rolls and its associated packaging and the transport of paper towel cases. Based on the de?ned system boundaries and assumptions made, life cycle stages expected to be associated with waste bins (required to discard used paper towels), liners required for the waste bins, and servicing/maintenance activities for the dispenser and dryer units were excluded from the LCI. The inventory analysis for this study is based on data provided by the Physical Resources Department at UoG, data from product system manufacturers, and information from technical literature. A hand dryer and a dispenser unit, both exactly similar to models in use on campus, were deconstructed (Fig. 2) towards developing their respective bill of materials (see Supplemental Table S-1) and thus forming the basis of the material inventory analysis in this study. The only resource consumption accounted for in both the product system assembly plants is electricity use. Data regarding energy use in the dispenser assembly plant was based on information provided by the dispenser manufacturer (Harvey. M, personal communication, March 2013). For the hand dryer assembly plant, similar data cited in a previous study was assigned as electricity consumption (Dettling and Margni, 2009). The distance information required under the transport group was computed using a mapping service based on the present location of the product system manufacturers. The two assembly plants were assigned to be distant from UoG campus by 798 km and 1112 km, respectively, while all sub-suppliers to the assembly plants were assigned a 250 km location distance. The power consumption of the hand dryer was based off the manufacturer's speci?cation sheet (1.8 kW rating) and a use intensity of 30 s per user, but no phantom power draw during its period of non-use was considered. The use intensity of paper towels was assigned as 2 sheets (weighing a total of 4 g) per user. Using SimaPro, appropriate unit processes available from the ecoinvent and US-EI database libraries were assigned to the material, energy and water resource ?ows associated with the life cycle stages identi?ed for both the product systems (see Supplemental Table S-2). US grid supplied electricity was set against unit processes associated with all material production and product manufacturing. This was based on the fact that the entire manufacturing scenario is in the US. For the hand dryer use phase, the electricity generation unit processes were adjusted to re?ect the power source mix scenario for Ontario in 2012 (57% nuclear, 22% hydro, 15% natural gas, 2.7% coal, 3.3% wind). 4. Life cycle impact assessment (LCIA) Life cycle impact assessment ascertains the environmental impacts that occur during the life cycle stages of the product systems and is based on the LCI data and subject to the reference ?ow (Environmental Resources Management, 2001; Jolliet et al., 2003). For this study, Impact 2002+?, a method available in SimaPro, was selected for the classi?cation and characterization of the environmental impacts. Using Impact 2002+ also allowed for comparison with previously published work. The Impact 2002+ method evaluates the environmental impact across ?fteen mid-point categories. It then assigns summed up scores, quantifying damages to human health and the environment as well as resource depletion, on to four endpoint categories (Dettling and Margni, 2009; Jolliet et al., 2003). These endpoint or otherwise called damage categories are climate change (referred to as ‘global warming’ henceforth in this report) expressed in terms of gramme carbon dioxide equivalent (g CO2 eq), human health quanti?ed by an estimation of lost years of human life and with its unit as disability adjusted life years (DALYs), ecosystem quality covering species loss and expressed in units of potentially disappeared fraction of species per square centimetre per year (PDF·cm2·yr) and ?nally, resources reported in terms of unit

Transportation

Use

Dispenser product system Material & Production of dispenser components (ore mining → material manufacturing re?ning → semi-?nished product forms) Assembly of dispenser unit from components Production of corrugated board packaging (except that for paper towel cases) Transportation Shipment of dispenser components from sub-suppliers to the dispenser assembly plant (within US) Shipment of dispenser units from the assembly plant in US to UoG campus in Canada Use Paper towel consumption by washroom users (note that the production of paper towel rolls and its associated packaging + the transport of paper towel rolls to UoG campus is assigned under this group)

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Fig. 2. Deconstructed hand dryer & dispenser units.

kilojoules primary (kJ Primary) and quantifying depletion of resources (Dettling and Margni, 2009; Jolliet et al., 2003). 5. Interpretation In this section, the LCIA results are interpreted towards determining how the two studied product systems comparatively score. Fig. 3 illustrates the resulting impact across the four endpoint categories, for both the product systems, as a result of achieving the functional unit. For each damage category, the depicted total impact in Fig. 3 has also been broken down across the three life cycle stage groups de?ned earlier, namely, material and manufacturing, transport and use. Across three of these endpoint categories, namely, global warming, human health, and ecosystem quality, the use of the dispenser product system has a greater impact (by 162%, 38% and 145%, respectively) than with

using the dryer product system. However, in the resources endpoint category, the dryer product system has a greater impact which is primarily contributed to by its use group or in essence, by its use (87%). Notably for the dryer product system, electricity derived from nuclear and natural gas sources alone contributes to 85% of the impact in the resources endpoint category. For the dispenser product system, the use group, which in essence translates to the cradle to gate impact associated with the two paper sheets, is the signi?cant contributor across all its four endpoint impact categories (range 93 to 99%). 5.1. Impact contribution analysis As mentioned earlier, the major impact for the dispenser product system is from its use group (range 93 to 99%). A contribution analysis conducted on the use group of the dispenser product system indicates

Fig. 3. Comparison of the environmental impacts of dryer (dryer product system) and paper towel (dispenser product system) use based on Impact 2002+ endpoint indicators during the phases of use, transport and material & manufacturing.

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Fig. 4. Contribution equity of lifecycle stages within the use group of the dispenser product system.

that the unit processes associated with raw material extraction and paper towel production life cycle stages, combined, contribute the major share (ranging from 74 to 79%) to the total impact in each end point category (Fig. 4). This is followed by the transport of roll towel cases from the assembly plant to UoG campus with its share ranging from 14 to 22%. For the dryer product system, the use and the material & manufacturing groups, together, hold the major stake (N 98%) as far as total impact in each end point category. 5.2. Uncertainty analysis In a LCA study, it is important to assess the amount of associated uncertainty, whether with input data, with assumptions made or with chosen scenarios, in order to ascertain the robustness of the ?nal life cycle assessment results (Gregory et al., 2013; Ross et al., 2002). Scenario analysis and sensitivity analysis that follow in Sections 5.3 and 5.4, respectively, can be regarded as methods to establish how uncertainty impacts the outcome of a LCA study. In this section, uncertainty aspects ascertained as probable for this study is ?rst reviewed. ? Hand dryer & paper towel usage — A user pattern survey on UoG campus conducted by the authors and guidance from previous studies (Dettling and Margni, 2009; Montalbo et al., 2011) corroborate the selected 30 s per dry and 2 sheets per dry use intensities. Moreover, the dispenser in this case is a controlled-use towel dispenser which deters usage excessiveness. It is however occasionally possible that the hand dryer can be used for more than 30 s per dry (start–stop cycle setting is 30 s) or for a use intensity of more or less number of paper towels per dry. In the event of the former, it will result in more electricity consumption and correspondingly increase the associated environmental impact. Likewise, a lower or higher paper towel use intensity will affect the resource ?ows associated with life cycle stages involving paper towels. A sensitivity analysis was thus assigned to investigate the impact of varying use intensities for both the product systems. A scenario analysis was also assigned for the hand dryer to understand how a change in the energy sources supplying the local grid could affect the use phase impact and thus the overall results. ? Number of washroom users — Over the time horizon of ?ve years, considered as service life for both the product systems, if more or less number of washroom users were to avail of the hand drying service, this would change the presently estimated ‘18,319,905 washroom users’ ?ve year ?gure. In other words, the allocation value to be applied to the reference ?ow will change, but equally for both the product systems. In a scenario that enables a higher allocation of a pair of dry hands against a dispenser or hand dryer unit, the environmental impact associated with the material and manufacturing group of both the product systems, per functional unit, will be reduced. The

impact resulting from the use group, for both product systems, will however remain the same. ? Manufacturing life cycle stages — Assumptions applied to the manufacturing scenario in both the hand dryer and dispenser assembly plants are not exact representations. For instance, electric motors are typically sourced as a single module from an external supplier. However, in this study, it is assumed that sub-components like copper windings are fed to the hand dryer assembly plant where, the electric motor is put together from its sub-parts before it is ?nally included in the hand dryer assembly. Capital equipment and scrap generation, inherent to any factory operation, has not been accounted for in this study. Further, for both the product system assembly plants, only electricity has been considered as resource consumption. Evidently, there are other resources like natural gas which are consumed during the operation of both these plants. However, review of literature (Dettling and Margni, 2009; Environmental Resources Management, 2001; Gregory et al., 2013) suggests that omission of capital equipment and of other resources used in the operation of both the product system assembly plants will not substantially impact the overall results of the comparative assessment. ? Transport/supply chain life cycle stages — With respect to logistics, this study considers a simple supply chain scenario and the burden associated with warehousing and distribution is not accounted for. The envisaged scenario in this study is that only three separate truck runs, one catering to the shipment of an entire ?ve year paper towel demand, one to the dispatch of 500 hand dryer units and a third run to the shipment of 500 dispenser units, are required to ful?l the full transport run requirements to the UoG campus. While this is a fair assumption to make as far as the hand dryer and dispenser units, this is not the case with the roll paper towel shipment as multiple runs may be required based on the purchasing department's ordering frequency. Nevertheless, even with an accurate representation of the supply chain scenario, it is assessed, based on the results from this study, that the impact from the transport group will still remain insigni?cant compared to the other group contributions.

5.3. Sensitivity analysis Sensitivity analysis identi?es how changing a key assumption in the LCA study affects the responsiveness of the LCIA results to the respective input. A sensitivity analysis was carried out covering use intensity, classi?ed as low, medium and high, for both the product systems. Paper towel use with 1, 2 or 3 towels and under hand dryer drying times of 15, 30, and 45 s, were analysed. The results of this analysis (Fig. 5) indicate that overall, the dispenser product system is more sensitive to use intensity than the dryer product system. This is particularly exempli?ed for two damage categories, namely, global warming and ecosystem quality, where the respective plot lines as seen in Fig. 5, indicate a much higher slope. The sensitivity analysis results also indicate that if a comparison of the product system impacts, in the human health end point category, is made with the dryer under high use intensity and dispenser product system under low use intensity, then contrary to the baseline case result for this damage category, the dryer product system will have the higher impact. Likewise, the resources end point category also witnesses a reversal of the baseline case result when, a product system impact comparison is made with the dispenser product system under high use intensity and the dryer product system under medium or low use intensity. 5.4. Scenario analysis The use phase of the hand dryer is solely related to its electricity consumption and under the context of this study, is supplied from the Ontario power grid. In order to demonstrate the effect of supplying the use

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Fig. 5. Sensitivity analysis for use intensity of the dryer and dispenser product systems.

phase with grid electricity from a different mix of sources, an impact assessment was carried out considering a US based use phase scenario for the hand dryer. The result of this scenario analysis, laid out in Table 2, shows a signi?cant increase in the overall impact under a US grid supply scenario. Across three damage categories, global warming, human health and ecosystem quality, this impact change ranges from 96 to 259%. When the US grid supply based revised impact ?gures for the dryer product system is then compared to the corresponding impacts for the dispenser product system, it is higher in three of the damage categories by an average of around 42% (Table 3). The US supply grid relies mainly on coal as a source fuel (~ 50%) with natural gas and nuclear power following as the other important sources (~20% each). This is in contrast to the 2012 scenario in Ontario where the contribution of coal as a source fuel was b 3%. Evidently, the increment in total impact

under a US grid supply for the use phase of the dryer is due to this change in the mix of source fuels powering the grid. 6. Results & discussion The results from this study indicate that per dry, the use of a warm air hand dryer has a lesser overall environmental impact than with using paper towels. This is based on a use phase located in Ontario, Canada and a US based manufacturing scenario for both the product systems. For the dispenser product system, raw material production and manufacturing associated with paper towels alone contribute the major impact (N 70% share) in each damage category. This is followed by the transport of ?nished paper towel rolls to the end user which contributes a greater than 13% share to each end point category. For the

Table 2 Scenario analysis of Ontario grid supply versus US grid supply for the hand dryer use phase. Column A — Ontario grid scenario Global warming (g CO2 eq) Human health (DALYs) Ecosystem quality (PDF·cm2·yr) Resources (kJ Primary) 3.6 4.82E ? 09 13.2 196.2 Column B — US grid scenario 12.9 1.01E ? 08 25.9 211.3 % Change in column B versus column A 259 109 96 8

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Table 3 Comparison of revised environmental impacts based on a US use scenario. Column C — dryer product system (use scenario in US) Global warming (g CO2 eq) Human health (DALYs) Ecosystem quality (PDF·cm2·yr) Resources (kJ Primary) 12.9 1.01E ? 08 25.9 211.3 Column D — dispenser product system 9.4 6.63E ? 09 32.2 152.7 % Difference — column C over column D 37 52 ? 20 38

dryer product system, the raw material production and electricity consumed during the assembly of the dryer unit and most signi?cantly, electricity consumed during dryer use, combined, dominate the impact (N 98% share) in all four endpoint categories. 6.1. Comparison with previous studies In order to allow for consistency in benchmarking with prior studies, only LCA study scenarios comparing warm air hand dryer use with the use of paper towels manufactured from 100% recycled stock, were considered. This led to selecting four previous LCA studies for benchmarking. While the present study is based on a cradle to gate scope unlike all four prior LCA studies which are cradle to grave, past studies suggest that omission of the end-of-life stages will barely change the impact for the dryer product system. On the other hand, for the dispenser product system, the impact could shift with prior studies suggesting a possible deviation of up to 20% in the global warming endpoint category and primarily contributed to by methane emission (Dettling and Margni, 2009; Montalbo et al., 2011). As for the other endpoint categories, impact contribution by the end-of-life stages for the dispenser product system, is observed to be of much lesser signi?cance (Dettling and Margni, 2009; Montalbo et al., 2011). Considering the margins in the impact difference between the two product systems in this study, it is assessed that accounting for end-of-life will not affect the ?nal outcome, which is that the dispenser product system has a higher impact across three of the four endpoint categories. Land?lling of waste paper which has nearly all its impact in the global warming endpoint category, waste transport to the land?ll and use of the bin liner have been reported as the major equity contributors to the end-of-life impact in the global warming endpoint category (Dettling and Margni, 2009). However, unlike the end-of-life scenario considered in all four past studies, the present study envisages composting of the waste paper towels and the disposable bin liner. This is a practice that is seeing increased adoption across university campuses as an alternative to land?lling. Composting is an aerobic process unlike the methane generating anaerobic decomposition that occurs in land?lls. A wellmanaged composting process produces little to no methane. This only af?rms the assessment that end-of-life stages are of much lesser importance for this study. A discussion of the comparative assessment presented in the four chosen LCA studies follows. A streamlined LCA study conducted in 2001 and based on a European fuel mix, reported hand dryer use as having a smaller environmental footprint than paper towel use (Environmental Resources Management, 2001). A similar result was also obtained by Budisulistiorini (2007) in a separate study at the University of Melbourne in Australia.

However another LCA study prepared by Quantis in 2009 based on a US manufacturing and use scenario, reported hand dryer use as having a higher overall impact (Dettling and Margni, 2009). A report by Montalbo et al. (2011) comparing various hand drying systems reported that overall, the environmental impact caused by warm air hand dryer use stood higher than with using paper towels. This study was based on a material production and manufacturing scenario in China except for paper towels (US based manufacture) and a US based use phase. Table 4 is a summary of the ?nal comparative assessment results (baseline scenario) covering the selected case studies and the present study. The global warming potential (GWP) metric associated with the global warming endpoint category is a universal and very commonly used comparison environmental performance metric (Montalbo et al., 2011). The corresponding GWP metric as ascertained from the four past LCA studies is also presented in Table 4. Reviewing the study results in Table 4, there is no consistent conclusion as to the product system with the lesser impact. It is observed from Montalbo et al. (2011) and the present study that this inconsistency in ?nal results can be attributed to differences in material and process data, the inventory data source for the unit processes, the manufacturing and use location, use intensity of product systems per functional unit, estimated reference ?ow, power rating of the hand dryer, grid mix for both the manufacturing and use stages, LCIA and GWP calculation methodology adopted and chosen end of life disposal scenario (recycling, incineration, or land?lling). Montalbo et al. (2011) in their case study carried out a scenario analysis based on Switzerland's grid mix in place of their study's baseline scenario and reported scenario speci?c GWP metric values of 3.36 g CO2 eq and 10 g CO2 eq for the dryer and dispenser product systems, respectively. Though not an exact representation, the Swiss grid mix is much more representative of the Ontario grid mix baseline scenario used in this study. On this basis, it is observed that the GWP metric values of 3.6 g CO2 eq and 9.4 g CO2 eq estimated in this study for the dryer and dispenser product systems, respectively, are both within range of values derived in Montalbo et al. (2011) for the Swiss grid mix scenario. 6.2. Conclusions The present study compared the environmental footprint resulting from the use of a warm air hand dryer and the use of paper towels as two alternative hand drying methods using a university campus as an example setting of a community. Similar hand drying methods are used in commercial, institutional and industrial settings in North America and elsewhere in the developed and developing world. The

Table 4 Summary of comparative LCA results — recycled paper towel use versus hand dryer use. Year 2001 2007 2009 2011 2013 Comparative assessment of overall environmental impact (hand dryer vs paper towel) Dryer (2400 W) b paper towel (2.5 sheets) Dryer (1000 W) b paper towel (2 sheets) Dryer (2300 W) N paper towel (2 sheets) Dryer (2300 W) N paper towel (2 sheets) Dryer (1800 W) b paper towel (2 sheets) Dryer product system g CO2 eq 12.4 10.3 17.3 17.2 3.6 Dispenser product system g CO2 \eq 16.8–48.4 10.6 17.3 14.8 9.4 References Environmental Resources Management (2001) Budisulistiorini (2007) Dettling and Margni (2009) Montalbo et al. (2011) Present study

T. Joseph et al. / Science of the Total Environment 515–516 (2015) 109–117

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use intensity per functional unit and the electric grid mix are identi?ed as two key elements, which upon varying from the study's baseline scenario, can affect the environmental impact results with a high degree of responsiveness. A more carbon intensive grid mix powering hand dryer use can result in the use of paper towels turning out to be the better choice for the environment. So while in the present study, the dryer product system is clearly the better choice offering a lesser environmental impact, this cannot be generalised for all comparative LCAs between warm air dryer use and paper towel use. This case speci?c nature of the outcome of the comparative LCA is mainly in?uenced by the electric grid mix available at the manufacturing and use locations of both the product systems. This study thus establishes the relevance of a caseby-case approach for comparative LCA studies between conventional hand dryer use and paper towel use. Further, the authors would also like to point out that in a comparative LCA study such as this, the focus of assessment is from an environmental sustainability perspective. Besides the environmental effect, a ?nal call on a better performing product system should also follow from taking into account other considerations such as hygiene ef?cacy. Acknowledgements The authors would like to thank Barb Baxter (UoG), Ed Martin (UoG), and Rob Watson (Swish) for their collaboration in providing the information and data for this study. The guidance provided by Eli Wasserman (UoG) during this project is also gratefully acknowledged. Appendix A. Supplementary data Supplementary data to this article can be found online at http://dx. doi.org/10.1016/j.scitotenv.2015.01.112. References
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