key: cord-0690441-k1bkme71
authors: Tao, Yanqiu; You, Fengqi
title: Can Decontamination and Reuse of N95 Respirators during COVID-19 Pandemic Provide Energy, Environmental, and Economic Benefits?
date: 2021-09-14
journal: Appl Energy
DOI: 10.1016/j.apenergy.2021.117848
sha: 2016204ea83dcc85dcceec113329c9e9853e49c6
doc_id: 690441
cord_uid: k1bkme71

The widespread COVID-19 pandemic led to a shortage in the supply of N95 respirators in the United States until May 2021. In this study, we address the energy, environmental, and economic benefits of the decontamination-and-reuse of the N95 masks. Two popular decontamination methods, including dry heat and vapor hydrogen peroxide (VHP), are investigated in this study for their effective pathogen inactivation and favorable performance in preserving filtration efficiency and structural integrity of respirators. Two multiple reuse cases, under which the N95 masks are disinfected and used five times with the dry heat method and 20 times using the VHP method, are considered and compared with a single-use case. Compared to the single-use case, the dry heat-based multiple-use case reduces carbon footprint by 50% and cumulative energy demand (CED) by 17%, while the VHP-based case decreases carbon footprint by 67% and CED by 58%. The dry-heat-based and VHP-based multiple reuse cases also present environmental benefits in most of the other impact categories, primarily due to substituting new N95 respirators with decontaminated ones. Decontaminating and reusing respirators costs 77% and 89% less than the case of single-use and disposal. The sensitivity analysis results show that the geographical variation in the power grid and the times of respirator use are the most influential factors for carbon footprint and CED, respectively. The result also reaffirms the energy, environmental, and economic favorability of the decontamination and reuse of N95 respirators.

and Brazil [4] , under acute supply shortages of FFRs. N95 respirators protect healthcare workers during high-risk, aerosol-generating procedures [5] . Conventionally, used N95 respirators are categorized as regulated medical waste (RMW) and are processed through the hospital, medical, and infectious waste incinerators (HMIWI). However, since early 2020, the COVID-19 pandemic has strained the health care system with remarkably high demand for N95 respirators [6] .

According to a survey conducted in 2020, one-third of over 20,000 U.S. nurses reported a shortage in FFRs, and 68% of them were required to reuse N95 masks in their workplaces [7] . Moreover, more than half of the nurses reused N95 respirators for at least five days [7] . Recently, India is experiencing raging outbreaks of COVID-19, reporting over 300,000 daily confirmed cases [8] .

This COVID-19 surge may make the severe shortage of FFR in India even worse Decontamination Systems (CCDS), each of which can decontaminate up to 80,000 N95 masks [11] . With decontamination systems increasing the availability of N95 masks, reductions in deaths and infections can be achieved, and pressure on healthcare systems is expected to be relieved to some extent [12] . Promoting the FFR decontamination and reuse under limited supply might support public health but may also require less energy, reduce environmental harms, and relieve financial burdens on healthcare facilities by reducing the FFR demand. However, the energy, environmental and economic benefits of decontaminating N95 respirators vary according to different technology options and the choices of operational parameters. Therefore, a systematic evaluation of the energy, environmental and economic performances for the FFR decontamination methods is urgently needed to identify the hotspots for further improvement of decontamination practices.

Previous studies on FFR decontamination investigated the impact of different decontamination methods [13] on the filtration performance of various FFR models [14] . Recent studies mainly focused on the maximum number of decontamination cycles under different conditions, including treatment time [15] , temperature [16] , and humidity [17] , before passing the threshold of filtration efficiency and structural integrity. Disinfected N95 respirators can maintain high filtration efficiency and structural integrity that effectively protect health care personnel, patients, and susceptible individuals [16] . Potential decontamination methods include dry heat [18] , moist heat [16] , ultraviolet irradiation [19] , ethylene oxide [20] , ethanol [15] , vaporized hydrogen peroxide (VHP) [21] , and microwave-generated steam (MGS) [22] . Dry heat and moist heat methods are accessible and easy to implement. Most studies find that low temperature (70-85℃)

[15] and intermediate humidity [17] are optimal for maintaining structural integrity under heat treatments lasting 30-60 minutes [15] , although filtration efficiency can be preserved under temperatures up to 100℃ [18] . Notably, since dry heat is not effective against all pathogens [17] , the respirators should be stored in a breathable paper bag for at least five days between each use to allow the pathogens to vanish [1] . VHP decontamination is more effective in pathogen inactivation for the heat-sensitive respirators [23] and less damaging to filtration efficiency and structural integrity [15] . However, the concentrations of VHP and pathogens, type of VHP decontamination systems, and types of commercially available FFRs vary extensively among existing studies [19] . MGS can also effectively decontaminate FFRs [24] , although it was reported to damage the respirators' components [22] and structure [14] . Ultraviolet is a highly effective method to sterilize most pathogens on FFRs with doses exceeding 1 J/cm 2 , as confirmed by many studies on a variety of examined pathogens [25] , types of FFRs [25] , doses of ultraviolet light [26] , and ultraviolet-generating systems [27] . Notably, few studies evaluate the effectiveness of sterilizing used respirators on SARS-CoV-2 contamination. The results of Ozog et al. [27] and

Fischer et al. [15] suggest that a dose exceeding 1.5 J/cm 2 may be required to kill SARS-CoV-2 effectively, and additional disinfection may be needed for the straps. Moreover, the effectiveness of ultraviolet varies considerably for different types of FFRs [19] , and the position and orientation of N95 masks must be carefully arranged to avoid shadowing [28] and allow complete exposure to ultraviolet light [27] . The efficacy and safety of the ethylene oxide method on disinfecting used respirators are uncertain and controversial due to the limited studies so far [19] . In particular, insufficient aeration of ethylene oxide may cause severe injury to human health [28] . Ethanol decontamination is found to destroy respirators' filtration efficiency after only the first decontamination cycle [15] . In addition, 3M, a leading manufacturer of FFR, discourages ethylene oxide, ethanol, and microwave on all their FFR products. Therefore, dry heat and VHP are considered in this work due to their data availability, high efficiency in pathogen inactivation, wide availability, relatively simple operations, and reliability in preserving filtration efficiency and structural integrity of N95 masks, with abundant evidence from existing literature as discussed above.

Reusing respirators is one of the best available solutions to protect the healthcare workers parameters, we conduct a sensitivity analysis to examine the impact of these uncertainties on the carbon footprint, CED, and economic results. We also assess the impact of the geographic variation in the power grid on climate change and energy use.

Key contributions of this work are summarized as follows:  The first LCA and TEA results on energy, environmental, and economic benefits of reusing N95 respirators through two most popular and reliable decontamination methods, namely dry heat and VHP, in comparison to the one-time use case;  The identification of environmental and economic hotspots that addresses the most influential contributors for FFR reuse and decontamination;  Comprehensive spatial and sensitivity analyses to determine the most sensitive parameters based on the proposed LCA and TEA models to further improve decontamination practices.

The remainder of this paper is organized as follows. We describe the decontamination processes and the proposed LCA and TEA methodologies in §2. The LCA and TEA results are presented in §3 to assess the environmental and economic benefits of the dry heat and VHP decontamination methods, followed by sensitivity analyses on the economic and environmental parameters. The conclusions are given in §4.

In this work, we performed a holistic LCA to systematically analyze and compare the energy use and full-spectrum environmental implications of reusing N95 respirators multiple times via two decontamination-based technology, in comparison with the one-time use case. The three cases are described as follows:

 Dry heat-based multiple reuse case: this case employs the dry heat decontamination technology to allow using/reusing the FFRs 5 times before final disposal via incineration.  VHP-based multiple reuse case: this case considers 20 times of using/reusing FFRs with the help of the VHP decontamination technology, followed by incineration of FFRs due to attaining the maximum numbers of reuse.  Single-use case: in this case, the FFRs are incinerated after their one-time use.

The LCA methodology is conducted in four phases: goal and scope definition, LCI, life cycle impact assessment (LCIA), and interpretation. The details of the four phases are presented in the following subsections. Moreover, techno-economic analysis is conducted to evaluate the economic benefit of the decontamination-and-reuse approaches.

The technology pathways of the three cases are shown in Fig. 1 . First, after each use, used

FFRs are labeled and collected in two layers of plastic biohazard bags. In the single-use case, the closed biohazard bags are placed in a reusable rigid container and transported directly to the HMIWI. The closed collection bags are placed into a carton for the dry-heat-based and VHP-based multiple reuse cases. The carton is ready for shipping to the decontamination facilities after labeling and taping. Once the decontamination facilities receive the used FFRs, the respirators are unpacked, inventoried, and hung on racks before being disinfected. And the carton and biohazard bags are sent to the HMIWI for disposal due to their containment of potentially infectious wastes.

After the decontamination and aeration, N95 masks are taken down, packed into cartons, and delivered back to the healthcare facility.

In this study, we adopt the Battelle CCDS with High-Efficiency Particulate Arrestance (HEPA) filters as a representative VHP method because it was approved by FDA and deployed at large scales across the U.S. Each Battelle CCDS consists of four decontamination containers, which treat up to 10,000 used FFRs per cycle [29] . The capacity of Battelle CCDS is 80,000 respirators per day. Each cycle consists of four phases: a 10-minute conditioning phase, a 20minute gassing phase, a 150-minute dwell phase, and a 300-minute aeration phase [23] . The VHP injection rate is 2 g per minute for the gassing phase and 0.5 g per minute for the dwell phase in the laboratory chamber (0.31 m 3 ) [23] . Hence, the average VHP concentration is estimated as 371 ppm in each decontamination container. Based on the size of the four chambers, 477.23 kg VHP is consumed for each cycle. After aeration, five chemical indicators are dispersed throughout the system to indicate the successful reduction of VHP to <1 ppm before the FFRs are released for packing [30] . Twenty decontamination cycles can be applied to a single N95 respirator [30] . In addition, 75 kWh of electricity is consumed per cycle [29] .

For the dry heat decontamination system, a commercial sterilizer with HEPA filters is used as a representative [31] . This commercial model is chosen due to its accessible economic and operational parameters. Each used FFR is sealed in an autoclavable paper bag with heat indicator tape and placed in the sterilizer. Pathogen inactivation by dry heat is highly sensitive to temperature and time [32] . Therefore, for each decontamination cycle, we follow the guidance from the FFR manufacturer and consider treating 1,000 contaminated N95 masks at 70℃ for 60 minutes [26] . FFRs. HMIWI denotes the hospital, medical, and infectious waste incinerators.

The scope of this "cradle-to-grave" LCA focuses on treating used N95 respirators. The system starts from the acquisition of raw materials (i.e., the components of FFRs and auxiliary materials) and ends at the disposal of the FFRs and wastes after multiple uses. The decontamination methods aim to extend the number of FFR uses. Therefore, the functional unit is defined as the 1,000 times of uses/reuses of N95 respirators, following the existing literature [33] . The system boundary includes five life cycle stages: N95 respirator production and distribution, production of auxiliary materials, respirator storage and transportation, respirator decontamination, and reuse and disposal. Detailed LCI for each life cycle stage is described in §2.3.

The materials and energy inputs and outputs associated with the 1,000 times of FFR uses are compiled using data estimated from technical reports, governmental documents, and product specification reports ( [35] . Similarly, the steel wires are manufactured from cast ingots through hot rolling, sheet rolling, and wire drawing. The final manufacturing step involves electricity consumption of 0.8 kWh per 1,000 masks associated with mask body forming, earloop cutting, and ultrasonic welding [36] . It is worth mentioning that the electrostatic charge step for improving the filtration efficiency of respirators is excluded with no reliable data on its electricity consumption [37] .

Missing this manufacturing step may lead to conservative estimates on the environmental impacts of N95 mask production. Each piece of the N95 mask weighs 11 grams approximately [38] .

Subsequently, 20 pieces of the N95 masks are packed per box [34] . Moreover, 40 boxes are shipped 1931 km in a carton from the manufacturer to the geographic center of New York State (NYS) [36] . As claimed by FDA in the instructions for healthcare facilities [12], the contaminated FFRs are first collected in a primary collection bag and closed. Then, the primary collection bag is placed into the secondary collection bag and closed [39] . Finally, the secondary collection bag is disinfected by decontaminant such as ethanol and put into a carton for shipping. Therefore, two biohazard bags and one carton are required for collecting, packing, and shipping a batch of FFRs to the decontamination system according to the U.S. CDC's instruction on the management of RMW in healthcare facilities. For the incineration of RMW, a reusable rigid container with proper labeling is permitted to contain the secondary biohazard bag to be shipped to the HMIWI [40] .

Notably, the number of FFRs in each batch may vary. Therefore, we consider packing an average of 120 contaminated N95 masks with two 10-gallon (equivalent to 0.038 m 3 ) biohazard bags with 70% full and a carton of the same size as one box of 120 standard N95 respirators. During the decontamination process, the VHP decontamination system exposes the N95 masks to the vapor H 2 O 2 without any shields. In contrast, the dry heat decontamination system requires the use of autoclave paper bags to protect the sterilizer and to indicate whether the desired temperature is reached [18] .

This subsection describes the storage and distribution of the used FFRs collected in the biohazard bags and decontaminated FFRs packed in cartons. Specifically, the used N95 masks are collected from the healthcare facilities and shipped to either the decontamination sites or the HMIWI by trucks specifically designed for medical waste transportation. Moreover, the incineration of waste respirators produces solid ash, which is further transported to landfilling [41] .

After decontamination, the disinfected N95 masks are delivered to the healthcare facilities and reused [30] . According to the New York State Department of Environmental Conservation [42] , most RMW are disposed of off-site. Thus, the waste respirators are assumed to be transported 80 km from the healthcare facilities to the HMIWI based on the distance from Ithaca, NY, to the nearest disposal site of a leading RMW management company [43] . The transportation distance between the healthcare facilities and the decontamination sites is considered to be 80 km for a fair comparison across the three cases of FFR uses. Other auxiliary materials for packaging, including cartons and biohazard bags, are shipped back and forth with the respirators. Sensitivity analysis is conducted to assess the uncertainty in the transportation distance.

This section aims to illustrate the material and energy input and output for the decontamination stage of the two multi-use cases. 

The reuse and disposal stage focuses on treating the waste respirators and the disposed packaging materials. FFRs reaching the usage limit are sent to the HMIWI for disposal. For auxiliary materials, the carton and biohazard bags used to contain and pack the used N95 masks are considered biohazard wastes and sent to the HMIWI. The incineration of waste N95 respirators is assumed to be equivalent to the combination of incinerating each component of N95 masks, following a previous study [44] . The decontaminated autoclave paper bags and cartons used to deliver the new and decontaminated FFRs are disposed of as municipal solid waste, following the Environmental Protection Agency's data on the waste paper and paperboard management [45] . A transportation distance of 50 km is assumed for the collection of municipal solid waste following the literature [46] .

The relative to CO 2 over the 100-time horizon [47] . CED assesses the direct and indirect energy use throughout the life cycle of a product [48] . Since the dry heat decontamination is energy-intensive,

we consider CED as one of the key indicators to be addressed. Three endpoint indicators and seventeen midpoint indicators of ReCiPe are adopted to examine the severity across different aspects of environmental issues, including damage to resource availability, damage to ecosystems, and damage to human health, agricultural land occupation, fossil depletion, freshwater ecotoxicity, freshwater eutrophication, human toxicity, ionizing radiation, marine ecotoxicity, marine eutrophication, metal depletion, natural land transformation, ozone depletion, particulate matter formation, photochemical oxidant formation, terrestrial acidification, terrestrial ecotoxicity, urban land occupation, and water depletion [49] .

The LCIA results of the dry heat-and VHP-based multiple reuse cases convey key knowledge about the contributions of material and energy consumptions to various impact categories. Therefore, we quantify the LCA results and illustrate the breakdowns of carbon footprint, CED, and a broad set of environmental impact categories. Moreover, we identify the environmental hotspots and present the sensitivity analysis results on selected parameters, as shown in Table A5 and Table A6 . Based on the interpretation of the LCIA results, more insightful directions are provided towards the practices of FFR decontamination under such pandemic conditions.

To quantify the economic benefits of decontamination-and-reuse of respirators, we account for the total cost generated from the decontamination system, disposal fees for the waste respirators and the associated packaging materials, and the cost of purchasing new FFRs. The economic benefit adds up the annualized capital cost (ACC), fixed operating cost, labor cost, utility cost, disposal fees, transportation cost, and avoided cost of FFR purchase. A discount rate of 10% is selected to annualize the total capital cost (TCC), as shown in Eq. (1) [50] .

(1)

The total capital cost is calculated by Eq.

(2) as the summation of the direct capital cost (DCC), indirect capital cost (ICC), working capital cost (WCC), and land cost (LC) [44] .

(2) TCC DCC ICC WCC LC    

Each decontamination system consists of multiple parallel decontamination chambers, which are designed and built with specific sizes. Therefore, we do not consider the economies of scale for the decontamination systems. Instead, the unit economic performances of the decontamination systems based on the functional unit are independent of their sizes. For the dry heat decontamination system, we collect a commercial model's equipment and installation costs to calculate the direct capital cost [31] . Land cost is computed as 6% of the equipment cost [51] .

Indirect capital cost is estimated as 123% of the direct capital cost, and working capital cost is estimated as 5% of the summation of the direct capital cost and land cost [51] . In terms of an enclosed VHP decontamination system with HEPA filter, we adopt the best available data and estimate the total capital costs from the original contract awarded to the Battelle Memorial Institute by the U.S. Department of Defense [52] . Fixed operating cost is the summation of operation labor cost and other fixed costs, including maintenance labor cost, overheads, maintenance materials, and taxes and insurance [50] . Operation labor cost is estimated from the number of workers based on the mean hourly wage of healthcare support occupations in NYS [53] . Other fixed costs are computed as 9% of the total capital cost [50] . Variable operating cost consists of utility cost, disposal fees, and transportation cost. Utility cost is based on the average industrial electricity price in 2020 for NYS [54] . Disposal fees [55] and transportation costs [44] are extracted from previous studies. Lastly, the decontaminated FFRs are not for sale, but they have economic benefits by substituting the new respirators bought from the market. To quantify the economic benefits of the decontamination-and-reuse of FFRs, we include the cost of FFRs. The recent price of an N95 mask is set as $1.27, according to the current pricing from the 3M Company [56] . However, N95 mask prices fluctuated significantly during the pandemic due to the high demand and supply shortages in these critical medical resources. The average price of an N95 mask before the COVID-19

pandemic was around $0.50 [57] , while it was inflated to as high as $4.92 in the U.S. around the first half of 2020 [58] . Given the wide price range of N95 respirators over time, a sensitivity analysis is conducted to analyze the influence of this parameter on the TEA results, and the results are presented in §3.3. Details about the economic parameters are provided in Table A2 in Appendix.

This section presents the breakdowns of carbon footprint, energy use, and other impact categories for the three use cases of respirators. As shown in Fig. 2 In contrast, the dry heat method is capable of decontaminating and reusing FFRs five times.

Accordingly, 1,000 times of FFR use can be attained by sterilizing 50 respirators for a total of 950 times using the VHP method or disinfecting 200 respirators for 800 times using the dry heat method. This also causes 300% more waste respirators sent to the HMIWI. Furthermore, mask incineration becomes one of the key contributors to the carbon footprint (10%) of the dry heatbased multiple reuse case while it is minor to CED. Other than the production and distribution of more masks, the inferior environmental performance of the dry heat-based case can be attributed to the intensive consumption of electricity and autoclave paper bags for the dry heat method.

Specifically, energy use and the extraction of raw materials, including pulpwood, printing ink, and packaging films, contribute to most carbon footprint and CED associated with autoclave bag production [59] . Among the carbon-and energy-intensive contributors of the VHP-based multiple reuse case, production of H 2 O 2 and carton are dominant due to the large energy requirement for H 2 O 2 production [60] and the unavoidable treatment of wastes and sludges from the carton production [61] . This result can be primarily explained by the land transformation in the mineral extraction site and dumpsite during the N95 mask production. The results also show that the VHP-based multiple reuse case consistently outperforms the other two cases for most impact categories. Nevertheless, the VHP-based multiple reuse case achieves the worst performance in water depletion, primarily due to the intensive water use of H 2 O 2 production. On the other hand, the dry heat-based multiple reuse case performs the worst in four impact categories, including agricultural land occupation, ionizing radiation, marine eutrophication, and terrestrial ecotoxicity, due to the intensive depletion of electricity and paper bags. Consequently, the dry heat-based multiple reuse case also results in the most damage to the ecosystems (Fig. 4) polyester can explain over 50% of the environmental impacts associated with the N95 mask production for all impact categories except agricultural land occupation, natural land transformation, and water depletion. Specifically, the non-woven polypropylene is produced from the melting, extruding, and spraying of the polypropylene granules. The non-woven polyester is produced from the mechanical needle punching of the polyester fibers. The environmental burdens of the non-woven polypropylene and polyester are mainly from the energy use, extraction of crude oil, and emissions from raw material production, including CO 2 , methane, the non-methane volatile organic compound, nitrogen oxides, sulfur dioxide, and particulates. The natural land transformation and water consumption of N95 mask production are mostly due to the production of aluminum strips. Other environmental hotspots are specific to the decontamination methods. In terms of the VHP-based case, H 2 O 2 production is one of the most environmentally expensive contributors to most impact categories, as shown in Fig. 6 . For the dry heat-based case, paper bag production and electricity consumption contribute considerably to most impact categories (Fig. 5) .

Due to the high penetration of nuclear power in the selected Northeast Power Coordinating Council (NPCC) power grid (over 30%) [62] , electricity consumption accounts for the highest proportion of ionizing radiation for both multiple reuse cases. Remarkably, the environmental profile of electricity consumption varies geographically due to the divergent composition of energy sources for electric power production from region to region. Therefore, we conduct sensitivity analysis to evaluate the geographical variation in electricity consumption, as discussed in §3.3. Electricity production H₂O₂ production Paper bag production Biohazard bag production Carton production Waste carton disposal Waste biohazard bag disposal Transportation N95 respirator production and distribution Mask incineration Waste paper bag disposal Electricity production H₂O₂ production Paper bag production Biohazard bag production Carton production Waste carton disposal Waste biohazard bag disposal Transportation N95 respirator production and distribution Mask incineration Waste paper bag disposal Fig. 6 Breakdowns of midpoint indicators for the VHP-based multiple reuse case.

To illustrate the economic benefits of used FFR decontamination technologies, we evaluate the total costs of the three cases, as presented in Fig. 7 . Owing to the lower cost of purchasing new respirators, the total costs of using N95 masks 1,000 times for the dry-heat-based and VHP-based multiple reuse cases are 77% and 89% lower than that for the single-use case ($1,282 per 1000 times of use), respectively. This result suggests the remarkable economic benefits of reusing FFRs.

It is worth mentioning that the superior capacity of the VHP-based multiple reuse case to decontaminate and reuse FFRs more times benefits not only its environmental performance but also its economic performance. Specifically, on the same basis of using respirators 1,000 times, the VHP method requires fewer respirators for providing the same function of 1000 times of respirator use than the dry heat method. Accordingly, fewer respirators are disposed of at the end of life. However, due to the low disposal cost (87 cents per 1,000 FFRs) for incineration, a larger number of FFR decontamination induces higher treatment costs. Therefore, there is a trade-off between environmental performances and decontamination costs. The reductions are modest compared to their total costs. In addition to the effect of the number of uses, the dry heat-based multiple reuse case costs less in terms of capital cost, fixed operating cost, and labor cost compared to the VHP-based case. Specifically, capital cost accounts for the highest proportion of the decontamination cost for both dry-heat-based (42%) and VHP-based (50%) multiple reuse cases.

As the fixed operating cost is computed as a proportion of the total capital cost, the higher capital cost of the VHP decontamination system widens the gap between the decontamination costs of the two multiple-use cases. Moreover, labor cost is responsible for 40% of the decontamination cost in the dry heat-based case and 35% for the VHP-based case. This result suggests that FFR decontamination is a labor-intensive process. 

This section performs sensitivity analysis to investigate the most influential parameters in terms of economic and environmental performances. As shown in Fig. 8 , the most sensitive economic parameter is the N95 mask's price for the dry heat-based multiple reuse case, which was approximately $0.50 [57] before the COVID-19 pandemic and $4.92 in the middle of the pandemic [58] . With a higher respirator's price, the economic benefits of decontamination-and-reuse of FFRs become more prominent, and vice versa. The number of FFR uses is the most volatile economic parameter for the VHP-based multiple reuse cases, and it has the same effects on the economic and environmental performance because fewer respirators are needed for a larger number of FFR uses. The effects of other parameters are negligible on the TEA results for both multiple reuse cases. It is worth noting that the influence of capital cost is more prominent in the VHP-based multiple reuse cases due to its substantially higher capital cost. The power grid and the number of FFR uses play the most critical roles in the sensitivity analysis in terms of the carbon footprint, as shown in Fig. 9 and Fig. 10 . This result also suggests that it is more impactful to choose a decontamination method with the capability of increasing usage cycles than to select an energy-efficient decontamination model for mitigating climate change. In contrast to the carbon footprint results, the CED of the VHP-based multiple reuse case is insensitive to the geographic variation in the power grid. Moreover, both the carbon footprint and CED of the dry heat-based multiple reuse case are more sensitive to the changes in electricity consumption relative to the VHP-based multiple reuse case. Fig. 11 and Fig. 12 

In this paper, we conducted the LCA and TEA for the dry-heat-based and VHP-based multiple reuse cases that could alleviate shortages of new FFRs in healthcare facilities. The energy and environmental performances of the decontamination-and-reuse cases were compared with the single-use case through carbon footprint, CED, and a full spectrum of midpoint and endpoint indicators. Compared to the single-use case, the dry heat-based multiple reuse cases reduced carbon footprint by 50% and CED by 17%, while the VHP-based multiple reuse case decreases carbon footprint by 66% and CED by 58%. The environmental benefits of the VHP-based multiple reuse case were highlighted in most impact categories. As for the economic benefits, the total costs of the dry-heat-based and VHP-based multiple reuse cases were 77% and 89% lower than that of 

Characterization factor for the life cycle assessment [41] . 

Effect of moist heat reprocessing of N95 respirators on SARS-CoV-2 inactivation and respirator function

Dry Heat as a Decontamination Method for N95 Respirator Reuse

Filtering Facepiece Respirator (N95 Respirator) Reprocessing: A Systematic Review

Evaluation of Multiple (3-Cycle) Decontamination Processing for Filtering Facepiece Respirators

Filtration Efficiency of Hospital Face Mask Alternatives Available for Use During the COVID-19 Pandemic

Impact of Three Cycles of Decontamination Treatments on Filtering Facepiece Respirator Fit

Final Report for the Bioquell Hydrogen Peroxide Vapor (HPV) Decontamination for Reuse of N95 Respirators

A pandemic influenza preparedness study: Use of energetic methods to decontaminate filtering facepiece respirators contaminated with H1N1 aerosols and droplets

Research to Mitigate a Shortage of Respiratory Protection Devices During Public Health Emergencies

3M. Decontamination of 3M Filtering Facepiece Respirators: Global Considerations

The effect of ultraviolet C radiation against different N95 respirators inoculated with SARS-CoV-2

Decontamination and Reuse of N95 Filtering Facepiece Respirators: Where Do We Stand?

Using the Critical Care Decontamination System (TM

Battelle Decontamination System -Letter of Authorization

Granulation Dryers

NPPTL Respirator Assessments to Support the COVID-19 Response

Comparative Life Cycle Assessment of Disposable and Reusable Laryngeal Mask Airways

Prospects for energy recovery during hydrothermal and biological processing of waste biomass

Engineering Design Process of Face Masks Based on Circularity and Life Cycle Assessment in the Constraint of the COVID-19 Pandemic

The environmental dangers of employing single-use face masks as part of a COVID-19 exit strategy. UCL Open: Environment Preprint

COVID-19 global pandemic planning: Performance and electret charge of N95 respirators after recommended decontamination methods

Technical Specification Sheet: 3M™ Health Care Particulate Respirator and Surgical Mask

Instructions for Healthcare Facilities (Open System

Department of Transportation. 49 CFR § 173.197 -Regulated medical waste

The ecoinvent database version 3 (part I): overview and methodology

Waste respirator processing system for public health protection and climate change mitigation under COVID-19 pandemic: Novel process design and energy, environmental, and techno-economic perspectives

Containers and Packaging: Product-Specific Data

Life cycle assessment of carrier bags and development of a littering indicator

Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change

Cumulative Energy Demand As Predictor for the Environmental Burden of Commodity Production

ReCiPe 2008: A life cycle impact assessment method which comprises harmonised category indicators at the midpoint and the endpoint level

Life Cycle Assessment and Technoeconomic Analysis of Thermochemical Conversion Technologies Applied to Poultry Litter with Energy and Nutrient Recovery

System Analyses of High-Value Chemicals and Fuels from a Waste High-Density Polyethylene Refinery. Part 1: Conceptual Design and Techno-Economic Assessment

Trump administration paying huge premium for mask-cleaning machines

State Occupational Employment and Wage Estimates

Cradle-to-Gate Emissions from a Commercial Electric Vehicle Li-Ion Battery: A Comparative Analysis

Municipal Solid Waste Incinerators: An Industry in Decline

3M Company. Get the Facts. N95 Respirator Pricing

Filtration Efficiency, Effectiveness, and Availability of N95 Face Masks for COVID-19 Prevention

The New York Time. It's Bedlam in the Mask Market, as Profiteers Out-Hustle Good Samaritans

ecoinvent database version 3.7.1. paper sack production, RoW, Allocation, at the point of substitution

ecoinvent database version 3.7.1. hydrogen peroxide production, product in 50% solution state, RoW, Allocation, at the point of substitution

ecoinvent database version 3.7.1. corrugated board box production, RoW, Allocation, at the point of substitution

United States Environmental Protection Agency. Emissions & Generation Resource Integrated Database

Waste Polypropylene Plastic Recycling toward Climate Change Mitigation and Circular Economy: Energy, Environmental, and Technoeconomic Perspectives

Retrofitting Municipal Wastewater Treatment Facilities toward a Greener and Circular Economy by Virtue of Resource Recovery: Techno-Economic Analysis and Life Cycle Assessment

Medical waste management -A review

Documentation of changes implemented in the ecoinvent database v3

1E-02 N95 mask market for synthetic rubber

3E-04 3.6E-02 1.6E-02 N95 mask market for polyurethane, flexible foam, RoW kg 5

Electricity market for electricity

Electricity market for electricity

Electricity market for electricity

Electricity market for electricity

Electricity market for electricity

Electricity market for electricity, low voltage, US-HICC kWh 8.9E-01 1.2E+01 5.9E-03 2.6E-01

Electricity market for electricity, low voltage, US-FRCC kWh 5.2E-01 9

Electricity market for electricity

YT and FY developed the models, conducted the analysis, and analyzed the results. YT and FY wrote the manuscript

All authors reviewed the final manuscript