A life cycle analysis of ionizing radiation shielding construction systems in healthcare buildings

A Life Cycle Analysis of ionizing radiation shielding construction systems in healthcare buildings 1 Gonzalo Sánchez-Barroso1, Manuel Botejara-Antúnez2, Justo García-Sanz-Calcedo3,* and Francisco Zamora-Polo4 1 Ms.C. Engineering Projects Area, School of Industrial Engineering, University of Extremadura, Badajoz (Spain), [email protected], ORCiD: 0000-0002-7006-1197 2 Ms.C. Engineering Projects Area, School of Industrial Engineering, University of Extremadura, Badajoz, (Spain), [email protected]. ORCiD: 0000-0003-2570-1658 3 Ph.D. Engineering Projects Area, School of Industrial Engineering, University of Extremadura, Badajoz (Spain), [email protected], ORCiD: 0000-0003-4449-2636 4 PhD. Design Engineering Department, Higher Polytechnic School, University of Seville, Seville (Spain), [email protected], ORCiD: 0000-0002-9700-6809 *Corresponding author: [email protected] Abstract Optimization of material resources, energy efficiency and reduction of environmental impact are basic aspects in selection of a construction system. The aim of this study is to evaluate the environmental impact generated by different shielding systems for walls of an X-ray room in healthcare buildings. Eight commercial construction systems for anti-X shielding were analysed. A Life Cycle Assessment (LCA) was performed by SimaPro using the Ecoinvent database, and a single-score damage category analysis was performed for midpoint and endpoint levels. Prices of installation and working time employed in the construction of a functional unit of each system were obtained. Solutions with clay brick, cast-in-place reinforced concrete and sprayed concrete were the most favourable for the different categories. Sprayed concrete obtained 6.739 points/m2 of against 165.12 points/m2 of rolled steel option. The damage to human health occupies between 41% and 87% of the total impact in the protection areas. The impact category of human toxicity is also the broadest in the midpoint approach. Considering time and cost of implementation, clay brick solutions proved to be the most favourable, along with cast-in-place reinforced concrete and barite concrete. System #6 is the most environmentally friendly, 1.6 times less than the next one (which is #4), although its unit price is 1.94 times the cheapest (which is #2) and its execution time is 1.89 times the lowest (which is #2 again). The knowledge generated in this study will improve investment decision making for the planning departments of the Sanitary Systems, obtaining an economic, social and environmental benefit. The main novelty of the work lies in the object of the study (X-ray room) as well as in the integration of LCA and economic aspects. Keywords: Healthcare design; Building materials; Healthcare Buildings; Sustainable radioactive shielding systems; Healthcare Engineering 1 Accepted version. DOI: https://doi.org/10.1016/j.jobe.2021.102387 1 Introduction The design and construction of an X-ray facility for medical diagnostic purposes must be safe for people. The radiation-equivalent doses that may be received by exposed personnel, patients, and accompanying persons should be as low as reasonably achievable [1]. Therefore, the armour of an X-ray room plays a critical role in absorbing as much radiation produced by these equipment as possible, to avoid it from being transmitted perimetrically [2]. In order to provide this mitigation of radioactivity, different materials are used: lead, steel, concrete, ceramics, among others. Each of these materials offers different advantages and disadvantages from a point of view of placement, costs, thickness, etc. In addition, these materials have a different impact on the environment. Lead is commonly used for anti-X shield. However, its use can cause harmful effects on people's health [3,4] and on the environment [5]. Conventional radiography equipment emits X-rays that cause adverse effects on workers in the room itself and other people in adjacent wards [6]. X-ray technicians at these facilities must carry individual protection equipment (IPE), personal radiation monitoring dosimeter and they must adjust their workload to minimize their exposure [3]. Other workers and users outside the room do not carry IPE, so the vertical walls enclosing the diagnostic X-ray machine must have radiological isolation characteristics that attenuate X-ray transmission to the outside of the room [2]. The doses emitted by diagnostic X-ray machines vary considerably depending on the angle of incidence of the beam [7] and its diagnostic application [8]. Radiopacity is achieved by superimposing layers of materials with anti-radiation properties of a certain thickness, so that a lead equivalent is achieved according to test IEC 6133-1:2014 [9]. Consequently, designing construction systems for protection against ionizing radiation is one of the complex problems faced by Healthcare Engineering [10]. In Spain, Nuclear Safety Council is the competent authority in this area, which has published various technical guides for the protection of exposure of people [11] applying commonly accepted experience-based design methods [12,13]. Research in this area of work has been focused on demonstrating the radiation attenuation capabilities of different materials. In this way, concrete can achieve anti-radiation properties by increasing its density through the incorporation of heavy aggregates and metal reinforcement (reinforced concrete) or incorporating additives such as barite sulphate (BaSO4) [14]. Other equally valid materials can be drywall [15], barite plasterboard [16] and steel [17]. There are even ceramic materials that have anti-radiation properties [18]. In order to achieve sustainability, the environmental dimension must be incorporated into the choice of construction materials and construction systems for radiological shields [19]. Life Cycle Assessment (LCA) is a quantitative method to evaluate the environmental and human health impact over the lifetime of a product, taking into account extraction and processing of raw materials, manufacturing, distribution, use, maintenance and repair, and disposal [20]. Notwithstanding, the evaluation of hospital infrastructures construction has not yet been widely addressed in the literature from an environmental perspective. Hui Li et al. [21] proved that hospital buildings have the highest environmental impact compared to residential, commercial and educational buildings. Regarding conventional radiology rooms, Lopresti et al. [22] investigated new epoxy-based lead-metal substitute materials with similar radiopacity properties. Despite the current knowledge, the study of radiology room shielding systems in healthcare buildings from an environmental perspective using LCA tools has not been carried out. The main objective of this study is to evaluate the environmental impact generated over the cradle-to-grave life cycle of different wall shielding systems used in healthcare buildings' Xray rooms, and to analyse their feasibility from an environmental perspective. In this way, architects, engineers and infrastructure managers will have a tool to select the construction system considering sustainability. This work is aligned with the achievement of the Sustainable Development Goals (SDG), the work agenda set by the United Nations for the period 2015-2030 [23]. Building hospitals in a sustainable way is clearly within SDG no. 3: “ensuring healthy and safe living for all ages,” but it is also related to SDG no. 9: “building resilient infrastructure,” SDG no. 11, about more inclusive, safe, resilient and sustainable cities, SDG no. 12 sustainable consumption and production, combating climate change (SDG no. 13) [24]. 2 Literature review In environmental management, internationally accepted standards describing the LCA process are ISO 14040 [25], which sets out principles and framework, and ISO 14044 [26], which describes requirements and guidelines for carrying it out. Uncertainty management of knowledge about environmental mechanisms revolves around Cultural Theory [27]. Individualist, Hierarchist and Egalitarian archetypes assume a short-, mediumand long-term perspective on the atmospheric lifetime scale of substances. The environmental damages identified by LCA are congruent with an egalitarian worldview [28]. Cradle-to-grave approach follows the linear economic model of product use from raw material extraction to product use and disposal [20]. Applying LCA to construction, Maria de Souza et al [29] conducted an LCA-based evaluation to compare ceramic brick exterior wall with concrete bricks and cast-in-place reinforced concrete. They found that environmental impact of the first one is 50-70% lower than the third one in the three areas of protection: climate change, human health and ecosystem quality. Ingrao et al. [30] identified the most sustainable solution for exterior walls according to the midpoint and endpoint approach. There are extensive reviews of LCA in the construction sector [31], on residential and commercial buildings [32], applied to renovation work [33] and even in the demolition process [34,35]. LCA has been proven as the right tool for analysing the environmental impact associated with the life cycle of buildings [36]. In hospital environment it has been used to measure environmental impact generated by different products and processes. For example, McGain et al. studied the environmental impact associated with the life cycle of an anaesthesia equipment. [37], of a catheter insertion kit [38] and of a plastic anaesthetic drug trays [39]. Igos et al. analysed the environmental impact of wastewater from sanitary buildings [40] y studied the elimination of pharmaceuticals [41]. Furthermore, García-Sanz-Calcedo et al. demonstrated the high potential for global warming associated with the construction of health centres [42] and the influence of the management of the energy consumption of a hospital with the reduction of its environmental impact [43]. Different databases are available to perform Life Cycle Inventory (LCI) in building industry. Lasvaux et al. [44] compared the generic (such as Ecoinvent, GaBi, DEAM, US-LC, etc.) and product-specific (i.e., Product Category Rules) databases in construction sector and listed the benefits of Ecoinvent database in France. Martínez-Rocamora et al. [45] found that Ecoinvent and GaBi databases showed the best features (scope, completeness, transparency, comprehensiveness, update and license) in construction sector among European, American, national, input-output and other databases. Althaus et al. [46] also noted that Ecoinvent database is suitable for building materials. Ecoinvent is one of the most widely used databases for LCI. In fact, a comprehensive review of LCA between 1995 and 2008 indicated that 59% of authors employed this data repository [47]. In order to develop the Life Cycle Impact Assessment (LCIA), ReCiPe is a method frequently used. Data from LIC is converted into impacts through this method by using 18 midpoints indicators and 3 endpoints indicators [48]. Bories et al. [49] evaluated the environmental impact of porous fired clay bricks with bio-based additives; Pushkar and Verbitsky [50] analysed environmental damage of four wall technologies; and Kono et al. [51] evaluated different thermal insulation materials using ReCiPe. Output of ReCiPe method is the valuation of metrics (points) called eco-indicators midpoint (problem oriented) and endpoint (damage oriented) [20]. Problem-oriented approach is associated with a low level of uncertainty but implies greater difficulty of interpretation due to the high number of impact categories. The opposite is true for damage-oriented approach. Controversy exists among experts. Nevertheless, Bare et al. [52] suggested that both methods could be used together to provide more information to decision-makers. This paper aims to address a gap in the scientific literature of hospital engineering. To the best of our knowledge, life cycle analysis of X-ray rooms has not been carried out. In the paper the different solutions are analysed both from an economic and environmental point of view. The paper addresses two issues of great interest to the scientific community, on the one hand environmental concerns, one of the main challenges facing mankind, as well as health care. The current pandemic situation caused by the COVID19 crisis requires resilient health systems with low environmental impact. 3 Material and methods 3.1 General method The multi-case LCA analysis followed a bottom-up methodology based on processes in accordance with ISO 14040 [25] and ISO 14044 [26] as shown in Fig. 1. Fig. 1. Life Cycle Analysis framework. Adapted from [25]. Goal and scope definition Firstly, a comparative evaluation of the environmental impact of eight X-ray room shielding systems in hospitals was defined as an objective of the analysis. The functional unit chosen was 1 m2 of shield for a radiology room in a hospital, being the most widely used parameter according to published scientific research [47]. The scope of the study (system boundary) in terms of life cycle stages covered raw materials extraction, manufacture of the materials to build the wall, transport to the hospital, implementation, useful life (25 years) and finally demolition, as shown in Fig. 2. LCI will be defined in Description cases section. Fig. 2. System boundary under cradle-to-grave approach. Life Cycle Impact Assessment Once the LCI was established, the ReCiPe method for characterizing environmental impact in the life cycle was used as this method is representative on a global scale [48]. The impact assessment was quantified using SimaPro v8.1 [53] software and the egalitarian perspective was chosen to take into account an infinite time horizon in the most pessimistic development framework [54]. Double weighting indicators (midpoint and endpoint) were chosen to disaggregate the results by damage routes and check individual contributions to the impact on each protection area. ReCiPe proposes 18 impact categories, but SimaPro v8.1 includes marine eutrophication within freshwater eutrophication. An outline of both approaches to impact assessment methodology followed in this work is shown in Fig. 3, which is a summary of the method and ReCiPe's own characterisation, normalisation and weighting factors [48]. Fig. 3. Single score calculation process according to midpoint and endpoint approach. For the selection of impact categories (midpoint), the RECIPE methodology points out the following aspects [55]: - Impact categories must have direct environmental relevance. - Impact categories are names, and category indicators are measurable aspects. Thus, characterization models are required. - Impact categories capture the common mechanisms involved in the effect of various substances. For the selection of the final level categories (endpoint), those that influence on policy and sustainable development are chosen. In the case of the methodology used: human health, environmental quality, and resource availability. The characterization factors of each protection area were expressed in different metrics. For those referred to the human health, DALY (disability adjusted life years) was used, which represents the years lost by a person due to a disease; ecosystems quality, in species lost per unit of time; and, finally, for resource scarcity, as the extra cost of extracting resources in the future. The standardization of characterization factors was done with global scale references to ensure the extrapolation of results. Midpoint approach does not weight the normalization to achieve the final score. However, unique score was obtained by an endpoint approach through the damage and weighting route after normalization. To complement the environmental impact analysis, other key dimensions for the decision to choose shielding systems were incorporated. For a given functional unit, cost and material execution time were obtained from unit prices of the necessary materials and the work performance of the necessary labour. These values were calculated from specialized databases of construction in Spain elaborated from information provided by manufacturers [56]. 3.2 Description cases An equipment with pipe power between 20 and 40 kW, maximum 125 kV, focal points of 1-2 m/m and filtration of 3 mm (Al), with a weekly load of 80 mA minutes per week, with a maximum field size of 40x40 cm was considered. The dose limits considered were 0.12 mSv/week for the radiologist work area and 0.02 mSv/week for the walkable area for patients and non-radiographic medical staff. The dimensions of the X-ray room considered were 3.60 m wide and 5.40 m long, with a free height of 2.70 m. Fig. 4 shows the floor plan of this room. Fig. 4. Floor plan of an X-ray room. Eight possible construction systems were considered for armouring (Table 1). The radioprotective walls are those that enclose the radiology machine and that separate the controlled zone from the monitored zone. The thickness of the wall varied according to the construction material. The horizontal faces were not taken into account because they are structural elements and the isodoses curves in a vertical plane to the machine are of less intensity [57]. These systems were designed to ensure an individual dose cap on the other side of the shield by estimating the attenuation factor (A) of the Equation (1) 𝐴𝐴= Г·𝑊𝑊·𝑈𝑈·𝑇𝑇 𝑑𝑑2·𝐻𝐻𝑤𝑤 (1) where Г is the equivalent radiation dose (in mSv) produced by a beam at 1 m, 𝑊𝑊 is workload (mAs·min/week), 𝑈𝑈 is the barrier use factor, 𝑇𝑇 is the occupancy factor, 𝑑𝑑 is the distance between the focus of the tube and the area to be protected, y 𝐻𝐻𝑤𝑤 is the weekly dose limit on the other side of the armour (in mSv/week). Although lower values were calculated, 1.5 mm thick lead was considered as a minimum shield since a safety factor of 1.5 was applied. Due to the suitability for the thickness and mechanical characteristics of the floor and ceiling, these were excluded from the study. Table 1. Description of the proposed shielding systems analysed Case Shielding material Description of layers Amount (kg) Constructive detail #1 Lead (EN 12588:2006) A) External hollow brick wall. 126.01 B) Lead sheet. 17.01 C) Support system made up of wooden battens. 1.84 D) Internal hollow brick wall. 72.01 E) Gypsum plaster. 10.00 F) Epoxy paint coat. 0.05 #2 Clay brick [11] A) Hollow brick wall. 353,70 B) Gypsum plaster. 10.00 C) Epoxy paint coat. 0.05 #3 Rolled Steel [11] A) External hollow brick wall. 126.01 B) Steel sheet. 183.09 C) Support system made up of wooden battens. 1.84 D) Internal hollow brick wall. 72.01 E) Gypsum plaster. 10.00 F) Epoxy paint coat. 0.05 #4 Reinforced concrete [11] A) Reinforced concrete wall. 365.10 B) Gypsum plaster. 10.00 C) Epoxy paint coat. 0.05 #5 Barite concrete [11] A) Barite concrete wall. 365.10 B) Gypsum plaster. 10.00 C) Epoxy paint coat. 0.05 #6 Sprayed concrete (EN 144871:2005) A) Hollow brick wall. 126.01 B) Reinforced concrete wall. 17.01 C) Gypsum plaster. 10.00 D) Epoxy paint coat. 0.05 #7 Barite plasterboard (EN 520:2004 + A1:2009) A) Hollow brick wall. 72.01 B) Support system made up of metallic steel profiles. 10.27 C) Barite plaster double panel system. 80 D) Epoxy paint coat. 0.05 #8 Leaded plasterboard (EN 520:2004 + A1:2009) A) Hollow brick wall. 72.01 B) Support system made up of metallic steel profiles. 10.27 C) Rock wool. 9.84 D) Leaded plasterboard 26.82 E) Epoxy paint coat. 0.05 *(Measurements expressed in mm) Following life cycle stages of each armour system, for each functional unit an inventory of materials and machinery involved in the processes of the scope was made using the Ecoinvent 3.1 database [58]. The transport of the material from the factory to a hospital using EURO3 trucks that travel the distances of Table 2 was considered. According to the cradle-to-grave approach, the energy consumed on-site construction activities for placing each system in the radiology room itself and the electrical energy for lifting construction materials using a 1.6 kW hoist according to the manufacturer's datasheet were considered. At the end of their useful life, it was estimated that machines would be used to dismantle the walls and transport 25 km to a waste disposal point using 16-32 metric ton EURO3 lorry. Table 2. Building materials inventory Materials Density (kg/m3) Distance (km) Lead sheet 11,000 600 Wooden batten 500 200 Epoxy paint 1,000 600 Clay brick 1,600 200 Gypsum plaster 1,000 200 Rolled steel 7,800 600 Concrete 2,400 200 Barite concrete 3,200 200 Barite plasterboard 1,440 200 Leaded plasterboard 784 + 11,000 600 Rock wool 160 200 4 Results 4.1 General results Fig. 5 shows the characterization of the impact categories. The most unfavourable impact category of the DALY set is human toxicity, in which systems #1, #3 and #8 stand out, with shield #3 being the one with the greatest impact (0.001 DALY). In the ecosystems quality set, system #3 is again the most undesirable, generating greater impacts in the categories climate change ecosystems (6·10-6 species·yr), marine ecotoxicity (2.6·10-6 species·yr) and natural land transformation (4.2·10-6 species·yr). Finally, for resources scarcity characterization, system #3 is again the most unwanted, presenting the highest score in the metal depletion category (34.6 $). environmental biosafety of hospitals [66]. In this sense, solutions that generate little dust and/or noise are usually recommended. On the other hand, all materials to be used in the healthcare buildings construction process should be labeled to facilitate the determination of their environmental impact. This environmental labeling should include at least the greenhouse gas emissions and embodied energy per unit. In any case, the characteristics of an X-ray installation and availability of resources and space will condition the type of shielding required. This work will help architects, engineers and infrastructure managers to select the most appropriate construction system, considering the perspective of sustainability taking into account the importance of passive elements [67]. This work is framed within the healthcare engineering discipline. Figure 11 shows an outline of the main subjects of this discipline according to Chu et al [68]. The work contributes to the green design of hospital facilities, which is within the design of healthcare infrastructures. Figure 11. Framing of the work within the discipline of health engineering. Source: Own elaboration based on [68] . Iconcredtis: www.onlinewebfonts/icon CC BY 3.0 This work contributes to the achievement of the Sustainable Development Goals. The use of Life Cycle Analysis tools contributes to the sustainability of the construction sector and thus to the fulfilment of the SDGs in the field of engineering projects [69]. More broadly, research is also needed to determine the environmental impact of electromedical equipment due to its intense technological load one the road towards infrastructure resilience [70]. Obviously, that equipment will be chosen mainly considering the technical specifications required by medical procedures. Besides, the environmental variable must also be incorporated in the decisionmaking process for equipment acquisition, which contributes to improve the overall performance of hospitals [71]. The main limitation of this study is that is focused on medical diagnostic imaging equipment using X-type ionizing radiation. However, it is perfectly applicable to equipment of similar technology applied in veterinary medicine, materials analysis, quality control in infrastructures, among others. Future works should be directed, on the one hand, towards the environmental evaluation of shielding of equipment that generates alpha, beta and/or gamma radiation emissions (i.e. linear particle accelerators) and, on the other hand, towards the modelling of these shielding systems using Building Information Modelling (BIM) technology, leveraging the connection between BIM, LCA and Life Cycle Cost (LCC). 6 Conclusions A multi-case LCA analysis followed a bottom-up methodology based on main standards within cradle-to-grave perspective applying ReCiPe method was carried out for assessing environmental impact of various shielding systems for X-ray room in a hospital. Furthermore, a unit estimate of both execution time and cost based on specialised databases of construction complemented the information for decision making. The findings of this study suggest that LCA is a suitable tool for designing X-ray rooms. As far as we know, the analysis of the life cycle of these installations had not been carried out before and constitutes a novelty of the work. This methodology allows the selection of the most adequate shielding system for walls, quantifying the environmental impact generated during its life span. In this way, it is possible to minimize the total environmental impact of a healthcare building. The results of this study indicate that solutions with clay brick (#2), cast-in-place reinforced concrete (#4) and sprayed concrete (#6) are the most favourable in the different environmental impact categories analysed. In terms of execution time and cost, solutions with clay brick (#2), cast-in-place reinforced concrete (#4) and barite concrete (#5) are the most recommended System #6 is the most environmentally friendly, 1.6 times less than the next one (which is #4), although its unit price is 1.94 times the cheapest (which is #2) and its execution time is 1.89 times the lowest (which is #2 again). In the field of engineering, decisions are usually made using economic criteria and ease of execution, this work allows the incorporation of sustainability and environmental care in decision making. This study permits to determine the most desirable alternative from an environmental perspective, based on endpoint indicators: human health, ecosystems quality and resources scarcity. The most favourable systems are clay brick (#2), concrete (#4) and sprayed concrete (#6) and the most unfavourable is steel (#3), followed by lead-based armour (#1). The system with the least environmental impact is shotcrete (#6), with a total of 6.739 points/m2, while the steel armour is the most unfavourable system in terms of environmental impact with 165.12 points/m2. The damage on human health occupies between 41% and 87% of the impact of the protection areas. Therefore, from an environmental point of view, in a new construction project, it is recommended to use concrete, clay brick and sprayed concrete shields, since they are the less harmful construction systems because they have a lower impact. The choice of one or the other will be determined by other factors such as the useful space available or the availability of materials. The findings of this study have several practical implications for future practice. This information can be used to develop targeted interventions aimed at choosing the system of isolation, which impacts on social, environmental, and economic benefit (three dimensions of sustainability). 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