Environmental Assessment of Demolition Tools Used in Townhouse Demolition: System Dynamics Modeling

: To accommodate population growth and migration to cities, many infrastructures have been demolished to build new residential units. Demolition processes cause various environmental problems globally and locally. The selection of methods used in demolition is crucial to reduce the long-term environmental impact. This study considers various combination tools used in townhouse demolition in Thailand, examines their environmental impacts, and suggests the combination of the tools to be used in the long term. The system dynamics (SD) modeling approach is utilized in this study to capture the changes in townhouse units, sizes, demolition tools, demolition time, and the work rates of tools and their effects on the environment. This approach has the capability to model complex relationships and examine long-term trends. Secondary data are employed to identify variables necessary for SD model development, such as the different sizes of townhouses in Thailand, the various types of demolition tools used in the construction industry, and environmental impacts from building demolition. The simulation results revealed that Combination 4, i.e., the use of demolition robots and hydraulic splitters, is the most effective combination to reduce the ﬁnal impact percentage in the long term. Compared with the other three combinations, it generates the lowest CO 2eq emissions, energy consumption, noise, dust, and heat. If demolition robots are not yet available, Combination 1 (i.e., the use of excavators, jackhammers, and ﬂame-cutters) offers the lowest environmental impact in the long term. This study provides guidelines for decision-makers in the construction industry to make sustainable choices of demolition tools and techniques used for townhouse demolition to reduce long-term environmental impacts.


Introduction
The residential construction market remains Thailand's largest segment of construction projects, accounting for 35.4% of the industry's total value in 2021 [1].Almost 20% of the nation's housing supply is in the Bangkok Metropolitan Region (BMR) [2].Bangkok has different housing mixes, with a lower proportion of detached houses and a higher proportion of townhouses.Townhouses are buildings containing three or more dwelling units connected side by side in a row.These units typically have entrances and appear to be one building or several distinct structures [3].With a significant increase in the population in Bangkok, the number of residential demands to accommodate Bangkok citizens has increased.A high rate of urbanization leads to enormous pressure for efficient utilization of the existing land.Many buildings are demolished before their expected lives to rebuild new structures.
Demolition operation is dangerous, and a building survey must be performed before the demolition so that it may not cause severe damage to the environment, public, and adjacent properties.Various studies mention various demolition methods.For example, The Constructor [4] categorizes demolition methods for buildings and structures into non-explosive, i.e., sledgehammers, excavators, bulldozers, wrecking balls, and explosive techniques.Jing et al. [5] discussed factors affecting the selection of concrete structure demolition methods and concluded that traditional and eco-friendly demolition tools should be used in concrete structure demolition work.Shweta and Khandvi [6] listed different applications of demolition tools, such as hammers, rammers, excavators, bulldozers, wrecking balls, and explosives.Several demolition tools have been adopted in different countries.For example, Singh et al. [7] highlighted demolition tools, such as hand-held tools, rig-mounted breakers, and rig-mounted crushers in building demolition in India.In Singapore, a top-down method is commonly used in demolition [8].Machineries, such as excavators and crushers, are lifted to the top of the building, and the demolition is carried out progressively from top to bottom [8].In Thailand, the demolition tools used in civil demolition include jackhammers, excavators, hydraulic splitters, flame-cutters, wall and saw cutters, and wrecking balls [9].In Japan, the traditional methods of explosives and iron balls are used in demolition [10].
The selection of demolition tools used in the demolition affects the environment differently.For example, excavators may generate noise, dust, and vibration in the local area and consume fuel that releases CO 2 into the atmosphere, causing greenhouse gas (GHG) emissions.Jackhammers, when in use, generate noise, vibration, and dust, while saw cutters and flame cutters create noise and heat, respectively [10].With more buildings to be demolished in Thailand, selecting demolition tools is crucial in terms of economic and environmental perspectives.For example, using excavators and jackhammers in demolition may cause higher dust levels but lower energy consumption than using excavators and hydraulic splitters [10].Many studies have utilized several methods in selecting demolition tools, for example, Abdullah and Anumba, [11] used the analytic hierarchy process (AHP) as one of the multicriteria decision-making approaches to develop a tool for demolition technique selection and concluded that by using developed tools, demolition engineers can make more informed decisions on demolition techniques, based on a sound technical framework.Anumba et al. [12] used an integrated system for demolition technique selection and concluded that the prototype system developed provides users with a clear and structured framework that could improve the decision-making process.Oryza et al. [13] utilized the selecting model of building demolition method based on an expert system and concluded that the model can make decisions on the selection of demolition methods with an accuracy of judgment.However, unstructured intuition by demolition engineers based on skill, experience, judgment, or knowledge may sometimes lead to error and inconsistencies, and the AHP utilized in selecting demolition tools are linear dependencies between items of different decision-making levels and not suitable for complex problems which are characterized by dependencies, interactions, and feedback and especially by the dynamic nature of the decision taken.To tackle these, the inadequacies system dynamics (SD) modeling approach is utilized in this study to capture relationships among crucial factors affecting the demolition process and environmental impacts, such as the number and sizes of townhouses to be demolished, the demolition tools used in the demolition process and environmental impacts from the demolition process.The study results are expected to provide a better understanding of the demolition process and guide the selection of tools to reduce the environmental impacts on local and global scales in the long term.

Townhouse Demolition in Bangkok
According to Macrotrends [14], the population in Bangkok in 2023 is 11,070,000 persons, and given the ongoing migration into the city, the population could potentially surge to 12,680,000 persons by 2030.This population growth has exerted significant pressure on the demand for housing in the city, prompting entrepreneurs to invest in construction projects to provide different types of housing, including detached houses, townhouses, and condominiums.In Bangkok, townhouses contribute to about half of all housing units as they offer more space than condominiums and lower prices than detached houses [15] (See Figure 1).projects to provide different types of housing, including detached houses, townhouses, and condominiums.In Bangkok, townhouses contribute to about half of all housing units as they offer more space than condominiums and lower prices than detached houses [15] (See Figure 1).In Bangkok, townhouses are divided into small, medium, and large sizes [1].Smallsized townhouses have increased significantly in recent years, rising from 20% of the total townhouse units in 2014 to 60% in 2022 [16].An increase in population and development in Bangkok has resulted in the reconstruction and demolition of buildings.Poombete et al. [17] stated that demolition units in Thailand make up about 10% of the new building permits each year.

Demolition Tools Used in Demolition in Thailand
In Thailand, traditional methods of demolition, which involve excavators, jackhammers, sledgehammers, wrecking balls, hydraulic splitters, flame cutters, and saw cutters, are used in building demolition [9].These tools have a wide range of applications in building demolition.For example, excavators are equipped with different tools, such as pulverizes, shears, breakers, and selector grab attachments to break out steel and concrete and strip the upper floor of the building [18].Jackhammers are made of a long handle, armature, cushion, and gear that perform concrete demolition and drilling operations [19].Flame cutters can cut through a maximum depth of 60 inches with or without a reinforcing rod [20].
According to Jing et al. [5], eco-friendly green demolition methods with no or minimal environmental impact should be adopted in Thai building demolition to reduce the environmental impacts in the long term.It is an excellent solution to minimize various environmental issues in demolition, such as noise, vibration, and dust [11].Although it is not yet available in Thailand, it should be considered as a technique used in the future to reduce the impacts of demolition on the environment.
This study considers five demolition tools used in townhouse demolition: excavators, hydraulic splitters, jackhammers, flame cutters, and demolition robots, as they were retrieved from the literature and were confirmed by experts in interviews.

Environmental Impacts of Demolition Tools Used in Demolition
In demolition, the right choice of tools is essential as demolition severely impacts the environment, safety, and the recycling of materials and components.High precautions and requirements should be employed and measured to mitigate the environmental In Bangkok, townhouses are divided into small, medium, and large sizes [1].Smallsized townhouses have increased significantly in recent years, rising from 20% of the total townhouse units in 2014 to 60% in 2022 [16].An increase in population and development in Bangkok has resulted in the reconstruction and demolition of buildings.Poombete et al. [17] stated that demolition units in Thailand make up about 10% of the new building permits each year.

Demolition Tools Used in Demolition in Thailand
In Thailand, traditional methods of demolition, which involve excavators, jackhammers, sledgehammers, wrecking balls, hydraulic splitters, flame cutters, and saw cutters, are used in building demolition [9].These tools have a wide range of applications in building demolition.For example, excavators are equipped with different tools, such as pulverizes, shears, breakers, and selector grab attachments to break out steel and concrete and strip the upper floor of the building [18].Jackhammers are made of a long handle, armature, cushion, and gear that perform concrete demolition and drilling operations [19].Flame cutters can cut through a maximum depth of 60 inches with or without a reinforcing rod [20].
According to Jing et al. [5], eco-friendly green demolition methods with no or minimal environmental impact should be adopted in Thai building demolition to reduce the environmental impacts in the long term.It is an excellent solution to minimize various environmental issues in demolition, such as noise, vibration, and dust [11].Although it is not yet available in Thailand, it should be considered as a technique used in the future to reduce the impacts of demolition on the environment.
This study considers five demolition tools used in townhouse demolition: excavators, hydraulic splitters, jackhammers, flame cutters, and demolition robots, as they were retrieved from the literature and were confirmed by experts in interviews.

Environmental Impacts of Demolition Tools Used in Demolition
In demolition, the right choice of tools is essential as demolition severely impacts the environment, safety, and the recycling of materials and components.High precautions and requirements should be employed and measured to mitigate the environmental effects of demolition operations.Environmental issues occur at different levels, including local and global levels.Hemlata et al. [21] listed local environmental issues as desertification, water scarcity, water contamination, soil contamination, noise pollution, heat, and dust.Global environmental issues, on the other hand, include global warming, ocean acidification, acid rain, and ozone depletion [21,22].Different combinations of demolition tools result in various environmental impacts.For example, excavators and jackhammers generate noise and dust, which are considered local environmental impacts, and CO 2 emissions and energy consumption, which are regarded as global environmental impacts [10].Flame cutters generate heat (i.e., local impact), energy consumption, and CO 2 emissions (i.e., global impacts) [20].Hydraulic splitters and demolition robots consume energy and release CO 2 into the atmosphere, causing global environmental impacts [22].
Several methods may be used to examine the environmental impacts in the construction industry.For example, Chooi et al. [23] utilized life cycle assessment (LCA) to assess the environmental impact associated with all stages of construction and demolition waste (CDW) from waste production to the end of life of waste material.Fantozzi et al. [24] utilized a life cycle cost analysis to identify the cost-optimal level among different design solutions to improve the energy performance of existing buildings in Italy.Abraham et al. [25] conducted an experimental study on concrete blocks using CDW to enhance waste recycling.Coelho and Brito [26] used the environmental analysis method to evaluate the CDW recycling plant in Portugal.Jones and Smith [27] utilized system dynamics to model the selection of demolition methods.The model identifies a few factors that influence the selection of demolition methods, including the size and type of structure to be demolished, the cost of demolition, the environmental impact of demolition, and the safety of the demolition worker.Brown and Smith [28] developed decision support tools for the selection of demolition methods using system dynamics.The tools consider many factors such as the cost of demolition, and the environmental impact of demolition.Jones and Smith [29] assessed the environmental impact of different demolition methods and concluded that some demolition methods such as controlled demolition have a lower environmental impact than other methods, such as wrecking ball demolition.Brown and Smith [30] utilized SD modeling to examine the safety of demolition workers; the study found that demolition is a dangerous occupation and that many factors contribute to harm and death among the demolition workers.

Importance Weights of the Environmental Impacts
Environmental impacts caused by demolition activities using different demolition tools vary.To determine the importance of each impact, academic journals related to the global and local impacts of the demolition process were retrieved from a well-known database, i.e., the Scopus database, on 23 April 2023 to be used to represent the importance of each impact [31,32].The 'title/abstract/keyword' was used to comprehensively search through the Scopus search engine to capture the impact associated with the building demolition process over 15 years, from 2009 to 2023.The search excludes irrelevant subject areas and is limited to English journal articles.The final number of articles related to this study is 90 articles.They are further input with environmental impacts found in the literature.Table 1 reveals five impacts, namely CO 2 equivalent emissions, energy consumption, noise, dust, and heat, in the demolition-related studies.These five impacts are weighted using the lowest-frequency impacts, which are heat and dust, as the base impact with a weight of 1 (see Table 1).The CO 2 equivalent emissions are the most important environmental impact in building demolition processes, with an importance weight of 21.7.It affects the environment globally and is confirmed by several studies.For example, Ali et al. [33] mentioned that CO 2 is one of the dominant compound elements of greenhouse gases and the principal causal factor of global warming.It accounts for overall global warming effects that are a main driver of climate change.The five key impacts and their importance weights were input into the SD model to calculate the total environmental impact of different combinations of demolition tools used in the demolition process.

System Dynamics Modeling Approach
In this study, an SD modeling approach was utilized to examine the environmental impacts of different combinations of demolition tools used in the demolition process in the long term.It is used to foresee possible long-term effects of policies that cannot be easily understood due to the complex nature of the system [34].It allows the relationships among important variables affecting a problem to be examined and provides a better understanding and possible solutions.The decisions of tool combinations used in the building and their expected impacts are complex systems and require joint efforts from various parties, such as the environmental protection department, demolition engineers, and the government.
The SD modeling approach has been utilized in several construction research studies, including waste management, environmental impact assessment, and construction performance.For example, Doan and Chinda [35] utilized an SD modeling technique to investigate the feasibility of a CDW recycling program in Bangkok, Thailand.Ding et al. [36] developed an SD model to examine the environmental performance of construction waste reduction management in China.Liu et al. [37] evaluated the environmental impact of various CDW management methods, namely illegal dumping, landfilling, and waste recycling and reuse in Guangzhou, China.It was found that socio-economic losses increased by increasing land loss and global warming potential, both of which are affected by illegal waste disposal and landfill disposal.

Secondary Data Collection
The secondary data used in the SD model development were collected from various sources, such as journals, statistical data from the government and related authorities, company reports, and websites [1].For example, the typical townhouses in Bangkok, Thailand, have three sizes: small, medium, and large [1].The power sound levels of excavators and jackhammers are 112 and 113 decibels, respectively [38].The dust levels of the manual (i.e., jackhammers) and mechanical (i.e., excavators) tools are 3.4 and 1.4 mg/m 3 , respectively [39].A summary of the secondary data used in the SD model development is in Table 2.Primary data were collected through interviews with experts in the construction industry.Dworkin [44] suggested that at least five interviewees be involved in the interviews.In this study, eight experts provided information and data input for the SD model development.They are involved in structural demolition projects, such as buildings, roads, bridges, basements, and retaining walls, with more than ten years of experience (see Table 3).They provide the necessary information, such as the demolition tools used in building demolition in Thailand, the work rates of demolition tools for different levels of townhouse demolition, and the use of demolition robots in Thailand.
Based on Table 3, three combinations of demolition tools were decided upon with an average work rate for each tool.The experts also agree on using demolition robots to replace excavators in the future to reduce the environmental impacts effectively.This results in an additional combination (i.e., Combination 4) of this study's demolition robot and hydraulic splitter.Details of each combination are summarized based on the interviews; see Table 4.

Development of an SD Model of the Environmental Impact of Demolition Tools Used in Townhouse Demolition
The SD model of the environmental impact of demolition tools used in townhouse demolition in Thailand was developed based on secondary and primary data.It consists of seven sub-models, namely (1) townhouse units demolished, (2) CO 2 equivalent emission percentage, (3) primary energy consumption percentage, (4) noise percentage, (5) dust percentage, (6) heat percentage, and (7) final impact percentage sub-model.

Townhouse Demolition Sub-Model
Bangkok's housing units were 2,400,540 in 2013, with an average increasing rate of 2.56% [2].Among those, 51% are townhouses [15].Poombete et al. [17] mentioned that the number of townhouses to be demolished is about 10% of new construction permits per year.This leads to the number of townhouses being demolished (THD) (see the SD model equations in Appendix A).Klinmalai et al. [3] stated that townhouses are divided into three sizes: small, medium, and large.On average, the number of small-sized townhouses tends to increase by 6.4% per year, while large-sized townhouses decrease by 8.5% per year [16].This leads to the number of small-, medium-, and large-sized townhouses to be demolished (i.e., STHD, MTHD, and LTHD, respectively).Different numbers and sizes of townhouses and tool combinations used in the demolition affect the environment differently.For example, large-sized townhouses require more extensive work time for excavators than medium-and small-sized townhouses.This may result in more dust, noise, and primary energy consumption from the excavators.

CO 2 Equivalent Emission Percentage Sub-Model
The CO 2 equivalent emissions of primary electricity generation were calculated using a conversion factor of 0.495 kgCO 2eq /kWh for demolition equipment using electricity and 2.025 kgCO 2eq /kWh for diesel-powered excavators [40].The CO 2eq emissions of each tool were estimated by multiplying the primary energy consumption, the conversion factors, the number of tools used, the work rates of the tools, and the time used for demolition.Equations ( 1) -( 3) show examples of CO 2eq emission calculation (in kgCO 2eq ) in Combination 1 using diesel excavators (CO 2eq EX1), electric jackhammers (CO 2eq JH1), and flame cutters (CO 2eq FC1) (see in Abbreviations).
The calculated CO 2eq emissions of excavators, jackhammers, and flame cutters in Combination 1 were summed to achieve the total CO 2eq emissions of this combination.The CO 2eq emissions of the four combinations were compared, and the highest calculated CO 2eq emissions were considered to have a 100% CO 2eq emission percentage (i.e., the worst impact percentage among the four combinations).The combinations with the lower CO 2eq emissions are adjusted to achieve the CO 2eq emission percentages (see Equations ( 4) and ( 5)).

Primary Energy Consumption Percentage Sub-Model
The primary energy consumption for the demolition tools used in Combination 1 (i.e., excavators, jackhammers, and flame cutters) was calculated by multiplying the power rating of the demolition tools, the energy conversion coefficient, the work rates of the demolition tools, the operating hours of the tools, and the number of tools used.For example, diesel-powered excavators have a power rating of 210 kW, an energy conversion of 0.086 kgoe/kWh, and a work rate of 50% of total work time in Combination 1. Jackhammers have a power rating of 2.2 kW, an energy conversion of 1.952 kgoe/kWh, and a work rate of 40% of total work time.Flame cutters have a power rating of 1.5 kW, an energy conversion of 1.952 kgoe/kWh, and a work rate of 10% of total work time.Small-, medium-, and largesized townhouses require one excavator each, two, four, and six jackhammers, respectively, and two, two, and four flame cutters for demolition, respectively.With the total work times of 64, 96, and 128 h for small-, medium-, and large-sized townhouses, respectively, the primary energy consumptions are calculated; see Equations ( 6)-( 8).The calculated primary energy consumptions of excavators, jackhammers, and flame cutters in Combination 1 were summed to achieve the total primary energy consumption and adjusted to achieve the primary energy consumption percentages of Combination 1.

Noise Percentage Sub-Model
Noise generated during the demolition process varies, depending on the nature of the equipment used [38].The noise percentage of each demolition tool in each combination is calculated based on the noise levels of demolition tools, the sizes of the townhouses to be demolished, the work rates of the demolition tools, the number of demolition tools used, and working hours (see Tables 2-4).Equations ( 9) and (10), for example, show the calculated noise of Combination 1 (i.e., noise from excavators and jackhammers, as flame cutters generate no noise).The calculated noises of excavators and jackhammers in Combination 1 were summed to achieve the total noise and adjusted to achieve the noise percentages of Combination 1.It is noted that only excavators and jackhammers generate noise during demolition.

Dust Percentage Sub-Model
The excavators and jackhammers in Combination 1 generate dust, as in Equations ( 11) and (12).The calculated dust of the excavators and jackhammers in Combination 1 was summed to achieve the total dust and adjusted to achieve the dust percentages of Combination 1.

Heat Percentage Sub-Model
The flame cutters in Combination 1 generate heat of 850 kJ, as in Equation ( 13).The heat generated is calculated from the number and sizes of the townhouses to be demolished, work rates, and the number of demolition tools in each combination.It is noted that only the flame cutters in Combination 1 generate heat.

Final Impact Percentage Sub-Model
The five calculated environmental impact percentages were weighted with their importance weights achieved in Table 1.For example, the estimated CO 2eq emission percentage of Combination 1 was multiplied by 21.7 (i.e., the importance weight of the CO 2eq emissions, see Table 1) to achieve the weighted percentage.In each combination, the weighted percentages of the five environmental impacts (i.e., CO 2eq emissions, primary energy consumption, noise, dust, and heat) were summed and divided by the total importance weight of 31.3 (see Table 1) to achieve the final impact percentage.Equation (14) shows the final impact percentage of Combination 1. FIC1 = ((TCO2eq1N × 21.7) + (TP1N × 6.3) + (TN1N × 1.33) + (TD1N × 1) + (TH1N × 1))/31.3(14)

Simulation Results
The SD model of demolition tools used in townhouse demolition was simulated for 20 years to examine the environmental impact of the different tool combinations used in townhouse demolition in the long term.However, Combination 4, which includes demolition robots and hydraulic splitters, was simulated after ten years to initiate the possibility of this new demolition method in actual practice.Table 5 shows the number of townhouses to be demolished in the next 20 years.More small-sized townhouses are to be built and demolished to accommodate the growth and migration of the population into the city.This is consistent with Risland Thailand [16] in that consumers tend to purchase small-sized townhouses in Bangkok due to the rise of land and townhouse prices.Combination 1 generates the highest noise and dust levels, thus receiving the highest noise and dust percentages of 100%; see Figures 4 and 5.This is because jackhammers are one of the demolition tools that generate noise and dust during demolition processes [38].In contrast, Combination 3 generates the least noise percentage compared with the other three combinations, i.e., Combinations 1-3.Combination 4 (i.e., green demolition) is recommended in the long term, as it generates no noise.Combination 1 is the only combination that generates heat from the flame cutters (see Figure 6).It results in a 100% heat percentage.Combination 1 generates the highest noise and dust levels, thus receiving the highest noise and dust percentages of 100%; see Figures 4 and 5.This is because jackhammers are one of the demolition tools that generate noise and dust during demolition processes [38].In contrast, Combination 3 generates the least noise percentage compared with the other three combinations, i.e., Combinations 1-3.Combination 4 (i.e., green demolition) is recom-mended in the long term, as it generates no noise.Combination 1 is the only combination that generates heat from the flame cutters (see Figure 6).It results in a 100% heat percentage.The final impact percentages of the four combinations were achieved when the importance weights were considered.The results show that Combination 4, using demolition robots, generates the lowest final impact of lower than 20%, mainly from primary energy consumption and CO 2eq emissions.The use of demolition robots proves to be the best demolition method to reduce the environmental impact in the long term as it generates almost four times less impact than the other three methods (see Figure 7).As CO 2 emissions and energy depletion are global environmental concerns [21], operations that reduce these impacts should be highly recommended.The final impact percentages of the four combinations were achieved when the importance weights were considered.The results show that Combination 4, using demolition robots, generates the lowest final impact of lower than 20%, mainly from primary energy consumption and CO2eq emissions.The use of demolition robots proves to be the best demolition method to reduce the environmental impact in the long term as it generates almost four times less impact than the other three methods (see Figure 7).As CO2 emissions and energy depletion are global environmental concerns [21], operations that reduce these impacts should be highly recommended.
Combination 3, in contrast, generates the highest final impact percentage, followed by Combinations 2 and 1, respectively.With no demolition robots available, Combination 1 offers the combination of tools with the lowest environmental impact in the long term.This may be because this combination utilizes the excavators with the lowest work rate, resulting in low CO2eq emissions and primary energy consumption, which are the two most significant impacts in the demolition process.Combination 2 may also be considered for townhouse demolition in Thailand in the early years as it generates a similar environmental impact as that in Combination 1.However, with more small-sized townhouses to be demolished, this combination has a higher impact in later years.

Model Validation and Sensitivity Analysis
The developed SD model of demolition tools used in townhouse demolition in Thailand must be validated to confirm its applications in real practices and ascertain if a shift in model parameters causes the model to fail the behavior test that was previously passed [46].Sensitivity analysis is a standard validation test to confirm the model's behavior and Combination 3, in contrast, generates the highest final impact percentage, followed by Combinations 2 and 1, respectively.With no demolition robots available, Combination 1 offers the combination of tools with the lowest environmental impact in the long term.This may be because this combination utilizes the excavators with the lowest work rate, resulting in low CO 2eq emissions and primary energy consumption, which are the two most significant impacts in the demolition process.Combination 2 may also be considered for townhouse demolition in Thailand in the early years as it generates a similar environmental impact as that in Combination 1.However, with more small-sized townhouses to be demolished, this combination has a higher impact in later years.

Model Validation and Sensitivity Analysis
The developed SD model of demolition tools used in townhouse demolition in Thailand must be validated to confirm its applications in real practices and ascertain if a shift in model parameters causes the model to fail the behavior test that was previously passed [46].Sensitivity analysis is a standard validation test to confirm the model's behavior and build confidence in the SD model [47].In this study, the experts provided various demolition periods for small-, medium-, and large-sized townhouses from 6-9, 10-13, and 14-16 days, respectively (see Table 4).The sensitivity analysis was then performed by varying the demolition days for each townhouse size.The simulation results, (Figures 8-11), confirm the validation of the developed SD model as only magnitudes of the results change and the model's behaviors remain the same.The results confirm that the final impact percentage decreases when the operation time decreases.This is in line with Ebrahimi [48] in that the equipment's impact on the environment depends on the time usage of the equipment.New technology, for excavators and hydraulic splitters in particular, is required to perform the tasks with the same performance in a shorter time.Some innovations are offered to dig and grade faster, eliminate guesswork, reduce fuel consumption, enhance operator comfort, and improve safety [49].Examples of technologies are using cameras to enhance site productivity and safety and having cylinder pressure data and machine sensors to calculate material weight while the excavator works continuously [49].
In summary, the simulation results reveal that Combination 4, green demolition using demolition robots, incurs the lowest final impact percentage of less than 20%, four times less than other combinations.Using demolition robots in Combination 4 provides various advantages over traditional methods.

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Its size is more compact than its traditional counterparts, such as excavators and mechanical jackhammering, while its power is much greater.

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It can work continuously without interruption or breaks.

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The remote-controlled aspect of demolition robots provides additional control to features, thus enhancing flexibility and efficiency.It also ensures the safety of operators as it can be controlled from a safe distance from the demolition sites.

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It can engage in high-risk demolition operations and reduce casualties.

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It requires fewer workers, resulting in reduced costs and more safety.

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It is environmentally friendly and solves many environmental issues, such as noise, dust, and vibration [5,50].

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It reduces the time require for demolition, thereby speeding up the redevelopment process.
In case Combination 4 is not yet available, Combination 1 generates the lowest final impact percentage, followed by Combination 2 and 3, respectively.This combination causes the lowest CO 2eq emission and energy consumption percentages (considered global environmental impacts) but the highest noise, dust, and heat percentages (considered local environmental impacts).As the dust issue is becoming a severe concern in Thailand, the work rate of jackhammers (i.e., a key tool in this combination) may be adjusted and replaced by other tools, if possible [51].Pusapukdepop and Pengsaium [51] stated that the dust risks in demolition depend on the demolition volume, the height of the buildings, the demolition methods, and the disposal methods.The Department of Trade and Industry [52] suggested using wet foam to catch the dust generated during collapse to reduce the dust produced when a building is demolished.

Discussion and Conclusions
Bangkok's population and development growth has generated an increasing demand for more housing units and development, leading to more building demolition to build new residential units.Concrete structure demolition is a complicated process that needs careful planning and management.Using different demolition tools incurs other impacts on the environment on global and local scales.It is necessary to optimize the selection of suitable tool combinations for safe demolition processes that have minimal impact on the surrounding environment.In this study, the SD model was developed with key factors, such as the number of townhouses to be demolished, the sizes of the townhouses, various environmental impacts, demolition periods, and different combinations of demolition tools, to examine the environmental impact of different tool combinations in the long term.Four combinations of demolition tools were considered for townhouse demolition.Combination 1 combines the use of excavators, jackhammers, and flame cutters.Combination 2 considers excavators, jackhammers, and hydraulic splitters.Combination 3 considers excavators and hydraulic splitters, while Combination 4 uses demolition robots and hydraulic splitters in the demolition process.Five environmental impacts in the demolition process are listed: CO 2eq emissions, energy consumption, noise, dust, and heat, with the importance weights of 21.7, 6.3, 1.3, 1, and 1, respectively.
The simulation results revealed that Combination 4, green demolition using demolition robots, incurs the lowest final impact percentage.In Combination 4, energy consumption and CO 2eq emissions highly contribute to the final impact percentage.However, these two impacts are lower compared with other combinations.This is consistent with Jing et al. [5] in that green demolition reduces 8.5% of CO 2 emissions compared to traditional processes.In case Combination 4 is not yet available, Combination 1 generates the lowest final impact percentage, followed by Combination 2 and 3, respectively.
The sensitivity analysis was performed to validate the developed SD model and suggest ways to reduce the environmental impact in the long term.In this study, the demolition periods for small-, medium-, and large-sized townhouses were changed to examine the final impact percentage of each tool combination.The results confirm the validity of the developed SD model and agree that shorter demolition periods result in lower final impact percentages.Various technologies, such as soundless chemical demolition, demolition robots, and electric methods, may reduce the demolition time and remain efficient.These can result in a quicker turnaround for land to be available for new projects, which can be advantageous for urban development and land use planning.
The developed SD model may be used as a guideline for demolition companies to plan for demolition tools used in townhouse demolition to minimize the environmental impact in the long term.Economic analysis may be performed together with environmental analysis to select the best strategies for long-term implementation.This research study has some limitations.The secondary data used in the model's development were collected from the literature in developed and developing countries and are not specific to the Thai context.The primary data were collected from a limited number of experts in the construction industry.The importance weights of the environmental impacts were acquired from the literature review and may be adjusted.Townhouses are used in building demolition.Other types of buildings may be considered.

Figure 3 .
Figure 3. Graphical results of primary energy consumption percentages.

Figure 7 .
Figure 7. Graphical results of the final impact percentages.

4 Figure 7 .
Figure 7. Graphical results of the final impact percentages.

Figure 8 .
Figure 8. Final impact percentages of Combination 1 when the demolition period is changed.

Figure 8 .
Figure 8. Final impact percentages of Combination 1 when the demolition period is changed.

Figure 8 .
Figure 8. Final impact percentages of Combination 1 when the demolition period is changed.

Figure 10 .Figure 11 .
Figure 10.Final impact percentages of Combination 3 when the demolition period is changed.

Table 1 .
Environmental impacts of demolition processes and their importance weights based on the Scopus database.

Table 2 .
Summary of secondary data used in the SD model development.

Table 3 .
Primary data used in the SD model development.

Table 4 .
Four combinations of demolition tools acquired from the interviews.

Table 5 .
Simulation results of townhouses to be demolished.Figures2 and 3show that Combination 3 has the highest CO 2eq emission and primary energy consumption percentages.This is because excavators are one of the most energyintensive tools, and long work times result in increased energy consumption and CO 2 emissions [45].