An Environmental Impact Causal Model for improving the environmental performance of construction processes

Journal of Cleaner Production 52 (2013) 425e437

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An Environmental Impact Causal Model for improving the environmental performance of construction processes Alba Fuertes a, *, Miquel Casals b, Marta Gangolells b, Nuria Forcada b, Marcel Macarulla b, Xavier Roca b a

School of Architecture, Design and Environment, Environmental Building Group, Plymouth University, Drake Circus, Plymouth, Devon, PL4 8AA, United Kingdom Department of Construction Engineering, Universitat Politècnica de Catalunya, C/Colom, 11. Ed. TR5, Terrassa, 08222 Barcelona, Spain

b

a r t i c l e i n f o

a b s t r a c t

Article history: Received 7 May 2012 Received in revised form 30 January 2013 Accepted 1 February 2013 Available online 13 February 2013

Despite the increasing efforts made by the construction sector to reduce the environmental impact of their processes, construction sites are still a major source of pollution and adverse impacts on the environment. This paper aims to improve the understanding of construction-related environmental impacts by identifying on-site causal factors and associated immediate circumstances during construction processes for residential building projects. Based on the literature and focus group findings, we have developed a construction-related Environmental Impact Causal Model consisting of a process-oriented causal network of thirty-nine environmental impacts, forty-five causal factors and over two hundred causal relationships. It is intended to contribute to a reduction in construction-related environmental impacts on building sites by supporting contractors and other decision-makers in the early identification of factors that are likely to lead to impacts or to exacerbate their consequences, as well as the later environmental performance evaluation and control. The causal model is validated by investigating over a hundred environmental incidents. Finally, possible methods to improve construction-related environmental performance are suggested. Ó 2013 Elsevier Ltd. All rights reserved.

Keywords: Environmental causal factor Environmental impact Causal model Construction process Building

1. Introduction Construction, defined as all the activities that contribute to the creation, maintenance and operation of the built environment, is a fundamental component of the economic and social development of a country (E-CORE, 2012). However, significant challenges have to be faced, in terms of construction’s influence on energy and climate change and its impact on natural resources (energy, water and materials) (EC, 2009). Due to increasing environmental awareness and tighter regulations, environmental management efforts have been growing rapidly in the construction sector (Rodríguez et al., 2011). Overcoming the inherent characteristics of construction projects, mostly in relation to the high variability techniques and systems (Casals and Etxebarria, 2000) and the transience of the processes (Cole, 2000), construction organizations have been urged to adopt environmental management systems (EMSs) in order to improve their environmental performance (Tam et al., 2006a).

* Corresponding author. Tel.: þ44 1752585196; fax: þ44 1752585155. E-mail address: [email protected] (A. Fuertes). 0959-6526/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jclepro.2013.02.005

Environmental aspects are the focus of an EMS, therefore a company implementing an effective EMS should build a system to address these aspects (Nawrocka and Parker, 2009; Gangolells et al., 2011). ISO 14001:2004, the international standard for EMSs, defines an environmental aspect as ‘the element of an organisation’s activities or products or services that can interact with the environment’, i.e. those elements that cause, or have the potential to cause, environmental impacts. According to Teixeira (2005), the identification of the environmental aspects that could lead to impacts is a key element of site planning, which is required by a construction company’s environmental management systems and increasingly demanded by construction clients and local authorities. Moreover, ISO 14001:2004 also requires that organizations establish and implement procedures to monitor and measure the environmental performance of their processes. Consequently, there is a need to identify which aspects need to be measured as well as when these measurements should take place (ISO 14005:2010), in order to facilitate the implementation of appropriate preventive and corrective measures on-site. Although the literature acknowledges the important role that environmental aspects play in the establishment, implementation and maintenance of an organization’s EMS (ISO

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14005:2010), their identification has high levels of uncertainty (Poder, 2006). The research presented here seeks to contribute to the knowledge of significant construction-related environmental impacts by identifying and describing the wide range of on-site causal factors involved in immediate impacts circumstances during the construction processes. A causal model is proposed indicating the manner in which on-site elements shape the circumstances on the construction site, giving rise to acts and conditions which, in turn, lead to environmental impacts. A better knowledge of the elements that cause, or have the potential to cause construction-related environmental impacts, will contribute to the efficiency of EMSs and to the improvement of the environmental performance of construction projects and sites. In essence, the construction organizations can use the causal model to identify in detail the environmental aspects and impacts related to the construction processes of their projects, focussing on elements of the construction site, such as material, machinery, workers and workplace aspects, as well as the existence of causal relationships between aspects. Moreover, the process-oriented character of the model and the level of detail of the on site causal factors will facilitate the design of an environmental performance monitoring plan which includes the aspects that need to be monitored in each construction process. The model is also expected to contribute to the investigation and recording of environmental incidents, as it identifies the underlying causes of the impacts by means of a robust taxonomy and classification system of environmental impact causal factors. This paper starts by exploring the impact of the construction sector on the environment by presenting the current state-of-theart. The systematic development of a process-oriented Environmental Impact Causal Model for building construction projects is described. Furthermore, the environmental impact causal factors included in the model are discussed in detail. Finally, the model is validated, the results are discussed and suggestions are made to improve construction environmental performance.

2. Literature review Construction sites are often criticised for their impacts on the surrounding environment and residents (CIRIA, 2005). Numerous studies have been conducted on the identification of the environmental impacts related to the construction process. Chen et al. (2005) classified the impacts associated to the on-site construction activities as soil and ground contamination, construction and demolition waste, surface and underground water contamination, dust, noise and vibration, impacts on wild life and natural features, hazardous emissions and odours, and archaeology impacts. According to Shen and Tam (2002), the construction process usually results in the extraction of environmental resources; the production of waste that requires the consumption of land for disposal; the extension of consumption of generic resources; and the pollution of the living environment with noise, odours, dust, vibrations, chemical and particulate emissions, and solid and sanitary waste. Moreover, Sharrard et al. (2007) concluded that the construction process has significant energy implications, especially on-site energy consumption and emissions to air. Glass and Simmonds (2007) summarised the environmental impacts which effect surrounding residents. The systematic approach for dealing with potential adverse environmental impacts at the pre-construction stage presented by Gangolells et al. (2009) is particularly noteworthy. In line with previous research findings, the results demonstrated the existence of thirty-nine significant environmental impacts related to the construction processes. Other approaches addressing the

construction-related environmental impacts are included in Teixeira (2005), Cole (2000), and Chen et al. (2000). The identification of the causal factors of environmental impacts on construction sites lacks sufficient attention. Causality, or causality relationships, is identified as an important issue in the wider impact identification, prediction and assessment field, as it relates the way impacts arise from the development action (Perdicoúlis and Piper, 2008). Perdicoúlis and Glasson (2006) recognised the existence of interaction pathways between environmental impacts and studied their contribution to Environmental Impact Assessment. In addition, Walker and Johnston (1999) explored the existence of impact interactions and concluded that the environmental effects which can result from these interactions can be significant and their early identification may contribute to sustainability improvement. Despite the apparent importance of causality, there is very little research on the identification of the impact causal factors and interactions in the construction field. Construction Industry Research and Information Association (CIRIA, 2004, 2005) developed the ‘Environmental best practice on site’ handbook. It states that dust arises from laying temporary roads, vehicle and plant usage, handling of materials, and storage and stockpiling. It also establishes that noise is the result of the use of trucks, reversing vehicle alarms, road sweepers, impact devices, drilling saws, cranes and demolition activities (CIRIA, 2004). This is also agreed by Tam et al. (2006b) and Tam and Le (2007). In addition, Tam and Le (2007) suggested that poor positioning and maintenance of material storage areas can result in damages and generation of waste. Bennett and James (1999), Jasch (2000), Tam and Le (2007) and Sharrard et al. (2007) reported that the use of construction plants, temporary lighting systems, and construction vehicles may increase the energy consumption and the greenhouse gas emissions generated on site. The maintenance of equipment has been related to the generation of emissions (Bennett and James, 1999). In summary, whilst there is a good understanding of the extent and pattern of environmental impacts in the construction industry, research regarding the identification of the environmental impact causal factors on construction sites remains simplistic and incomplete. According to Julien et al. (1992), to improve the environmental performance of the processes it is important to determine the causeeeffect relationships between activities and the environmental elements. With this background, it can be concluded that an approach for the detailed identification and classification of the environmental impact causal factors in construction processes needs to be undertaken. 3. Research approach and scope definition 3.1. Research approach The research presented in this paper provides a systematic analysis of the causal factors that contribute to the significant environmental impacts associated with residential building construction. It focuses on the highly severe environmental impacts identified in the literature review (Gangolells et al., 2009) and the processes and activities that are common in residential building construction projects (IteC, 2006). The method followed in this research is illustrated in Fig. 1. Following a process-oriented approach (Zobel and Burman, 2004; Gangolells et al., 2009), together with a cause and effect approach (Walker and Johnston, 1999; Perdicoúlis and Piper, 2008), the on-site causal factors that contribute to the occurrence of environmental impacts or exacerbate their consequences were identified for each construction process. Causal network analysis techniques were employed for this purpose, as these can reveal causal relations between impacts. Firstly, we assumed the

A. Fuertes et al. / Journal of Cleaner Production 52 (2013) 425e437

Significant environmental impacts

Construction processes

Environmental Impact Causal Model 1. Definition of the causal relationships between environmental impacts

427

on-site facilities; (3) landscape gardening works; (4) earthworks; (5) foundations; (6) structures; (7) roofs; (8) partitions and closures; (9) impermeable membranes; (10) insulation; (11) coatings; (12) pavements; and (13) door and window closures. 3.3. Environmental impacts that were initially considered

3 different causal relationship typologies 178 causal relationships between impacts

2. Development of the environmental impact causal chains Environmental impact causal factors related to the construction processes 3. Development of the Environmental Impact Causal Model framework 5 categories, 13 subcategories and 27 sub-subcategories of environmental impact causal factors

List of on-site causal factors of the significant environmental impacts related to the construction processes of a residential building project Fig. 1. Research process.

existence of links and interaction pathways between environmental impacts. We then used an impact matrix to identify the cause and effect relationships and interactions among these impacts. Secondly, the causal chains that could trigger environmental impacts, including individual causal factors and links among them, were identified through the development of fault tree diagrams. Domain expert focus groups were formed to discuss and refine the findings. The results were used to develop a process-oriented Environmental Impact Causal Model for building construction projects. This model included a comprehensive, structured, robust hierarchical classification system for causal factors. The model was validated on the basis of validity measures proposed by Shappell and Wiegmann (2001). Finally, the results were discussed and some suggestions were made to improve construction environmental performance. 3.2. The construction processes that were initially considered A total of 220 processes and activities that are common in residential building construction projects were considered. They were obtained from the MetaBase database developed by the Catalan Institute of Construction Technology (ITeC). This robust and extended database includes up-to-date reference prices, technical characteristics, certifications and environmental data for 220 work sections and construction products. It is the most widely used information source by official and private entities (designers and contractors) in Catalonia (Spain) since 1985. In the research field, this taxonomy has been used in different studies related to the environmental and safety management in the construction sector, which have been published in peer-reviewed journals (Gangolells et al., 2009, 2010, 2011; 2013). Other standards (e.g. ISO 12006), taxonomies (e.g. Lexicon, BARBi-Building) and ontologies (e.g. UNICLASS, e-Cognos) exist in the construction field (Lima et al., 2007). However, they do not include a detailed list of construction processes or are not concise enough. ITEC, on the other hand, presents a complete, concise and robust list of construction processes. These were classified into the following main categories (ITeC, 2006): (1) materials, equipment and waste management; (2)

We considered 39 highly severe environmental impacts associated with residential building construction activities, that were previously identified in Gangolells et al. (2009) by evaluating their level of significance in each specific construction stage according to their spatial scale, the probability of occurrence and the duration (ISO 14004, 2004; Poder, 2006). The validity and robustness of this study has been previously acknowledged in the literature review (Gangolells et al., 2011; El-Anwar et al., 2010; Li et al., 2010). These impacts were classified into nine main categories: (1) atmospheric emissions, which includes impacts derived from the emission of greenhouse gases, VOCs and CFCs; (2) water emissions, including the dumping of pollutant products and contaminated water which may affect the quality of the surface water, groundwater or the sewage system; (3) waste generation, including human waste, excavated material generated during earthworks or excess off-cuts of construction materials; (4) soil alteration, which includes all the aspects related to land occupancy and potential adverse impacts due to the dumping of pollutant liquids; (5) resource consumption, mainly water, electricity, fuel and raw materials consumption resulting from the construction activities; (6) local issues, related to the potential impacts to the surrounding residents, e.g. suspended particles emission, dirtiness, noise, vibrations and visual impacts; (7) transport issues, related to the increase or interferences of external road traffic due to the construction site transport; (8) effects on biodiversity, including all aspects related to vegetation loss, loss of soil fertility and potential adverse impacts due to the interception of river beds.; and (9) incidents, accidents and potential emergency situations, mainly related to potential fires onsite. Non-significant environmental impacts were not considered. See the detailed classification of environmental impacts in Table 1. 4. Development of a process-oriented Environmental Impact Causal Model for the construction processes 4.1. Identification of the environmental impact causal factors The causal factors associated with each environmental impact and construction process were identified following a causal network analysis approach. According to Walker and Johnston (1999), causal network analysis is an advantageous causality analysis method as it makes explicit the multiple and often complicated nature of impacts resulting from a project, including the impact interactions, which are not always apparent using simpler forms of analysis. Causal factors were identified as follows. Firstly, we defined the causal relationships between impacts. Secondly, we systematically developed causal chains for each environmental impact and construction process. Causal relationships and causal factors were identified by the researchers on the basis of their judgement and knowledge, supported by the literature review. The findings were subsequently refined by construction and environmental domain experts in focus groups. 4.1.1. Definition of the causal relationships between environmental impacts According to Walker and Johnston (1999), there are links and interaction pathways between individual elements of the environment. When one element is specially affected, it has an effect on the elements that interact with it.

428

A. Fuertes et al. / Journal of Cleaner Production 52 (2013) 425e437 Table 1 List of construction-related environmental impacts (Gangolells et al., 2009). AE

Atmospheric emissions

AE-1 AE-2

Generation of greenhouse gas emissions due to construction machinery and vehicle movements. Emission of VOCs and CFCs.

WE

Water emissions

WE-1 WE-2 WE-3

Dumping of water resulting from the execution of foundations and retaining walls. Dumping of concrete or water resulting from the process of cleaning concrete chutes or other basic fluids. Dumping of sanitary water resulting from on-site sanitary conveniences.

WG

Waste generation

WG-1 WG-2 WG-3 WG-4 WG-5

Generation Generation Generation Generation Generation

SA

Soil alteration

SA-1 SA-2 SA-3 SA-4 SA-5 SA-6 SA-7 SA-8 SA-9

Land occupancy by the building, provisional on-site facilities and storage areas. Dumping derived from the use of concrete release agent and concrete on-site. Dumping derived from the use of cleaning agents or surface-treatment liquids on-site. Dumping derived from the use and maintenance of construction machinery. Dumping of water resulting from the execution of foundations and retaining walls. Dumping of concrete or water resulting from the process of cleaning concrete chutes or other basic fluids. Dumping of sanitary water resulting from on-site sanitary conveniences. Dumping derived from the use of paints and water resulting from the process of cleaning paint-related tools on-site. Dumping derived from the use of special agents on-site.

RC

Resource consumption

RC-1 RC-2 RC-3 RC-4

Water consumption. Electricity consumption. Fuel consumption. Raw materials consumption.

L

Local issues

L-1 L-2 L-3 L-4 L-5 L-6

Dust generation in activities with construction machinery and transport. Dust generation in earthworks activities and stockpiles. Dust generation in activities with cutting operations. Dirtiness at the on-site entrances. Generation of noise and vibrations due to site activities. Landscape alteration.

T

Transport issues

T-1 T-2

Increase in external road traffic due to construction site transport. Interference in external road traffic due to the construction site.

B

Effects on biodiversity

B-1 B-2 B-3 B-4 B-5

Vegetation removal. Loss of edaphic soil. Soil erosion. Soil compaction due to opening site entrances. Interception of river beds.

AC

Incidents, accidents and potential emergency situations

AC-1 AC-2 AC-3

Fires at areas for storing flammable and combustible substances. Fires due to breakage of underground pipes. Fires due to breakage of receptacles with harmful substances.

of of of of of

excavated waste material during earthworks. municipal waste by on-site construction workers. inert waste. ordinary or non-special waste. special waste.

An impact matrix (Walker and Johnston, 1999; Perdicoúlis and Piper, 2008) was developed to express the different causal relationships among the environmental impacts (see the Impact matrix in Table 2). In particular, Impact A (in rows) contributes to Impact B (in columns). Thus, Impact B is caused or exacerbated by Impact A. A total of 178 interactions were identified among the 39 environmental impacts. Three different causal relationships were recognised: - Interaction ‘a’: the occurrence of Impact A causes or exacerbates Impact B. This also refers to the incremental changes in Impact A itself (See the a-type interaction in the matrix diagonal). For example, the higher the impact ‘Increase in external road traffic due to construction site transport’, the greater the noise generation.

- Interaction ‘b’: the corrective measures associated to Impact A cause or exacerbate Impact B. For example, ‘Dirtiness at construction site entrances’ might require the use of a sweeping vehicle, which also contributes to the generation of noise. - Interaction ‘c’: the occurrence of Impact A, combined with particular contextual conditions, causes or exacerbates Impact B. For example, the incorrect storage of the special waste generated on-site might cause the occurrence of dumping of special agents onto the ground.

4.1.2. Development of the environmental impact causal chains. The basic component of network analysis is the impact chain, which illustrates the process of cause and effect, including secondary effects on other environmental aspects (Walker and

Table 2 Causal interactions among the environmental impacts. Impact A (rows) contributes to impact B (columns). Relation ‘a’: Impact A causes or exacerbates impact B. Relation ‘b’: Corrective measures of impact A cause or exacerbate impact B. Relation ‘c’: Impact A, combined with particular conditions, causes or exacerbates impact B. AE1 AE2 WE1 WE2 WE3 WG1 WG2 WG3 WG4 WG5 SA1 SA2 SA3 SA4 SA5 SA6 SA7 SA8 SA9 RC1 RC2 RC3 RC4 L1 L2 L3 L4 L5 L6 T1 T2 B1 B2 B3 B4 B5 AC1 AC2 AC3 a a a a a

b a a a

c

a a

b b b b b b b b

a a a a a a

a a a

b

c

c c

a

b b a b b

a a

b b b b b

a a

b b

a a

b b b b b b b b

a

a a a

b b b b b

b b b b b

b

b

c c c

c

a

b a

c c

a

c c

a

b b

a a

b

a a a a

b b b b b b b b

a a

a

c a

a

a

a

b

a

a b

b

c

a b b b b

a

c

a a a b

b

b

b

a

b a a

a

a

A. Fuertes et al. / Journal of Cleaner Production 52 (2013) 425e437

AE1 AE2 WE1 WE2 WE3 WG1 WG2 WG3 WG4 WG5 SA1 SA2 SA3 SA4 SA5 SA6 SA7 SA8 SA9 RC1 RC2 RC3 RC4 L1 L2 L3 L4 L5 L6 T1 T2 B1 B2 B3 B4 B5 AC1 AC2 AC3

a a

a a

a a

a a

a a

b b

a a

a

a a a a a

a a a

a a a

a a a

b b b

a a a

a a a

429

430

A. Fuertes et al. / Journal of Cleaner Production 52 (2013) 425e437

Johnston, 1999). Impact chains can also be linked together to express impact interactions. A tree diagram is a causal network method that employs graphical means of expression to describe impact causal chains (Walker and Johnston, 1999; Perdicoúlis and Piper, 2008). They are aimed at identifying all the realistic ways in which an undesired event can occur, following a topedown approach (Dokas et al., 2009). As with any other causal network method, they are characterised by attributes such as simplicity, clarity, abstraction, and aggregation. By the use of a fault tree diagram method, all the environmental impacts were broken down systematically and logically into causal chains for each construction process. Different considerations were taken into account during the decomposition of the impacts: (i) environmental impacts can be caused or exacerbated by one or more causal chains; (ii) causal and exacerbating relationships exist between impacts; (iii) the causal or exacerbating character of the relationships and factors can vary for each construction process and impact. Fig. 2 illustrates a fault tree diagram example. Focus groups are an established rigorous technique for collective interviews (Fellows and Liu, 2008). Three such groups were organised to discuss and refine the fault tree diagrams. Participants were experts in construction management with special interest in the environment. They included eight construction site managers, two managing directors and two environmental co-ordinators of Spanish construction companies specialised in buildings. Moreover, three professors from the Universitat Politècnica de Catalunya’s Department of Construction Engineering also took part. During the focus groups, the domain experts were asked to analyse the fault tree diagrams and validate, add, change or erase the existing causal factors and relationships, if necessary. Participants discussed the diagrams out loud and their thoughts were recorded. Later, their comments were jointly processed and suggestions were implemented on the initial diagrams. At the end of this process, highly developed fault tree diagrams were obtained. 4.2. Development of the Environmental Impact Causal Model internal framework An Environmental Impact Causal Model, consisting of causal factors categories and subcategories, was built by systematically

analysing and drawing together previous findings from the fault tree diagrams. These findings suggested that (i) constructionrelated environmental impacts are caused or exacerbated by a process-dependant network of on-site causal factors; (ii) impacts broadly arise from the interaction between workplace, equipment, material, workers and task factors, giving rise to varying immediate impact circumstances; (iii) task factors are the main cause of the environmental impacts related to the construction processes; and (iv) specific workplace, equipment, material, and worker-related factors lead to environmental impact exacerbating circumstances, including those derived from emergency operating situations. Fig. 3 illustrates the Environmental Impact Causal Model, which aims to express the previous findings in a single representation. The timeline is used to illustrate the evolution of the immediate causal circumstances that can lead to environmental impacts in each construction process, resulting from the inherent transience of construction projects. The model also illustrates the interaction of the causal factors that could lead to an impact. These causal factors are classified into five categories: (i) Task factors; (ii) Workplace factors; (iii) Equipment factors; (iv) Material factors; and (v) Worker factors. Firstly, the model represents the Task factors in an outer circle, with all the possible causal interactions directly derived from construction processes. Secondly, it contains Workplace, Equipment, Material, and Worker factors, which are defined as causal factors that might be catalysts for exacerbating circumstances of construction related environmental impacts and for potential emergency situations. The approach employed in the model builds upon the findings established in previous research on accident causation (Haslam et al., 2005; Mitropoulos et al., 2005; Gibb et al., 2006) and quality defect causation (Love et al., 2009) in construction. The five main causal categories included in the model are further broken down into subcategories, so as to draw together all the findings of the fault tree diagrams (See Table 3). The following sections discuss the elements of the model in further detail. 4.2.1. Task factors The Task factor category presents the causal factors of environmental impacts directly related to the construction processes. Thus, they are linked to issues related to workplace, equipment,

Generation of noise due to site activities

Handling of material at the storage areas

Use of construction vehicles and machinery

(b)

Storage areas close to limits of the const.site

More equipment than planned is used on site

The equipment is in operation for longer than expected

The worker makes an error and the activity needs to be repeated

The worker does not stop the equipment in use

The worker does not have enough information

Equipment without auto-turn off engine system

The equipment generates more noise than expected

Inappropriate location of storage areas on the const. site

Equipment does not conform to noise regulations

The level of lighting is not sufficient to carry out the activity

Activities planned in non-working hours

Equipment in bad conditions

(a)

SA-4

(a)

B-2 B-1

Undesired environmental conditions

Worker drives the vehicle too fast

Fig. 2. Example of fault tree diagram. Note 1: SA-4 dumping derived from the use and maintenance of construction machinery; B-1 vegetation removal; B-2 loss of edaphic soil. Note 2: Symbols based on NTP 333. Solid lines represent causality relationships; dashed lines represent exacerbating relationships.

A. Fuertes et al. / Journal of Cleaner Production 52 (2013) 425e437

Task factor Task factor

Operational conditions

Task factor

Workplace factor

Material factor

Environmental impact

Equipment factor

Equipment factor

Equipment factor

Worker factor Exacerbating conditions Construction processes

Fig. 3. General approach of the Environmental Impact Causal Model.

431

material and worker factors associated with the nature of the tasks. Work scheduling aspects, such as the inadequate activity planning and the performance of work during non-labour hours, were also included in this category. The findings concluded that most of the impacts are associated with the on-site elements or actions that have an important role for the development of the construction processes, and consequently, they appear to be present in all the causality trees developed in the study. For example, the generation of greenhouse gas emissions, the consumption of fuel or the generation of noise are directly related to the use of construction machinery and equipment during the construction activities. Similarly, the generation of waste or the consumption of resources is associated with the nature of the tasks. The identification of the causal factors that lead to these impacts was considered to be important and necessary for an accurate and efficient environmental management. Moreover, the findings also revealed a significant amount of opportunities prevent these impacts or reduce their consequences, so to improve the environmental performance of the processes. These opportunities consisted of identifying the immediate circumstances that lead to

Table 3 Environmental Impact Causal Model framework, including the results of the incident analysis and causal factors classification. Category

F.1 Workplace factors

Subcategory

F1.1

Site condition factors

F1.2

Outdoor environmental factors

F1.3

Site layout factors

Factors involved

Proportion of impacts in EICM in which involved (%)a

Proportion of real incidents in which involved (%)a

Existing impact due to current or past surrounding activities Impact produced on-site Rain/wet/high humidity Sun/heat/low humidity Cold/snow/ice Wind Lighting Inadequate element or activity location on-site Inadequate delimitation of specific areas on-site Insufficient space on-site or in the designated area to carry out a task Equipment in bad condition

18

(0)

64 18 33 33 18 8 49

(22) (2) (9) (1) (0) (0) (4)

23

(1)

8

(0)

13

(8)

15

(1)

8

(0)

F2.3.1

Inappropriate characteristics of the equipment Equipment does not conform to relevant regulations Inadequate use of the equipment

41

(32)

F3.1.1

Material in bad conditions

10

(3)

F3.2.1

10

(0)

13

(0)

F3.3.1

Inappropriate characteristics of the material Material does not conform to relevant regulations Inadequate use of the material

26

(1)

F4.1.1 F4.1.2

Physical limitations of workers Incorrect performance

3 72

(0) (95)

F4.2.1

Insufficient information to carry out the task Inadequate activity planning Activities programmed in non-labour hours Workplace-related Equipment-related Material-related Worker-related

36

(5)

38

(8)

13

(1)

26 28 44 3

(3) (72) (24) (3)

F1.1.1

F1.1.2 F1.2.1 F1.2.2 F1.2.3 F1.2.4 F1.2.5 F1.3.1 F1.3.2 F1.3.3

F.2 Equipment factors

F2.1 F2.2

Equipment condition Equipment suitability

F2.1.1 F2.2.1 F2.2.2

F2.3 F.3 Material factors

F3.1 F3.2

Equipment usability Material conditions Material suitability

F3.2.2 F3.3 F.4 Worker factors

F4.1

F4.2 F.5 Task factors

F5.1

Material usability Worker actions and capabilities Information/ communication Work scheduling

F5.1.1 F5.1.2

F5.2

a

Task nature

F5.2.1 F5.2.2 F5.2.3 F5.2.4

Values higher than 100 due to multiple involvement of factors per environmental impact or incident.

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the exacerbation of these Task factors and impact consequences. They are further detailed in the next sections.

consumption and noise generation caused by vehicles and machines left unattended with the engine running.

4.2.2. Workplace factors Workplace factors revolve around issues related to site conditions and characteristics. The term ‘workplace’ is defined as the area included within the limits of the construction site. The causal factors included in this category mostly refer to undesired outdoor climate conditions and site layout aspects. Less notable, but also identified in the impact causal chain analysis, are past environmental impacts whose consequences are still present on-site. Regarding outdoor working conditions, research results suggested that climatic conditions such as rain, sun exposure, and high or low temperatures may exacerbate the generation of wasterelated impacts, by damaging unprotected stored materials. Other examples are the generation of dirtiness due to the mud generated on-site caused by rain and snow (Teixeira, 2005), or the generation of dust due to the use of construction vehicles and earthworks exacerbated by high temperatures and wind. It is apparent from this research that site layout factors could also contribute to some environmental impacts. Deficiencies in the location of the activity to be undertaken or the material storage area on-site might increase impacts such as the generation of waste due to damage to the stored material by construction vehicles moving too close to it. This was also agreed by Tam and Le (2007). When a storage area is too close to the boundaries of a construction site, this can contribute to increased nuisance to the neighbours or to robberies or vandalism, which again increases the consumption of resources. Problems related to an insufficient delimitation of specific areas, e.g. for construction vehicle maintenance, or to space availability are also identified as factors that contribute to impacts such as ‘Dumping derived from the use and maintenance of construction machinery’, or ‘Land occupancy by the building, provisional on-site facilities and storage areas’, respectively. However, it is not easy to deal with workplace factors. The conditions are inevitably difficult, given the constantly changing workplace and work activities that occur on the construction site (Haslam et al., 2005).

4.2.4. Material factors Material factors are similar to equipment factors. The Material factors category encompasses issues such as inadequate conditions, unsuitability of materials, and inappropriate use of materials, where ‘material’ is understood as any product stored on the construction site or used during the processes. The findings suggested that bad conditions of the material (due to expiry or damage) are a possible contributory factor. This could be related to inadequate storage, which may damage the material, or to inappropriate inventory management, leading to the existence of expired products on-site. Deficiencies in suitability included inappropriate characteristics of the material, i.e. high levels of contamination or packing and closure related aspects, and the use of material that does not conform to relevant regulations. Teixeira (2005) and Teixeira and Couto (2000) stated that although there are situations in which alternatives are available, e.g. vegetable and synthetic-based oils instead of fossil fuels, they are not in use in construction due to their significantly higher costs. In addition, the results revealed problems with the usability of products, including deficient handling and storage or excessive use during the performance of an activity. Material-related causal factors were considered to be present mostly in impacts associated with soil alteration, such as ‘Dumping derived from the use of paints and water resulting from the process of cleaning paint-related tools’ or ‘Dumping derived from the use of cleaning agents or surface-treatment liquid’. The atmospheric emissions of VOCs and CFCs associated with paints and varnishes may be higher due to the choice of highly polluting products or the excessive use of a product. The results also suggested that materials in bad condition may contribute to the increase in waste generation, due to the fact that they become unusable.

4.2.3. Equipment factors Causal factors related to insufficient maintenance, as well as the unsuitability and inappropriate use of equipment employed on-site are included in the Equipment factors category. In this case, ‘equipment’ refers to construction vehicles, machinery and tools located on-site. The results revealed that the maintenance level of equipment is an important aspect to take into consideration. Deficiencies in the condition of equipment were considered to have been present in environmental impacts such as dumping derived from the use of construction machinery (e.g. oil and fuel), the generation of greenhouse gases (as stated by Bennett and James (1999)), and the consumption of fuel, particularly in construction vehicles. The maintenance levels of the machinery may also affect the generation of noise or dust (e.g. cutting machines or hammers) or the consumption of water, due to leaks or inefficient closure systems. Problems with suitability seem to be related to inappropriate characteristics of the equipment, e.g. there are no dust extractors in cutting machines or the equipment does not conform to the relevant standards, directives or recommendations. Finally, findings also revealed causal factors associated with usability. This factor was found to be related to the increase in waste generation due to damage to the materials during operation or to the generation of dust by operators who drive construction vehicles too fast on-site. Another example is the increase of emissions, fuel

4.2.5. Worker factors Worker factors, in which a ‘worker’ is considered any site-based personnel, may also cause or exacerbate environmental impacts. Worker factors were judged to be potentially involved in most of the impacts. This is based on the fact that humans naturally make errors, and these unsafe acts dominate most incidents (Shappell and Wiegmann, 2001). Human error has been broadly studied in the literature on construction, in areas such as accidents (Reason, 1990; Haslam et al., 2005; Gibb et al., 2006), and quality defects (Atkinson, 1998, 2002). Nevertheless, the identification of worker factors is still a complex task. The following Worker factors were identified: incorrect performance of an activity; workers’ physical limitations that might hinder the performance of an activity; and a lack of information or communication during the process. Deficiencies in the performance of an activity included errors such as the incorrect storage of special agents leading to possible dumping, or the inappropriate operation of construction vehicles by leaving the engine running, which contributes to atmospheric emissions, noise generation and fuel consumption. Workers’ physical limitations (auditory, visual and mobility) were associated with instances in which operational requirements exceed the capabilities of the individuals or when workers’ limitations prevent them from understanding or being aware of an impact. Finally, it was considered that training is not always enough to prevent incidents, if the information required to carry out the process is lacking. For example, a worker in charge of the digging machine is trained to operate the equipment correctly but he is not aware of the existence of underground pipes. This could lead to sanitary water spilling onto the floor.

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Although worker factors were only broadly defined and might need further research, the findings revealed the importance of environmental awareness, training, information and communication among construction site workers, as a preventive measure to reduce environmental impacts. 4.3. Validation of the Environmental Impact Causal Model Construction management models have been identified as being difficult to validate in a real context due to the complexity and cost of the majority of construction projects (East et al., 2008). The literature suggests alternative methods to demonstrate the validity of a causal model within the built environment. Gibb et al. (2006) and Sun and Meng (2009) suggested the comparison of the developed model to other existing models. Other authors such as Haslam et al. (2005), Georgiou (2010), and Gambatese et al. (2008) validated the model by mapping its categories against a set of real incidents. Moreover, Shappell and Wiegmann (2001) proposed a set of criteria which ensure that the causal model had utility in an operational context, i.e. as an incident investigation and data analysis tool.

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Based on Shappell and Wiegmann (2001), the content, face, and construct validity were assessed to demonstrate the comprehensiveness, reliability, usability, and diagnosticity of the Environmental Impact Causal Model. Content validity relates to the comprehensiveness of the model and is aimed at determining whether the internal classification system covers a representative sample of the domain. Face validity refers to whether the model looks reasonable and valid to its potential final users, and is aimed at demonstrating the usability of the model. Construct validity refers to the extent to which evidence indicates that the model is useful in a scientific field, and it relates to diagnosticity. Finally, the study of reliability is aimed at assessing the level of agreement among the users of the model. 4.3.1. Comprehensiveness In the context of the research, comprehensiveness refers to the extent to which the causal model can cover all the main categories and issues associated with the causal factors that contribute to the occurrence of construction environmental impacts (Shappell and Wiegmann, 2001). It was demonstrated by mapping its categories and subcategories onto more than one hundred environmental

Table 4 Example of the contribution of the Equipment factors and the material factors to the environmental impacts included in the Environmental Impact Causal Model. F.2 equipment factors F2.1.1 Atmospheric emissions Water emissions

Waste generation

Soil alteration

Resource consumption

Local issues

Transport issues Effects on biodiversity

Incidents, accidents and potential emergency situations

Number of impacts in EICM in which involved Proportion of impacts in EICM in which involveda Number of real incidents in which involved Proportion of real incidents in which involvedb a b

AE-1 AE-2 WE-1 WE-2 WE-3 WG-1 WG-2 WG-3 WG-4 WG-5 SA-1 SA-2 SA-3 SA-4 SA-5 SA-6 SA-7 SA-8 SA-9 RC-1 RC-2 RC-3 RC-4 L-1 L-2 L-3 L-4 L-5 L-6 T-1 T-2 B-1 B-2 B-3 B-4 B-5 AC-1 AC-2 AC-3

F2.2.1

F.3 material factors F2.2.2

F2.3.1

F3.1.1

1 (1)

1 1 (12) 1

1 (4)

1 (1)

F3.2.1

F3.2.2

F3.3.1

1

1

1

1 (1) 1 (1) 1

1 1 1 1 1

1 1

1 1

1

1 1

1 (1) 1

1 (1) 1 (2) 1

1 (2) 1 (2)

1 1 1

1

1

1 (1)

1

5 13% (9) (8%)

6 15% (1) (1%)

Based on the 39 environmental impacts included in the Environmental Impact Causal Model. Based on the 106 environmental incidences used in the validation.

1 1

1

3 8% (0) (0%)

1 (1) 1 (10) 1 1

1 (1)

1

1 1 (5)

1 1 (2) 1 17 41% (34) (32%)

4 10% (3) (3%)

4 10% (0) (0%)

5 13% (0) (0%)

1 10 26% (1) (1%)

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incidents from residential building projects recorded in a year by five different Spanish construction companies. The sampling method was defined to achieve a spread of incidents across the main environmental impact categories included in the causal model. Incidents had been reported individually by the on-site supervisor of each company and they were often rich in detail. The set of incidents were reviewed in-depth by the authors of this study through an accident-specific approach (Haslam et al., 2005), i.e. an investigation of paths of causality in individual incidents. An analysis of the causal factors involved in each incident was performed, and based on the researchers’ judgement, they were systematically matched with the model categories. In case of confusion, the research team made direct inquiries, where possible, to the stakeholders who were associated with the incident. Table 3 shows between brackets the number of environmental incidents investigated that were caused, or their effects exacerbated, by the causal factors in the table. The number of times that these factors were related to the occurrence of the impacts during the development of the fault tree diagrams is also illustrated in Table 3. Similarly, Table 4 illustrates, by means of two examples, the relationship of the causal factors to each environmental impact included in the model. The number of environmental incidents investigated that were caused by an Equipment factor or Material factor are illustrated between brackets and related to each impact. Table 4 also shows the number of times that these particular factors were related to the impacts in the fault tree diagrams. A comparison of both columns in Table 3 shows that the categories of the causal model could account for all the causal factors related to the 106 environmental incidents. Thus, none of the factors were left unaccounted. Moreover, the results revealed that there were no common causal factors for all the incidents, so no unnecessary categories were identified. Finally, although eight causal factors in the model were not identified during the incident analysis, the systematic analysis of causal factors by means of the fault tree diagrams did justify their role. Overall, the comprehensiveness of the model was demonstrated, suggesting that it was robust and its categories were complete. 4.3.2. Reliability Reliability was demonstrated by means of an inter-rater agreement test, based on Cohen’s Kappa index. Ten face-to-face structured interviews were undertaken with ten project managers who had over 10 years’ experience in construction project management and construction work supervision. Interviewees were asked to analyse 20 environmental incidents, randomly chosen from the initial set of 106, and categorise the causal factors using the model. Table 5 illustrates the inter-rater reliability index obtained at the end of the test, which indicates the degree of agreement among all interviewees. With a Kappa index value of 0.783, between 0.61 and 0.80, the results revealed that there was substantial agreement among raters (Landis and Koch, 1977). Thus, future results obtained using the model would be reliable and consistent across users. 4.3.3. Usability The usability of the causal model was demonstrated by assessing how the framework supported the categorisation of causal factors of environmental impacts and by feedback from the Table 5 Summary of the reliability test. Incidents

Raters

Cohen’s Kappa index

SE (k)

Range (95% confidence interval)

Level of agreement

20

10

0.783

0.031

0.845e0.721

Substantial agreement

potential beneficiaries of the model (Hollnagel, 1998; Shappell and Wiegmann, 2001). During the reliability test, we supervised participants’ categorisation of the 20 incidents. No major problems were observed and participants needed 3 min on average to map the causal factors of each incident in the model. At the end of the previous reliability test, the ten domain experts were asked about the perceived usability and relevance of the model. According to the interviewees, the practicality and degree of acceptance of the overall framework of the causal model was positively perceived. 4.3.4. Diagnosticity Diagnosticity is defined as the ability of a framework to identify relationships between errors and to penetrate all levels of the system in such a way that previously unforeseen accident trends or causes are revealed (Shappell and Wiegmann, 2001). The internal framework of the causal model was built on 39 environmental impacts related to 220 building construction processes. Moreover, 178 causal relationships, classified into three typologies, were defined among the set of impacts. In addition to the causal relationships among impacts, 45 causal factors were identified and classified in three hierarchical levels. Furthermore, more than 200 causal relationships were identified during the development of the environmental impacts causal chains for each construction process. By means of the complex causal network of causal factors and environmental impacts, the diagnosticity of the model was considered to be guaranteed. 5. Discussion of the results Through the development of the construction-related Environmental Impact Causal Model, this research has identified the possible immediate circumstances and potential on-site factors involved in significant environmental impacts of construction processes in building projects. Firstly, the results suggested that construction-related environmental impacts broadly arise from the interaction between workplace, equipment, material, worker and task factors, giving rise to different immediate impact circumstances in each process undertaken during the construction phase. This indicates the process-dependency of the causal factors and impacts. Secondly, an integrated analysis of the set of significant construction-related environmental impacts indicated the existence of 178 causal relationships. In particular, 93 causal relationships were identified that consisted of an impact that may cause or exacerbate another impact, or may produce incremental changes to itself. In 70 situations, corrective measures implemented to reduce or resolve the consequences of an impact could cause or exacerbate another impact. And finally, the results suggested that there were 15 causal relationships consisting of an impact that, combined with particular contextual conditions, could cause or exacerbate another impact. Thirdly, findings from the fault tree diagrams revealed a complex environmental impact causal network consisting of 45 causal factors and over 200 causal relationships. In particular, the results indicated that Task factors were associated with impacts that occurred during the normal operation of the construction processes. If we accept the multiple involvement of factors per impact, the Task factors were considered to be involved in 151 per cent of the 39 significant environmental impacts. Therefore, these factors not only contribute to most of the impacts, but they are also involved in multiple possible immediate circumstances leading to the same impact. Consequently, the prevention or control of these factors could significantly contribute to the reduction of associated impacts by decreasing the probability of their occurrence or the exacerbation of their consequences. Among the Task factor

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subcategories, Material factors, i.e. the use of materials on-site, were identified as the main contributors in normal operating conditions, with a contribution of 44 per cent. They were followed by Equipment factors, with 28 per cent involvement. It was also observed that there are a considerable number of opportunities for the reduction of the environmental impact consequences by eliminating the immediate circumstances that contribute to their exacerbation. The results indicated that Workplace factors were categorised as most involved in the causation or exacerbation of impacts. They were shown to be responsible for up to 272 per cent of impacts: Site conditions factors (82 per cent), Outdoor environmental factors (110 per cent) and Site layout factors (80 per cent). Consequently, these findings suggested that aspects such as the occurrence of rain, high temperatures or wind should be taken into consideration in decisions about the daily management of activities. However, meteorological conditions are sometimes difficult to predict and changes to the construction plan may have considerable financial consequences, which companies may not accept. Nevertheless, more attention may need to be paid to the definition of the construction site layout during the preconstruction stage. In particular, it should be taken into account that the inappropriate location of construction elements or activities on-site is responsible for 49 per cent of the impacts. Worker factors were categorised as having the second highest involvement in the exacerbation of impacts (110 per cent). Therefore, it seems that construction companies should focus on environmental training to reduce the impact of activities that involve the workforce. Equipment factors were ranked in third place on the list, contributing to 77 per cent of the impacts. Within this category, the inappropriate use of equipment accounted for 41 per cent of impacts, which could also be considered to be closely related to the Worker factors and the improvement of training programmes. This was followed by unsuitable equipment, which accounted for 23 per cent of impacts, and inappropriate maintenance conditions, which was rated with 13 per cent. Although more environmentally friendly alternative equipment is available, organisations may prefer not to use it, as they may not want to change procedures and may consider that the costs are higher. In these cases, more accurate, continuous maintenance of the equipment is a reasonable option. Finally, Material factors were identified in the last place, contributing 59 per cent to the environmental impacts. Similarly to Equipment factors, inappropriate use of material was the most relevant factor in this category (26 per cent). This highlights the importance of a robust training programme. Material suitability was identified as the next factor, accounting for 23 per cent, followed by material conditions, rated at 10 per cent.

element of site planning. This process involves the identification of the environmental aspects related to the on site construction activities and prioritising the most significant ones. A brainstorming session with the project team supported by an environmental aspects and impacts review matrix is the most common way of doing this in construction organisations. The matrix contains a list of common construction processes to be assessed against the environmental aspect categories identified for the construction industry. Despite the perceived effectiveness of this method, the environmental aspects are normally defined generically and disassociated with the elements of the site (e.g. construction plant, labour, material), which complicates the implementation of preventive, corrective and monitoring measures. In this regard, the proposed model improves the current method by providing a predefined detailed list of the on site causal factors that could lead to the environmental impacts associated to each construction process. Moreover, the original detailed analysis of the impacts, the causal factors as well as the causal relationships between them during the development of model has established the causal factors that are most likely to contribute to the environmental impacts. Practitioners can use this information together with other assessment criteria (e.g. spatial scale, severity or duration) to assess the significance of the aspects and impacts and prioritise those that require more attention. Focussing on the operational control phase, the model provides the environmental manager with the list of on site elements that should be measured and controlled to assess the effectiveness of the preventive measures implemented. In the event of an incident on the construction site which has had an impact on the environment, it is necessary to investigate the causes to find suitable corrective actions. In this regards, the challenge for incident investigators and analysts alike is how best to identify the causal factors of events. Besides the incident investigation, it is also important to record the details of this investigation to have evidence of how the incident occurred in case any legal actions must be initiated in the future. Moreover, systematic statistical analyses of the data recorded during the investigations could point out elements that require further attention. It is our belief that the model provides investigators, i.e. site managers or environmental management representatives, with a complete, comprehensive and structured framework for identifying and classifying the on site causal factors of environmental incidents. In particular, the model offers the investigators a refined list of possible causal factors for each impact and construction process involved. Therefore, the investigators can benefit from the model by adopting the common set of terminology of causal factors into the environmental incident/non-conformance forms used for both incident investigation and recording purposes.

6. Practical application of the model in construction organizations

7. Conclusions and reflections

The proposed Environmental Impact Causal Model is intended to support the day-to-day person responsible for environmental issues, i.e. the environmental management representative and site manager, to identify the causes that are likely to lead to impacts or to exacerbate their consequences. In the context of a construction company which is considering the development of an EMS or wants to improve an existing EMS, the model supports the environmental management representative to (i) identify the aspects and associated impacts related to the construction processes and prioritise the aspects to be addressed; and (ii) to improve the investigation and recording of environmental incidents. As suggested by the literature review, the acknowledgement of the environmental aspects that could lead to impacts is a key

This article has sought to develop an Environmental Impact Causal Model for supporting construction organizations to reduce the environmental impacts related to their construction processes by identifying the causes that are likely to lead to impacts or to exacerbate their consequences. The proposed model offers a complex and robust process-oriented causal network consisting of construction processes, environmental impacts, causal factors and their causal relationships. It is expected that the model will help the person responsible for environmental issues on the construction sites and other decision-makers investigating where and how impacts arise. Rather than replacing management involvement in decision-making, the model aims to complement environmental managerial decisions, mostly related to the identification and assessment of the environmental aspects

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related to the construction processes, the definition of the environmental performance control and measurement strategy and the investigation and recording of the environmental incidents occurring on site. The research results have also suggested that there are some opportunities for improvement, to achieve better environmental performance levels for construction projects and reduce impacts on-site. Some of these should be taken into consideration not only by contractors, but also by suppliers in the construction industry. They revolve around the following issues: - There are several immediate circumstances that could lead to the exacerbation of the consequences of impacts related to the construction processes. More importance should be given to the identification and control of these exacerbating factors to reduce the consequences of the impacts. - The prediction of meteorological events, such as high temperatures, rain or winds, can also contribute to the reduction of environmental impacts by supporting proactive decisionmaking. - Special attention should be paid to site layout and on-site warning sign-related issues to reduce or prevent those impacts derived from the interaction of construction vehicles or machines and material storage areas, among others. - Where environmental incidents depend on workers’ performance, it is important that a robust training and awareness programme is established on site. Information regarding materials, including on-site reception, storage, handling and waste classification procedures is necessary to increase the environmental awareness of employees. Similar information should be given concerning the maintenance and handling of construction vehicles. - More considerations should be taken into account in relation to the selection of construction equipment. In some cases, environmentally friendly alternatives are available, but they are not employed by organisations due to habit, cost or availability. For example, low consumption and carbon emission vehicles, low noise generation machines and equipment with auto start-stop engine systems or automatic shut off valves should preferentially be selected. - Continuous, complete control of the maintenance of equipment on site is important to carry out, as several impacts are directly related to equipment condition. For example, impacts such as noise generation, carbon emissions, water consumption, etc. are exacerbated by deficient maintenance of the construction equipment. - Greater attention should be paid to the selection of materials, with special consideration of environmental aspects, rather than economic issues only. This concerns aspects such as contamination levels, material packaging or the material receptacle. - Much importance should be given to the implementation of procedures for the investigation of environmental incidents, not only by contractors but also by the regulatory bodies. Contributing factors could be revealed that support the implementation of a proactive EMS in future projects. Therefore, one key benefit of the current study is that it has highlighted priority areas for further work. These areas could be examined in detail, starting with the most highly rated factors, such as workplace factors including the influence of the construction site layout on the environmental performance, and worker factors including the impact of training programmes and communication methods on the reduction of incidents. Finally, due to the consistency among some of the model’s causal factors and those of other

causal models used in health and safety and quality management, the development of an integrated causal model could also be considered.

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