Application of Prevention through Design (PtD) to improve the safety of solar installations on small buildings

Safety Science 125 (2020) 104633

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Application of Prevention through Design (PtD) to improve the safety of solar installations on small buildings

T

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Chung Hoa, Hyun Woo Leea, , John A. Gambateseb a b

Department of Construction Management, University of Washington, Architectural Hall 120, Campus Box 351610, Seattle, WA 98195, USA School of Civil and Construction Engineering, Oregon State University, 201B Kearney Hall, Corvallis, OR 97331, USA

A R T I C LE I N FO

A B S T R A C T

Keywords: Solar installations Construction safety Prevention through Design Small buildings

As a viable, clean and renewable energy resource, solar energy has gained a significant interest in the US residential sector. Most solar systems are installed on rooftops to take advantage of available space and reduce land use. However, this installation environment also exposes workers to unique safety hazards related to existing roof conditions such as slippery roofing materials, irregular roof layouts, and steep roof slopes. Although Prevention through Design (PtD) has been widely considered as an effective way to address safety issues during the design phase, little to no studies have applied PtD to improve safety in solar energy installations. To fill this knowledge gap, this research aimed to investigate how, during the design phase, to address the safety concerns of solar workers when installing solar energy systems on residential buildings. Through a series of interviews, four case studies, and a seminar, seven solar PtD attributes were identified: roofing materials, roof slopes, roof accessories, panel layouts, fall protection systems, lifting methods and electrical systems. Based on the attributes, a PtD protocol was developed that can serve as guidance for implementing PtD in solar installations. This paper presents the research activities and findings, and feedback gained from solar contractors through a seminar on the study. The study is expected to contribute to reducing safety hazards by implementing PtD, help improve safety performance in solar installations on small residential buildings and support the promotion of safety in sustainable construction.

1. Introduction Solar energy has received considerable interest from the public as a viable, efficient, clean and renewable energy source. Solar capacity has experienced an exponential growth globally (REN21, 2017). In 2015, the US residential solar sector achieved larger than 50% annual growth for a fourth consecutive year (STM/SEIA, 2016). Most solar installations take place on the rooftops of existing houses and are carried out by small- to mid-sized contractors. These conditions expose workers to unique safety hazards in terms of existing conditions and panel installations. Although many studies have recommended using Prevention through Design (PtD) as a proactive safety intervention in the design process to eliminate safety hazards, little to no studies have attempted to determine how PtD could be applied to improve safety during solar installations. To bridge this knowledge gap, this study aims to investigate how, during the design process, to address safety concerns of solar workers during the installation of solar systems on small buildings. The study was conducted using a series of interviews with solar installers in the Pacific Northwest, four in-depth case studies, and

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a seminar. The research occurred from August 2016 to July 2017 and the final report is available from the Center for Construction Research and Training (Lee et al., 2018). The main study outcome consists of solar PtD attributes and a solar PtD protocol that small solar contractors can apply to improve their safety practices. This paper presents the activities and findings of the study and is an extended version of Ho et al. (2018). The structure of this paper includes: a literature review about PtD and safety in solar installations; a description of the research methodology; a summary of the research findings; and the conclusions that can be derived from the study. The study results are expected to contribute to reducing safety hazards by implementing PtD and improving safety performance in solar installations on small residential buildings. 2. Literature review 2.1. Solar installation labor and safety Solar installation in the US has increased significantly in recent

Corresponding author. E-mail addresses: [email protected] (H.W. Lee), [email protected] (J.A. Gambatese).

https://doi.org/10.1016/j.ssci.2020.104633 Received 31 March 2019; Received in revised form 2 January 2020; Accepted 22 January 2020 0925-7535/ © 2020 Elsevier Ltd. All rights reserved.

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installers during the design process. Bucher (1998) carried out a study about photovoltaic modules and suggested that solar module safety documents need to include testing information such as insulation tests, glass breakage tests, edge sharpness tests, wet leakage current tests, etc. Nonetheless, the impacts of roof conditions on solar installation safety were not addressed in the study. Although no study addressing safety from the solar design process has been found, attention has been paid to potential hazards created by solar energy systems for fire fighters when fighting fires on buildings. Studies on this aspect have led to specific requirements about the clearance between solar panels and roof edges. While aiming to assist fire fighters, these requirements can also positively impact safety of solar installers by providing more space for workers to move around on the roof. A study by Kreis (2009) identified potential hazards associated with solar systems for fire fighters during firefighting, including:

years. As of 2015, the residential solar sector had gained more than 50% annual growth for a fourth consecutive year (GTM/SEIA, 2016). The State of California alone reported that over half a million homes had solar systems installed in 2012, and with its Million Solar Roofs Initiative, California aims to reach the target of a million homes with solar installed by 2020. The increased utilization of solar energy also creates new business opportunities and generates more jobs for the labor market. According to the Solar Energy Industries Association (SEIA, 2018a,b), California stands as the leading solar market in the US with more than 2840 solar companies, providing jobs for 86,414 people. Even in Washington State where the weather is not as favorable for solar energy generation, the numbers are still high with 168 solar companies and 3433 workers. While the proliferation of the solar industry indicates positive impacts for the environment and society, its labor intensiveness also raises a concern about the safety of workers involved through the lifecycle of solar systems. Solar energy installations have a high labor usage in comparison with other energy jobs. Wei et al. (2010) reviewed 15 studies about potential jobs created by renewable energy, energy efficiency, low carbon sources, and nuclear power. Wei’s research found that solar photovoltaic (PV) energy is job intensive with more jobs created per year per gigawatt hour (GWh) of electricity in comparison with other energy technologies. PV technology can create up to 1.42 job-years while job creation is 1.05 job-years for landfill gas, 0.26 for wind energy, and 0.11 for natural gas. Pollin’s study (2009) also found that solar energy generation can create 5.5 direct jobs per million dollars of output, while this value is only 1.9 for coal generation, and 0.8 for oil and gas generation. The high labor usage for solar energy means that many workers are involved in the supply chain of the solar industry. This characteristic is obvious for solar installations since the work is normally done manually and highly depends on varying roof and weather conditions. Because of the often-limited amount of convenient and available space that is exposed to the sun without shading, most solar installations are expected to take place on the rooftops of existing houses, forcing workers to be exposed to safety concerns associated with existing roof conditions. A report from the US Bureau of Labor Statistics about Green Jobs (Hamilton, 2011) indicates that safety is a priority consideration during the installation of solar energy systems. Caution is needed during the installation because solar panels are heavy, fragile, and expensive to replace if broken. Information about the impact of varying roof conditions on safety during solar installations was revealed from an interview with a solar contractor (Torpey, 2009). According to the interviewee, the roof must be strong enough to be able to accommodate the installation of solar panels. If the roof is not strong enough, reinforcement would be needed. Many solar installations occur on pitched roofs or on loose or fragile roof materials, both creating a high risk of falling. Special precautions are required when working on the roof. Solar contractors must use safety equipment such as guardrails or personal fall arrest systems. However, safety equipment may not be very effective in mitigating hazardous outdoor conditions. Hot days or cold days can create unique hazards such as glare, heat stroke, frost nip or slippery surfaces. In addition, solar installations often require heavy lifting; each solar panel weighs 30–40 pounds, and batteries used in solar systems can weigh more. Previous studies have provided instructions about safety practices for solar installations. Guidance on safety for solar construction which complies with the Occupational Safety and Health Administration (OSHA) standards and considers unique conditions of solar energy installations was published by the Oregon Solar Energy Industries Association (OSEIA, 2012). Information about solar safety is also included in guidance for solar electric system design, operations, and installations issued by the Extension Energy Program of Washington State University (WSUEEP, 2013). However, the authors have found no studies that have investigated how to reduce safety hazards for solar

▪ Energy stored in solar panels that cannot be turned off. ▪ Breaking of the glass protecting solar panels may cause electrical shocks. ▪ Cutting through the solar system batteries and fires on solar panels may release toxic fumes. ▪ Additional load due to solar panels may affect roof performance. ▪ Solar systems may make it difficult to access the roof. Similarly, according to Paiss (2009), the primary hazards for fire fighters are electrical shocks and trips caused by stepping on conduit. Solar panels are still energized by the sun even if the alternating current (AC) has been cut off when shutting down the inverter. Although the influence of solar systems on the fire fighters is out of the scope of this research, the regulations regarding a clear access pathway and the clearance between panel edge and roof ridge can contribute to improving safety in solar installations and are included in the PtD protocol developed in this study. 2.2. The concept and applications of prevention through design Prevention through Design (PtD), as defined by Schulte (2008), is “The practice of anticipating and “designing out” potential occupational safety and health hazards and risks associated with new processes, structures, equipment, or tools, and organizing work, such that it takes into consideration the construction, maintenance, decommissioning, and disposal/recycling of waste material, and recognizing the business and social benefits of doing so.” PtD includes all efforts to recognize and design out working hazards, ranging from working methods to the permanent facility, equipment, tools, materials and technologies. In 2007, NIOSH launched its PtD initiative, aiming to make it a standard practice to design out occupational hazards. Up to 2014, over 25 industry standards have included PtD (NIOSH, 2014). In a PtD workshop sponsored by NIOSH to study opportunities to incorporate PtD into social and business units, four areas of focus were identified: research, education, policy and practice. With respect to further understanding PtD and its impacts, the workshop participants agreed that the acceptance and implementation of PtD in various industry sectors cannot happen without a continued effort in research and dissemination (Gambatese, 2008). To facilitate and encourage PtD dissemination, the workshop participants focusing on the education functional area recommended including PtD instructions at the secondary school level and a workforce education and training event (Mann, 2008). The education should include both formal and informal teaching, as well as practical training. Those workshop attendees who focused on the policy functional area for PtD discussed initiatives to implement PtD in organizations and suggested establishing a broad alliance that advances the goals and initiatives of national strategies about PtD (Howe, 2008). Lastly, with respect to PtD in practice, the attendees recognized that one way to integrate PtD in different organizations is to develop guidance for PtD integration through standard 2

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2.3. Safety in green jobs

procedures and checklists (Lin, 2008). Many research studies described in the literature also investigated different aspects of PtD. Albattah (2013) utilized data from previous research to develop and test a web-based PtD tool for the design and construction of sustainable buildings. Doan (2016) discussed the outcome of the 2016 IEEE Industry Application Society Electrical Safety Workshop with many discussions addressing PtD for electrical systems. Manuele (2008) provided guidance on how to incorporate occupational risks into design and redesign processes to eliminate, reduce, and control occupational risks. The study covers the lifecycle of facilities, materials, equipment and processes. Anderson (2014) identified benefits of PtD and the process to implement PtD. In the study, Anderson confirmed that PtD can minimize risks by eliminating the hazards before they occur on the site and can reduce costs by minimizing injuries and claims. It is critical that safety personnel participate early in the design process to integrate PtD practices. Gangolells (2010) developed a quantitative method to support designers in implementing PtD by using a risk analysis-based approach to evaluate the safety-related performance of design. This method ranks the significance of the risks in design features and compares overall risks of the design. Lyon (2016) also presented a PtD risk assessment tool to support decision making during design processes. Specifically addressing educational issues, Lopez-Arquillos (2015) investigated how PtD is taught in engineering and architecture programs in Spain by carrying out a survey of 454 engineering and architecture students, focusing on concrete construction. The study indicated a lack of education about PtD in these courses and suggested an enormous improvement in the understanding and implementation of PtD is needed. Regarding policies, Toole (2016) claimed that PtD needs to be addressed not only in environmental and economic sustainability, but also in social sustainability aspects. Research is needed that studies how to educate owners and designers about PtD applications, which design tools are effective, and how owners can avoid incurring inappropriate liability for designers when requiring PtD. Regarding practices, Hallowell (2016) used site observations and interviews to measure the extent that hazards can be recognized during the design, the skill of designers in recognizing the hazards, and the extent that the hazard recognition skill in design can be improved through training. The results of the experiment revealed that approximately 25% of all hazards are latent in design. For patent hazards, the average hazard recognition skill of designers is 51%, and hazard recognition by designers with construction field experience is 45% higher than for designers without field experience. Regarding how to apply PtD to construction, especially roof construction, Young-Corbett (2014) investigated the application of PtD in the design of tools, equipment, and installation methods for asphalt roofs to reduce safety hazards. There are safety hazards caused by toxic fumes emitted from heating asphalt materials, and from hot work processes. Young-Corbett’s study suggested applying PtD to minimize these hazards. Research by Rajendran and Gambatese (2016) is the most relevant to the scope of the present study. Their research focused on the financial impacts and risks of roof fall protection solutions through a case study. The costs for design and installation of roof anchors and a parapet were compared with those of other design options on the same project. The research results indicated that it is more expensive, but safer to install a parapet system than install a roof anchor system. The roof anchor system requires additional temporary fall protection measures during construction, leading to more exposure to safety hazards and higher risk for workers. Nevertheless, there has been no study specifically aimed at addressing the application of PtD to improve safety in solar installations. The present study is expected to bridge this knowledge gap and make a valuable contribution to the effort in reducing safety hazards in solar installations.

Solar installation is one of the green jobs that have become a new tide in all economic sectors. Green jobs contribute to reducing environmental impacts and preserving the environment for future generations by reducing resource consumptions, emissions, and wastes. However, the prevalence and growth in green jobs does not necessarily mean that they are performed safely. Regardless of the “color” of the job, work generates hazards and always contains risks. A number of key technologies associated with green jobs, such as wind energy, solar energy, bioenergy, carbon capture and storage, battery technology, and electricity transmission, could lead to new and emerging risks to occupational health and safety (EU-OSHA, 2011). In other words, workers performing green jobs are faced with not only hazards that are common in traditional workplaces, but also new hazards that have not been identified previously (Bello, 2010; ILO, 2012). For example, the installation of rooftop solar systems poses traditional construction hazards such as falling from heights, confined space, and electrocution, as well as new hazards such as exposure to carcinogens or toxic fumes from burning solar panels in a fire (ILO, 2012). Similarly, the installation of wind turbines generates safety hazards such as working from high elevations, falling materials and equipment, exposure to electrical circuits, and lifting heavy objects (Adem et al., 2018). As a way to mitigate safety hazards in maintaining offshore wind turbines, Mentes and Turan (2018) proposed a resilient risk management model focusing on human and organizational factors through four focus areas: responding, monitoring, anticipating and learning. An ANSI/ASSP standard (2018) also establishes minimum requirements to protect workers from safety hazards when working on wind generation and turbine facilities. The opportunities created by the growing trend of green buildings as well as the threat that the trend poses to workers in term of safety hazards are also discussed by Chen (2010). The report claims that green construction causes an increased risk of existing occupational hazards including falls, ergonomics, strains, punctures, slips, and heat stress. The report suggests that a green job should “Contribute significantly to preserving or enhancing environmental quality; be economically sustainable (e.g., the job should pay a living wage, include benefits, and provide avenues for career advancement); promote the health and safety of workers; and never compromise the health and safety of surrounding communities.” To enhance safety in green construction, a set of actions are recommended including incorporating worker health in the debates about green jobs, promoting the application of Prevention through Design, incorporating safety into green building certification programs, and promoting training about construction safety. The concept of PtD as a solution for safety improvement in green jobs has been addressed in previous studies, including studies for skyline greenery in Singapore (Behm and Poh, 2012) and for green vegetated roof in the U.S. (Behm, 2012). However, PtD is still not widely utilized in sustainable construction. Karakhan and Gambatese (2017) investigated the perception in the construction industry about adopting Prevention through Design into sustainable design and construction. The study revealed a resistance in construction industry professionals to incorporate PtD into sustainable projects. This resistance comes from a fear of liability, contractual issues, and a lack of safety knowledge. Hence, the present research on application of PtD to improve safety in solar installations could contribute to the effort to enhance occupational safety in green jobs. 3. Research methodology This research focused on contextual data from actual solar projects and people who are involved directly in the design and installation of solar systems. The contextual data aimed at supporting the identification of: (1) safety risks and hazards associated with roof conditions and solar system characteristics; and (2) solar PtD attributes. The 3

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installation processes of solar contractors are similar in general, and include: (1) receiving interest from a homeowner to buy a solar system; (2) performing a site assessment to determine the feasibility of the intended solar system; (3) designing the solar system; (4) executing the installation; and (5) requesting an inspection and whether the owner can start using the solar system if it passes the inspection. However, safety performance and the perspective about safety varied from contractor to contractor. Although all solar contractors acknowledged the importance of following safety rules for solar installation and many followed them strictly, some solar contractors still sacrificed certain safety rules to reduce labor hours and increase the installed area for solar modules. When the researchers suggested the application of PtD to improve safety in solar installations, most of the solar contractors expressed an interest, some were neutral with no interest or objection, and a few suggested focusing on enforcement of current safety regulations rather than PtD. Although attitudes toward the solar PtD concept also varied between the solar contractors, most of the contractors expected positive impacts of PtD on the safety of solar installers.

researchers used a mixed-methods approach that incorporated experiential data from interviews with solar contractors and observational data from solar case study projects. The following are the specific tasks conducted for the study: ▪ Task 1: Investigate safety management practices in solar design and installation ▪ Task 2: Identify PtD attributes of solar systems ▪ Task 3: Analyze PtD attributes through case study projects ▪ Task 4: Develop a PtD protocol for solar design and installation ▪ Task 5: Obtain industry feedback regarding the PtD protocol The detailed process and accomplishments of each task are described hereinafter. Task 1: Investigate safety management practices in solar design and installation This task involved determining the current design and installation practices of solar contractors when working on small buildings. To accomplish this task, the research team conducted interviews with solar contractors, targeting small businesses in the Pacific Northwest region that are experienced in solar design and installation. Given the research setting and high level of knowledge required, the team mimicked purposeful sampling for the interview efforts. The purposeful sampling method is widely used in qualitative research by focusing on suitable cases with rich information where available resources are limited (Patton, 2014). The process started with developing a list of 40 solar professionals and contractors through our professional connections and online search for solar contractors in Washington. Then, companies that are located within a 2-hour drive from Seattle, WA were contacted for interviews and site visits based on their accessibility. In addition, the research team participated in a solar workshop in Washington State, called Washington Solar Summit 2016, to learn more about current practices in the solar industry and to seek more interview opportunities. As a result, a total of 13 interviews were conducted with 16 solar professionals, including solar designers, salespersons, site managers, electricians, and field workers. The interview questions focused on the current solar design and installation process, safety planning for solar installations, and factors considered during solar design and construction. The research team asked the interviewees to describe how existing roof conditions and solar panel characteristics can make installations hazardous, and to help identify a list of parameters that should be considered to mitigate potential hazards during field operations. Table 1 lists the interviews conducted for this study. After finishing the interviews, a cross-content analysis was performed to compare different practices and perspectives of the interviewed contractors. The interview results revealed that the design and

Task 2: Identify PtD attributes of solar systems Based on the information captured from Task 1, Task 2 involved categorizing primary attributes that should be considered while implementing PtD. First, a comprehensive list of attributes was developed based on the data obtained during Task 1. These attributes include: roofing materials, roof slope, roof accessories, panel layout, fall protection system, lifting methods and electrical system. Second, to augment the extensiveness of the identified attributes, the research team investigated the types and nature of previous accidents that occurred in the solar industry in the past 10 years by using the publicly available databases provided by OSHA (Occupational Safety and Health Administration) and NIOSH (National Institute for Occupational Safety and Health). This investigation resulted in identifying a series of potential risks such as falling from roof, falling from ladder, falling through roof opening, objects falling from roof, electric shock, being struck by falling objects, tripping, and slipping. These causes of injury/ fatality were used to analyze the case studies performed in the next task. Task 3: Analyze PtD attributes through case study projects Task 3 entailed analyzing the applicability and significance of the developed attributes through investigating case study projects performed by small-business solar contractors. Four solar projects in Washington State were selected to study. These projects represented the roof conditions, roof features, and solar panel characteristics of typical single-family houses in Washington. Fig. 1 shows satellite photos of the houses and Table 2 summarizes the characteristics of the case studies. Both Case Study Projects 1 and 2 are single-story houses with gable roofs and dormers. These houses are located next to each other and the solar installations were performed by one solar contractor at the same time, but by two separate installation teams. The houses have a composite roof with a slope of 25–27 degrees, which is common in Washington State. The solar panels were placed on the south-west-facing portions of the roofs. It took 4 days for the solar workers to install the solar systems on these houses. The third and fourth case studies are located in different areas in Washington and were completed by two different contractors. Case Study Project 3 is a two-story house with a crossed gable roof and dormer. It has a composite roof with a slope of 30–35 degrees. The solar panels were installed on the south-facing and west-facing portions of the roof. It took only 2 days to install the solar system on this house. Case Study Project 4 is a one-story house with a crossed gable roof. Similar to the other houses, it has a composite roof with a roof slope of approximately 30 degrees. The solar energy system on this house comprised of two solar arrays, both located on the south-facing portion

Table 1 Interview list. No.

Number of interviewees

Interviewee's position

Interview date

1 2 3 4 5 6 7 8 9 10 11 12 13

1 1 1 1 1 1 2 3 1 1 1 1 1

Project Engineer Company's Founder, Designer Project Engineer President, Design Manager Sales Associate Vice President, Sales Sales Engineers Electrician, Roof Workers Roof Worker Site Manager Electrician Site Manager Project Manager

24-Sep-16 14-Oct-16 30-Sep-16 14-Oct-16 26-Oct-16 21-Oct-16 9-Nov-16 18-Nov-16 23-Nov-16 23-Nov-16 2-Dec-16 2-Dec-16 19-Jan-17

4

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Project 2 Project 1

(a)

Project 4

Project 3 (c)

(b)

Fig. 1. Aerial views of case study project houses: (a) Projects 1 and 2, (b) Project 3, and (c) Project 4 (Google Map, 2017).

task was a seminar that the researchers organized in Seattle, WA in May 2017 to introduce the PtD concept, present the PtD protocol, and gather feedback from solar contractors. During this task, the research team sent out a survey to the 40 solar professionals and contractors who were contacted during Task 1 and throughout the research process, asking them to review the PtD protocol and provide feedback. The researchers received seven responses out of 40 online survey requests (17.5%). The overall feedback about the importance of the protocol was positive. A part of the survey asked the solar contractors to provide their opinion regarding whether the solar PtD protocol is practical, sufficient, and important based on a 1–5 Likert scale (1 = Strongly Disagree; 5 = Strongly Agree). An analysis of the responses revealed that the average level of agreement for each question in this section was equal to or higher than 4.0, equivalent to “Agree” and “Strongly Agree”. While the sample size is low, given the lack of accessibility to the industry, the team believes that from the perspective of purposeful sampling, the survey results are still significantly valuable. The survey participants were experienced and knowledgeable about solar industry practices and safety, a necessary requirement to answer the research question. As part of the survey document, the researchers also obtained comments from the respondents regarding ways to improve the protocol. The recommended improvements included: the need to consider the national safety regulations versus those within the local jurisdiction; the need to include flat roof materials; the need to consider the influence of existing utility lines and trees on the safety of the workers; and the need to add more examples and pictures of different types of roofing. One participant expressed a concern about the limitation in ladder usage in which one local code requires that both hands must be free to hold on to the ladder while climbing. Feedback obtained from the survey and the seminar discussion was subsequently incorporated into the final version of the protocol.

of the roof. The installation time for the solar system on this house was 2 days. To evaluate the significance of each attribute with respect to safety, the researchers asked 13 workers from the case study projects to participate in a short survey to provide their opinions about the identified attributes. The workers were asked to evaluate the attributes with respect to their impact on safety, using a 1–5 Likert scale (1 = Strongly Disagree; 5 = Strongly Agree). For example, the survey participants were asked to indicate their level of agreement regarding whether the roof slope impacts safety when installing solar panels. Based on the survey responses, all attributes received mean responses higher than 3, ranging from 3.2 to 4.7. This result means that their opinions were “Neutral” to “Strongly Agree” that the attributes have an impact on safety. The level of agreement about impact on safety was the highest for roof slope and roof material, while there was less agreement that roof accessories, electrical system, and installation sequence have an impact on safety. Fig. 2 presents the results of the survey. Task 4: Develop a PtD protocol for solar design and installation The purpose of this task was to develop a PtD protocol that small businesses can apply to improve their safety practices. From this protocol, solar contractors can identify potential safety hazards based on various types of existing roof conditions and proactively eliminate them from the design of solar panel layouts and installation methods. The protocol was created based on the seven attributes that were verified through the case studies. The protocol comprises two main sections. The first section provides a brief explanation about the PtD concept and solar PtD implementation procedure. The second section describes the role of each PtD attribute in regard to safety in solar installations and how to incorporate these attributes into the design process for safe construction. Fig. 3 shows examples of some pages in the PtD protocol. Task 5: Obtain industry feedback regarding the PtD protocol

4. Results of the interviews and case studies

This task was carried out to validate the protocol’s applicability and identify improvement opportunities. The primary component of this

Following are discussions about the results obtained from the interviews and case studies. Table 3 summarizes the contents of the

Table 2 Case study characteristics. Case study

Con-tractor

Business type

Project location

Installation duration

Crew size (people)

No. of stories

Roof features

Solar panel location

1

A

Tacoma, WA

18–23, Nov-2016

5

1

Gable roof and dormer, composite tiles, 25–27° slope

South-west-facing roof

2

A

Tacoma, WA

17–23, Nov-2016

4

1

Gable roof and dormer, composite tiles, 25–27° slope

South-west-facing roof

3

B

Small, 16–20 employees Small, 16–20 employees Small, 5–10 employees

Seattle, WA

1–2,

4

2

Crossed gable roof and dormer, composite tiles, 30–35° slope

South-facing and westfacing roofs

4

C

Rochester, WA

Dec-2016 13–15, Mar-2017

4

1

Crossed gable roof, composite tiles, 30° slope

South-facing roof

Small, 5–10 employees

5

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Fig. 2. Level of agreement regarding impact of PtD attributes on safety, where 1 = Strongly Disagree and 5 = Strongly Agree (n = 13).

roof types such as shake roofs to gain more traction and avoid breaking roof tiles. Nonetheless, the special footwear could also hamper movements and cause other tripping hazards. In addition, solar contractors need to evaluate the strength of roof structures when performing site assessments. Reinforcement is required if roof structures are not strong enough to support solar systems. Since the lifespan of a typical solar system is approximately 25 years, roofing materials should last over that period. The homeowner should consider replacing roofing materials before installing solar systems if the materials are old because it is difficult to replace roofing materials after installing a solar system. All of the case study projects have roofs made of composite shingles, which are typical in Washington State and are less slippery than metal or wood roofs. In particular, composite shingles make it easier for the installation of mounting systems because to install a mounting system, roof tiles at connection locations need to be lifted up to insert connection plates. Composite shingles are thin and easy to lift compared to metal, concrete, and wood tiles which are thicker and heavier. The age of the roofing materials can also create a difference in safety. The composite shingles in Case Study 4 were newer than those in the other case studies. Newer shingles have more grains and are less slippery. Aged composite shingles tend to adhere to each other, making it harder to lift up the shingles to insert the connections for solar systems.

results. 4.1. Roofing materials Since a majority of solar installation activities take place on a rooftop, roofing materials play an important role in the safety of solar workers. Composite shingle roofs are most preferable since they are not very slippery, even under rainy conditions. Wood roofs, tile roofs, metal roofs, and older roofs that are losing granules are more slippery, especially when wet, making them more dangerous for the work crew. The case studies revealed that installation crews still worked even in rainy weather. However, for safety reasons, solar installation on metal and wood roofs when raining should be carefully considered and postponed if possible. Metal roofs and wood roofs present some unique issues. First, besides being slippery, metal roofs create glare on sunny days, causing visibility concerns and dizziness for workers if standing on the roof for hours. Second, it is more difficult to drive nails onto wood roofs to install mounting systems. It is also hard to determine whether nails have gone through wood tiles and reached a roof framing member without pre-drilling. This difficulty results in a high chance that the solar panel mounting system is not fully attached to roof frames. Third, workers may need to put on special footwear when working on certain

Fig. 3. Examples of pages in the PtD protocol. 6

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Table 3 Summary of the results from the interviews and case studies. Attributes

Findings

Roof materials

Influence of roof materials on solar system installation decisions, the location of safety anchors, and the safety operation in unfavorable weather conditions Influence of roof slope on working platforms and working methods Different safety impacts caused by roof vents, chimneys, skylights, and other roof accessories Influence of clear access pathways and the clearance between panel edge and roof ridge on safety in solar installations Influence of roof conditions on the design of fall protection systems Influence of panel size, panel weight, and wind conditions on lifting methods Electrical shock hazards caused by solar energy power, and tripping hazards created by wires and conduits. Influence of installation sequences and weather conditions on safety performance

Roof slope Roof accessories Panel layout Fall protection system Lifting method Electrical system Other safety factors

case. As a result, no barricade or covering was installed for the skylight. It was interesting to note that the crew actually took advantage of the skylight by placing tools and materials against the side of the skylight to prevent them from sliding down the roof. No skylight was present on Case Study 2. However, a chimney, dormer, and a few roof vents were present on the southwest facing section of the roof where solar panels were installed. The panel layout was significantly impacted by the existing roof accessories on this project. Because of the limited roof area, some solar panels were installed on the dormer’s roof. In addition, a small area of roof adjacent to the dormer was utilized for solar panels. Two solar panels were oriented horizontally to fit into this space (Fig. 4). From a safety perspective, the chimney and dormer sometimes blocked the lanyards used by the workers and hindered the workers’ movements. The safety lanyard was occasionally trapped by the installed racking, forcing the workers to stop to untangle the lanyard. Different from Case Studies 1 and 2, Case Study 3 had no skylight, dormer, or chimney present on the south-facing and west-facing sections of the roof where the solar panels were installed. However, some roof vents were present, posing tripping hazards for workers. No skylight was present on Case Study 4, yet a chimney was at the middle of the south-facing roof section that caused a need to separate the solar system into two arrays. Although this separation was due to the chimney, clearance between the arrays made it more convenient for the workers to move around the roof. Some roof vents on the southfacing roof section posed tripping hazards. However, the workers could still take advantage of these accessories by leaving tools and materials resting against the vents, using the vents as backing objects to prevent materials from sliding down the roof.

Compared with the other case study projects, the newer composite shingles in Case Study 4 made it easier and safer for the installation process. 4.2. Roof slope Roof slope impacts safety performance in different ways. The steeper the roof, the more dangerous the work is for solar workers. For moderately-sloped roofs, solar contractors can use ladders to get to the rooftop and stand on the roof surface to perform the installation. With steeper roofs, solar contractors may need to use a scissor lift as a working platform instead of standing on the roof surface. For steeper roofs, the bottom solar panel racks (lowest racks) are always installed first and the installation progresses upward toward the roof peak. Therefore, the lower installed racks can serve as backing objects for solar workers. Normally, each worker needs one safety anchor for fall protection. However, on steeper roofs, each worker may need to have two safety anchors to cope with the more severe safety hazard. The roof slopes in Case Studies 1 and 2 are approximately 25–27 degrees, and 30–35 degrees in Case Studies 3 and 4. Since the roof slopes are not very steep, the workers could move around on the roofs without special working platforms for rooftop operations. Nevertheless, it should be noted that these roofs are classified as “steep roofs” per the OSHA standards and the workers must adhere to the following OSHA regulation: “1926.501(b)(11): Each employee on a steep roof with unprotected sides and edges 6 feet (1.8 m) or more above lower levels shall be protected from falling by guardrail systems with toeboards, safety net systems, or personal fall arrest systems” (OSHA, 2017a). 4.3. Roof accessories

4.4. Panel layout Chimney, skylight, and roof vent are common types of roof accessories. The presence of roof accessories causes both advantages and disadvantages for solar installations. Since the shading of a chimney can reduce the efficiency of solar systems significantly, solar panels must be located at a certain distance away from the chimney to reduce the shading impact. Although some workers presented an idea of using a chimney as an anchorage for a temporary fall protection system, most solar contractors recommended not to do that unless the chimney is structurally designed to support adequate loads. Some small roof accessories such as roof vents create a high risk of tripping hazards for solar workers. In addition, solar contractors should install a temporary barricade or cover to protect workers from falling through a skylight or other roof openings. Despite these safety hazards, roof accessories such as a chimney or skylights could sometimes be used as backing objects to hold up tools and materials and prevent them from sliding down sloped roofs. There was one skylight and a few roof vents on Case Study 1. The panel layout was designed to avoid the skylight location. The skylight and roof vents posed a tripping hazard to the workers. The skylight opening was covered by a fixed glazing panel, and the safety hazard of falling through the skylight opening did not appear significant in this

To generate the desired electrical output, solar designers may try to

Fig. 4. Panel layout in case study 2 (Based on a Picture Taken by Chung Ho). 7

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Table 4 Pathway requirements based on roof types (IFC, 2012). Roof types

IFC requirements

Hip Roof

A clear access pathway that is 3 feet wide or larger extending from the eave to the ridge should be provided on each roof slope where the panels are located. At least two clear access pathways A clear access pathway should be more than 1.5 feet wide if there will be panels on both sides of the valley. On the other hand, if panels will only be on one side of the hip or valley that is of equal length, no clearance is required.

Single Ridge Roof Hips and Valleys

from falls. Sections 1926.501 (b)(10) and 1926.501(b)(11) of the OSHA regulations indicate that guardrail systems, safety net systems, or personal fall arrest systems could be used as a fall protection option when working on sloped roofs. If a guardrail system is used on a steep roof, it must include toeboards (OSHA, 2017a). The interviews and case studies revealed that most solar contractors prefer using personal fall arrest systems, including either lifelines or individual anchorage points. The anchors for fall arrest systems should be included as a part of roof construction for different roofing activities during the lifetime of buildings. At least two anchors should be available on residential buildings. The distance between the two anchors should be small enough to ensure that workers can move within the lanyard length. Since large roof accessories such as a dormer, chimney, or skylight could obstruct lanyards when the workers are moving around, anchors should be installed on both sides of these accessories if movements are needed on both sides. The OSHA standards (Section II.m, Subpart M, Appendix C) also recommend considering obstructions when identifying tie-off locations (OSHA, 2017a). In Case Study 1, the crew installed two anchors in addition to the two existing safety anchors on the rooftop. Three safety anchors were installed in Case Study 2, since it had no existing safety anchors. In both Case Studies 1 and 2, all workers were equipped with personal fall arrest systems (see Fig. 5), including a safety harness, lanyard, and lifeline. It took time for the workers to install a personal fall arrest system and additional time to hook and unhook from the safety anchors during the operation. It was also observed that usage of the system slowed down the movements of workers. Nevertheless, it is still an utmost important safety measure to mitigate fall hazards. In Case Study 3, the workers did not wear any personal fall arrest systems, which appeared to make the workers move faster and be more productive. The workers also mentioned that no safety anchor installation shortens the installation duration. The installation duration on this project was two days, relatively fast compared with Case Studies 1 and 2. However, the lack of fall protection was a violation of the safety regulation in section 1926.501(b)(11) of the OSHA standards for steep roofs (OSHA, 2017a), and could lead to significant injuries for workers if they fall from the rooftop. No existing safety anchor was available in Case Study 4, so the workers installed new safety anchors for this project. Although the

install as many solar panels as possible. Nevertheless, the number of solar panels is influenced by many factors such as available roof space, roof direction, roof accessories, and other regulations (e.g., voltage limit set for residential building or the required clearance between solar panels and roof edges). To assist fire fighters in case of fire, the International Fire Code (IFC) requires that panels should be located no higher than 3 feet below the roof ridge to allow for smoke ventilation operation. The IFC also sets requirements about the clear access pathway from the eave to the ridge on each roof slope as summarized in Table 4. While no formal definition is provided, a clear access pathway provides a path on the roof for workers to walk that is free of obstructions. While the pathway is required only for residential buildings with 2:12 or steeper roof slopes, the clearance between panel edge and roof ridge is required for all slope ranges. Although the clearances set by the IFC are for fire fighters, the clearances also help enhance the overall safety in solar installations by providing more clear space for solar workers to move around on roof tops. In addition, the clearance between panel edge and roof edge makes it easier to install safety anchors that are usually located on roof ridges. The clearances between panel edges and roof edges in Case Study 1 were relatively small, approximately 12 in. The limited space created a relatively higher level of falling hazard for the workers when moving along the roof edge, requiring them to take great caution. Even though the IFC sets the 3-feet minimum clearance between panel edge and roof ridge, the solar workers who participated in this research said that they need only a 1-foot clearance for the installation of safety anchors. Besides the clearance requirements, the layout of panels should be carefully designed to allow for a convenient loading point for material hoisting as well as an access point for workers. The solar panels were extended to the roof edge in Case Study 2, leaving no clearance from the panel edge to the roof edge. As a result, although the workers could move along the roof edge during the installation of the mounting system, no access to the installation area was possible after the panels had been installed. Then, the roof valley along the dormer became the only egress for the workers. The unoccupied area along the valley appeared to help facilitate the safe movement of workers and reduced the shading impact of the chimney on the panels. Nevertheless, the installation sequence had to start from the space with limited access and end at the space with ample access. The sequence was needed in order to secure an exit point for the workers after installing all of the panels. The layout of panels in Case Study 3 included an 18-inch clearance between panel edge and roof edge. This clearance allowed the workers to move easily along the roof edge, although the roof slope on this project was steeper than that on Case Studies 1 and 2. In addition, the movement of the workers on the roof was also easier because of the valley along the crossed gable roof. Similar to Case Study 3, Case Study 4 also had an 18-inch clearance between panel edge and roof edge. This ample clearance, plus the clearance between the two solar arrays, allowed the workers to move around on the roof easily. 4.5. Fall protection system According to OSHA, workers located adjacent an unprotected side or edge that is more than 6 feet above the lower level must be protected

Fig. 5. Fall protection system on case study 1 (Picture Taken by Chung Ho). 8

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possible to outside wall as direct as possible to reduce trip hazard and maximize ventilation opportunity.” In addition, the National Electrical Code 2014 NEC 690.12 (NEC) requires including a rapid shutdown function that could be used to quickly de-energize a conductor associated with solar systems. While a centralized rapid shutdown system was installed in Case Studies 1 and 4, an optimizer was installed at each solar panel in Case Study 2 instead of the centralized rapid shutdown. The optimizers functioned as a rapid shutdown as well as a device to balance the electricity generation among panels and make the system more productive. Case Study 3 complied with the requirement for rapid shutdown by using a micro inverter at each solar panel.

workers used personal fall protection systems with the safety anchors during the first visit of the research team, none of the workers used any fall protection methods during the second visit. It appeared that the workers did not prefer using the systems even if they were available onsite. 4.6. Lifting method The size of solar modules can impact lifting methods. The solar modules commonly used on residential buildings are 40″ × 66″ or 40″ × 78″ in size, and weigh between 30 and 40 pounds. The weight is within the manual lifting limit of 50 pounds allowed by OSHA. Nonetheless, to bring solar panels and components to the rooftop, OSHA’s article titled Green Job Hazards (OSHA, 2017b) suggests using lifting equipment such as ladder hoists, swing hoists, or truck-mounted cranes/conveyors whenever possible. However, the interviews and case studies revealed that most residential solar contractors prefer using manual lifting with a ladder because it is more convenient and saves time compared to using mechanical lifting equipment. On all four of the case studies, the workers used ladders to lift panels and other materials to the rooftop. It was observed in the first three cases that when lifting up panels through a ladder, the workers used one hand to hold up a solar panel or other material while their other hand was used to hold onto the ladder. When getting close to the roof, the worker stayed on the ladder and handed the panel or other material to another worker on the rooftop who was waiting to take it. Regarding safety regulations on ladder use, OSHA section 1926.1053(b)(22) (OSHA, 2017a) requires that “An employee shall not carry any object or load that could cause the employee to lose balance and fall.” More specifically, OSHA (2017b) states that “Workers should never be allowed to climb ladders while carrying solar panels.” Although the workers said that it is more convenient for them to carry panels to the roof by climbing the ladder, this activity was apparently a violation of the safety rule and could lead to injury incidents, such as slipping and falling from the ladder. In Case Study 4, the workers did not carry solar panels up the ladder. Instead, the workers pushed panels along the ladder while climbing. A worker first rested a solar panel on the ladder, then pushed the panel up to the rooftop. Both of the worker’s hands held and pushed the solar panel, concurrently leaning on the ladder’s side rails while the worker was climbing. When getting close to the roof, the worker still stayed on the ladder and another worker on the roof took the panel and set it on the roof. Although no specific regulation in the OSHA standards prohibits pushing solar panels up the ladder to the rooftop, this action is still a violation per Washington Administration Code: “WAC – 296-876-40025 Climbing and Descending: (1) You must have both hands free to hold on to the ladder” (WAC, 2016).

4.8. Other safety factors In addition to the above-listed PtD attributes, the research team recognized other factors that could impact safety including installation sequences and weather conditions. These additional safety factors are described below. Installation sequence plays an important role in reducing safety hazards. Installation should begin from the bottom (lowest) racks of the mounting system and move upwards toward racks higher on the roof. The racks should be installed horizontally rather than vertically. This installation sequence makes it safer for solar workers since the bottom rack can serve as a backup for the installation of the upper components. For access points, it is suggested to install solar panels from the point with limited access to the point with ample access so that workers can easily exit the roof after finishing the installation. The researchers recognized that these installation sequences were applied efficiently in all case study projects as a common practice. Since most solar installation work is performed outside, weather conditions may impact work operations significantly. Sun can create glare on metal roofs and cause heat stress for solar workers. Big wind gusts may knock over solar panels, leading to falling object and striking hazards. Rain can cause slips and falls, and cold temperature can cause fatigue or even frostbite. Safety plans should consider potential hazards caused by weather conditions. In the case of unfavorable weather conditions, solar contractors should consider postponing or rescheduling the installation. The impacts of cold and rainy weather on safety were apparent during the site visits. In Case Studies 1 and 2, the weather was cold and dry during the first visit, but rainy during the second visit. The air temperature was approximately 45 degrees Fahrenheit. The weather during the first visit did not create significant issues for the workers since it was dry and activities warmed up the workers at that moderate temperature. However, the rain during the second visit worsened the coldness and impeded the workers’ movements. It was rainy and much colder during the site visit for Case Study 3. The air temperature dropped to approximately 40 degrees Fahrenheit. Despite the unfavorable weather, the crews in these case studies still performed their work as planned. Although the rain made the roofs more slippery, it did not cause any serious issues on the projects because of the composite roofing materials. However, the cold weather made it harder for the workers in Case Study 3 to perform the work; their hands got very cold and their movements slowed down. The workers also got tired faster and took more breaks to warm up. It should be noted that one of the workers dressed in a battery heated jacket. The heated jacket kept the worker warm and made him comfortable while working in the chilly weather. This observation showed that proper protective clothing is important to protect the workers in unfavorable weather and can improve their safety.

4.7. Electrical system Solar installations involve a significant amount of electrical work that must be carried out by qualified electricians and strictly follow electrical safety rules and regulations. Although the scope of the present study did not delve deeply into electrical safety hazards, it is worth noting some electrical safety concerns relating to the general solar installation activities. Each case study project had one electrician who was in charge of the electrical installation for the solar system. As informed by the interviewees, all electricians are required to participate in an extensive safety training designed specifically for their work. Since electrical hazards can cause serious injuries, electricians in solar installations are required to follow strict safety rules for electrical work (OSHA, 2017c). IFC section 605.11.1.2 addresses safety concerns relating to the electrical work in solar installation as follows: “Conduit, wiring systems, raceways for photovoltaic circuits shall be located as close as possible to the ridge or hip or valley, and from the hip or valley as directly as 9

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electricity does not flow until the crew has completed the circuit, which does not happen until the solar panels have been installed. According to a solar contractor, electrical connectors that connect the solar panels with other panels are “fully enclosed, fully wrapped, fully insulated … and have to have a special tool to even take them apart.” In addition, the electrical components have been fully tested from the manufacturing side before reaching the market. Furthermore, in Washington State, a solar contractor must have a licensed electrician on site, and all electrical work must be carried out by the licensed electrician.

5. Findings from seminar with solar contractors 5.1. Difference between federal and local safety regulations There are differences between federal and local laws and regulations related to safety and solar installations. These differences make it confusing for solar contractors when implementing safety requirements. Moreover, each state, city, and county may have different code and standard revisions. One solar contractor complained, “It is tricky, even for us to look at different codes and figure it out.” In general, the local building code governs over the national code. The PtD protocol refers to the national IFC, which is more stringent than some local codes about the clearance between panel edge and roof ridge. Similarly, safety requirements are also governed by local regulations. However, OSHA sets a higher standard for local laws regarding safety as it requires that local laws be “at least as effective” as OSHA standards (OSHA, 2017d). For example, when addressing ladder usage, OSHA section 1926.1053(b)(22) only states “An employee shall not carry any object or load that could cause the employee to lose balance and fall”, while the Washington Administrative Code – WAC296-876-40025 sets forth a more stringent requirement, “You must have both hands free to hold on to the ladder” (WAC, 2016). Addressing each local regulation is out of scope of the solar PtD protocol; the protocol is designed for use nationally. Thus, the researchers recommend protocol users refer to corresponding local regulations when implementing the protocol on their specific projects.

5.5. PtD opportunities in solar panel manufacturing versus solar panel installation While all solar contractors provided positive feedback about the application of PtD during manufacturing of the panels, they were generally not interested in PtD application during the installation of the panels. The solar contractors stated that they prefer the manufacturing side as an opportunity to implement PtD. To the solar contractors, the implementation of PtD on the construction side does not seem very practical. The contractors indicated that the application of PtD practices will eliminate a significant amount of roof area to lay out solar panels and may not meet the desired solar capacity if strictly following the clearance requirements of the IFC. The suggestion to use ladder hoists to bring solar modules to the roof is not preferable because of additional setup time. The solar contractors also complained that personal fall protection systems are too heavy and may create tripping hazards. One contractor even mentioned that he thought that the available safety devices are not practical for solar installations.

5.2. General resistance toward safety requirements Although all of the contractors that participated in the research study try to follow the safety regulations at certain levels, the researchers still recognized a general resistance from the contractors toward safety requirements. To explore the reason behind this objection, the solar contractors were asked about how they balanced safety with other criteria in decision-making. While one solar contractor said that he would not mind designing less panels on a rooftop to make it safer while ensuring an effective solar system, another solar contractor stated that strictly following safety regulations would increase labor costs. The latter contractor said that a ladder hoist would take two hours to install and two hours to take down. Therefore, using it would turn a one-day job into a two-day job. The contractor added “There is not enough profit in the solar industry to double the hours needed to do the work.” Other contractors also complained about the inefficiency of ladder hoists, even though all contractors believed that safety during solar installations could be enhanced through technology improvement. For instance, a ladder hoist should take less time to set up, and improved, higher efficiency solar panels should require less footprint for the same electrical output.

6. Conclusions The growing interest in sustainable construction, including solar system installations, not only creates job opportunities but also poses unique safety hazards and risks to solar workers. This paper has presented the implementation and findings of the study investigating the application of Prevention through Design (PtD) to improve worker safety concerns during the installation of solar energy systems on single-family homes. This study is expected to contribute to the improvement of safety in solar installations as well as enhance safety awareness in the field of sustainable construction. Through a number of interviews and four case studies, seven solar PtD attributes have been identified and a solar PtD protocol has been developed. The attributes and protocol were verified through four case study projects and a seminar discussion. The purpose of the protocol is to serve as a guidance document for implementing PtD in the design and installation of solar energy systems in small buildings. Several key findings obtained from the course of the study were presented, including the findings from the interviews and case studies, and the findings from the solar seminar discussions. The findings from the interviews and case studies revealed seven PtD attributes (roofing material, roof slope, roof accessary, panel layout, fall protection system, lifting method, and electrical system), installation sequences, and weather conditions. It should be noted that the findings from the present study are largely aligned with the information indicated in the interview in the Torpey study (2009). The feedback from a seminar with solar contractors exposed the difference between federal and local safety regulations, the general resistance toward safety requirements, safety perspectives about sloped roofs versus flat roofs, electrical safety issues in solar installation, and PtD opportunities on the manufacturing side versus on the construction side of solar installations. Throughout the conduct of this study, the research team encountered significant resistance about safety regulations from small solar contractors. The resistance focused on three areas including: clearances required by the IFC that could considerably reduce the available roof space for laying out solar panels; the lengthy setup of ladder hoists or other mechanical lifting equipment; and the heavy

5.3. Safety perspectives about sloped roofs versus flat roofs Sloped and flat roofs render different impacts on worker safety. In terms of production, sloped roofs may make it easier to orient solar panels because sloped roofs do not require additional frames that are needed for flat roofs to achieve the desirable slope of the solar panels. In addition, workers need to kneel down to work on flat roofs more than on sloped roofs. When asked if it was more convenient for workers to work on sloped roofs than flat roofs, the contractors responded that even though flat roofs require more kneeling, they are still preferred over sloped roofs since flat roofs do not require workers to stand on a sloped surface for a long time. 5.4. Electrical issues in solar safety While solar panels generate energy when exposed to the sun, electrical hazards are not a big concern to solar contractors since the 10

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