# Literature Review of Digital Twins Applications in Construction Workforce Safety
## 3 Methodology  
Since DT is only a concept, many studies have addressed the concept but did not mention it in the title, keywords, abstract, or even the content of the articles. Therefore, we chose the content-analysis based review method, which has been widely applied in the construction field [41; 42]. Three common literature review databases, Scopus, Web of Science, and Google Scholar, were used to exhaustively retrieve articles. As the purpose of this study was to review the application of DT in construction workforce safety, the selection criteria were as follows:  
1. The articles should focus on the targeted areas. They should involve construction safety and cover at least one of DT, sensor technology, and visualisation technology.
2. Papers to be reviewed should be journal articles. Compared with other paper types, such as reports, editorials, and conference papers, journal articles are typically peer-reviewed and more exhaustive.
3. Journals used for retrieving articles should have significant impacts on the targeted areas and should be indexed in Science Citation Index (SCI), Science Citation Index Expanded (SCI-E), or Engineering Index (EI) databases, which guarantee the professionalism and reliability of articles.  
According to the selection criteria, the literature retrieval process is shown in Figure 2. A total of 13 keywords in four categories were selected for an exhaustive search of the required papers (Figure 3). There were two compulsory keywords: construction and safety. Combined with the compulsory keywords, other keywords were used one by one to filter the papers. The selected keywords related to DT were: digital twins, synchronisation,and digitisation. The keywords related to sensor technology were selected as sensor, monitoring, positioning, and camera. The selected keywords related to visualisation technology were: visualisation, virtual reality, augmented reality, and mixed reality. At the same time, according to the second criterion, the filter is set to keep only the journal literature. These two steps identified more than 3600 related journal articles.  
Figure 3: Keywords for the literature retrieval.  
Figure 2: Literature retrieval process.  
According to the third criterion, the sources of articles are limited to the below-listed journals:  
* Automation in Construction (AC);
* Journal of Construction Engineering and Management (JCEM);
* Safety Science (SS);
* Journal of Computing in Civil Engineering (JCCE);
* Advanced Engineering Informatics (AEI);
* Journal of Information Technology in Construction (JITC);
* Accident Analysis and Prevention (AAP);
* Journal of Engineering, Design and Technology (JEDT);
* Applied Ergonomics (AE);
* Journal of Performance of Constructed Facilities (JPCF).  
At this point, automatic filtering reduces the number of articles to 347. After a visual examination of the content of the article, 256 articles were excluded due to lack of relevance. In total 89 articles were obtained for further analysis. The retrieval approach may not comprehensively cover the articles related to the application of DT in construction workforce safety; however, this method was sufficient to provide a significant number of state-of-the-art research works, from which this review could generalise findings and recommend future works.