# Literature Review of Digital Twins Applications in Construction Workforce Safety
## 6 Virtual Construction Simulation and Visualization Technology
### Construction Activity Visualisation  
The monitoring described in Section 5 is able to provide massive amounts of dynamic information for construction management. The huge amount of information enables the safety officers to have a more comprehensive understanding of the construction situation, but increases their workload and mental load to process the information for decision making. Only after the synchronised data are processed and delivered to specific users can construction safety be improved. A VCS system was proposed to process the data collected from safety planning and construction. [PERSON] et al. [53] developed a prototype to analyse and visualise the risk of a workplace based on field-monitoring data and 4D BIM-based safety planning, which provides safety officers with timely information to make decisions regarding construction safety issues. VCS is also expected to offer solutionsautomatically. To address the limitations of safety knowledge, ontology was used to model safety knowledge and semantic information [78]. By building an ontology model, a complete knowledge base can be built. The knowledge base includes hazards, precursors of the hazards, and solutions to deal with the hazards [79]. When precursors are outside the acceptance criteria, the situation is identified as a hazard, and corresponding solutions are automatically generated to solve the hazard. With the aid of ontology, the response of structural members in different loads, such as seismic loads [80, 81], blast loads [82, 83], and impact loads [84, 85], has the opportunity to be integrated, which can provide the knowledge basis for accident simulation.  
A proactive construction management system (PCMS) developed by [PERSON] et al. [86] combined a real-time location system (RTLS) and a VCS system. The RTLS can locate workers, equipment, vehicles, and other moving objects and transmit their position to the VCS system. The VCS system simulates the 3D construction workplace with hazard zones. The coordinates of identified construction equipment and workers are translated and visualised in the VCS system. Once a worker approaches a hazard zone, a process is triggered to report the situation and warn the worker. Similarly, many studies have focused on the visualisation of workers' locations [87] and behaviours [61, 62] in virtual construction sites, helping safety officers to quickly determine the workers' locations and unsafe situations to manage the emergency. VCS integrates BIM, ICT, and ontology into construction safety management, increasing the digitisation and automation of hazard identification and prevention.  
Warning mechanisms are used to keep workers away from hazardous zones. Vibration and sound are commonly used to deliver warnings to on-site individuals without interrupting their work [8], which is effective in deterring workers from taking risks. Innovative visualisation technology has been introduced to avoid accidents for on-site individuals. For example, for equipment operators and drivers, real-time images displaying the location of surrounding workers and facilities can effectively reduce strike accidents caused by blind spots [59, 88]. [PERSON] et al. [89] presented pipeline information through AR using a cabin monitor to prevent an on-site individual from safety issues. A wearable hazard avoidance AR system was developed by [PERSON] et al. [58]. They visualised the direction, distance, and the degree of danger of a vehicle nearest to its user through a coloured arrow with a safety level indicator. The system provides a new method to avoid accidents by integrating on-site safety warnings and a head-mounted display (HMD). By overlapping a virtual environment on the real world, the view provided by AR or MR HMD fits better with the human visual mode than conventional displays. Considering the dynamic nature of a construction site, the introduction of HMD solves the problem of the time lag between the action and notification in the traditional on-site warning method.