# Literature Review of Digital Twins Applications in Construction Workforce Safety
## 7 Discussion
### Challenges and Future Works
#### 7.2.4 Warning Mechanisms  
The purpose of the practical application of DT in construction safety is to simplify complex construction sites and display construction safety information, including hazardous areas, worker behaviour, and emergencies, to help safety officials and workers make quick decisions and avoid accidents. The method of transmitting real-time safety information to off-site security officers is mature, whereas the research on transmitting safety information to an on-site individual is still in an early stage.  
Workers exposed to danger are the last defender against accidents. However, in a disorderly construction site filled with invalid visual and auditory information, incorrect decisions can be made due to workers being unable to distinguish useful from useless information. Even if a worker succeeds in obtaining the safety information related to a hazard, they need to recognise the hazards revealed by the information. Later, to ensure their own safety, the worker needs to perceive responses and choose a safety response. Finally, only if this safety response is properly executed can workers avoid accidents [110]. Several cognitive analysis models describe this process, revealing that it involves human factors such as attention, safety awareness, safety knowledge, memory retrieval, and safety attitudes [60, 111, 112]. Under normal circumstances, workers are competent enough to complete the cognitive process correctly and avoid accidents. However, unsafe behaviour still occurs from time to time during construction activities due to negligence and a lack of vigilance [112]. The provision of warnings is an important approach to help on-site workers avoid accidents by providing workers with useful safety information about the surrounding workplace. However, the mechanisms through which warnings can affect workers' behaviour through cognitive processes are unclear, such as which step in the cognitive process is affected by the safety information provided and what information is helpful to prevent accidents. Therefore, the design and evaluation of warning mechanisms have been hampered.  
With the help of automated monitoring technology, hazardous areas and unsafe behaviours can be identified in real-time. A warning approach was proposed: when an on-site worker approaches a hazardous area or acts unsafely, a device on their helmet warns them with a sound [4], which allows workers to understand the existence of the hazard. However, it fails to help the worker identify the hazards in the surrounding workplace for active decision making. MR and AR visualization technology have been widely studied for collaboration [113], operation [114; 115], maintenance [116; 117], and inspection [118; 15]. They are advantageous in displaying context-aware safety information [58]. However, too much information may block the view of the users to some extent, and workers need to spend time and attention reading the extra safety information, causing distraction. Therefore, effectively conveying safety information to workers through technical approaches to achieve the purpose of warning needs to be explored.