## 2 Research Background
### Site Hazard Information Communication  
There would be four critical components in site hazard information management: site rules, site inductions, permits to work, and on-site training, such as toolbox talks [33]. Among these, site inductions and toolbox talks play a crucial role in site hazard management, as they affect workers' knowledge and skills to recognize and appropriately respond to site hazards. [PERSON] et al. [34] conducted an experimental study and found that workers involved in toolbox meetings had a significant increase in interaction with their supervisor, and as a result, they had higher levels of hazard awareness. [PERSON] et al. [35] reviewed the literature on the effectiveness of on-site safety training programs and found that specific training and safety meetings were the two most effective programs among the twelvedifferent types of safety training programs they reviewed. [PERSON] et al. [36] found that the participation of contractors in safety meetings had the most significant relationship with the reduction of the injury rate. With an understanding of the importance of toolbox meetings and hazard information communication with workers, many safety authorities require toolbox meetings in site safety management systems [37; 38; 39]. However, researchers also indicated limitations in the current toolbox meeting practices in the construction industry. [PERSON] et al. [40] reviewed the toolbox meetings in the US and found that the time for workers and subcontractors to talk and engage needs to be increased. They also found that more visualization and specific incident case studies can increase the effectiveness of toolbox meetings in increasing workers' hazard recognition.  
Site induction is another commonly used method to increase hazard awareness in construction workers. Since OSHA started a hazard awareness program called Smart Mark in the US in 1997, such site induction programs have become a norm in construction sites across the US [41]. In 2007, the Western Australia government also developed a similar mandatory site induction program called Construction Induction Training (CIT), and more recently, an online version of this type of training also became available [42]. Similar site induction programs are required in other countries in Asia and Europe as well [33; 43]. Researchers investigated the effectiveness of the current practices in site induction programs applied in the construction industry. [PERSON] and [PERSON] [42] conducted two studies in 2006 and 2010 in Western Australia to assess the benefits of site induction training programs from the worker's perspective. They found that practitioners in general changed their attitudes from indifference or even a refusal to support them. [PERSON] and [PERSON]'s subsequent research found that site induction programs contributed to decreasing accident rates in Western Australian construction workplaces [44]. Other research also proved that safety training intervention programs could reduce injuries at construction sites.  
Despite the successful results of those worker safety training and site induction programs, researchers indicated that a worker's ability to appropriately recognize site hazards and correctly perceive the level of safety risks can still be compromised due to distraction [17], blind spots [19], and their emotional state [20]. In addition, workers' sensitivity to important hazards and safety risks can be reduced over time. For example, [PERSON], [PERSON], and [PERSON] [45] found experienced workers who regularly worked at heights underestimating the risk of falling when using a ladder. Such unrecognized or underestimated safety hazards increase the possibility of catastrophic workplace incidents [46]. These limitations of the current methods for communicating site hazards and the human nature of becoming insensitive to hazards motivated researchers to look into the possibility of using sensor-based systems to address the problem of the hazard recognition and risk perception of workers, as discussed in the following section.