## 3 Beacon-Based Hazard Alarm System Design
### Detailed Design of the Components
#### 3.3.1 Beacon-Based Distance Monitoring
In that sense, this method of hazard information communication is not only helpful for enhancing workers' hazard recognition and risk perception but the record keeping of the fulfillment of the construction manager's duty of care regarding site hazard information communication. Such on-time, on-the-spot hazard information notification can be effective and supplementary to conventional hazard information communication methods such as signage, toolbox meetings, and site induction and help increase the workers' situation awareness regarding all the hazards they might miss otherwise. The results also show that careful planning would be strongly required regarding beacon sensor deployment. Depending on the beacon sensor's location, many workers can receive redundant, irrelevant hazard alarm notifications, which will unavoidably create alarm fatigue, or workers might not receive any hazard notifications until they enter the workspace and start to be exposed to the hazard. The heat maps shown in Figure 5 might look like they suggest the best location for beacon sensors for hazard alarms to be behind the front side wall near the entrance, but it all depends on the type of hazard to the \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Sensor Position 1** & **Sensor Position 2** & **Sensor Position 3** & **Sensor Position 4** \\ \hline The rate of successful alarm notification & 89\% & 68\% & 48\% & 19\% \\ The longest distance of hazard alarm notification reception & 11.6 m & 10.6 m & 5.8 m & 2.8 m \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of experiment results. workers are notified about. If the hazard can expose workers in a wide area to a threat, such as a gaseous poisonous chemical, the hazard notification and risk mitigation method information, such as wearing respirators, needs to be broadcast to the widely affected area. Therefore, in this case, placing the beacon sensor near the entrance would be most appropriate. On the other hand, if the hazard exposes a worker to a threat only when he or she contacts an object or a structure, placing the sensors on one of the internal walls of the workspace would be more suitable, as this would prevent sending hazard notifications to workers unrelated to the hazard, such as those workers just passing by the room. In addition, understanding the relationship among the type of hazard, the location of the on-site beacon sensor, and the location of the hazard notifications with sensor configurations would help develop a sensor deployment planner system and enhance the personalized notification of hazards for construction workers. A sensor deployment planner system would assist construction managers in deciding the best location of each beacon sensor according to hazard type and location by visualizing the first alarm location on the site before the actual installation of the sensors and even recommending the optimized location of sensors to construction managers. Such a system would reduce workers' fatigue by receiving unnecessary alarms by the sensors without compromising the effect of the beacon sensor-based hazard alarm system. Last but not least, this type of sensor- and IoT network-based hazard notification system should be planned with consideration of the failure modes that can be caused by malfunction or disconnection of the communication network involved. The proposed BLE-based system relies on existing communication network services and several cloud computing platforms, including the LTE network, Estimote Cloud, and Google Firebase Cloud. The LTE network is known to have good indoor data rates, indoor penetration, and SMS services. In addition, the communication between the two cloud systems uses HTTP and MQTT protocols, and these protocols have high reliability in data transmission. However, if any of these system components has a breakdown or delays in response, it can disrupt the entire hazard alarm system, creating a great risk for those workers relying on the system.