Beacon-Based Individualized Hazard Alarm System for Construction Sites: An Experimental Study on Sensor Deployment  
[PERSON]  
1 School of Civil Engineering, Xi'an University of Architecture and Technology, Xi'an 710055, China; [EMAIL_ADDRESS]  
[PERSON]  
2 Department of Civil and Environmental Engineering, Hongisk University, Seoul 04066, Korea 2  
[PERSON]  
3 Department of Building and Real Science, Hong Kong Polytechnic University, 11 Yuk Choi Rd, Hung Hom, Hong Kong, China; [EMAIL_ADDRESS]  
[PERSON]  
4 Division of Architecture and Urban Design, Incheon National University, 119 Academy-ro, Yeonsu-gu, Incheon 22012, Korea; [EMAIL_ADDRESS]  
[PERSON]  
1 School of Civil Engineering, Xi'an University of Architecture and Technology, Xi'an 710055, China; [EMAIL_ADDRESS]  
Footnote 1: [[https://www.mdpi.com/journal/applsci](https://www.mdpi.com/journal/applsci)]([https://www.mdpi.com/journal/applsci](https://www.mdpi.com/journal/applsci))  
Footnote 2: [[https://www.mdpi.com/journals/pdf/10.390/journals/pdf/10](https://www.mdpi.com/journals/pdf/10.390/journals/pdf/10)]([https://www.mdpi.com/journals/pdf/10.390/journals/pdf/10](https://www.mdpi.com/journals/pdf/10.390/journals/pdf/10)). those administrative controls are limited in preventing accidents and have proven to be less effective than other measures in the hierarchy of controls, as they require significant effort by the workers involved [1]. With interest in finding how to help workers maintain adequate recognition of hazards and risk perception, researchers have investigated the effectiveness of training. Previous research works unanimously state that safety training programs have a positive impact on construction workers' risk perception and safety attitude [2; 3; 4] but provided limited discussion on how much safety training programs increase workers' ability to recognize all hazards and perceive appropriate risks in the work environment. Specifically, [PERSON] et al. [4] found that their data did not support the links between safety training and workers' ability to recognize the probability and severity of specific safety risks. Several researchers approached the problem of worker hazard recognition by developing a sensor-based hazard alarm system designed to alert construction workers in a timely manner when they were around a hazard. The researchers used various types of sensors, including Radio Frequency (RF) [5; 6], Bluetooth Low Energy (BLE) [7; 8; 9; 10], Global Positioning System (GPS) [11], Chirp Spread Spectrum (CSS), and Inertial Measurement Unit (IMU) [12] sensors, to name just a few examples, to create a system to quickly give a warning to the worker exposed to a critical hazard. In addition, researchers reviewed the use of these different types of sensor-based location- or proximity-based warning systems for construction safety and found that the number of publications discussing sensing and warning-based technology for construction safety has increased dramatically since 2013, especially for BLE-based proximity warning systems [13; 14; 15]. However, the application of BLE-based hazard alarm systems on construction sites is in an early stage in the construction industry, and many questions need to be answered before such a system can be fully implemented. One of the important questions is about the suitability and reliability of Bluetooth signal-based distance measures and proximity detection in construction work environments. Researchers indicated that BLE sensors are influenced by the ambient temperature and humidity, and therefore, the performance of proximity sensing and alert systems can be compromised by these factors [8].