SITUATIONAL AWARENESS LOCATION TRANSPONDER (SALT):

A PHASE DIFFERENCE OF ARRIVAL (PDOA)-BASED SYSTEM FOR ENHANCING CONSTRUCTION SAFETY (EXTENDED ABSTRACT)

Pang Yu Yin, LIU Pak Hin, MA Sze Long, SZE Chung Lam, CHEUNG Ho Hin

Hong Kong University of Science and Technology; {yypangaa, phliuab, slmaaa, clszeac, hhcheungab}@connect.ust.hk

ABSTRACT

SALT is a proposed safety solution for construction sites that aims to provide real-time situational awareness to reduce accidents involving heavy machinery and workers. It employs Ultra-Wideband technology, Bluetooth Low Energy communication, and Inertial Measurement Units. The SALT system comprises tags attached to workers and machinery, anchors installed at fixed points, and displays for alerts and warnings. Tags and anchors utilize UWB for precise positioning, while Bluetooth enables long-range communication. IMUs in tags determine the orientation of machinery to provide context. The multi-faceted approach addresses the practical constraints of construction sites.

An extensive design process involving preliminary research, problem identification, goal and objective definition, analysis of current solutions, interviews, and agile development of the proposed solution was performed for developing SALT. Findings from the evaluation results show that SALT significantly reduces the risk of accidents involving heavy machinery and workers on foot, supporting its main claims. The performance assessment indicates that the system performs well across key areas, including technical performance, applicability, practicability, and the application of technology. The development of SALT involved collaboration with various external parties, including advisors, faculty members, and domain experts, who provided guidance and insights throughout the project.

KEYWORDS: Construction site safety; Real-time situational awareness; Ultra-Wideband positioning; Bluetooth Low Energy communication, Inertial Measurement Unit integration

I. INTRODUCTION

"Safety first!" has long been at the top of the agenda at any construction site and the safety of workers is critical for the industry's sustainability^[1]. Significant efforts from multiple directions such as regulatory measures and adoption of new technologies have been made to address this notion. While the work site conditions and safety measures for construction workers have gradually improved, due to the nature of the outdoor and complex geographical and technical matrix of uncertainties, the rates of accidents remain high, especially when involving heavy machinery.

Fig.1 Highlights of Industrial Accidents in the Construction Industry in 2021^[2]

The 2021 Occupational Safety and Health Statistics report (Fig 1) reveals the most concerning accidents: 1) Falls from height, 2) Collisions with moving objects, and 3) Entrapment between objects. The Situational Awareness Locator Transponder (SALT) project addresses these issues by developing a safety solution that integrates technology and practical design principles to reduce risks on construction sites.

II. METHODOLOGY

A. PRELIMINARY RESEARCH & DESIGN APPROACH

Fig.2 Extraction Pie Chart of Industrial Accidents in the Construction Industry in 2021^[3]

Figure 2's pie charts show that a significant portion of construction industry accidents and fatalities stem from "Striking against or struck by moving objects" and "Trapped in or between objects" categories. Collectively, these 2 categories, representing 23.6% of total accidents and 26.1% of deaths, highlight the dangers posed by such incidents. Consequently, our team has resolved to delve deeper into the intricacies of these two types of accidents with the development of SALT.

The project's main challenge lies in navigating the constraints of real worksite environments, including equipment regulations, worker preferences, weather conditions, and cost-benefit considerations. The SALT system's design process involves multiple stages, such as preliminary research, problem identification, goal definition, solution analysis, interviews, and agile development, ensuring technical feasibility and real-world applicability.

B. DESIGN JOURNEY

Based on the previous findings, the team set out to develop a safety device that would address the limitations and shortcomings of existing safety solutions. The design process involved brainstorming, ideation, prototyping, and iterative testing to ensure the SALT system's effectiveness, scalability, and adaptability to different construction environments. Throughout the design process, the team drew inspiration from various sources, such as existing safety devices, academic research, and expert advice.

Fig 3. Interview with a safety officer (Left);

Fig 4. Site visit to Sheung Shui Public Estate Construction site (Center);

Fig 5. Presenting the SALT solution to SOCAM Development and Housing Department (Right).

We perform interviews with the construction site manager and safety manager to gather valuable insights such as workers’ routines and requirements of safety officers. We also conducted a site visit to an active construction site situated in the New Territories to assess the environmental constraints and equipment setup of heavy vehicles. To refine our approach, we delivered several presentations to the engineers from SOCAM Development and Housing Department to gain their feedback in terms of compliance regulations and large-scale production demands.

C. DESIGN PRINCIPLES

The design principles guiding the development of the SALT system include simplicity, user-friendliness, scalability, and adaptability. These principles ensure that the system is easy to use and deploy, making it accessible to construction companies of all sizes. The team drew inspiration from various sources, including existing safety devices, academic research, and expert advice from industry professionals in order to make an intuitive and Worker-Oriented solution.

III. RESULT

A. HOW SALT WORKS

Fig 6. System Diagram of SALT

As illustrated in Fig 6, the SALT system comprises three primary hardware components: the tag, anchor, and display. The anchor provides 360-degree coverage by utilizing three boards and algorithms, each covering a 120-degree Field of View (FOV). Employing UWB Phase Difference of Arrival (PDoA) technology, the anchor determines the tag's location and transmits it with the type-b board, along with Inertial Measurement Unit (IMU) data in the type-a board, to the display for enhanced situational awareness.

The SALT tag uses Bluetooth for long-distance communication while searching for the anchor, and switches to UWB upon detecting the anchor. The wirelessly charged tag also features buttons for status changes and a beeper to alert workers. Both the anchor and the tag are waterproof and shock-resistant, ensuring adaptability to various site conditions. The SALT display features a Thin Film Transistor (TFT) monitor that incorporates a Raspberry Pi Zero board, a waterproof speaker, and four operational buttons. These buttons enable users to adjust the detection range and issue warnings to workers, enhancing overall safety. The display is designed to accommodate an unlimited number of tags, dynamically adjusting based on the number of workers in proximity to the anchor.

Fig 7. SALT Display UI:  Safety Levels (Left to Right: Safe Zone, Warning Zone, Danger Zone)

As seen in Fig 7, the SALT Display UI showcases three safety levels, from left to right: Safe Zone, Warning Zone, and Danger Zone. The UI not only displays the positions of workers but also predicts their movement directions using a long arrow, thanks to a specialized algorithm. When a worker enters the Warning Zone, their position is marked directly on the display, and the actual distance is shown. In this stage, the screen starts to blink slowly as an alert. If a worker progresses into the Danger Zone, their location is prominently displayed on the cabin display, along with visual and audio alerts for both parties. Additionally, the screen undergoes a significant colour change to indicate the direction in which the driver should exercise heightened awareness.

B. BRIEF OVERVIEW OF SALT

IV. DISCUSSION

A. COMPETITIVE ADVANTAGES

In the competitive landscape of construction site safety systems, various products are available, each with its own strengths and limitations. Common solutions include proximity warning devices, camera systems, and RFID-based systems. Proximity warning devices offer some level of collision prevention but may not provide comprehensive situational awareness.^[4] Camera systems can help monitor specific areas but may suffer from blind spots and be less effective in low-light conditions.^[5] RFID-based systems can track worker location but may not offer real-time updates or accurate positioning, especially in complex environments.^[6] And most of these solutions rely on external networking such as WIFI, GPS or cellular data.

The SALT system, on the other hand, has been designed to address these shortcomings and offer several advantages over existing solutions, which include

• Increased safety awareness: Utilizing SALT's 360° real-time detection, operators and workers can optimize safety decisions, leveraging blind spot-free detection to mitigate accident risks.
• Reduced false alarms: delivering accurate, timely alerts, fostering heightened attention and reducing annoyance for workers and signalers with visual and auditory warnings.
• High scalability: SALT's scalable architecture enables seamless integration for construction projects of any size, with theoretical support for an unlimited number of tags, ensuring adaptability and versatility.
• Low cost of deployment: SALT offers a cost-effective option at just 1/10th the price of other competitors in the same sector, increasing accessibility for construction companies.
• High feasibility and adaptation: The bespoke locking mechanism and weatherproof materials ensure dependable performance in various construction environments, without necessitating network connectivity.

  ---

B. EVALUATION

Fig 13. The day we showcased our SALT solution to construction engineers.

The SALT system has received positive feedback for its potential to improve worker safety on construction sites. In order to evaluate the effectiveness of the SALT system, a testing schedule and methodology will be developed around June 2023, focusing on the areas of technical performance, applicability, and practicability. The testing process will involve several stages, including:

• Regulatory compliance: Ensuring that the SALT system meets all relevant international safety regulations, such as OSHA standards, before deployment on construction sites.
• Controlled environment testing: Conducting a series of tests in controlled environments to assess the accuracy of the positioning system, the responsiveness of the alerts, and the overall performance of the hardware components.
• Field testing: Deploying the SALT system on active construction sites and monitoring its performance in real-life scenarios.
• Staff training and integration: Involving safety managers and other key personnel in the testing process to familiarize them with the SALT system and its capabilities. This will ensure that the system is used effectively to complement existing safety procedures and routine checks/tasks.

Upon successful completion of these testing stages, the SALT system can be employed on construction sites as an additional safety measure to gather more data. Safety managers can then utilize the system to enhance their daily tasks, such as hazard identification, worker monitoring, and accident prevention, ultimately contributing to a safer working environment.

V. CONCLUSIONS

In conclusion, the SALT system shows promise as a comprehensive approach to enhancing safety on construction sites. By integrating UWB, BLE, and IMU technologies, the system provides real-time situational awareness to workers and machine operators to help avoid potential accidents. The multi-pronged approach aims to address the practical constraints of construction sites while ensuring cost-effectiveness and adaptability.

VI. ACKNOWLEDGEMENT

The development of the SALT system was made possible through collaboration with various external parties. The  team would like to acknowledge the invaluable contributions of advisors, faculty members, and domain experts who provided guidance, feedback, and insights throughout the project. Additionally, the team recognizes the importance of existing safety solutions that served as inspiration for the development of the SALT system.

Course advisor: Chi Ying TSUI, Chi Ming CHAN, Jac Leung, Ming CHAN

Course sponsor: SOCAM Development Limited

Student Helper: Chan Ming Chun

Interviewees: Cheng Tak Sum (Senior Construction Manager) from Zhuhai Engineering Limited,

(Former Safety Officer) from Fortune Jet Management & Training Co. Limited