Baywatch 2.0: Rescuing drowning persons with an underwater robotic lifeguard

The number of people drowning in the sea or in lakes rises from year to year. However, drowning also occurs in private or public swimming pools. According to the statistical data, an average of more than 400 people drown in Germany every year. The numbers are similar for other countries across the world or even higher. On the other hand, the number of lifeguards decreases every year around the world majorly due to the shortage of trained personnel. Some of the tasks of a human lifeguard can be addressed by robotic systems, like detecting an emergency, approaching the target person quickly in the water, securing the person and bringing the target to a safe position. Therefore, we designed, built and tested a robotic underwater vehicle for autonomously rescuing people from drowning. This rescue vehicle uses an external camera system to detect a drowning incident above the water and then sends the robotic vehicle to the detected position. After reaching the target position, the vehicle detects the person based on sensor data (camera, position, orientation), picks the person up and returns it to the surface. There, the person will be rescued by lifeguards who have been alerted automatically in the meantime. A second version of the vehicle will be suitable adapted for supporting rescue forces in search and rescue missions in open waters. This version will therefore be larger and equipped with various other sensors, such as sonars or a GPS system. As a first step of the development, an existing underwater vehicle was modified by adding a top side rescue device, which can be used to securely lift a person underwater to the surface and stay in position until human lifeguards arrive. With the rescue device, it is possible to test the ascending behavior of the vehicle and the secure lift of a person on the rescue system. Important for the design of the rescue system was the safe positioning of the person on the vehicle and the fixation during the transport to the water surface to prevent slipping of the target while rescuing. A lifelike dummy (approximately 1.85m, 80kg) was used for the evaluation trials of the system in a test basin. The next key point of the development is to realize a safe and fast transportation of the person to the water surface. For this purpose, the necessary buoyancy was defined by mathematical evaluations and the buoyancy given in DIN EN 12402 group of standards [3]. In addition, already existing buoyancy devices were selected, an novel approach was designed and tested to fill the new fast emerging system quickly with air. The resulting prototype of the rescue system was intensively tested and evaluated in the test basin at the Fraunhofer IOSB-AST, through which its functionalities were adapted and improved. As a proof of concept at the end of the project, the final verification of the developed system was demonstrated along with our partners from the German lifeguards in the lake Hufeisensee near Halle (Saale) (Germany). The trial was done in December with temperatures around $4 ^{\circ}\text{C}($ air and water). In the demonstration, the dummy was placed in a depth of 4m in the lake. The goal was to detect, approach and safely bring back the dummy to the water surface in the shortest time possible. The paper will give more details on this trial, the performance of the system and the lessons learned from the real life evaluation – and most important: answer the question whether (if) this robotic lifeguard could really replace David Hasselhoff. The development of the prototype is a collaborative work between the Water Rescue Service (WRD) of the German Red Cross in Halle (Saale) and Fraunhofer IOSB-AST (AST) in Ilmenau, (Germany). The research group of Underwater Vehicles the AST is responsible for the technical implementation of the rescue system, the WRD provided the knowledge of rescuing people as well as the evaluation and the test site for the prototype.

I. Introduction

Rescuing drowning people is a dangerous task – especially for a lifeguard. Driven by panic, victims may attack their rescuers. Lifeguards are trained to help themselves in such situations, others are less fortunate. As an example, in August 2022, 3 double drowning deaths (when the person in need and the rescuer dies) were registered in Germany. In another accident during this month a lifeguard died trying to save a child.