Drowning Behaviour and Signs

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This entry is adapted from the peer-reviewed paper 10.3390/s24020331

Drowning poses a significant threat, resulting in unexpected injuries and fatalities. To promote water sports activities, it is crucial to develop surveillance systems that enhance safety around pools and waterways.

drowning detection systems image processing sensor-based technologies

1. Introduction

In recent decades, the popularity of swimming pools and other water attractions has significantly increased. To ensure the safety of individuals in pools, rivers, and beaches, it is crucial to have accessible and well-maintained surveillance systems. Drowning is responsible for approximately 7% of all injury deaths and is ranked the third leading cause of accidental-injury-related death by the World Health Organisation (WHO, Geneva, Switzerland) ^[1]. Globally, an estimated 230,000 people lose their lives to drowning each year, making it a threat to individuals of all age groups, from infants to senior citizens ^[2].

Despite the significant risk that drowning poses to public health, global estimation might significantly understate its true extent ^[3]^[4]. Specific demographics, such as children and young men, who engage in water-based activities are more susceptible to this danger ^[5]. Drowning is a multifaceted issue with various underlying causes ^[6]^[7]^[8]^[9]. However, the primary factors contributing to drowning include the inability to swim, fear of water, and insufficient supervision of children ^[10]. It is important to note that drowning is often a silent event, and victims rarely exhibit convulsive movements. Instead, they exert considerable energy to keep their heads above water, often unable to call for help or signal their distress. When water enters their larynx or trachea, panic and spasms can occur, preventing them from shouting for assistance. Detecting drowning is typically challenging, as victims may struggle in the water, have trouble breathing or have an irregular heartbeat. Without the intervention of a trained lifeguard, individuals may remain on the water’s surface for only 20 to 60 s before submersion occurs. Therefore, locating a missing person in the water is crucial for their survival.

2. Drowning Behaviour, Signs, and Statistics

From 2008 to 2020, Connecticut researchers ^[11] conducted autopsies on 500 bodies retrieved from the water categorised by age, gender, location, type of water body, cause of death, method of death, decomposition symptoms, body mass index (BMI), brain weight, lung weight, pulmonary oedema, stomach contents, and toxicological tests. Men more frequently drown than women (excluding cases of suicide). Two common characteristics of drowning deaths are water retention in the lungs and brain swelling. It is essential to look at the big picture while assessing anatomical data. In salt water, the brain and lungs both increase in mass. However, BMI and fat distribution also have a role. Figure 1a shows the total number of drowning victims at different locations. As depicted in Figure 1b, swimming or other recreational activities are the most common activities leading to drowning, regardless of age or location (except in the ocean or a harbour). In 80% of drowning deaths, it was unclear if drugs or alcohol played a role. However, among the remaining 20% where such involvement was determined, 58% involved legal drugs (56% involved alcohol), 19% involved illegal drugs, 15% involved legal and illegal drugs, and 8% did not involve either ^[12].

Figure 1. (a) Number of yearly drowning deaths by location. (b) Activities before drowning incidents by location (river/creek; beaches; lake/dam) in 2019/2022 ^[12].

Drowning can be categorised as active or passive. Active drowning is when a person actively tries to swim to the surface. For example, the swimmer can perform “ladder climbing” or other actions that cause them to break the water’s surface (splashing and flailing their limbs), or they may remain submerged without generating an audible sound or visual ripple. If a swimmer is actively drowning, they are either immersed or unable to keep their head above water and cannot call or signal for help. Passive drowning occurs when swimmers lose consciousness while submerged in water, preventing them from resisting and leading to death ^[13]^[14]. It was commonly thought that non-swimmers drown due to a ‘fight or flight’ response characterized by frantic movements. However, observations from witnesses indicate that drowning typically does not involve such thrashing behaviours. In some instances, a body was reported to float on the water when it stopped moving. The swimmer sank and disappeared. These reports show that drowning is a hidden killer, as the victim cannot signal for help.

While drowning mainly results from asphyxiation, incidents involving falls or dives into the ocean can sometimes lead to secondary complications such as spinal or brain injuries, which are exacerbated by oxygen deprivation but are not direct causes of drowning. Alcohol and drugs can also influence drowning and death. Drowning is a form of death through asphyxiation and severe cerebral hypoxia, also known as suffocation ^[15]^[16]. Both active and passive drowning have phases that last 10–12 min. During this interval, the person can be rescued and resuscitated without permanent harm: (1) The person inhales water. (2) If a person is at risk of drowning or oxygen depletion, their airways will close. (3) The swimmer loses consciousness, and their body slows down to conserve oxygen. (4) Water enters the lungs through the windpipe. (5) Low oxygen causes muscle twitching. (6) Without oxygen, brain damage is permanent. (7) Oxygen-deprived brain death occurs. Before stage five, a drowning swimmer can be rescued and resuscitated without long-term health effects. However, once brain damage from lack of oxygen commences, the chances of rescue and survival without long-term implications quickly diminish until stage seven. Therefore, while it takes seconds for someone to start drowning, it takes minutes to accomplish a rescue without irreversible damage, and any drowning prevention method must account for this ^[14]^[17].

Drowning often results in death and injury, but in fortunate cases, the aftermath of a non-fatal drowning may not result in significant health issues. Nonetheless, there have been documented instances where non-fatal drowning has negatively affected a person’s health and quality of life ^[18]^[19]^[20]^[21]^[22]^[23]. The brain or other organs may sustain damage, a condition known as hypoxic brain injury (owing to oxygen shortage). Preventable drowning is the leading cause of death for children under four. It has been found that swimming pools are the most common location for non-fatal drownings, especially among children ^[24]. In contrast, most adult and adolescent drownings occur in natural bodies of water such as lakes, rivers, and beaches ^[25].

The National Drowning Report by the Royal Life Saving Society Australia for 2022/23 ^[12] comprehensively analyses drowning incidents in Australia. It revealed a marginal increase in drownings, with 281 cases, a 1% rise compared to the 10-year average of 279. A significant 77% of these incidents involved males. Adults aged 45 and older accounted for 57% of the drownings, with 44% occurring in major cities. Rivers and creeks, beaches, and oceans/harbours were the most common locations, accounting for 27%, 27%, and 12% of incidents, respectively. The primary activities leading to drownings were swimming and recreating (33%), falling into water (15%), and boating (8%). Children aged 0–4 years and adults over 75 years were particularly vulnerable to drowning due to falls into water, representing 69% and 22% of their respective age group drownings. Notably, boating-related drownings decreased by 40% compared to the decade-long average. For young children under four years, fatal drowning cases decreased significantly, representing 6% of the total in 2022/23, marking a 6% drop from the previous year and a 33% decline from the 10-year average. Similarly, the crude fatal drowning rate for this age group decreased by 32% from the 10-year average and 59% from the rates observed 20 years ago. Drownings in the 5–14-year age group constituted 2% of the total, a 53% reduction from the previous year and a 35% decrease from the 10-year average. The 15–24-year age group represented 11% of drowning cases, down 17% from the previous year and 7% from the 10-year average. Interestingly, the 25–64-year age group, which accounted for 54% of drowning deaths, showed a 1% increase compared to the 10-year average. The age groups with the highest drowning rates were 45–54 years, 55–64 years, and 65–74 years, representing 15%, 15%, and 14% of the drownings, respectively. This is important when training AI models. If it is not trained using images of sufficient numbers of both males and females, an algorithm may achieve, for instance, 80% accuracy, while failing to safeguard any females. While the report does not explicitly address race, it is important to consider factors like age, gender, and other visible differences to ensure that any model appropriately protects everyone who could use or purchase an AI-based drowning detection device. Table 1 provides a summary of the most common technologies for drowning detection.

Table 1. Summary of recent methods of drowning detection with advantages and limitations.

Method	Advantages	Limitations
Lifeguard	Human judgment and experience Immediate response and rescue capability Communication and coordination with authorities	Limited physical endurance and potential for fatigue Restricted field of view and potential for human error
Video processing-drones	Aerial view for wide coverage and surveillance Rapid response and quick deployment Real-time video feed for situational awareness	Limited battery life and flight time Restricted flight regulations and airspace limitations Vulnerability to environmental conditions (e.g., wind) Affordability and accessibility in low-to-medium income countries.
Image-processing technology	Continuous monitoring and real-time data collection Accuracy and effectiveness in recognising and differentiating drowning incidents. Customisable thresholds for personalised detection Underwater drowning detection	Limited detection range and requires regular maintenance and calibration. Expensive and complex to implement. Requiring high-end AI techniques and infrastructure. Affordability and accessibility in low-to-medium income countries. Dependence on camera placement and quality
Wearable sensors	Continuous monitoring and real-time data collection Cost-effectiveness and wide availability Customisable thresholds for personalised detection Easy integration with artificial intelligence system which increases the accuracy. Affordability and accessibility in low-to-medium income countries.	Sensitivity to environmental conditions and false alarms Limited detection range and coverage Maintenance and calibration requirements Limited underwater communication

Although the number of drowning deaths is important, it is not the whole story. For every fatal drowning, there are around 2.5–2.7 times as many non-fatal episodes ^[18]. Furthermore, drowning can result in various adverse consequences other than death. Only 5% of people who survive drowning do so without suffering a permanent handicap. Considering the years of life lost, estimated lost productivity, and hospitalisation and search and rescue expenses, the average annual economic impact of fatal drownings in Australia was calculated to be around 1.24 billion AUD for the period from 2002 to 2017 ^[26]. Contrary to popular belief, drowning is extremely difficult to detect unless one is trained to detect it. There are a few basic movements or physical indications which usually indicate a swimmer is in distress, such as (1) agitated movement of the arms, (2) glossy or closed eyes, (3) tilted head with the mouth barely keeping above water level, (4) hair covering the entire face/forehead, thus obscuring a person’s vision, (5) aberrant breathing and hyperventilating, (6) swimming without a direction, and (7) floating on one’s back without any leg movement ^[27]. These signs may be commonplace indicators of drowning, but only a few are measurable parameters and are consistent occurrences for every scenario. Research shows this is mainly because drowning indicators for one person may not be applicable or legitimate for another. This can lead to either false alarms or, in some cases, failure of detection ^[28].

References

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1. Introduction

2. Drowning Behaviour, Signs, and Statistics

References