Dr Paul Luckin has spent years learning what happens to the human body when immersed in water. Based in Brisbane, he is an anaesthetist with a background in pre-hospital emergency medicine and rescue. His experience began long before his formal medical training, having trained as an ambulance paramedic in Tasmania. He spent eight years with a mountain rescue team in South Africa while specialising and practising in anaesthesia. He teaches the medical aspects of search and rescue (SAR) and advises Police across Australia on survivability during SAR operations. His insights have influenced national policies and helped save lives across Australia and the Pacific.

Paul explains that water immersion hazards are not always obvious, with hypothermia in warm waters being highly misunderstood. Many believe hypothermia can’t occur in water above 22 or 23 °C, but water conducts heat much faster than air does, causing the human body to lose heat much faster in water than in air. People in warm water will become hypothermic; it just takes longer. In warm water, the body's core temperature will drop, resulting in hypothermia. Symptoms like decreased ability to remember training, think clearly, take measures to promote survival, and progressive muscle weakness, often start well before a person recognises they are in serious danger.

Sudden immersion in cold water causes a gasp response. This is likely at water temperatures below 20 degrees, but most severe at temperatures below 15 degrees. The gasp response encompasses an immediate, involuntary and uncontrollable increase in respiratory rate, to as much as 20 - 30 breaths per minute. Tidal volume increases, possibly to two litres per breath or more. This lasts anything from about 30 secs to two minutes. With the rapid, uncontrolled breathing there is a very high risk of aspiration of water. Some may enter the lungs, but even just a few drops can cause the vocal cords to go into spasm.

Partial or complete laryngospasm reduces or completely obstructs air entering the lungs. The person is now burning up oxygen rapidly while trying to swim or stay on the surface, but is unable to take air in. Hypoxia follows, with loss of consciousness, and once unconscious and face down in the water, death is inevitable. In normal swimming, the arm and leg movements are coordinated; this is not possible during the gasp response, so swimming becomes ineffective; if the person is not wearing a lifejacket, drowning is likely to follow.

Cold water causes marked peripheral vasoconstriction, shunting blood from the peripheral vessels to the body’s core. This can raise the risk of cardiac arrhythmias, particularly in vulnerable individuals. The increased central volume causes the kidneys to increase urine production. This process, diuresis, hastens the development of dehydration. Over time, as brain function declines, individuals become less capable of swimming, thinking clearly, and keeping their airways above water. As Paul explains, "Your brain slows, your muscles weaken, and your chances of survival drop dramatically." Swimming becomes increasingly ineffective, especially without a life jacket.

Lifejackets save lives. Having a lifejacket on is the single most important determinant of survival in the water. Paul explains that people who survive do not find and slip on a lifejacket after entering the water; it has to be on before entering the water.

Paul also emphasises the importance of mental state during any water-based emergency. A calm and controlled response is essential in any life-threatening situation, both for the person under threat and for the responder. If the person under threat panics, their ability to take steps to survive is greatly reduced. A rescuer, of any organisation or level of training, can only function to their highest standard if they are fully in control of themselves. This is why emergency medical and rescue teams practice emergency situations repeatedly; you already know what to do, the exercise is to learn how to remain calm and in control and do what you have to do quickly and efficiently. More specifically, it teaches you to react quickly and get past the emotional block of confronting a life-threatening situation.

Rescue is just the beginning. Paul emphasises that the medical consequences of immersion do not end when someone is pulled from the water. There may be a delayed onset of pulmonary oedema due to aspirated water, especially if the person initially feels fine and refuses medical attention. Additionally, hydrostatic pressure and cold exposure can result in dehydration. This, combined with a sudden drop in adrenaline when rescue becomes imminent, can lead to dangerously low blood pressure, particularly if the person is lifted vertically from the water. For this reason, Paul and many water-rescue teams advocate horizontal recovery techniques, which are now standard practice in organisations like the Royal Australian Navy.

Paul admits that estimating survival time in water is extremely challenging. It depends on various factors, including physical aspects like body fat distribution and hydration, as well as environmental conditions such as water temperature, wind speed, swell and wave height, the time of day, and the individual's psychological state in the water.

He states, “There is no simple answer, or a table that includes all the many variables. Every immersion incident is different; an estimate of Time Frame For Survival (TFFS) depends on an understanding of the many physical, physiological and environmental factors involved. In each search, there are a number of different possible survival scenarios, with a different TFFS for each scenario. Given that a TFFS can only be a best estimate based on the information available, it is common for search efforts to continue beyond the end of the TFFS.

When Police call Paul, they provide a mass of detailed information about the missing person and the circumstances, including a pro-forma setting out much of the detail needed. He constructs the possible survival scenarios and the TFFS for each. Police incorporate this in the planning and conduct of the SAR.

He emphasises the importance of the close working relationship and mutual trust developed over many years, which has many times been a key factor in bringing a missing person home alive.  "It is a privilege to work with the extraordinary people involved in search and rescue who are immensely capable, highly trained, and adaptable. They come from many agencies, including Police, State Emergency Services, aircrew, ambulance and fire services."

Paul is astounded and dismayed by how many individuals still enter the water without proper preparation. He observes a common pattern: people underestimate risks, rely on inexpensive safety gear that just meets regulations, buy a lifejacket, and then neglect to wear it. They also lack familiarity with using the Emergency Position Indicating Radio Beacon (EPIRB), haven’t practised boarding the life raft, and don’t consider the unforeseen.

His message is clear: effective training and preparation are crucial for saving lives.

“Don't just plan for a pleasant outing, but plan and prepare to survive,” he adds.

This advice is relevant for the public, maritime professionals, and experienced responders alike. Anyone participating in water activities must understand how to stay afloat, signal for help, conserve energy, and operate all the equipment on their vessel. Most importantly, they should regularly practice these skills, so they are ready when needed.

Paul will also present at the Australia Regional Seminar in Sydney in August, with his presentation titled 'Medical Factors Affecting Survival in Water'.