The first 30 seconds of Immersion in open water is dangerous

The first 30 seconds of Immersion in open water is dangerous

Mon, 20 Apr 2015

Be careful


Our thoughts go to the family and friends of the young 19 year old man who tragically lost his life in the waters of Hampstead Pond last week. His loss is a sad one not just for those who knew him well but also for those who swim in open water.

This piece is not about speculation as to what happened but to advise on one of the many dangers of open water swimming. 

Spring is a dangerous time of year when air temperatures can greatly exceed water temperatures and sudden immersion in open water can lead to death.

This can happen when a person’s two types of skin surface heat sensors conflict with each other when the swimmer makes contact with cold water. 

One theory regarding what can happen is that when a person jumps from warm air into cold water, two distinctly different things happen; first the heat sensors in the body say to the brain pump more blood and oxygen as we need to get warm.  Secondly when the heat sensors in your face feel the cold water, they think you are drowning and they say slow down, save oxygen. Both these reactions happen at the same time. This can be compared with the ‘accelerator’ and the ‘brake’ in our system or ‘United’ versus ‘City’. When both systems are challenged by sudden immersion the body’s natural protection system is conflicted. This is especially relevant when waters are below 15C or (60F) and when the air temperature feels ‘warm’.

A suggested cautionary measure on entering water is to always splash your face and neck with water first, thus alerting your system about what is going to happen, and then gradually enter the water. This is especially important if you have not been in the recent habit of getting into cold water.


 Below is a more detailed summary of the condition known as ‘autonomic conflict’ as written in an academic paper by Professor Mike Tipton from the University of Portsmouth.

For some swimmers, there is a risk of drowning when swimming in waters below 15C. Sudden death can occur with ten seconds of the first breath exhalation. It’s believed that this happens because the heart tries to rebalance blood flow by pumping quickly and slowly at the same time, leading to a system crash. 

Professor Mike Tipton from the Extreme Environments Laboratory of the University of Portsmouth believes that some swimmers with predisposing conditions can suffer sudden death when entering waters below 15C (60F). His research paper Autonomic Conflict’: a different way to die during cold water immersion presents the case for believing that following sudden entry into cold water, a swimmer’s heart is subconsciously compelled to perform two competing jobs at the same time. The heart is asked to both pump blood quickly, and simultaneously, to also pump blood more slowly. Tipton compares this to driving with your foot on the brake and the accelerator at the same time. Cars might cope, but certain swimmers cannot. He calls this ‘autonomic conflict’ and believes it causes sudden death in some swimmers.(The autonomic nervous system is the part of our peripheral nervous system, which controls bodily functions usually sub-consciously.)


Approximately 500 immersion-related deaths occur annually in Britain. And drowning is the second most cause of accidental death in children and the third most common in adults. Tipton and Mike Shattock, his co-researcher, were puzzled as to why 67% of drownings occurred in strong swimmers, with 55% of those occurring three metres from safety.  They believe that the greatest danger is when the water temperature is below 15C and when there is a distinguishable difference between air temperature and water temperature. 



One of the easiest methods for inducing autonomic conflict is to rapidly submerse yourself in water below 15C (60F). In layman’s terms and using football rivalry to interpret Tipton’s “autonomic conflict”, it’s a bit like United versus City where the conflict is split into two sides; with ‘cold shock’ taking on the ‘diving response’. 

When you dive into cold water your heart receives two conflicting messages, one from the brain and the other from the skin. Your brain reacts with the diving response and tells your heart to slow down the rate of blood circulation and thus conserve oxygen. At the same time, your skin reacts with the cold shock response and tells the heart to accelerate the flow of blood.  

Cold shock involves a reflex action when water hits skin surface receptors on the body, where following a gasp, the heart rate rises. Hyperventilation can also occur. The skin receptors send a message to the heart to pump blood more quickly to radiate more heat across your body. 

Diving response is a reflex action stimulated by the brain, which sends a signal by the vagal nerve to the heart telling the heart to conserve oxygen and thus extend time underwater. The brain’s message is to reduce the flow of oxygen as it thinks you might be drowning and will need to preserve oxygen.

The diving response causes vasoconstriction in the body and legs. The primary function of the diving response is to conserve oxygen consumption and extend the time someone can be underwater. 

The diving response is activated by the cooling of the cold receptors on the face and by stimulation of the vagal nerve in the larynx (voicebox) and the passage behind your nasal passage (larynx). 

This becomes more complicated if the lungs are expanded, which they would be during swimming. The brain would then tell the heart to pump more blood.

The heart tries to rebalance blood flow by pumping quickly and slowly at the same time, leading to a system crash. 



Many people dive into cold water giving the body no advance warning regarding what will happen. So perhaps, one method of alerting the body to what will happen is first to ensure that your breathing is normal, enter slowly, feet first, and splash your face and neck with cold water to provide an early signal to the subconscious about your swimming intentions. At all times maintain a strong breathing pattern. An even safer method is to not submerge your head below water for the first twenty strokes. 



Tipton also cited research regarding Korean women divers whose rate of arrhythmia increases from 43% IN summer, to 72% in winter. When young healthy volunteers were assessed using head-out immersion, the rate of arrhythmia was around 2%. Tipton tested people on a body and head-submerged basis, and also on a head-out basis. Incidences of arrhythmias were more frequent when head and body were submerged resulting in rates of 62-82% occurrence. Tipton believed that release of breath holding was also a point at which arrhythmias occurred. 



Tipton believes that the most dangerous time of year for sudden drowning is early summer in the Northern hemisphere when air temperatures rise in advance of water temperatures. He rules out hypothermia as the cause as he believes that it requires a longer time to develop. 



It is not clear whether the wearing of a wetsuit has an impact of either a positive or negative nature or whether it masks conditions. But what was clear, was that arrhythmias were more frequent in less aerobically fit individuals.



Tipton included a caveat in his paper saying that autonomic conflict “may be more widely responsible for sudden death in individuals with other predisposing conditions.”  This includes those taking antihistamines, antibiotics, antipsychotics drugs or alcohol. 



To reduce the chances of suffering autonomic conflict, you should be aerobically fit as part of your lifestyle. On entering water, focus on establishing steady breathing patterns, walk in and use some water and splash this on your face and throat. Continue getting in slowly and swim head up for a while until you feel in control of your swimming, and then if you feel comfortable, drop your face in the water. 

You swim at your own risk and never swim alone.

[John Tierney]