The 45-Second Summary
- The 1-10-1 is a landmark, not a stopwatch. It shows the order in which the threats arrive, but the timelines vary widely from one person and one situation to the next.
- The first priority is keeping the airway out of the water. Float, get your breathing back under control, then decide what to do.
- The inability to swim or hold on may occur before hypothermia sets in. The hands and arms may become useless even while the core body temperature is still normal.
- Repeated exposure to the cold mainly lessens the initial shock. It does not protect against loss of strength, cooling of the limbs, or hypothermia.
- During a rescue, handle the victim gently, remove them while they are lying down whenever possible and safe to do so, and then protect them from the cold, wind, and moisture. After a drowning, CPR must include rescue breaths and chest compressions.
It was while reading a recent post by Jørgen Melau that I started thinking again about how we teach cold water immersion.
Many of you already know his work on cold physiology and on the Norseman Extreme Triathlon. His post draws on a narrative review he has just co-authored in the Journal of Applied Physiology with Laura Leuci, Antonio Messina, Mike Tipton and Luca Carenzo. The authors revisit, one by one, the four classic phases of cold water immersion: cold shock, swimming failure, hypothermia and collapse around the rescue.
Their central message is simple: in cold water, hypothermia is generally not what kills first.
It took me back to a course I took with Gordon Giesbrecht about fifteen years ago. He asked the group what we thought was the leading cause of death after a fall into cold water. Almost everyone answered hypothermia. Yet the room was full of experienced people, several of whom were already teaching the subject.
We had the right phenomenon, but at the wrong moment.
The British data cited in the new review illustrate the problem well. Roughly 60 % of cold water deaths are thought to occur during the first two phases, before significant hypothermia has had time to set in. Between 2019 and 2023, 55 % of accidental open water drowning victims in the United Kingdom were within three metres of a place of safety; about two thirds were regarded as competent swimmers.
Three metres, and yet unable to cover them.
So I went back to look at what we teach on this side of the Atlantic.
The good news is that the Canadian framework remains highly relevant. The 1-10-1 puts the threats in the right order and directs attention to the first few minutes, when most victims still have a chance to act. It does need to be taught for what it is: a memory aid, not a physiological stopwatch.
The 1-10-1: An Excellent Framework, as Long as You Don't Take It Literally
Gordon Giesbrecht popularized the 1-10-1 in the mid-2000s, notably through the Cold Water Boot Camp project run with the Canadian Safe Boating Council.
1. About one minute to let the initial shock pass and regain some control over breathing.
2. About ten minutes of useful movement before cooling of the limbs seriously compromises the ability to self-rescue.
3. Up to one hour before loss of consciousness attributable to hypothermia.
As a teaching tool, it is hard to beat. Three numbers, three phases, one message that is easy to remember.
But the timelines vary enormously. Water temperature, clothing, whether a personal flotation device is worn, body composition, health status, activity in the water, wind and waves all change the trajectory. The initial shock can last more than a minute. Functional incapacity can appear in two minutes or in thirty. And “one hour” is certainly no guarantee of consciousness or survival.
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The 1-10-1 therefore describes a sequence. It does not provide a reliable timeline. |
The First Minute: Protect the Airway Above All
The gasp reflex occurs within the first few seconds. It can amount to an involuntary inspiration of two to three litres, followed by hyperventilation that is difficult to control and often persists for one to three minutes.
If the face is under water at the moment of the reflex, the victim may aspirate immediately. If the airway stays clear, the hyperventilation produces hypocapnia, reduces cerebral perfusion and promotes dizziness, disorientation and panic. Voluntary breath-hold time can drop from about a minute to a few seconds.
The point to drive home in your courses is this: willpower alone cannot reliably override this response. Repeated exposure can blunt it, and I will come back to that, but no one should count on their composure, their experience or their fitness to make it disappear.
The immediate priority is therefore to keep the airway out of the water and to reduce effort. With a flotation device, you let yourself float and wait for your breathing to settle before deciding what to do. Without flotation, you first look for a position that keeps the mouth and nose clear. This is not the moment to set off swimming without a plan, or to waste energy removing clothing.
The HELP position remains relevant when someone is wearing a flotation device and has to wait for rescue. But it comes after the airway and breathing are under control. Float and breathe first; then reduce heat loss.
The Minutes That Follow: The Core Can Be Warm While the Limbs Stop Responding
The second phase probably deserves the most attention, because it is often where the victim still has a chance to save themselves.
As the arms and legs cool, peripheral nerve conduction slows, muscle strength falls and movements become less precise. Manual dexterity deteriorates markedly once finger skin temperature drops below about 15 °C. Below about 8 °C, tactile sensitivity can be almost abolished.
In water near freezing, these thresholds can be reached within minutes. A person may then lose the ability to grip a line, pull themselves onto a boat, operate a buckle or swim effectively, while their core temperature is still normal.
This is an essential distinction: cold-induced incapacity generally precedes hypothermia.
It also helps explain deaths that occur very close to a place of safety. Cold is not necessarily the only cause; alcohol, waves, injuries, current, fatigue, acute illness or the absence of flotation can all contribute. But peripheral cooling can be the factor that turns three metres into an impossible distance.
It is also what explains how a victim can drown while their core temperature is still nearly normal. Cold may have caused swimming failure, or contributed to an arrhythmia, long before true hypothermia appeared.
Can You Get Used to the Cold?
The short answer is yes, but far less than people think.
Repeated cold water exposure can blunt the initial shock. A systematic review published in 2024 concludes that measurable habituation often appears after roughly four repeated immersions, with substantial variability between studies. Respiratory rate, minute ventilation and the cardiac response can all decrease. The experience does become genuinely more tolerable.
This habituation is useful. It can make the first few seconds less distressing and support a calmer response. But it is not armour against the cold.
The metabolic and insulative adaptations described in humans are modest and inconsistent. More importantly, nothing shows that they meaningfully prevent the loss of strength, dexterity and coordination that follows when peripheral nerves and muscles cool. Brown fat and non-shivering thermogenesis are physiologically interesting, but they cannot be presented as demonstrated protection against drowning or swimming failure.
In other words, the experienced winter swimmer may well have a far more comfortable first minute than a beginner. That does not mean their hands will keep working for long in near-freezing water, or that they are protected against prolonged hypothermia.
In training, I would therefore put it this way: you can habituate the shock response, but you do not become resistant to the effects of cooling.
This nuance matters, because subjective comfort can grow faster than actual protection. It is not an argument against cold water swimming. It is an argument for keeping a margin of safety, staying near an exit point, avoiding swimming alone and using suitable flotation.
The Hour: The Most Variable Marker in the Model
After prolonged immersion, core temperature does of course eventually fall. Shivering increases, then fades as hypothermia worsens. Cognitive function deteriorates and loss of consciousness becomes likely as core temperature falls toward 30 to 28 °C. Below about 28 °C, the risk of ventricular arrhythmia rises sharply.
But the time needed to reach those thresholds is not fixed. A lean person, without flotation, active in rough and very cold water, does not follow the same trajectory as someone in a wetsuit and a PFD, motionless in calmer water. The idea of “one hour” should reassure enough to prevent panic, without creating a false sense of security.
Hypothermia remains a major threat during prolonged immersion. The correction to make is not to minimize it, but to place it back in the sequence: in many cold water drownings, aspiration and hypoxia occur while the victim is still relatively warm.
Autonomic Conflict: Plausible, Important, but Not Fully Proven
Sudden immersion triggers a strong sympathetic nervous system response: tachycardia, vasoconstriction and a rise in blood pressure. Facial immersion and breath-holding simultaneously activate the diving reflex, predominantly parasympathetic, which favours bradycardia.
The heart can therefore receive two opposing signals at the same time. This is what is known as autonomic conflict.
Arrhythmias, generally non-lethal, have been observed in healthy volunteers during immersions combining cold water, facial immersion and breath-holding. The mechanism of a fatal arrhythmia nevertheless remains difficult to prove in humans. It appears most concerning in the presence of a pre-existing condition, for example long QT syndrome, catecholaminergic polymorphic ventricular tachycardia, structural heart disease, or the use of a medication that prolongs repolarization.
Congenital long QT syndrome is thought to affect roughly one person in 2,000. In a selected series of unexplained swimming-related drownings, close to 30 % of victims carried a cardiac channel mutation consistent with an inherited arrhythmia syndrome. That figure cannot be applied to all drownings, but it is a reminder that a drowning can sometimes be the first manifestation of an electrical heart disease, particularly in a young person.
In training, I would therefore teach it as a plausible and clinically important mechanism, but not as a certain explanation for every sudden death in cold water.
Afterdrop: Real, but Probably Not the Whole Story
Collapse at the moment of extraction was long explained by a simple scenario: very cold blood returns abruptly from the limbs to the heart, core temperature falls and the patient fibrillates.
The reality is more complex.
Afterdrop is the continued fall in core temperature after the exposure ends, and it is entirely real. It results from a combination of conductive heat transfer toward cold peripheral tissue and convective transfer through the blood. In most experimental exposures the fall is modest, often in the range of 0.5 to 1.5 °C. In a deeply hypothermic and already unstable patient, however, even a limited fall can become clinically important; larger decreases have also been reported.
So one dogma should not simply be replaced by another: afterdrop is neither a myth nor the sole explanation for collapse around a rescue. The haemodynamic mechanism is probably at least as important as afterdrop, even if its exact contribution remains hard to quantify.
In the water, buoyancy reduces the effects of gravity. Some of the blood that would normally pool in the legs is redistributed toward the thorax, increasing central blood volume by roughly 500 to 700 mL. On extraction, that shift reverses abruptly: blood pools again in the limbs and venous return to the heart falls. Most people compensate easily, but a deeply hypothermic and already unstable victim can develop a drop in blood pressure, syncope or, more rarely, cardiac arrest.
This is the main physiological reason for favouring horizontal extraction of a victim.
What This Changes on Scene
Extract Horizontally When It Is Possible and Appropriate
When someone appears moderately or severely hypothermic, we try to bring them out lying down rather than upright. For example, when raising them from a crevasse, hauling them aboard a boat or evacuating them by winch, we avoid leaving them hanging vertically as much as possible.
The priorities do need to stay in the right order, though. Rescuer safety and airway management come before a perfect position. If going horizontal complicates the rescue, delays necessary ventilation or increases the risk of losing the airway, the manoeuvre is adapted. The principle should guide the rescue, not paralyse it.
Interpret a Shockable Rhythm Without Delaying the Shock
Shockable rhythms are a minority in drowning-associated arrests, on the order of 2 to 12 % depending on the series. The usual trajectory of a hypoxic arrest leads instead to bradycardia, then to pulseless electrical activity (PEA) or asystole.
Ventricular fibrillation or pulseless ventricular tachycardia, two normally defibrillable rhythms, therefore remain atypical. They must be treated immediately, as always, but they should also widen the differential: did a primary cardiac event precede the submersion? In a young victim, or when the circumstances remain unexplained, the investigation may warrant toxicology, a molecular autopsy and, depending on the results, family screening.
Don't Forget the Rescue Breaths
Drowning is first and foremost a problem of hypoxia. AHA/AAP recommendations therefore insist on CPR that includes both ventilations and compressions. For a trained rescuer, starting with either ventilations or compressions is acceptable; what matters is integrating both quickly and not delaying CPR.
Compression-only CPR is not the preferred approach after a drowning. It remains preferable to no CPR at all, however, when a bystander is untrained, unable or unwilling to ventilate.
Handle the Moderately or Severely Hypothermic Victim Gently
In a patient who is confused, without effective shivering or very cold, we avoid exertion, unnecessary limb movement and vigorous rubbing. Wet clothing is removed once the patient is protected from the cold, ideally by cutting it if that limits handling. We insulate from the ground, add a barrier against moisture and wind, then apply appropriate external rewarming to the trunk.
In the field, the essential step is wrapping the victim well, with good insulation underneath the body, dry layers and protection against moisture and wind. Skin-to-skin contact adds little to shivering and ties up a rescuer for limited gain. Hot water bottles or heat packs wrapped in cloth can be added over the chest, the upper back and under the armpits.
Measure Temperature With What You Have
In hospital, oesophageal temperature remains the reference measurement in an intubated patient. It tracks core temperature changes quickly, but this type of probe is rarely available in the field.
In the absence of a reliable measurement, we rely mainly on clinical status. The Revised Swiss System uses level of consciousness as its main criterion: alert, responding to voice, responding to pain, or completely unresponsive. We then check whether vital signs are still present. Shivering is still worth observing, but it is too variable to determine the severity of hypothermia on its own. The temperatures associated with each stage are approximate and can overlap.
If temperature can be measured in the field, the rectal route often remains the most practical, once the victim is sheltered and well protected from the cold. It does respond slowly to change. Teams equipped with an epitympanic thermistor, which should not be confused with an infrared tympanic thermometer, can use it in a spontaneously breathing patient: this is the measurement favoured by ICAR MedCom in that setting. Oral, infrared tympanic and skin temperatures are too unreliable to guide management.
The Line to Remember
Hypothermia is real, dangerous and decisive during prolonged immersion. But in many cold water drownings, it is not the first threat. The initial shock, aspiration and loss of motor capacity can kill well before core temperature has fallen significantly.
On scene, the question is therefore not only: how cold is this person?
We also have to ask: which came first, the cooling or the hypoxia?
That distinction shapes prognosis, resuscitation, destination and the interpretation of a cardiac arrest.
In my opinion, the 1-10-1 remains an excellent teaching tool—provided it is presented as a hazard map, not as a weather forecast.
Message During Your Training Sessions
The 1-10-1 as a Teaching Anchor
The 1-10-1 remains an excellent tool for teaching the order of the threats. It does need to be presented as a landmark, not as a stopwatch.
1 minute to secure your airway and regain control of your breathing. The priority is to float and let your breathing stabilize before attempting to swim or get out of the water.
10 minutes of useful movement. This is an approximate time frame. The hands and arms may stop functioning much sooner, even while the core body temperature is still normal.
1 hour before losing consciousness due to hypothermia. This is a rough estimate, not a guarantee. Water temperature, clothing, buoyancy, body type, and physical activity can significantly affect this timeframe.
The Reminders to Add Around the Model
- Cold-induced incapacity often precedes hypothermia. A person can be unable to swim, to grip or to pull themselves out of the water while their core temperature is still nearly normal.
- Repeated exposure mainly blunts the shock of the first minute. It does not protect against cooling of the limbs, loss of strength or prolonged hypothermia.
- In a very cold victim, horizontal extraction is preferred when it is possible and safe.
- After a drowning, CPR must include ventilations as well as compressions. Compressions alone remain a fallback when the rescuer cannot ventilate.
- A shockable rhythm is unusual after a drowning. It must be treated immediately, while also raising the possibility that a cardiac problem preceded the fall into the water.
- In the field, rewarming rests first on a good insulating wrap and protection against moisture and wind. Hot water bottles or heat packs wrapped in cloth can be added over the chest, the upper back and under the armpits.
- In the absence of a reliable temperature measurement, we rely on level of consciousness, vital signs and the overall clinical picture. Oral, infrared tympanic and skin temperatures should not guide management.
References
4. Leuci L, Melau J, Messina A, Tipton M, Carenzo L. Beyond hypothermia: mechanisms of death, rescue, and prevention in cold water immersion - a narrative review. J Appl Physiol (1985). Publication en ligne le 30 juillet 2026. doi:10.1152/japplphysiol.00578.2026.
5. Melau J. Beyond Hypothermia. Jørgen Melau's Mixed Physiology. 7 août 2026.
6. Giesbrecht GG. Cold stress, near drowning and accidental hypothermia: a review. Aviat Space Environ Med. 2000;71(7):733-752.
7. Giesbrecht GG, Wilkerson JA. Hypothermia, Frostbite and Other Cold Injuries: Prevention, Survival, Rescue, and Treatment. 2e éd. Mountaineers Books; 2006.
8. Barwood MJ, Eglin C, Hills SP, et al. Habituation of the cold shock response: a systematic review and meta-analysis. J Therm Biol. 2024;119:103775. doi:10.1016/j.jtherbio.2023.103775.
9. Shattock MJ, Tipton MJ. 'Autonomic conflict': a different way to die during cold water immersion? J Physiol. 2012;590(14):3219-3230. doi:10.1113/jphysiol.2012.229864.
10. Tester DJ, Medeiros-Domingo A, Will ML, Haglund CM, Ackerman MJ. Unexplained drownings and the cardiac channelopathies: a molecular autopsy series. Mayo Clin Proc. 2011;86(10):941-947. doi:10.4065/mcp.2011.0361.
11. Dow J, Giesbrecht GG, Danzl DF, et al. Wilderness Medical Society Clinical Practice Guidelines for the Out-of-Hospital Evaluation and Treatment of Accidental Hypothermia: 2019 Update. Wilderness Environ Med. 2019;30(4S):S47-S69. doi:10.1016/j.wem.2019.10.002.
12. Dezfulian C, McCallin TE, Bierens J, et al. 2024 American Heart Association and American Academy of Pediatrics Focused Update on Special Circumstances: Resuscitation Following Drowning. Circulation. 2024;150(23):e501-e516. doi:10.1161/CIR.0000000000001274 .
13. Weenink RP, Wingelaar TT. The circulatory effects of increased hydrostatic pressure due to immersion and submersion. Front Physiol. 2021;12:699493. doi:10.3389/fphys.2021.699493.
