WHETHER YOU’RE DIVING the Antarctic, chilly Scandinavia or your local lake or quarry, you make temperature one of the components of your dive plan.
You do this by asking questions such as: What’s the ambient temperature topside What’s the water temperature Are there any thermoclines How deep will I dive and for how long What exposure protection do I need – will a 7mm wetsuit be enough
In essence, you’re asking yourself: How cold am I going to get on this dive
You’re also answering that question with your dive-planning. Hypothermia can affect even tropical dives, if you’re wearing only a swimsuit or dive-skin and remain immersed for a long time.
Hypothermia is a condition of reduced body core temperature, defined as a temperature below 35°C. Exposure to cold results in heat loss at a rate dependent on several variables, including:

  • protective clothing
  • the temperature gradient between skin and the environment
  • the heat capacity of the environment (much greater for water than air)
  • body structure (lean versus fat fractions and mass-to-surface area)
  • wind or water movement

Water conducts heat 20-27 times faster than air. Sudden exposure to water colder than 15°C with no thermal protection results in an involuntary gasping response. This can cause inhalation of water and cardiac dysrhythmias.
In such instances, a response usually continues for one to two minutes, with extremely rapid breathing.
When this happens, the hypothermic person can experience pain and mental disorientation, leading to fear and panic.
Thermal protection by a wetsuit, drysuit or other survival-type suit dramatically decreases the immediate effects, but heat loss will still occur over time.
Swimming may not help. Heat production is increased by exercise or shivering, but for those with little or no thermal protection, swimming increases the exposed surface area and rate of heat transfer to the water.
On average, swimming can help maintain core temperature in water warmer than 24°C.
The core temperature of unprotected swimmers drops in colder water, resulting in an inability to continue swimming (known as swimming failure).

In deep water
Divers who are immersed unprotected in cold water should remain still, holding a position to minimise their exposed surface area (this is far easier to accomplish with some kind of
buoyant support).
Pulling the knees together and up towards the chest – into the heat-escape-lessening position, or the “help” or rescue position – provides improved protection of the high heat-loss areas of the armpits, groin, anterior chest, abdomen and thighs.
Hypothermia can also occur in relatively warm or even tropical waters up to the 29-33°C range, as a result of slow body cooling if you have no thermal protection.
You may not be aware of the slow heat drain for some time, but then the common signs (observable manifestations) and symptoms (subjective, non-observable manifestations) of hypothermia emerge.

Mild hypothermia
Hypothermia may be mild, with little risk to the individual, or it may be severe, with the possibility of death. If you suspect that you’re dealing with a hypothermic diver, you can use a variety of rewarming strategies.
These depend on the degree of hypothermic injury, the level of consciousness of the victim, the nature of other injuries and the availability of resources and additional medical aid.
Someone with mild hypothermia will be awake, conversing lucidly, complaining of cold and probably shivering.
Assuming that he or she has no other injuries, you can rewarm a mildly hypothermic diver with a variety of passive or active techniques.
Remove wet clothing and replace with dry insulating inner and windproof outer layers, including the head, whenever possible.
Shivering at this point will provide effective rewarming. A diver who feels comfortable exercising at this point can increase the rewarming rate by this type of movement.
Exercise will transiently increase the “afterdrop” – a continued decline in core temperature after removal of (or from) the cold stress – but this should not be problematic in most cases of mild hypothermia.
A fully alert and co-operative hypothermic diver can have warm liquids to drink. This delivers negligible amounts of heat but will help to correct the inevitable dehydration and provide a sense of comfort.
Most beverages can be used, but avoid alcohol. It can compromise awareness and contribute to dehydration and inappropriate vasodilatation.
Light snacks can help, too. Food helps to augment the victim’s caloric reserves.

Moderate hypothermia
A diver with moderate hypothermia will be awake but may be confused, apathetic or unco-operative, and have difficulty speaking. Moderate hypothermia demands more caution, because this injury can lead to cardiac dysrhythmias.
If possible, use gentle handling and active techniques such as heated blankets, forced-air rewarming and heated and humidified breathing.
Physical exercise is not recommended for a moderately hypothermic diver. Physical co-ordination is likely to be compromised, and exercise at this point may increase the potential for afterdrop.
When it occurs, afterdrop can increase the risk of physiological collapse sometimes observed during or shortly after rescue from immersion (called circum-rescue, or post-immersion collapse).
Handle hypothermic divers gently, including keeping them supine (at rest, on the back) and completely at rest. This reduces the risk of collapse. Be attentive, and use the most effective alternatives at hand when rewarming.
Take care to insulate injured divers from the ground or surroundings, even if they do not communicate the need.
A warmwater bath is another good option for the moderately hypothermic diver. You will need to provide physical support, however, throughout the transfer and immersion.
The initial immersion temperature should be lukewarm, definitely not more than 40°C, to avoid the sensation of burning that the person would be likely to experience.
After immersion, the water temperature can be progressively increased, but to no more than 45°C, to avoid burns.
If hot water is not available, augment insulated clothing with chemical packs or electric pads.
To avoid burns, never apply these directly to the skin.

Severe hypothermia
Divers with severe hypothermia may be unconscious, with a slow heart rate and respiration, or may even appear dead, with no detectable heartbeat.
Look very carefully for signs of life, such as breathing, movement, or a pulse at the groin or in the neck over the carotid artery.
Assess breathing and check the pulse for at least one minute to confirm respiratory arrest or pulseless cardiac arrest, which requires CPR.
If there is either breathing or heartbeat, external heart massage (chest compression) is not needed.
If you observe breathing or movement, the victim’s heart is beating, even if it’s very slow. Because of this, it’s essential to spend sufficient time checking for spontaneous pulse.
For the unconscious hypothermic diver, the main goals are to maintain adequate blood pressure and respiration and to prevent further heat loss.
If the breathing rate is six breaths or fewer per minute, start very gentle mouth-to-mouth breathing at a slow rate.
Severe hypothermia leaves the victim susceptible to cardiac arrest. Extremely gentle handling – supine position, fully supported, no physical activity – and aggressive (and often invasive) rewarming strategies are required to save anyone so affected.
The heart is especially susceptible in these cases. The severe cold can lead to cardiac arrhythmias, but rewarming too aggressively can also trigger them.
In most cases of severe hypothermia, basic life support takes precedence over efforts to rewarm.
Death from coldwater immersion usually results from loss of consciousness and subsequent drowning.
If drowning preceded the hypothermia, successful resuscitation is unlikely. If there are no signs of life, begin CPR and arrange for emergency transport to the nearest medical facility.
Complete rewarming of a diver with severe hypothermia is almost impossible to accomplish in the field. Protect against further heat loss, however.
If CPR is required, it should be continued, if possible, until medical assistance arrives. There have been successful resuscitations after prolonged CPR, in part because of the protective effect of hypothermia.
The outlook is poor in adults who have a core temperature below 28°C, have been immersed for more than 50 minutes, have life-threatening injuries or are more than four hours from definitive medical care.
Although the injured can appear to be clinically dead because of marked depression
of the brain and cardiovascular function, full resuscitation with intact neurological recovery is possible, if unusual.

Discontinue CPR only if:
  • The person is successfully resuscitated
  • Rescuers become too fatigued to continue
  • The diver has completely rewarmed and is still unresponsive to properly applied CPR.
  • A medically trained and qualified person arrives at the scene and, after examination, declares the diver dead.

    The prevention of hypothermia requires preparation. Divers must understand the use of protective garments to conserve body heat and control heat loss.
    Most divers will benefit from wearing thermal protection in water cooler than 27°C, and significant thermal stress can be expected in water colder than 24°C.
    Divers should ensure that they have the proper protective equipment and experience to dive safely in cool or cold waters.
    Don’t let the cold keep you out of the water. Just be prepared when you go.


    • Assess ABCs – Airway, Breathing and Circulation of the injured diver
    • If CPR is required, continue until the emergency services arrive
    • Give as much oxygen as possible
    • Determine cause for immersion
    • Support and immobilise the neck if injury is suspected
    • Arrange transport to a medical facility
    • Prevent further heat loss
    • Rewarm if needed

    DO NOT
    • Risk your life in a rescue attempt
    • Interrupt CPR unnecessarily.


    MILD HYPOTHERMIA (core temperature 32-35°C)
  • Increased heart rate
  • Shivering
  • Impaired co-ordination
  • Introversion/inattentiveness
  • Uncomfortably cold
  • Decreased motor activity
  • Impaired ability to concentrate
  • Fatigue
    MODERATE HYPOTHERMIA (core temperature 28-32°C)
  • Increasing lack of muscular co-ordination
  • Stumbling gait
  • Shivering slows or stops
  • Slurred speech
  • Weakness
  • Confusion
  • Drowsines
  • Amnesia
  • Hallucinations
    SEVERE HYPOTHERMIA (core temperature below 28°C)
  • Inability to follow commands
  • Absence of shivering
  • Decreased heart rate
  • Dilated pupils
  • Inability to walk
  • Decreased blood pressure
  • Loss of consciousness
  • Appearance of death
  • Decreased respirations
  • Muscle rigidity

    This article is the copyright of DAN Europe Foundation