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Scuba Diving Heat Loss Management

During lengthy immersions, recreational divers lose body warmth underwater due to two heat transfer mechanisms - conduction and convection.

This section explains how heat loss occurs in scuba diving and how to handle mild and severe cases of immersion-related hypothermia during and after a dive.

What is Hypothermia in Scuba Diving Terms

The key factors that affect loss of body heat in cold environments are:

The temperature gradient between bare skin and the surroundings.
Heat capacity of the environment (this is far greater for water).
Exposure protection (e.g. neoprene wetsuit or diving dry suit).
Body composition (high "lean-to-fat" ratios and lower "body-mass-to-surface-area" ratios speed up the cooling process).
The weather and water conditions (e.g. wind, rain, water movements, cold upwelling currents).

Pro Tip: The simple definition of scuba diving hypothermia is when the core temperature of the body drops below 35° Celsius (95° Fahrenheit).

Dangers of Heat Loss in Diving

The main reason why immersion in cold water leads to hypothermia is because water conducts heat away from the body more than twenty (20) times faster than air.

Without adequate thermal protection, an abrupt dive into water colder than 15° Celsius can trigger the Cold Shock Response. The effect can also cause salt water aspiration syndrome for divers, snorkelers, and swimmers.

Furthermore, the heart beats faster and there will be an increase in the breathing rate. The sudden cold shock may also lead to pain (e.g. headache), mental disorientation, and panic.

Tips for Preventing Scuba Diving Hypothermia?

Are you a diver that gets super cold while scuba diving or snorkeling? If the answer is yes, there are several things you can do to prevent hypothermia - or at least reduce the severity.

Wear the Right Exposure Suit

First, always wear an exposure suit that is adequate and heat loss efficient. It's fair to say some of the best places to scuba dive have warm water.

Even so, wearing a thin wetsuit (e.g. 3mm shorty wetsuit), or a hooded vest, will provide some protection against rapid heat loss and hazardous marine life.

Of course, you will need to wear a much thicker wetsuit (or even dry suit with undergarments) if you dive in very cold water or you enjoy making deep dives. If so, remember to wear dive gloves, a hood (or a scuba beanie), and dive shoes (boots)

Have a Windproof Jacket

One of the common mistakes beginners make is not having any appropriate clothing to wear after the diving has finished. Almost always, exiting the water is going to expose your body to the chill of the wind, and in some cases, cold rain.

So, it is best to remove your wetsuit as soon as you get out of the water and put on a warm and windproof jacket and a woollen hat. Remember, wearing a damp wetsuit is going to contribute to evaporation - and lead to further heat loss.

Recognise the Signs of Hypothermia

There are some common factors that make divers more vulnerable to heat loss and hypothermia. Typical examples include:

Dehydration (including drinking alcohol or taking drugs)
Being in poor physical condition
Strenuous exercise (e.g. swimming against a current)

Pro Tip: As a scuba diver, you should know what to do if you get cold while diving and you can't stop shivering, or you see your dive buddy shivering. End the dive in a safe manner (without delay) get out of the water, dry off, and put on some warm clothing.

Mild Hypothermia Symptoms

Shaking, shivering, quivering, and trembling
Pale, cool skin
Slow, shallow breathing
Poor coordination and low energy
Slurred speech (clumsiness, mumbling)
Usually responsive with apathy and slow thinking
Weak pulse

Mild Hypothermia Treatments

Change into dry, warm clothes if available.
Protect bare skin and the head from inclement weather.
Provide warm, sweet drinks (excluding alcohol and caffeine).
Seek medical evaluation if the victim fails to make rapid improvements.

Symptoms of Severe Hypothermia

Most of the body shivers start to slow down or stop and there will be increasing muscle stiffness.
The patient's consciousness will be more clouded and there will be less rambling or slurred speech.
Breathing and pulse gets slower and will be difficult for first responders to detect any signs of circulation.
As the condition worsens, there may be heartbeat irregularities (arrhythmia). The patient may have fixed and dilated pupils and they may have no signs of life whatsoever (appear dead).

Severe Hypothermia Treatments

If Responsive

Seek urgent medical assistance (e.g. call the DAN 24 Hotline number). Lay the victim down as flat as possible and handle them gently.
Insulate them from the environment and wrap their body in blankets, or apply extra clothing.
Monitor the patient's vital signs and give them warm sweet drinks if they are responsive, stable, and able to swallow.
Do not rub or massage the patient.
Do not expose the patient to sources of excessive heat (e.g. fire, heater).

If Unresponsive

Seek urgent medical assistance, lay the victim down flat, handle them with care, and insulate them from the environment.
Monitor the patient's vital signs.
Check responsiveness and breathing, commence CPR if not present.
If available and trained to do so, give oxygen to the injured diver (warmed if possible).

Extreme Cold: Special Considerations

In some situations active rewarming may be appropriate, such as if the victim is no longer shivering and medical aid is delayed.

Following the recommended care guidelines, apply wrapped heat packs or warm hot water bottles to the armpits, groin, trunk, and side of the neck. The source of heat should be warm or tepid, but not too hot.