Cold Water Shock – What Happens and How to Survive It

Cold water shock is one of the most serious hazards faced by boaters, paddlers, sailors, open water swimmers and anyone working or playing near the water. It is sudden, frightening and can affect strong swimmers just as easily as beginners. The danger is not simply “getting cold”. Cold water shock occurs the second you hit cold water and is the bodies reaction to sudden immersion in cold water.

Beneath the skin are hundreds of thousands of cold receptors which in normal circumstances can detect subtle temperature fluctuations of a degree or more of difference between what the body comes into contact with and your core body temperature. When you are immersed in cold water (water at 15C or less) these cold receptors feel “cold pain”. They send a message to the brain. Sudden skin cooling triggers powerful automatic reflexes. The body reacts as if under threat: you gasp, breathing becomes rapid and hard to control, heart rate rises and blood pressure increases. Cold water shock can kill very quickly. It usually does so indirectly, by causing an involuntary gasp, uncontrolled breathing, water inhalation, drowning, or a sudden cardiovascular event. The casualty may die long before hypothermia has had time to develop.

Involuntary breathing when in water can clearly lead to drowning, for this reason it is important to keep your mouth above water and to protect your airway. If your mouth is underwater when that first gasp happens, you can inhale water before you have had any chance to think.

The accelerated circulation can put enormous pressure on the heart and in turn a sharp rise in blood pressure (and panic and loss of movement) so you must not further strain the heart and should avoid sudden exercise. It may seem intuitive to swim to help or climb out of the water, but you should allow the heart a chance to slow down again and for the involuntary breathing to pass. The worst of the breathing response often reduces after about a minute or two, but cold shock can last up to 2–3 minutes. During that period, protect your airway, float if you can, and avoid sudden hard swimming unless there is an immediate life-threatening reason to move.

The good news is that cold water shock can be survived. The key is understanding what happens to your body, wearing the right equipment and knowing what to do in those first vital moments.

What is cold water shock?

Cold water shock is the body’s immediate reaction to sudden immersion in cold water. In UK waters this is a year-round risk. The sea, rivers, lakes, reservoirs and docks can remain cold even when the air temperature feels warm.

Cold water shock is most commonly associated with water at or below 15°C, but individual reactions vary. Tiredness, alcohol, poor fitness, medical conditions, heavy clothing, panic and unexpected entry into the water can all make the situation worse. The 15°C figure is a useful rule of thumb, not a cliff edge. Some people can be affected in warmer water, especially if entry is sudden, they are tired, poorly dressed, unwell, or panicking.

Cold water shock is not the same as hypothermia. Hypothermia happens when the body’s core temperature falls. That takes longer. Cold water shock happens immediately.

What happens when you hit cold water?

The first response is usually the involuntary gasp described above. This is why sudden immersion is so dangerous. If your head is underwater, that gasp can draw water into your airway.

Your breathing then becomes rapid and difficult to control. You may feel as if you cannot get enough air. At the same time, your heart rate and blood pressure rise sharply. For some people, especially those with underlying heart problems, this can be extremely dangerous.

You may also lose the ability to swim properly. Your arms and legs may not do what you expect. Even good swimmers can find that their normal stroke disappears. Panic makes this worse, because the instinctive response is often to thrash around or try to swim hard immediately.

That instinct can be fatal.

The first rule: swimming can make things worse

The first effects of cold water shock will usually reduce after around a minute or two. Once your breathing is under control, you can make a better decisions: call for help, swim to safety, hold onto something, or await rescue.If you fall into cold water, there are 3 steps to increase your chance of survival.

1/. Do not try to swim hard immediately unless you must do so to keep your airway clear or avoid an immediate danger.

2/.Float.

If you are wearing a lifejacket use the HELP position (described below) as it reduces heat loss from high-loss areas such as the groin, chest/armpits, neck and head. This will slow cooling, conserve heat and will reduce the number of cold receptors effected.

If you do not have the benefit of a life jacket, simply float. Lean back in the water. Try to get your ears into the water. Spread your arms and legs. Keep your airway clear.

Focus on breathing out slowly and getting your breathing back under control.

3/. Following about 90 seconds (1-2 minutes) your breathing and circulation should return to more normal levels. At this point you should carry your basic survival actions that have not already been carried out. This could be as simple as swimming to the side or may involve things such as activating a PLB, a light or personal AIS. If your lifejacket is fitted with a spray hood and you have not already deployed it, do so. If your oilskins have velcro straps at the cuffs do them up as they help to trap air (insulation) within your suit. Over the next few minutes your manual dexterity will reduce quite rapidly so completing these basic survival actions promptly is beneficial

HELP POSITION- The Heat Escape Lessoning Position

The HELP position — Heat Escape Lessening Position — is for a person alone in the water, normally wearing a lifejacket or PFD. The Huddle is the group version, where several people close up together to reduce heat loss and make themselves easier to spot.

The HELP position is a sensible way of a life jacket wearer reducing heat loss and the effects of cold waters shock. Your lifejacket will have made you float face up so simply cross your ankles and pull your knees up toward your chest while also crossing your wrists across your chest and try to tuck your hands in between the life jacket and your chest. If you do not have a spray hood you may have to use your hands to protect your airway.

The image above shows a RYA Sea Survival student protecting his airway during a training session. Note his life jacket has risen a little too high. His life jacket crotch strap needs to be tighter. The image below show a small group of 3 students forming a 3 person huddle (3 person HELP).

Float to Live

If you are not wearing a lifejacket, the RNLI’s advice is simple: Float to Live.

If you are in trouble in the water:

1. Tilt your head back with your ears in the water.
2. Relax and try to control your breathing.
3. Move your hands gently to help you stay afloat.
4. Keep floating until the shock passes.
5. Only then decide whether to swim, signal, shout or move towards safety.

This advice works because it buys time. It stops you wasting energy. It helps prevent panic. Most importantly, it keeps your mouth clear of the water while your breathing is at its most unstable.

The danger of cold water on a hot day

Cold water shock often catches people out during warm weather. The sun may be out, the air may be hot, and people assume the water is safe. In reality, open water can remain cold long after the weather improves.

This is particularly true of deep water, shaded water, fast-moving rivers, docks, reservoirs, quarries and the sea in spring and early summer.

Warm air makes people more likely to enter the water suddenly. Cold water makes that sudden entry dangerous.

How to reduce the risk

The best survival strategy is to avoid falling in unexpectedly. Good preparation makes a major difference.

Wear a suitable lifejacket or buoyancy aid whenever there is a real risk of falling into the water. Check that it fits, is appropriate for the activity and is properly fastened.

Dress for the water, not just the weather. A wetsuit, drysuit or suitable layers can reduce the impact of cold water. Clothing should be appropriate to the activity and should not prevent you from swimming or climbing out.

Plan how you would get back out before you go afloat. Many people focus on launching and forget recovery. Docks, canal walls, pontoons, steep banks and marina edges can be very difficult to climb out of, especially with cold hands.

Carry a means of calling for help. For boating this may include a VHF radio, mobile phone in a waterproof pouch, personal locator beacon or other suitable equipment. Paddlers and small craft users should think carefully about how they would raise the alarm if separated from their board, boat or group.

Tell someone where you are going and when you expect to return. Avoid going afloat alone where possible, especially in colder conditions.

Avoid alcohol before or during activity near the water. Alcohol increases risk-taking, reduces coordination and makes cold water immersion more dangerous.

If are forced to enter the water (ie your are abandoning a sinking vessel or a vessel on fire), lower your self in slowly, ideally keeping your face dry, this will reduce the number of cold receptors effected and therefore reduce the cold waters shock.

What to do if someone else falls in

If you see someone in trouble, do not automatically jump in after them. A rescuer can quickly become a second casualty.

Use the simple approach: Call. Float. Throw.

Call for help (VHF Mayday or Phone 999). At the coast, ask for the Coastguard. Inland, ask for the Fire and Rescue Service.

Tell the person to float on their back and control their breathing. Keep speaking to them. Clear, calm instructions can help reduce panic.

Throw something that floats. This could be a lifebuoy, throwline, lifejacket, paddleboard, fender, dry bag, football or anything else that helps them stay afloat. If possible, keep hold of the end of a line so you can help guide them back.

Only enter the water as a last resort and only if you are trained, equipped and it is safe to do so.

After rescue: the danger is not over

Once someone is out of cold water, they still need care. They may be exhausted, confused, unsteady, shivering or unable to help themselves. Remove them from wind and further cold. Keep them as still as possible. Insulate them from the ground. Replace wet clothing with dry clothing if this can be done safely and modestly, or wrap them in blankets, coats or a survival bag.

Do not them give alcohol. Do not put them in a hot shower. Do not rub their arms and legs aggressively. Sudden movement and rapid heating can cause further problems.

If the casualty is very cold, weak, confused or barely responsive, handle them gently, keep them as horizontal as possible, insulate them, and seek urgent medical help.

If they are very cold, confused, drowsy, have slow breathing, slurred speech, poor coordination, chest pain, or have inhaled water, call 999 or 112 for medical help.

The 1-5-1 idea

A useful way to think about cold water survival is the “1-5-1” principle:

You may have around one minute to get your breathing under control.

You may have around five minutes of useful movement before cold affects your muscles and coordination.

You may have 1 hour or more before unconsciousness from hypothermia, (depending on the water temperature, clothing, body type and conditions).

This is not a timetable and it should not be treated as a guarantee. Cold water affects people differently. However, it is a helpful reminder that the first minute is about breathing, the next few minutes are about useful action, and after that survival becomes increasingly difficult without flotation and rescue.

Key message

Cold water shock can kill quickly. It can cause an involuntary gasp, uncontrolled breathing, water inhalation, drowning, cardiac arrest or a heart attack. It can affect strong swimmers, experienced sailors and confident paddlers.

If you fall into cold water:

1. Protect your airway and do not try to swim hard immediately.
2. Float, or use your lifejacket to keep your mouth and nose clear. Control your breathing.
3. Once the initial shock has eased, call for help, hold on, swim to safety if able, or activate distress equipment. If you are wearing a lifejacket and awaiting rescue, deploy your spray hood and use HELP to reduce heat loss.

If someone else is in trouble: call for help, tell them to float, and throw something that floats. Do not become the second casualty.