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On a boat in cold water? - You should know these 5 things

1. You better be wearing a life jacket before you end up in the water.

The gasp reflex in action   (source: 3Nues)
Woman gasping in cold water

Cold water forces a rapid, uncontrollable gasping in everyone and that lasts from 1-3 minutes. If you happen to gasp while your mouth is underwater, you will draw the cold water into your windpipe and lungs which can then spasm and contract. Even if you manage to get your mouth above water, you may still not be able to clear the water and get enough oxygen. If things go really wrong, your epiglottis may spasm closed and you will dry drown. (The epiglottis is the cartilage flap that  keeps liquid out of your lungs when you drink.)  

There is some evidence that keeping the cold water off your face and head may lessen the gasp reflex. That is why you want the life jacket on before you hit the water. It helps to keep your face and mouth out of the water. The initial immersion in cold water causes a sudden constriction of surface blood vessels which causes an immediate jump in blood pressure and heart rate; sometimes to maximum heart rate. If your heart cannot handle this jump, it stops and you die. This seldom happens in healthy and fit people but the danger is still there. If you have a choice, make sure to wear a life jacket that is self-righting so that it keeps your face out of the water if you are unconscious....

Other tips: Delay or avoid getting in the water. Enter the water as slowly as possible. Wear protective clothing. Even poor clothing is better than no clothing. Wool or synthetic fleece still provides some insulation when wet.


2. You better have some waterproof way to signal for help on your person and you better know how to use it.

Your best chance for survival is to get help from someone else. In cold water, you only have about 10 minutes of meaningful movement before your muscle and nerve tissue ceases to function. You need to use those first 10 minutes to get help on the way. You do not want to squander those first 10 minutes trying to recover your communication device. Swimming around looking for it will just exhaust you and even if you find it you may then lack the physical dexterity to use it. It needs to be on you, waterproof and you need to know how to use it. Of course, if you don't have your life jacket on before you hit the water, you won't be doing anything except trying to keep your head above water or getting the jacket on. You will be wasting valuable time that you could have used to get help on the way. You will also be reducing the time you can survive in the water until help arrives. A cell phone in a zip lock bag can work if you know that you will have signal and you have the appropriate numbers on speed dial.


3. Don't swim to shore unless it is your last option and it is very close. 

Your ability to swim in warm water has no relation to your ability to swim in cold water. On March 6th, 1968, nine elite marines, trained as water survival instructors, capsized while paddling across the Potomac River. Not one of them was wearing a life jacket and not one of them was able to swim the 100 yards to shore in the 36 °F water. Every single one of them drowned. Had they been wearing life jackets the results could have been very different. Remember, you only have about 10 minutes of meaningful movement. If you don’t have a life jacket on you will expend most of your energy keeping your mouth out of the water instead of propelling yourself forward. Self rescue is a complicated decision. The temperature of the water, the water conditions, your level of fitness, your clothing will all be a factor. Self rescue by swimming should only be attempted if you are sure it is your best chance for survival and that you can accomplish it in the time that you still have meaningful movement. If help is on the way, your best chance of survival may be to stay still. You have about an hour before you lose consciousness but only if you remain still.

What is very close? It depends on many factors but here are some ball park figures; Less than 100 yards in ice water and less than a quarter mile in 45 °F water. Both are assuming you have a life jacket on and you are a good swimmer. Weather conditions, clothing, etc. could reduce these figures markedly. 


4. You can remain conscious for one hour in freezing cold water if you don't thrash around. 

The Heat Escape Lessening Position: Used to conserve heat
image of woman in a ball position - knees tucked to chest, arms crossed.

Dr. Gordon Giesbrecht (University of Manitoba) studies cold water survival and he has come up with a guideline to remember what to do if you find yourself immersed in cold water. He calls it ‘1-10-1’. You have 1 minute to get your breathing under control from the initial cold shock response. Then you have 10 minutes of meaningful movement in which you can rescue yourself or signal for help. Then you have about 1 hour before you lose consciousness from the cold. If you are forced to wait for help, you will want to adopt a posture such as H.E.L.P to reduce heat loss.




5. You can die after you have been rescued.

In 1980, sixteen Danish fishermen were forced to jump into the North Sea after their fishing boat floundered. After about 1.5 hours in the water another boat approached and lowered a cargo net which they used to climb on board. They thanked their rescuers and they walked across the deck and went below to the galley where they were supposed to have hot drinks and warm up. Instead, all sixteen of them dropped dead. They suffered from profound acute hypothermia.

To understand how this might have been prevented, we need to understand what happens as hypothermia develops. 

Chronic hypothermia is the lowering of the core temperature below 95 °F (35 °C) over a period of six hours or longer. This develops by simply not having enough clothing to maintain a thermal balance with the environment. The body uses vasoconstriction to reduce heat loss to the extremities by shutting down blood flow to them. The rescue of a chronic hypothermic individual requires the prevention of further heat loss. When the core temperature is above 90 °F (32 °C) virtually any method of handling the victim is fine. Heat may be added rapidly or slowly. The victim may engage in any activity they want. Just get them heat, shelter, food, hydration and rest.

Profound chronic hypothermia occurs when the core temperature is slowly lowered (six hours or more) to below 90 °F (32 °C). The vasoconstriction at this point will have caused a profound dehydration and a compacting and alteration of the blood to allow the tremendous decrease in blood volume. This individual needs to be handled very carefully. Rapid heat replacement can cause ‘rewarming shock’. This person needs gentle handling, slow addition of heat, prevention of further heat loss and litter evacuation. They cannot simply be wrapped up in a sleeping bag because they lack the energy to regenerate their lost body heat and rapid warming will likely kill them.

Acute hypothermia occurs when a person is subjected to a massive heat loss occurring in two hours or less (Like cold water immersion) The body doesn’t have time to make changes to the blood composition or volume. The danger is that even after rescue the core temperature can continue to drop to lethal levels because of the huge heat deficit. They can be allowed to move around but they need heat fast.

Profound acute hypothermia is when the person has been immersed for more than half the time it is expected that they would reach a lethal temperature. For example: If a naked person in ice water was expected to reach a lethal core temperature in one hour, they would be considered profoundly acute after half an hour of immersion. Profound acute hypothermics must not be allowed to run around. Often they are able to do so but it causes a massive movement of blood into the cold muscles and back to the core. This causes a temperature afterdrop that only adds to the massive heat deficit. The ideal treatment is rapid heat replacement such as a hot water bath of 110 °F (43 °C). If a bath is not available a large fire will do.

Profound acute hypothermia can progress to profound chronic hypothermia after the 2 hour mark of cold water immersion. Somewhere between 2-6 hours the body starts making changes to blood composition and it becomes more and more dangerous to rewarm the victim rapidly. They need to be treated as a profound chronic hypothermic.


Great videos to show you more



Cold water boating video (Alaska Office of Boating Safety) Part 1:


Part 2:

Part 3:

Part 4:

Part 5:

Part 6:

Part 7:


1.) Dr. Gordon Giesbrecht has a wealth of information on his website.  Including demonstrations of him falling through ice on a frozen lake and what to do to escape.

2.) Basic Essentials Hypothermia,  by William W. Forgey  A very good guide to hypothermia.

3.) Cold Water Boot Camp  was a video produced by the US Coast Guard about cold water survival. It shows some good footage of average people being subjected to immersion in 45F water and how it diminishes their ability to swim.

4.) Jane Blockley has written some excellent cold water safety guides and some hypothermia guidelines.   Nice summaries of current information.

5.) Survival in Cold Waters: Staying Alive by the Canadian Department of Transport. This (.pdf)  document is VERY in depth.  

6.) Sudden Failure of Swimming in Cold Water -  W. R. Keatinge, C. Prys-Roberts, K. E. Cooper, A. J. Honour, and J. Haight.  An interesting medical study from 1969.



This is fantastic information. I suspect you've already considered some material for the complimentary article dealing with extreme heat.

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