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What really kills you when you fall into cold water?

PortandTerminal.com, January 3, 2021

HALIFAX, NOVA SCOTIA – The Atlantic ocean’s water temperature today in Halifax, Nova Scotia is a frigid 43ºF, a fact that our local fishermen and first responders are well aware of.

Cold water is deadly and the colder it is, the more likely you are to die if you fall into it. A study done in 2007 found that you are five times more likely to die in a boating accident when the water is under 59º F than you are when the water is between 70-79º F (Source: USCG Drowning Report 2007).

How you die in cold water is often misunderstood. Many people believe that hypothermia is what kills you. That’s simply not true according to Mario Vittone, a retired USCG helicopter rescue swimmer and an expert in immersion hypothermia, drowning, sea survival and safety at sea.

“Most of what you know about hypothermia is wrong” says Vittone. “You can’t get hypothermic or even mildly hypothermic in under 10 minutes. The average adult can survive over an hour in cold water.”

So what usually kills people in cold water? There are four phases.

1. Cold Shock Response

Man overboard in cold water
When the body is suddenly immersed in cold water it experiences a number of physiological responses that can rapidly incapacitate and even kill. 

It turns out that, of all the people who die in cold water, around 20 percent of them die within the first two minutes – long before hypothermia has a chance to set in.

When the body is suddenly immersed in cold water it experiences a number of physiological responses that can rapidly incapacitate and even kill. Cold Shock Response causes an immediate loss of breathing control. You take one or more huge gasps, followed by hyperventilation – very rapid breathing that is hard or impossible for you to control. Often people will swallow and begin to choke on water as they gasp uncontrollably.

Gabe Wilson, associate medical director at New York’s Saint Luke’s–Roosevelt Hospital emergency room had this to say about the body’s reaction to sudden immersion in cold water.

“When you first go into extremely cold water there is this weird response called a cold-shock response. People start to hyperventilate immediately. For one to three minutes you breathe very fast and deep, uncontrollably. If you go underwater, you could swallow water and die. …I can’t tell you how often this occurs but it’s certainly a very real phenomenon. Once that response goes away, you’re fine…for awhile.”

Being able to swim won’t help you at this first stage of cold water immersion. Cold Water Shock causes involuntary body reactions that can be as swift as they are deadly – and the ability to swim well has no impact on these responses.

Surviving this stage is about getting your breathing under control, realizing it will pass and staying calm.

So assuming that you manage to survive this first deadly “Cold Water Shock” stage — what happens next?

2. Cold Incapacitation 

The second phase of cold water immersion is called cold incapacitation and usually occurs during the first 10 to 15 minutes of cold-water immersion. 

Put simplistically, your body “circles the wagons” to protect its vital organs. Blood from your extremities (arms, legs, hands and feet) rushes to your core to protect your heart, lungs and other vital organs. As the blood flows away from arms and legs your muscles get weak, they lose coordination and strength and you lose your ability to swim.

Generally, a person can survive in 41-degree F water for 10 to 15 minutes before their muscles get weak, they lose coordination and strength.

“Over 50 percent of the people who die in cold water die from drowning following cold incapacitation” – Mario Vittone, retired USCG helicopter rescue swimmer.

At this point, having a personal flotation device on is a matter of life or death.

3. Hypothermia

Drawing of man in water with lifevest
Remember to crunch up into the HELP position to slow down heat loss and delay the onset of hypothermia

If you make it past the Cold Shock and Cold Incapacitation phases and are able to keep your head above water, congratulations — you still have a bit of time before the third phase of cold water immersion kicks in — hypothermia.

You don’t have much time though – maybe an hour. Heat loss when the body is immersed in cold water can occur 25 times faster than it would if exposed to the same air temperature.

Hypothermia occurs when your body loses heat faster than it can produce heat, causing a dangerously low body temperature. Normal body temperature is around 98.6 F. Hypothermia occurs as your body temperature falls below 95 F.

There are various stages of hypothermia. Early on as it sets in you body tries to keep warm by shivering. As hypothermia progresses symptoms such as confusion, shallow breathing and drowsiness appear.

Ultimately, hypothermia can kill you — but that only happens in about 15 percent of cold water deaths.  The previous two stages kill most people first.

4. Post-rescue collapse

Even after you are rescued after being immersed in cold water, you’re not out of the woods yet. Post-rescue collapse, aka Circum-Rescue Collapse, is the fourth and final dangerous phase and it can also be deadly.

Despite being recovered in an apparently stable condition, a survivor of cold-water immersion can suffer from post-rescue collapse ranging from fainting to cardiac arrest during the rescue period. Deaths from post-rescue collapse have occurred within minutes before rescue to 24 hours after rescue. There are a number of different theories as to why this can happen that we won’t get into here. If you would like to read more click here.

Suffice to say, that even during and after rescue from cold water, victims are kept in horizontal position and kept under strict medical supervision.

“Over the years, I’ve rescued a number of people from cold water. Once they’re settled in the helicopter, I enforce a rule: They must lie down and stay down until a doctor says they can stand.” – Mario Vittone

Learn more

Learn how to survive a fall into cold water

Other articles you may find interesting

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