Here's what happens to your body during cold-water immersion, and what to do if you find yourself in this situation.
On a sunny spring day, or during the early days of winter, the sparkling water beckons. Surrounded by natural beauty and excitement, it's easy to forget the ever-present danger of cold water, and that it can kill within minutes, if not seconds, if you fall in. We spoke with two experts to understand the science behind what happens to a person in the critical minutes after being plunged into cold water, and the best strategies for survival.
0:00–3:00 Minutes: Cold Shock
At the moment of cold water immersion, the initial and greatest threat is cold shock. According to a study published in the journal "Experimental Physiology," cold shock accounts for the majority of immersion deaths in the United Kingdom. When you first plunge into cold water, your heart rate, breath rate, and breath volume spike dramatically. This cardiorespiratory response is driven by the cutaneous cold receptor that sits just beneath the surface of the skin. The instinct to gasp is uncontrollable, and deadly.
"The lethal dose for drowning in saltwater is about 1.5 liters [just over one-third gallon]," says Professor Mike Tipton, MBE, FTPS, a professor of Human and Applied Physiology at the University of Portsmouth (U.K.). "The gasp I get when I got into cold water is between 2 to 3 liters. I've already crossed the lethal dose for drowning if I happen to be under the water or have waves breaking over my airway."
If you manage to hold your breath, it sets off a potentially fatal cascade of physiological responses. As cold shock sends your heart rate through the roof, water on your face triggers the diving response — something all mammals have — which works to slow down the heart and prolong breath-hold. "The heart is being accelerated by the cold shock response and slowed by the diving response. Where that competition occurs, that's where you see arrhythmias. We've called it 'cold shock autonomic conflict,'" says Tipton.
While predisposing factors, like certain heart diseases, increase the chances of a fatal arrhythmia, cold shock autonomic conflict affects most people, including the young and healthy. "If I told you to go underwater and hold your breath for as long as you can, within 10 seconds of breaking, roughly 82% would show some form of arrhythmia or dysrhythmia," says Tipton. Cold shock only lasts for the first few minutes of immersion and there are a few vital things you can do to improve your chances of survival.
"Your No. 1 objective on immersion, in those first couple of minutes, is to keep the airway clear of the water," says Tipton. "Hold on to something. If you can't do that, then float."
Hopefully, you'll be wearing a life jacket that will help keep your head above the surface. If for some reason you're not, floating becomes imperative. "If you fight that instinct and stay still, you'll float," Tipton says. The body is less dense than water, and clothing traps air, making you more buoyant. "Don't swim immediately, float first, do as little as possible to stay afloat, rest, and recover."
If it's an option, enter the water slowly. "Cold shock is dependent on the speed and size of the surface area of the skin," says Tipton. As for reducing the chance of a heart attack, "Avoid coincident face immersion and long breath-holds, as they're really potent drivers for arrhythmias."
Prevention Is Key
- Wear a life jacket. According to the U.S. Coast Guard 2020 Recreational Boating Statistics, 75% of fatal boating accident victims drowned. Of those, 86% were not wearing a life jacket. A life jacket will help protect you from cold shock, swim failure, and hypothermia. For cold water, Butierries recommends Coast Guard-approved Type III and Type V life jackets. "Make sure it has a light. Make sure it has a splash guard," said Tipton. "When you become unconscious, your legs will act like a sea anchor. They'll turn you into the oncoming waves that will splash up the life jacket and drown you."
- Carry an emergency communication device like a waterproof hand-held VHF radio or emergency locator beacon on your person.
- Ensure your boat has a reboarding device that can be used in the event someone falls overboard. This includes a transom or swim-platform ladder, or a foot sling.
- Check the weather and water temperature before you go out.
- Wear appropriate clothing. "Dress for the water temperature, not the air temperature," said Butierries. If you end up in the water, a dry suit can significantly prolong your life, and he recommends wearing one when the water temperature falls below 60 F. He also recommended carrying an immersion suit, which can be tricky to don, so practice putting it on.
- File a float plan with a family member or friend before you head out.
- Eat a good meal before going out on the water so your body has something to draw on in an emergency.
- Practice with your emergency equipment. "Know what your survival equipment is, get it out, practice with it," said Tipton. "Inspect it and ask, ‘Is this going to work? Am I going to be able to do that when I'm in a rough sea and it's freezing cold?'"
- Stay fit. "The fitter you are, the smaller the cold shock response," said Tipton.
- Don't fall in. While it may seem obvious, there are plenty of measures you can take to avoid falling into cold water. Keep your lifelines and jacklines tight and in good condition. Wear grippy footwear and install nonskid deck patches. Wear a harness and tether and always clip in when sailing shorthanded, going forward, at night, in poor visibility, or in rough sea conditions.
10:00–40:00 Minutes: Swim Failure
"You've survived the cold shock response. Now it's the superficial nerves and muscles that are cooling, particularly in the arms," says Tipton. This cooling will gradually lead to neuromuscular dysfunction and physical incapacitation. "At around about 81 F local temperature, neuromuscular function fails," Tipton says. "It first shows itself in reductions in grip strength and speed of movement on the fingers, and then progresses to limb movement and coordination." As you swim, your body will go from a horizontal position to increasingly upright with a greater sinking force and drag.
The time it takes for this to happen largely depends on water temperature. It takes "about 40 minutes in 68 F, 20 minutes in 54 F, and 10 minutes in 41 F," explains Tipton. This cooling will also drastically reduce your ability to perform vital tasks like release a flare or open a bailer in a life raft. "You'll lose manual dexterity, you lose strength, you lose the ability to grip," he says. "Be aware, stay still, and after the cold shock, you've got about 10 to 20 minutes to do all the things you need to do to get into long-term survival mode."
It's better to stay still because exercise causes you to cool more quickly. However, if you need to take action, "do leg-only exercise," says Tipton. "An enormous amount of heat is lost through the arms when you start exercising" because you're stirring cold water around your torso. When you don't exercise your arms, they help insulate your torso.
If it's not possible to self-rescue, Chief Warrant Officer Daniel Butierries, search and rescue mission controller for U.S. Coast Guard Sector Virginia, suggests huddling together in a group or going into the H.E.L.P. position: "If you're by yourself you can get into a fetal position, with your knees to your chest, to preserve what warmth you have left in your body.
How Cold Is 'Cold Water'?
While there's no strict definition of "cold water," it's considered most dangerous below 59 F. That's not to say that higher temperatures aren't hazardous. Even balmy Florida sees water temperatures in the 60s and low 70s — cold enough to cause cold shock and hypothermia.
30:00+ Minutes: Hypothermia
So far your core temperature has remained normal. "Humans don't become hypothermic in less than 30 minutes," Tipton says. In cold water immersion, you don't generally die directly of hypothermia. "With hypothermia, you lose consciousness," he explains. "Then you get swim failure and drown if you don't have a life jacket on or can't keep your airway clear of water."
Signs & Symptoms Of Hypothermia
According to Butierries, a whole host of factors determine how long you will survive after 30 minutes. "There's body composition, water temperature, air temperature, water turbulence, sea state. If it's rough weather, you'll succumb to hypothermia quicker. On a relatively calm day you may be able to hold on longer."
In an ideal world, rescue would mean the end of a harrowing event. But for the cold-water victim, the battle isn't over. Tipton says that sometimes the condition of the victim continues to worsen after rescue, that "this person who has been OK, collapses."
"Circum-rescue collapse" can occur just before, during, or just after rescue. "We think it partly has to do with autonomic conflict — you just relax, and with that comes a collapse in arterial pressure." The withdrawal of the will to survive can have catastrophic consequences, made worse by a rescuer saying things like, "It's OK, you can relax, we've got you." Tipton suggests rescuers say, "We're here to help. Keep fighting for your survival."
It's also important to be careful how you pull someone from the water. "If you start lifting people up and holding them vertically, there's a collapse of arterial pressure," says Tipton. "This is the consequence of losing the hydrostatic pressure that was squeezing blood back to the heart." If their blood pressure collapses, there's a chance "they'll either faint and fall back into the water and drown, or they'll have a heart problem."
Tipton suggests positioning them out horizontally, though he says this isn't always possible if their airway is under threat. In which case, he suggests, "Get him out anyway you can. You're better off dealing with a faint than you are with a drowning."
Once you've got them aboard, "keep the person immobilized, lying horizontally, and try to keep them warm," says Butierries. "Put a life jacket under their head so they're comfortable. If you have blankets or articles of clothing, keep them wrapped up." You should already have called the Coast Guard, so they can send a helicopter or boat to get them to a higher level of care as soon as possible.
While we all hope to never find ourselves in this situation, just understanding the body's response to cold water can help you survive.
"If you know that you're going to have a cold shock response, but that it's going to go away in about a minute or a minute and a half, you have a completely different mindset," says Tipton.
Beautiful spring weather may beckon, while water temperatures remain hazardous. According to the U.S. Coast Guard, cold-water incidents peak on nice, sunny weekends. The National Weather Service and United States Coast Guard Sector Virginia, created the "Think 60 — Cold Water Danger" program to help alert people to cold water dangers on warm air temperature days. If you live in Virginia, you can monitor social media for #paddlecraftrisk and #think60 notifications.