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Comment by willyt | Hacker News Reader

This guy was incredibly lucky. Wear a life jacket. Carry a means of calling for help on your person. Ideally a Personal Locator Beacon (>£150), a handheld marine VHF radio (>£75), at least a phone in a waterproof pouch.

In water less than 15ºC[0] average life expectancy follows very roughly a rule of threes. Three minutes without a life jacket, 30 mins without suitable warm clothing, 3 hrs without a life raft, 3 days without water and 3 weeks without food.

I volunteer for a marine SAR unit and people fall in and die from causes 1 and 2 on that list all the time, at least once a year just in our patch.

[0] Eg pretty much all U.K. waters pretty much all the time.

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I didn’t learn until late in life that you’re not dying of hypothermia in that water as I’d always been lead to believe. Your muscles get too cold to respond and you just drown. Horrifying.

Your general point is totally valid -- cold water is dangerous. But your survival times for 15C are ridiculously pessimistic. 15C is just not that cold! The table here shows longer expected survival times than that even at 0C:

https://seagrant.umn.edu/programs/recreation-and-water-safet...

Survival even without floatation at 15C is measured in hours.

With training and when you are expecting to go into the sea yes obviously you can swim 20 miles across the English channel but all the cardiac arrests from cold water shock and general panic in the first 15 seconds bring the average down. The rule of 3 makes it easier to remember; they are approximate average numbers which are meant to drive the point home which is to wear a life jacket. We would prefer to find you shivering on a beach than face down in the sea.

This has nothing to do with trained cold water swimmers. Your figure is just completely off. 15C water does not kill people in three minutes. It does not cause cardiac arrest. An average person could last hours at that temperature. See the well cited link I provided.

Lying to people to try and encourage safe behaviour isn't wise. The truth is good enough.

https://rnli.org/safety/know-the-risks/cold-water-shock

he did say what brings that number down (it's an average). and yes, jumping/falling into cold water can lead to shock/cardiac arrest

Does regular warm clothing keep you warm in 15c water or are you referring to a wetsuit or equivalent?

Probably a wetsuit or survival suit are the only relevant clothing to help with a prolonged submersion situation

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