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Comment by hackandtrip | Hacker News Reader

Slightly off topic, but you should shower to avoid temperature difference too, specially in hot days. I don't know about the lifeguard situation in USA, in Italy it's pretty terrible; it should be absolutely required to have a shower before jumping in the water.

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Why are sudden temperature changes bad? When I was a kid in the north of Scotland we'd always jump in as gradual exposure to cold water was miserable - the shock of jumping in was always quite bracing ;-)

Mind you - as I doubt if it was much above 20C most of the time I doubt the temperature difference between air and water was that large!

I think the idea is that a sudden immersion in cold water when the weather is hot can cause a sudden contraction of your blood vessels which can result in a syncope. At least that's what I've always been told, but I know there's a lot of cargo culting and urban myths surrounding these topics so it's hard to know what's really dangerous and what's just superstition. For instance as a kid I've always been told that it was risky to swim just after eating a meal (because of the bloodflow required for digestion or something like that) but as far as I know it's been debunked and doesn't make biological sense.

Syncope == faint(ing)

TIL a new word, https://en.m.wikipedia.org/wiki/Syncope_(medicine)

I actually ended up with this word while attempting to translate the French word "hydrocution" but after some more googling it looks like "cold shock response" is the right term: https://en.wikipedia.org/wiki/Cold_shock_response

I find it hard to imagine how a swimming pool could be cold enough in a hot climate for this to be an issue for anyone healthy. If it's hot for more than a couple days, the pool water will start to warm up too.

I've heard of this concern more in the context of much larger bodies of water like the ocean or snow-fed mountain lakes, which can stay cold a lot longer than a pool by virtue of their size (and in the case of the latter, a continuous influx of very cold water).

The cardiovascular system has to suddenly adjust its rate to keep the body warm enough. If your heart is weak, it may not be up to the task and a heart attack is possible.

It might be fine for young people and people with people with peak cardiovascular health, but for older people or anyone with impaired cardiovascular health, the risk goes up.

Does how you get into the cold water make a difference? Specifically, entering in a way that does not trigger the mammalian diving reflex, such as wading in up to your chest or neck, versus entering in a way that does trigger it, such as holding your breath and jumping completely in?

Yes, because then the body doesn't have to adjust to the new environment in a second but gradually adjust instead.

Now, I'm thinking of all those images of old Russians going in to frozen outdoor pools, AFAIR they always climb down a ladder/steps. This might explain why.

Slowly getting in to cold water is some kind of torture to me, I always dive in. But frigid water is not my thing at all.

I don't know about the lifeguard situation in USA, in Italy it's pretty terrible;

Interesting, because my impression was that there's a decent amount of staff comparing to my country (Poland).

Also it's the first place at which I've seen a line of lifeguards on rafts making sure nobody reaches the point where they can collide with motorboats.

I don't know about the Poland situation, but the main problem in Italian (I guess other lifeguard certs too) it's the lack of any required refresher course. Things are changing fast on first aid practices best practice and a lot of people are behind.

Personal example: I'm 20, I am a certified lifeguard (I did the training because I was a competitive swimmer), no experience but I could extend my certificate till I am 65 year old, in whatever physique condition with whatever knowledge of best practice. That's just plain wrong, and I know that a lot of States work in a really different way with refresher courses and such, making pools and sea a safer place.

Luckily, it's much better in the USA, even though many regulations vary across state and county lines. Where I worked, we needed an in-pool refresher course and test every year, with a pool management course (chemicals, filter, etc) every 2 or 3 years. After getting you American Red Cross CPR certification, you needed to take a short refresher course every year for the next 2 years, after which you'd need to retake the course.

Could you explain the thing about the temperature difference? What's that about?

Also, where do you have lifeguards? Indoors, outdoors? I don't remember seeing any at all here in Sweden.

There are a variety of reasons why it's considered best practice to make people have a shower before entering the pool. They already explained it, talking about elderly people / etc. If it's sunny and you are out of the water from three hours tanning, your heart adjust to a certain frequency. If you jump in with any prior advice to your body into the water, heart has to adjust to a much different frequency, and an heart attack is possible.

The problem here is that a lot of people doesn't know what's going on with their hearth and certainly a lifeguard doesn't know about.

Also, adding to that, https://en.wikipedia.org/wiki/Cold_shock_response

I don't know about Sweden situation, but it seems really weird that no lifeguard was there. In Italy every public or private place with a pool needs a number of lifeguards according to the number of people of the pool / the pool's dimension. It's really easy to have some heart attack or hypoxia going unnoticed, example: X person jump in, simply doesn't get up. Also, time is key, if an heart attack occurs a close defribillator with someone able to use that / a lifeguard able to transport that person out of the pool without damages (it's not that easy as it sounds) can be really important. Drowning situations are even more dangerous, a drowning person can have a force in their arms able to do real damage and everything needs to be deal in the safest way.

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