Keep my hot tub at 98.6F, please!

June 29, 2006 1:36 PM

I've been reading a fiction book set in Antarctica, which goes into a lot of detail on frostbite, severe cold, etc. One of the characters gets caught in an underground hot spring, but thinks that he is safe because the water is relatively warm. His companion says that "human beings can die of hypothermia even in a bath at 90F if they are immersed long enough." Could this really happen?

It seems that even though, yes, you will be losing heat to the environment at a much higher rate than you would in air, the delta T just seems so slight!

What temperature water is generally considered REALLY dangerous to be immersed in for a long period of time?

posted by gregvr to Science & Nature (7 answers total)

I know a guy who got hypothermic in his outdoor hot tub. Fell asleep in it, in the winter, and the tub heater couldn't keep ahead of the cold indefinitely. Eventually it dropped below body temp and dragged his temp down with it, to about 92 if I recall. I don't remember if someone found him there, or if reflexive shivering and chattering finally woke him up.
posted by Tubes at 1:43 PM on June 29, 2006

That's borderline, but yes according to this link.
posted by edd at 1:48 PM on June 29, 2006

Yes, it can happen, or something like it—I don't think it's hypothermia per se, but basically you are in a medium that wicks away heat. It was a concern for Diana Nyad when she swam Florida-Cuba, despite the fact that the Carribean waters were quite warm.

You're right that the delta-T is slight, but if you stay there long enough, it becomes significant.

According to the wikipedia article on hypothermia, "Children can die of hypothermia in as little as two hours in water as warm as 16°C, typical of sea surface temperatures in temperate countries such as Great Britain"
posted by adamrice at 1:49 PM on June 29, 2006

Water is something like 1000 times denser than air, and therefore wicks away heat at an astonishing rate. When it feels "warmer" in cold water than in cold air, what you're feeling in the cold air is the evaporation of water on the surface of your skin (the same thing as sweating). You don't feel that evaporation when submerged, so you *think* you're warmer than you are.
posted by frogan at 2:31 PM on June 29, 2006

I remember hearing that you are in danger of hypothermia if the air tempeture and water tempeture add up to less than 150.
posted by prjo at 2:32 PM on June 29, 2006

When I was in high school, we did a whole unit on winter hiking and hypothermia. The general rule I think everyone has learned is hypothermia is a combination of wet, wind and cold. And if the conditions are wet and windy, eventually your body temperature will drop, no matter if it's the heat of summer or the dead of winter.

But I think if you were immersed in a bath at 90 degrees, it would take a while, since I'm assuming only your head would peek out...but then you lose the most heat from your head, I guess. Yeah, it could happen. But it would take a while, I bet.
posted by SassHat at 12:57 AM on June 30, 2006

gregvr - could you tell us the name of the book? I wouldn't mind reading it.
posted by azuma at 8:13 PM on June 30, 2006