My wife asked me this question and I didn’t really have any idea - it stumped me.
I’m only looking for a rough guide, just a rule of thumb so to speak. I checked on the net but didn’t find much.
I think it might differ from person to person, and depend on a number of variables, so to set the conditions a bit more concretely, please assume:
An average healthy adult male.
Clothed in your average t-shirt/shirt, jeans, sox and sneakers.
Enclosed in an auditorium (so no wind).
The person has enough food and water (at the ambient temperature). Is there a (very rough) temperature range where, if that temperature is kept constant, a person will start to go into hypothermia given the above conditions?
Wikipedia says: “Heat is lost more quickly in water than on land. Water temperatures that would be quite reasonable as outdoor air temperatures can lead to hypothermia. A water temperature of 10 °C (50 °F) often leads to death in one hour, and water temperatures hovering at freezing can lead to death in as little as 15 minutes. Water at a temperature of 26 °C (79 °F) will, after prolonged exposure, lead to hypothermia.” But doesn’t mention how much difference being in water makes…
There is no single answer to your question, even with your proposed scenario. Everyone is different. Based on your scenario I’ve felt chilled to the bone as well as quite comfortable. What it boils down to is your body’s metabolism sufficient to generate enough heat to make you feel comfortable and not detect any symptoms of being chilled, for an extended period.
It makes a huge difference. Just being in wet clothes on land will increase your chances of hypothermia dramatically. If you are dry while exercising and keeping up with food and water you can go for very long times in cold temps. If you stop moving and are only concerned with not losing heat the times would be much shorter. But I have no idea of absolute numbers.
Without wind, sheltered, with food, WATER and dry clothes? That doesn’t sound like a very lethal situation. In fact barring diseases or lethal wounds this is gonna take a while.
Now if you allow it to be cold enough to freeze liquids and make the food inedible…
Just popping in to add that I heard an interview with a Navy SEAL who spent a lot of his career in a cold weather platoon-he said that the closest he had ever come to dying from hypothermia was in 85 degree water in Hawai’i-apparently he was in a partially flooded compartment when the exit hatch got jammed shut. It took them almost 12 hours to get it open, and despite the water’s warmth he was shivering violently by that point.
One of the times I was coldest while camping was in the deep south in the middle of summer trying to sleep in a tent with just a very thin cover sheet with shorts and a tshirt on.
I don’t know the number and it obviously depends on the person’s build. But if you limited a persons caloric intake to their normal intake, I don’t think it would take a very low a temp to kill em off. A person with more fat/muscle reserves would last longer but it still only be a matter of time.
Most of the people who succumbed were wet, either via rain or sweat, and I bet wind was a serious concern as well. Being dry and out of the wind at 50-60 is not uncomfortable and a well fed and hydrated person can last a very long time at those temps.
Thermal conductivity is 26 times higher in water compared to air. Source. That’s why you’ll find a plenty of information regarding the dangers of hypothermia in water and not much on land.
As for the hypothetical, an adult male with access to food and water is a pretty efficient heater, humans with minimal shelter lived through winters and even ice ages after all. Those who die of exposure are usually sick or children or the temperature is well below freezing.
I’ve heard that if you are lost or stranded in the winter, it’s very important to keep you activity level s such that you don’t sweat, in order to keep your clothes dry so they will continue to protect you from the cold.
There have been experiments with this, although not intentional set up as so. I’ve read the accounts of prisoners who are kept in conditions set out in the OP (but obviously in much smaller cells). One recounted how it was so cold they would have to sleep laying over while kneeling, with their just legs and foreheads touching the bare concrete in order to lessen the amount of heat loss.
Being in a closed environment also offers a great deal of protection because there is no wind. Air isn’t a good conductor of heat, so in the absence of wind, the diffusion of heat will take much longer than it would outdoors.
I’ve known incredibly fit men carrying food and water die of Hypo while carrying weight on punishing mountain run/walk endurance tests over long distances in adverse weather conditions.
They died on the Brecon Beacons while undergoing S.A.S. selection.
I read a quote somewhere, IIRC, A healthy adult could sunbathe nude in 32 degree weather comfortably. This is assuming no wind, clouds, or onlookers with water balloons.
Is that a joke? 50 Degrees in nothing jeans and a T-shirt? If the subject is not actively working ( just standing there), I think most people would get uncomfortable pretty quickly at 50 degrees.
To find an answer to the question it helps to think about where and how we evolved. The ambient air temperature when we had no ability to make fire or clothing was about 28 degrees celsius (about 82 F). That is the temperature were heat loss equals heat production for the human body, unclothed and at rest, known as the thermoneutral zone.
The Selk’nam people of Tierra del Fuego wore little or no clothing, and flourished in a climate that ranged from below freezing to rarely as high as 70F.
I am from So Cal so what I am used to may vary. I worked nights for many years and sedom felt a need for a jacket at about 44 degrees and above. I went hunting in south Texas at 45 degrees and thought I was going to freze to death, I go hunting in Wisconsin at about 12 degrees and am quite comfortable with a medium jacket.
The question asked what is the lowest safe temperature range. He gave the range that it starts to become dangerous, because that was the relevant information he had. It is not unresponsive.