Human temperature tolerance

[lemur]

Humans can tolerate wide ranges of temperature variation. With increasing hot or cold, however, discomfort is reached and ultimately health problems may result. I'm wondering about the limits of sustainable indoor temperature. I have read about acclimatization studies where native Alaskans were observed to walk barefoot in very cold temperatures and were measured as shivering at lower temperatures than other students who did not engage in acclimatization practices. Does anyone know what the minimum consistent indoor temperature humans can tolerate without encountering health problems? Obviously clothing and other factors make a difference, but I would guess around 50F and I'm not sure if that is sustainable for multiple weeks without running into health problems. Anyone have any thoughts on this?

[Nexium Tao]

Impossible question to answer. A dangerous body temperature for humans is above 40 centigrade, and below 35 centigrade. But because their are so many variables at play here such as clothing, height, health, age, heart rate, bodies ability to dissipate or absorb heat, ect. There is no clear cut answer to this question because it is body temperature and only body temperature that dictates heat related health issues. The indoor temperature of where on lives is just one variable of many that helps constitute body temperature.

Edited December 27, 2010 by Nexium Tao

[Sisyphus]

I don't know, but I would guess it's higher than you think. For example, you'll eventually get hypothermia in water that is lower than about 80 degrees. Normally, you are heating the air around you with your body (air being a lot easier to heat than water) and wearing clothes to trap that warm air, so you're not actually exposed to ambient temperature. That's what wind chill is - air at ambient temperature replacing air warmed by your body.

 

So really, I'm not even sure you could stay in ordinary room temperature, if you were naked, sedentary, and there was a breeze.

[CaptainPanic]

I think (i.e. it's an opinion rather than a fact) that our tolerance is for a large part related to the heat transfer, rather than absolute temperature.

 

With that I mean to say that we may have a limit to the amount of Joules we lose per second per person. This way, we include all factors: insulation because of body fat, clothing and other forms of protection, sweating, immersion into cold water (which radically changes the heat transfer) and also differences in air humidity.

 

At rest, an average human will generate about 150 W of power, which are almost all converted to heat eventually... and therefore must be transferred to the environment.

The peak power of an average human is about 400 W... which is why we sweat when we do sports (getting rid of excess heat), or why we shiver when we're cold (burning excess "fuel" to heat ourselves).

 

This way, we can greatly simplify the question... and we can realize that with proper equipment we are able to withstand very extreme temperatures for long periods of time (or even indefinitely)... Heat transfer is a function of temperature difference, surface area and the heat transfer coefficient. If you decrease the heat transfer coefficient enough (by insulation), you can have a massive temperature difference, while keeping the total heat loss at a healthy level.

 

This obviously does not take into account the trouble of breathing in very extreme conditions...

Edited December 27, 2010 by CaptainPanic

[lemur]

Impossible question to answer. A dangerous body temperature for humans is above 40 centigrade, and below 35 centigrade. But because their are so many variables at play here such as clothing, height, health, age, heart rate, bodies ability to dissipate or absorb heat, ect. There is no clear cut answer to this question because it is body temperature and only body temperature that dictates heat related health issues. The indoor temperature of where on lives is just one variable of many that helps constitute body temperature.

Good post, though I think you didn't mean "below 35C." I guess I am looking to understand the factors that make consistent cold unhealthy and how those are related to temperature.

 

I don't know, but I would guess it's higher than you think. For example, you'll eventually get hypothermia in water that is lower than about 80 degrees. Normally, you are heating the air around you with your body (air being a lot easier to heat than water) and wearing clothes to trap that warm air, so you're not actually exposed to ambient temperature. That's what wind chill is - air at ambient temperature replacing air warmed by your body.

 

So really, I'm not even sure you could stay in ordinary room temperature, if you were naked, sedentary, and there was a breeze.

True, but I'm more interested in how cold you can keep your indoor temperature consistently and remain healthy, including the use of all mitigating factors such as warm clothing, hot drinks, etc. In other words, if someone wanted to win a bet for how low they could set their thermostat for an entire winter, at what point would their health suffer despite warm clothes, exercise to keep warm, etc.?

 

I think (i.e. it's an opinion rather than a fact) that our tolerance is for a large part related to the heat transfer, rather than absolute temperature.

That's a very good point. Core heat is what causes shivering, I understand. Still, I'm also wondering about skin temperature (hands and face esp.) and breathing cold air (throat/lung cold exposure).

 

At rest, an average human will generate about 150 W of power, which are almost all converted to heat eventually... and therefore must be transferred to the environment.

The peak power of an average human is about 400 W... which is why we sweat when we do sports (getting rid of excess heat), or why we shiver when we're cold (burning excess "fuel" to heat ourselves).

These are useful numbers, thanks. Imagine that in a good sleeping bag or warm bed with head-covering, you can basically stay 'toasty warm' with just 150W internal heating! And you can generate that perpetually on @2000 calories of food per day. That's @2.5 kwh of energy. That's equivalent to @1 cup of gasoline.

Edited December 27, 2010 by lemur