If you can dig up a copy of the 1962 book "Space Medicine" by U. Slager, it's really interesting. It makes you realize how many questions they needed to answer experimentally before going into space. For example, how much acceleration can someone withstand. How much vibration and tumbling. Minimum and maximum survivable temperatures. How long can you be exposed to a vacuum. This was the era of putting people on rocket sleds to see what happens ( http://en.wikipedia.org/wiki/John_Stapp ). My favorite factoid from that book is that guppies can tolerate 10000G for 30 sec. It also describes a guy who survived 482 degrees F for 4 minutes.
I messed up °F/°C and it was "only" 250°F. I don't have the book "Space Medicine" available, but I found a different reference† explaining that it was Dr. Charles Blagden and other researchers in 1774 who went into a room heated above 250°F and cooked steak and eggs in there, proving the importance of perspiration in maintaining body temperature. It has to be dry heat; if there is humidity, the tolerable temperature is much lower. The original paper ‡ is also online; in order to read it, note that "ſ" is a "long s", not a "f".
For people of the world, that's about 121°C. BTW, I've been in a sauna in Sweden where the thermometer displayed 100°C. The women sauna, according to my mother, was only 96°C.
