In 1948 Dr. Craig Taylor at the University of California at Los Angeles created a heat chamber to determine the human tolerance for extreme heat. He experimented on himself. In the picture (from the Life archive
) you can see him sitting in his hotbox, heated to a pleasant 220° fahrenheit. The egg on the metal pan in front of him was frying. The highest temperature he ever endured was 262°.
There was a practical point to this. He was trying to determine the maximum heat a fighter pilot could withstand, should the refrigeration system in their plane fail.
For more info about Dr. Taylor's heat experiments, check out the old article from Popular Science
posted on the Modern Mechanix blog.