In 1948 Dr. Craig Taylor conducted experiments on himself to figure that out and the highest heat he endured was 262 degrees but he survived. We do not know if that is the maximum.
One pint of blood contains 250 milligrams of iron. An average sized human body contains around 10 pints of blood..
250 x 10 = 2500 milligrams of iron..
So the human bloodstream contains approximately...