Unseasonably low temperatures in Tehran, Iran, lead to the deaths of at least 40 people on this day in 2003. Rarely do such large groups die at the same time.
In general, death from freezing occurs when the body's core temperature reaches 77 degrees Fahrenheit, a fact discovered by Nazi doctors during experiments on prisoners at the notorious Dachau concentration camp during World War II. In 1994, however, a two-year-old child in Canada survived a body temperature of just 57 degrees suffered when she wandered away from her Saskatchewan home.
When core body temperature goes down to 97 degrees, neck and shoulder muscles tighten and extremities begin to ache. When it gets to 95 degrees, mild hypothermia sets in and involuntary trembling and shivering occurs as the body tries to generate its own heat. Two degrees lower and amnesia and short-term memory loss is common. When body temperature reaches 88, shivering is no longer possible and people experience general numbness.
In some cases, a phenomenon known as "paradoxical undressing" occurs, in which a person about to freeze to death actually rips off their clothes. The effects of hypothermia can also be delayed--in one instance, Danish fishermen stuck in the North Sea for 90 minutes were able to walk on the deck of a rescue ship before falling down and dying.
One notorious incident of hypothermia occurred at the Four Inns Walk in England in 1964. The race involved 240 racers (all in excellent condition) hiking 43 miles over the English moors. Although the temperature never fell below freezing, the wind and rain caused three people to freeze to death and put another four in critical condition. Researchers later determined that a key factor in the deaths was that the victims had failed to take in enough calories during the hike.
The 2003 freeze in Tehran was unusual in that so many people died in a single night. The previous year in Moscow, between 5 and 10 people froze to death every day during the winter for a total of more than 300 in the city alone.