People who are exposed to very cold environments, whether air or water, can develop hypothermia after a relatively short time.
When your body temperature starts to dip below the normal 98.6 degrees Fahrenheit, you may be unable to think clearly or move normally. Because your thinking is clouded, you may not realize you have hypothermia.
When the body's temperature drops below 95 degrees, the situation is critical, according to the Centers for Disease Control and Prevention. You should seek medical attention immediately.
In responding to the water landing Thursday of US Airways Flight 1549 in New York, the main goal of rescuers and medical personnel was to prevent hypothermia. When the plane hit the water, the water temperature was 41 degrees at a buoy five miles south and the air temperature was 20.
Since most people were rescued in a relatively short time, the risk of developing serious hypothermia is low.
According to the Mayo Clinic, people can survive one to three hours in water that is 40 to 50 degrees Fahrenheit. But they might lose consciousness in 30 to 60 minutes in water that cold.
In extreme cases, people can get frostbite, lose fingers, toes or limbs, or even die.
To treat hypothermia, the first thing to do is remove wet clothing and replace it with something dry. In addition to wrapping people in blankets or other coverings, emergency personnel would monitor breathing and start resuscitation if necessary.
At the hospital, medical personnel might give survivors warm fluids intravenously. If the hypothermia is severe, dialysis is sometimes used to circulate a person's blood through a warming machine before returning it to the body.