It is against the law to place a living person under cryonic suspension. So
in order to take advantage of this service, one has to die first. Death, in
this case, is defined as when ones heart stops beating, though certain brain
function still exists.
The moment ones heart stops beating and one is pronounced dead, an emergency
team from a facility like Alcor goes into action. They stabilize the body,
supplying the brain with enough oxygen and blood to maintain minimal function
until it can be transported to a cryonics facility. The body is packed in ice
and injected with heparin, an anticoagulant, to prevent the blood from clotting
during the trip.
Once the body is at the cryonics facility, the actual process of preservation
begins. One does not just freeze a body by, say, immersing it in a vat of
liquid nitrogen. This would cause the water in the body’s cells to freeze,
causing the cells in turn to shatter. First, the water is removed from the
body’s cells and is replaced with a glycerol-based chemical mixture called a
cryoprotectant, a kind of human antifreeze. The purpose is to protect the
organs and tissues from forming damaging ice crystals. It facilitates cooling
down the human body without actually freezing it.
Then the body is placed in dry ice until it reaches a temperature of about
minus 202 degrees Fahrenheit. Then the body is placed head down in an
individual container of liquid nitrogen at a temperature of minus 320 degrees
Fahrenheit. And there the body stays until such time as it can be revived, in
theory.