LONDON - Hanging is a process scientifically designed to break the neck and choke a person to death as efficiently as possible.

In the recent Iraqi executions, Saddam Hussein on Dec. 30 and two of his accomplices early yesterday were hanged from a gallows.

In such judicial hangings, those being executed typically are dropped a distance greater than their height through a trapdoor. At this point the rope becomes rigid, and the force of the noose should break the neck, causing immediate paralysis and unconsciousness.

The procedure causes a classic "hangman's fracture" - a break between the head and the neck, effectively snapping the upper cervical spine. In most cases, asphyxiation causes the death.

Although no one really knows how long it takes a person to die from hanging, experts say it probably ranges from a few seconds to a couple of minutes.

In judicial hangings, as opposed to suicides, there is significant damage to the spinal cord. If those hanged fall more than the prescribed distance, they may even pick up so much speed that the noose itself decapitates them, as happened yesterday to Hussein's half brother Barzan Ibrahim.

"Hanging is a very cruel way of killing people," said Harold Hillman, an expert in executions who teaches at the University of Surrey. "The fracture obstructs their breathing, and they are left gasping for breath."

Criminals have been hanged since the Persian Empire adopted the practice 2,500 years ago. The last major advance in the technology of hangings was made in the 19th century, when tables were devised to calculate both the length of rope needed to kill and the distance of the necessary "drop."

According to these "drop tables," the heavier the prisoners, the shorter the distance needed to produce sufficient force to break their neck.

Still, these drop tables are only a rough guide, said Geoffrey Abbott, author of Execution: The Guillotine, the Pendulum, the Thousand Cuts, the Spanish Donkey, and 66 Other Ways of Putting Someone to Death.

"A person could weigh an amount that required a length of eight feet," he said, "but because his neck is particularly scrawny, his head might come off."