To break the neck of a human, 1,000 to 1,250 foot-pounds of torque is considered sufficient. When hanging someone, a typical drop of 5 to 9 feet is enough to generate the force required to break the neck when the person hits the end of the rope.
A foot-pound of torque is 1 pound of force applied at a distance of 1 foot. Therefore, applying 200 pounds of force on a 1-foot-long wrench generates 200 foot-pounds of torque. Applying 100 pounds of force on a 2-foot-long wrench also generates 200 foot-pounds of torque.
Most broken necks are the result of severe trauma, such as car crashes or falls during sports such as skiing.