Honestly, it's the most complicated version of Hanging to execute. We're normal people, not trained military personnel. Many mistakes can occur.
There's a website dedicated entirely to this topic; it has so much information that it's impossible to summarize it in a single post. I've left the link below.
---- [The processes of judicial hanging: There are four main forms of hanging] ----
Short drop hanging where the prisoner drops just a few inches, and their suspended body weight and physical struggling causes the noose to tighten, normally resulting in death by strangulation or carotid or Vagal reflex. Pole hanging is a variation on this method.
Suspension hanging where the executee is lifted into the air using a crane or other mechanism. Death is caused in the same way as with short drop hanging.
Standard drop hanging where the prisoner drops a predetermined amount, typically 4-6 feet, which may or may not break their neck. This was the normal method adopted in America in the later 19th and early 20th centuries.
Finally, measured or "long drop" hanging which became universal in Britain from 1874, where the distance the person falls when the trapdoors open is calculated according to their weight, height and physique and is designed to break the neck. This method was adopted in British Colonies and by some other countries who wished to make executions more humane.
The "Short Drop" method.
Hanging using little or no drop is still used by some Middle Eastern countries, notably, Iran.
The prisoner could be suspended by a variety of means, from the back of a cart (or later a motor vehicle), from a horse as was sometimes used in America, or by removing the platform or ladder on which they stood, as was used in Nazi hangings and also in present day Iranian ones carried out inside prisons, or by some form of trap door drop mechanism as was used in Britain from 1760 and adopted by many other countries.
The Rules of Execution of Sentences require the body of the convict to remain hanging for 20 minutes up to 45 minutes. After that, the executioners take the body down from the gallows, the doctor confirms the death, and the body is taken to the morgue.
Suspension hanging.
This method is currently used in Iran for public hangings and was also used for some executions when the Taliban controlled Afghanistan where executees were hanged from the barrels of tanks and from mobile crane jibs. In Iran, both mobile crane and recovery truck jibs are used. All of these have hydraulic mechanisms for raising them, so the jib serves as both the gallows and the means of getting the prisoner suspended.
In America, instead of the conventional gallows that dropped the prisoner through a trapdoor, some states used a method where weights connected to the rope jerked the person upwards when they were released by the hangman. This method was used in 1874, for the hanging of William E. Udderzook in West Chester, Pennsylvania and also for Charles Thiede in Utah in 1896.
Connecticut used a similar arrangement for the execution of Gerald Chapman on April the 26th, 1926. A weight was connected to the rope which passed over a pulley. The warden operated a lever with his foot to allow the weight to fall, so pulling Chapman 12 feet into the air with such force that his neck was broken.
Standard drop hanging.
A standardised drop, of between four and six feet, was used in many American hangings during the later part of the 19th century and into the early 20th century.
This was not worked out against the weight of the individual, but was often equivalent to their height. It was considered as an advance on the short drop method previously used. A drop of this distance was often not sufficient to break the prisoner's neck, however, and many still died by strangulation, although in a lot of cases they were knocked unconscious by the force of the drop and the impact of the heavy coiled knot against the side of the neck. Occasionally, they were decapitated when the drop proved to be too long, as happened at the execution of Eva Dugan in Arizona in 1928.
The "Long drop" or measured drop method.
In 1872, William Marwood introduced the concept of an accurately calculated drop for the execution of Frederick Horry at Lincoln prison, as a scientifically worked out way of giving the prisoner a humane death.
The long drop method was designed to break the prisoner's neck by allowing them to fall a pre-determined distance and then be brought up with a sharp jerk by the rope. At the end of the drop, the body is still accelerating under the force of gravity but the head is constrained by the noose. If the eyelet is positioned under the left angle of the jaw it rotates the head backwards, which combined with the downward momentum of the body, breaks the neck and ruptures the spinal cord causing instant deep unconsciousness and rapid death. The later use of the brass eyelet in the noose tended to break the neck with more certainty. It is only in the last six inches or so of the drop that the physical damage to the neck and vertebrae occur as the rope constricts the neck and the force is applied to the vertebrae. The duration of this part of the process is between 0.02 and 0.03 of a second depending upon the length of drop given. Generally the diameter of the noose is found to have reduced some five to seven inches after the drop.
The drop given in the later part of the 19th century was usually between 4 and 10 feet depending on the weight and strength of the prisoner. The weight used to calculate the correct drop is that of the prisoner's clothed body. In accordance with the recommendations of the Aberdare Committee, from 1886 to 1892, the length of drop was calculated to provide a final "striking" force of approximately 1,260 ft. lbs. force which combined with the positioning of the eyelet caused dislocation of the neck, usually at the 2nd and 3rd or 3rd and 4th cervical vertebrae. The length of the drop was worked out by the formula 1,260 foot pounds divided by the body weight of the prisoner in pounds = drop in feet. Between 1892 and 1913, a shorter length of drop was used, presumably to avoid the decapitation and near decapitations that had occurred with old table. The 1892 table produced a force of 840 ft. lbs.
After 1913, other factors were also taken into account and the drop was calculated to give a final "striking" force of around 1,000 ft. lbs. The Home Office issued a rule restricting all drops to between 5 feet and 8 feet 6 inches as this had been found to be an adequate range.
From around 1939 it became customary to add a further nine inches to the drop calculated from the 1913 table, to give a force of around 1100 ft. lbs..
---- [How judical hanging causes death] ----
Short drop and simple suspension hanging.
Short drop/suspension hanging accounts for a majority of all executions worldwide as well as a large number of suicides.
Iran is the leading user of this method and uses a coiled noose with the knot placed at or towards the back of the neck. Hanging with little or no drop typically causes death by a combination of the tightening noose occluding the carotid arteries and jugular veins causing cerebral hypoxia (ischemia), i.e. a severely reduced flow of oxygenated blood to and from the brain and asphyxia due to the weight of the person's body forcing the base of the tongue upwards against the back of the mouth, blocking the airway and thus preventing breathing. It may also constrict the trachea (air passage), however this requires some 33 pounds per square inch of pressure to compress. Compression of the carotid arteries may also cause rapid heart stoppage due to carotid/Vagal reflex, this requiring just 11 pounds per square inch of pressure, whereas compression of the jugular veins only requires some 4.5 pounds per square inch of pressure. The vertebrae protect the vertebral and spinal arteries which also supply blood to the brain. However, these arteries go outside the fourth vertebrae instead of inside it, which subjects them to blockage if the pressure on the neck is high enough (usually about 40-50 pounds per square inch of pressure). Consciousness can be lost in as little as 8-10 seconds. It is thought that brain death will occur in around six minutes and the heart will stop beating within 10-15 minutes.
The convulsive phase which it is thought occurs after consciousness has been lost. There may be spasmodic and uncoordinated rippling movements of the limbs which occur for some time and which are usually attributed to nervous and muscular reflexes caused by the build up of carbon dioxide in the blood stream.
Decerebrate posturing is caused by lesions of the brainstem due to the coils of the noose pressing on it. As the prisoner's arms are invariably handcuffed behind their backs, Decerebrate posturing of the arms is largely prevented.
Standard drop hanging.
Where the standard drop proves inadequate to break the neck or cause unconsciousness, the prisoner seems to suffer a more cruel death than where little or no drop is used. The force generated by a drop of 5 or 6 feet is very considerable and does great damage to the skin, muscles and ligaments of the neck but does not necessarily induce asphyxia any sooner.
Fortunately not all standard drop hangings were so gruesome and many prisoners did not show any signs of physical suffering as they were rendered unconscious by the force of the drop, even though their spinal cord was not severed.
The measured or long drop.
It takes between a half and three quarters of a second for a person to reach the end of the rope after the trap opens, depending upon the length of drop given. The force produced by the prisoner's body weight multiplied by the length of fall and the force of gravity, coupled with the position of the noose is designed to violently jerk the person's head backwards and sideways. In medical terms this is known as hyperflexion of the neck, which causes dislocation of the upper neck vertebrae and may also cause fracture of the vetebrae, ideally between the C2 & C3 vertebrae, crushing or severing the spinal cord leading to immediate unconsciousness.
This leads to a number of factors, all of which can cause death. The Phrenic nerve which controls the diaphragm emerges between the C3 and C4 vertebrae and thus if the dislocation occurs above C4 the person's breathing ceases immediately, leading to asphyxia. The rope constricts the carotid arteries and the jugular veins, with the same results described in "Short drop hanging" above. Typically the neck is constricted by as much as five inches from its original circumference.
Fractures of the hyoid bone and larynx typically occur which on their own can prove fatal as breathing is severely restricted or prevented. The normal cause of death is given as comatose asphyxia. Some slight movements of the limbs and body may occasionally occur but are almost certainly due to muscular reflexes.
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Website (source): https://capitalpunishmentuk.org/