Asphyxia is the key cause of death from things such as strangulation, drowning and carbon monoxide poisoning. It involves low level of oxygen in the body, combined with high carbon dioxide and acidosis (i.e. build up of lactic acid). In forensics there are 3 key categories of death via asphyxiation: Strangulation, Chemical Asphyxia, and Suffocation.

Strangulation is the method most commonly used during murders. It was also used as a method of execution in the past. For example, the garrote was a device used for capital punishment in Spain, until as late as 1940. It involved tying a rope around the neck of the condemned, and twisting it until it was tight enough to cause strangulation. However, self-strangulation, often auto-erotic, is also very common. The auto-erotic type often involves taking in alcohol or other substances, such as drugs, while being strapped and positioned with the head lowered relative to the rest of the body. Several famous people died that way, including the American actors David Carradine and Albert Dekker, and the 1700s composer Frantisek Kotzwara, who was famous for the classical music composition "The Battle of Prague" (listen on YouTube: Quite an undignified way to go for very talented people, but we can only hope it will teach others a lesson.

Strangulation used as a method of execution depicted in the book,"Ten Years in Equatoria and the Return with Emin Pasha" by G.Casati. Property of the British Library.
Chemical, or toxic, asphyxia typically involves a substance which interferes with the body's cells' ability to take in oxygen, such as by preventing oxygen binding to haemoglobin in the blood, which is the case with carbon monoxide. Concentrated hydrogen sulphide is also classified as a chemical asphyxiant as it can paralyse the respiratory centre of the brain. Chemical asphyxia is very common in environments such as mines and sewers.

Suffocation can have many causes. For example, some children can suffocate by being trapped in refrigerators, which are left unattended by the parents. In addition, there were and still are, some reported instances of people running out of oxygen due to being buried alive in a coffin (more about that in future posts). Meanwhile, others can suffocate by being smothered with a pillow. Although usually this is a method of murder, smothering can also be accidental, such as when a baby lies face-down on a pillow in its crib for too long. Homicide cases of suffocation often are referred to with the term "Burking", when a combination of traumatic asphyxia and smothering is observed, and it was named after its "inventor", William Burke. In the 19th century Burke and his "business partner", William Hare used to sell corpses to medical schools, usually obtained by excavating graveyards. However, as increasing law measures were being taken to prevent grave robberies, Burke and Hare decided that preying on inconvenient lodgers and local alcoholics would be easier. The murders were usually carried out by sitting on the victim's chest, while covering their mouth and nose with their hands.
Suffocation may occur due to crushing. The bird's oxygen supply may become obstructed if it gets squeezed harder.
Another method of suffocation is when someone, usually accidentally, enters an area depleted of oxygen. For example, some underground fungal infestations may cause a dangerous reduction in oxygen levels in the given area. Drowning is also a method of suffocation, as the ingested fluid replaces oxygen in the body. Moreover, suffocation can occur by choking, i.e. when air flow to the body is obstructed by a piece of food or a small swallowed object. Mass suffocation of people living near volcanoes has also been reported, being attributed to springs and cracks underneath craters feeding nearby lakes and delivering high concentrations of carbon dioxide gas to the environment. As a result, entire villages get poisoned, with victims being mostly children, as they tend to be the ones breathing air closer to the ground (carbon dioxide is heavier than the usual air). It should be noted that this is not a case of chemical asphyxia, as being a simple asphyxiant, carbon dioxide prevents oxygen from being transferred to cells due to displacing it, rather than competing with it on a cellular level or directly damaging the respiratory system.

During postmortem examinations the cause of death is usually established by checking medical records and examining the corpse for physical signs such as tiny haemorrhages on the heart, skin, eyeballs, and other organs. Their presence would imply a likely death by asphyxiation. Moreover, cyanosis, i.e. a dark blue or purple discoloration of the skin and body tissues, develops in cases of significant oxygen depletion. Moreover, analysing the viscosity of the blood can also help assess the cause of oxygen depletion. Nevertheless, death from asphyxia cannot be stated with absolute certainty when only presented with these signs, as other things might have happened before or after death (e.g. the murderer could apply a ligature to the neck after death). The exact cause of death is typically established by taking into account all factors involved, including the environment and personal circumstances of the deceased.


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