Asphyxia is a broad term encompassing a variety of conditions that result in interference with the uptake or utilization of oxygen together with failure to eliminate carbon dioxide. Because the brain is most sensitive to oxygen deprivation, it is the organ most intimately affected in all types of asphyxial death. Asphyxia falls into four categories including compression of the neck, as in hanging and strangling; obstruction of the airway, as in smothering, aspiration of foreign material, and swelling of lining membranes; compression of the chest with sufficient force to prevent respiratory movements; and exclusion of oxygen by another gas or chemical substances, as in carbon dioxide poisoning, carbon monoxide poisoning, and cyanide poisoning. Death by hanging usually results from arrest of the arterial blood supply to the brain or obstruction of the venous return from it. Loss of consciousness occurs within 2 or 3 minutes. Neck grooves or furrows provide recognizable evidence of hanging. Strangulation may be homicidal, suicidal, or accidental. The hallmark of manual strangulation is fingernail marks on the neck of the victim, and fractures of the larnyx may sometimes occur. In smothering victims, blockage of the nose and mouth causes death due to the inability to breathe. Smothering is homicidal in the majority of cases. Accidental asphyxia may occur as a result of aspiration of foreign material or severe reactions to insect bites or drugs, causing swelling of the larnyx membranes. Examples of chest compression asphyxia include victims buried under rubble of collapsed buildings and victims of stampeding crowds. Within the final category, carbon dioxide causes asphyxia by excluding oxygen. Common places that may contain carbon dioxide in excess include manholes, wells, silos, and cellars. Carbon monoxide causes asphyxia by blocking the respiratory pigment of the red corpuscles from carrying oxygen to the body tissues. Automobile exhaust fumes are a primary source of carbon monoxide. Cyanide poisoning causes vital function paralysis and death within seconds. Various means of accidental asphyxia associated with sexual perversion are encountered. Photographs and 16 references are included. For related documents, see NCJ 69731-37 and 69739-47.