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Causes of asphyxic death
Suffocation is the result of a decreased oxygen tension in the inhaled air due to lower atmospheric oxygen tension, or PAO2, or lower partial oxygen pressure. An example of low atmospheric pressure is the sudden decompres-sion of an aircraft cabin at high altitude, with a drop in the barometric pressure in the cabin. The oxygen can also be consumed or displaced by other inert gases such as carbon dioxide or nitrogen. This is seen when oxygen is consumed by a fire, or in an enclosed space such as a fridge. An interesting example which often occurs in the agricultural regions of our country, is when people die in wine tanks or silos. During the process of fermentation in these tanks or silos, oxygen is consumed and carbon dioxide produced. This process is similar to the fermentation process responsible for the production of ginger beer or wine, or when yeast causes bread to rise. Carbon dioxide is a heavy gas and it will accumulate at the bottom of the tank or silo. If the person enters this space, the oxygen-poor/carbon-dioxide-rich air will overwhelm him, and death will follow. A similar situation occurs in ships' hulls. Rust is the product of iron oxidation. When steel rusts, (which is common in ships) oxygen is consumed and replaced by inert gases. More examples of an oxygen-poor atmosphere are wells in lime soil (lime contains carbon dioxide, a heavy gas which will accumulate in the deeper parts of a well), and defective scuba-diving gear.
Although hypoxia plays the most important role in these deaths, inert gases like nitrogen and carbon dioxide may also caused death due to neurogenic cardiac arrest. This condition will be discussed below.
On post-mortem examination there are seldom signs of asphyxia. Where the death is due to a fire, signs of carbon monoxide poisoning may also be present. Note that a fire does not only consume oxygen, but also produces carbon dioxide and carbon monoxide, depending on the availability of oxygen. Other poisonous products such as sulphur-containing substances are also produced, depending on the type of material. These substances are toxic and inter alia damage the airways.
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