Spontaneous combustion
Spontaneous combustion is a type of combustion which occurs without an external ignition source.
Cause and ignition
- A substance with a relatively low ignition temperature begins to release heat, which may occur in several ways, such as oxidation or fermentation.
- The heat is unable to escape, and the temperature of the material rises
- The temperature of the material rises above its ignition point
- Combustion begins if a sufficiently strong oxidizer, such as oxygen, is present.
Pyrophoric substances
Main article:
PyrophoricityThe element sodium is an example of a pyrophoric material which can undergo a kind of spontaneous (and potentially very violent) explosion when exposed to oxygen, water, or moisture in the air. Pyrophoric substances have an autoignition temperature below room temperature and often require mere contact with air or water in order to spontaneously ignite. A characteristic of pyrophoric materials is also their large specific surface of contact with air. Raney nickel is pyrophoric because of the very fine size of its particles. Rieke metals are even more dangerous.
Affected materials
- Haystacks, compost piles and unprocessed cotton may self-ignite because of heat produced by bacterial fermentation.[1][2]
- Linseed oil in a partially confined space (such as a pile of oil-soaked rags left out in an uncovered container) can oxidize leading to a buildup of heat and thus ignition.[3][4]
- Coal can spontaneously ignite when exposed to oxygen which causes it to react and heat up when there is insufficient ventilation for cooling.[5]
- Pyrite oxidation is often the cause of coal spontaneous ignition in old Mine tailings.
- Pistachio nuts are highly flammable when stored in large quantities, and are prone to self-heating and spontaneous combustion.[6]
- Large cow manure piles can spontaneously combust during conditions of extreme heat.
- Cotton /Linen. when these materials come into contact with polyunsaturated vegetable oils(linseed, massage oils) bacteria slowly decompose the materials, producing heat. If these materials are stored in a way so the heat cannot escape, the heat build up increases the rate of decomposition and thus the rate of heat build up increases. Once ignition temperature is reached, combustion occurs with oxidizers present (oxygen).
In addition large areas of woodland, shrubland and grasslands during periods of dry hot weather are known to be capable of spontaneously combusting - though the mechanisms causing this are poorly understood. This has been proven to occur via the lifecycle of a variety of plants which require the area to be burned prior to germination.
People have also been reported as spontaneously combusting. This phenomenon is not considered true spontaneous combustion, as it is largely attributed to the wick effect, whereby an external source of fire ignites nearby flammable materials and human fat.
In engines
In internal combustion engines, spontaneous ignition is called either compression ignition or preignition, depending on whether it is intentional as in diesels or unintentional and related to detonation as in spark ignition engines.
In humans
The spontaneous combustion of people (i.e. death from a fire originating within the victim's body without a direct external cause) is a theorised explanation for a number of unexplained cases, some of which are well-documented and many of which are not. The more convincing cases share the following characteristics:
- The body is completely or almost completely incinerated, while nearby furniture that should normally have been damaged under such temperatures remains intact. Damage is limited to the victim's clothing, to the area of the floor or furniture on which they died, and to the ceiling above the corpse.
- The torso is the focus of the fire, and if remains are found these are of the extremities, such as the feet.
- There are no traces of fire accelerant, and the fire does not have an evident external cause.
- The victim is typically alone at the time of death, and is thought to have been alive when the fire started, despite showing little sign of having struggled.[7]
Various theories have been put forward to explain these cases, though none have yet achieved consensus.
References
External links