Spontaneous combustion

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Spontaneous combustion is a type of combustion which occurs without an external ignition source.

How spontaneous combustion occurs

1. A substance with a relatively low ignition temperature begins to release heat, which may occur in several ways, such as oxidation or fermentation.
2. The heat is unable to escape, and the temperature of the material rises
3. The temperature of the material rises above its ignition point
4. Combustion begins, if sufficient oxygen is present.

Some materials which can spontaneously combust

• Haystacks and unprocessed cotton may self-ignite because of heat produced by bacterial fermentation.
• Grain dust in a hot metal silo can explode violently, destroying the structure.
• Boiled linseed oil in a partially confined space (such as a pile of oil soaked rags left out in an uncovered container) can evaporate leading to a subtle tremendous buildup of heat and thus ignition.
• Coal can spontaneously ignite when exposure to oxygen causes it to react and heat up when there is insufficient ventilation for cooling.
• Pistachio nuts are highly flammable when stored in large quantities, and are prone to self-heating and spontaneous combustion.

Pyrophoric materials

The element sodium is an example of a pyrophoric material which can undergo a kind of spontaneous (and potentially very violent) explosion when exposed to 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.

Safety

In general practice, the threat of spontaneous combustion can be substantially reduced by placing the material in a tightly confined, self-closing disposal container (thus greatly limiting the supply of oxygen or water vapor), or submerging it in a fluid which smothers the reaction before it can begin. Depending on the hazard, this protective fluid may be water, kerosene (especially for a reactive metal such as sodium, which ignites upon contact with water) or an inert gas such as nitrogen or argon.

See also

• Combustion
• Spontaneous human combustion

References

External links

• Article on the spontaneous combustion of coal
• Spontaneous combustion demonstration

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Last updated on Thursday March 13, 2008 at 20:15:08 PDT (GMT -0700)
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