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Explosive

Definition

• (adjective) Refers to a chemical compound, mixture, device etc. that is capable of exploding. Example: "Gasoline forms an explosive mixture with air."
• (noun) An explosive is a compound or mixture susceptible (by heat, shock, friction or other impulse) to a rapid chemical reaction, decomposition or combustion with the rapid generation of heat and gases with a combined volume much larger than the original substance.

Explosives can be broken into two general categories that reflect the rate of the transformation.

High explosives are capable of detonating and are used in military ordinance, blasting and mining etc.. These have a very high rate of reaction, high pressure development, and the presence of a detonation wave that moves faster than the speed of sound (1,400 to 9,000 meters per second). Examples include primary explosives such as nitroglycerin that can detonate with little or no stimulus and secondary explosives such as dynamite (trinitrotoluene, TNT) that require a strong shock (from a detonator such as a blasting cap). Low explosives change into gases by burning or combustion. These are characterized by deflagration (burning rapidly without generating a high pressure wave) and a lower reaction rate than high explosives. The overall effect ranges from rapid combustion to a low order detonation (generally less than 2,000 meters per second). Gun powder (black powder) is the only common example.

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MSDS Relevance

Flammable vapors can form explosive mixtures with air under certain circumstances. Accidental ignition by a spark, heat source or static electricity can trigger an explosion. These vapors can travel a significant distance from their source (along hallways and stairwells, for example), so always be sure to reduce or eliminate vapor formation whenever possible.

Some materials are shock-sensitive, meaning that they can be detonated (explode) merely by friction or touch. Examples include organic peroxides, nitrogen triiodide and dry picric acid. Such materials should only be dealt with by explosives-trained experts.

Other explosions can be caused by mixing incompatible chemicals. This is a common sort of laboratory accident (and one of the most terrifying).

Explosions can also be caused by over-pressurized containers. There is an utterly remarkable account of a large liquid nitrogen Dewar explosion at UC Davis (9 MB, PDF) that demolished a laboratory and rocketed through the concrete ceiling. On a smaller scale, pressure can build up inside reaction vessels or containers if they are not properly vented, leading to catastrophic failure.

Never rely on the absence of a smell alone to indicate that propane or natural gas vapors are not present, particularly in a confined space. The odorants used in these gases can sometimes fade upon storage; see the entry on anosmia for more information on this phenomenon.

Additional Reading

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An example of a real-life laboratory explosion caused by mixing incompatible chemicals. The American Chemical Society's journal Chemical & Engineering News maintains a list of Safety Letters concerning materials involved in unexpected explosive decompositions. An archived version of the US Geological Survey's The Dictionary or Mining, Mineral and Related Terms. The University of Rhode Island's Center of Excellence for Explosives Detection, Mitigation and Response has courses, an Explosives Database and more. Anatomy of an Explosion at Fenwal Protection Systems. OSHA's Fatal Fact Sheet #3 discusses a gasoline storage tank explosion. OSHA's Fatal Fact Sheet #53 is similar.

See also: flammable, peroxide.

Additional definitions from Google and OneLook.

Disclaimer: The information contained herein is believed to be true and accurate, however ILPI makes no guarantees concerning the veracity of any statement. Use of any information on this page is at the reader's own risk. ILPI strongly encourages the reader to consult the appropriate local, state and federal agencies concerning the matters discussed herein.