Flour bomb

There are two types of flour bomb:

* The relatively innocuous use of flour in a fragile container, thrown at a person or object to produce an inconvenient stain.
* The dangerous explosion that can occur when an air suspension of the fine organic, often starchy, substance is ignited.

Prank or protest

Flour in a fragile container thrown at an object or person of derision is a classic protest method, along with the throwing of eggs and overripe tomatoes. A recent example was the use of purple-dyed flour in condoms thrown at Tony Blair in the chamber of the House of Commons by protesters campaigning for improved access rights to their children. The event highlighted the poor security methods employed in and around the Houses of Parliament at the time.

The effect of flour bombs is made worse by the inclusion of eggs, or containers of other liquid, making the removal of the resultant mixture difficult.

Grain elevator explosions

The classic educational flour bomb demonstration shows the explosive power of flammable powders under the right circumstances. Given a large enough suspension of combustible flour or grain dust in the air, a significant explosion can occur. An example is the 1998 explosion of the DeBruce grain elevator in Wichita, Kansas, which killed 7 people. cite web | last = | first = | authorlink = | coauthors = | year = 1998 | url = http://www.wichitagov.org/CityOffices/Fire/Photos/Gallery1.htm | title = June 8, 1998 - DeBruce Grain Elevator Explosion | format = | work = City of Wichita | publisher = City of Wichita | accessdate = 2007-06-22] . A famous historical example of the destructive power of grain explosions is the 1878 explosion of the Washburn "A" Mill in Minneapolis, Minnesota, which killed eighteen, leveled two nearby mills, damaged many others and caused a destructive fire that gutted much of the nearby milling district. The Washburn "A" mill was later rebuilt and continued to be used until it was shut down in 1965.

Almost any finely divided organic substance will produce an explosive mixture in an air suspension. For military use, so-called hyperbaric or thermobaric fuel-air bombs have been produced that work by initially creating a mist of jet fuel (kerosene) or diesel fuel, then igniting the mist. The resulting explosion not only destroys structures, but depletes the atmospheric oxygen in the immediate vicinity, as this type of bomb does not use an explosive that contains its own oxidizing agent. Hyperbaric bombs are designed to produce maximal overpressure, and hence structural damage; whereas thermobaric bombs are designed to produce a very high temperature in the zone of explosion/combustion.

Very fine flour is dangerous in air suspension, as it too can explode. This is a significant risk when milling grain to produce flour, so mills go to great lengths to remove sources of sparks. These include carefully sifting the grain before it is milled or ground to remove stones which could strike sparks from the millstones, and the use of magnets to remove metallic debris which can also strike sparks.

The earliest recorded flour explosion took place in an Italian mill in 1785, but there have been many since. The following two references give numbers of recorded flour and dust explosions in the USA in 1994 [cite web
url=http://www.oznet.ksu.edu/historicpublications/Pubs/1994Dust_Explosions.pdf
title=A report of grain dust explosions that took place in 1994
accessdate=2007-06-23] and 1997 [cite web
url=http://www.oznet.ksu.edu/historicpublications/Pubs/1997Dust_Explosions.pdf
title=A report of grain dust explosions that took place in 1997
accessdate=2007-06-23] . In the ten year period up to and including 1997, there were 129 explosions.

References

ee also

*Dust explosion