Dust explosion
Dust explosions can occur where any dispersed powdered combustible material is present in high-enough concentrations in the atmosphere or other oxidizing gaseous medium, such as pure oxygen.
They are also commonly used by special effects artists, filmmakers, and pyrotechnicians, given their spectacular appearance and ability to be safely contained under certain carefully controlled conditions.
[1] If rapid combustion occurs in a confined space, enormous overpressures can build up, causing major structural damage and flying debris.
Primary dust explosions may occur inside process equipment or similar enclosures, and are generally controlled by pressure relief through purpose-built ducting to the external atmosphere.
In addition, many otherwise mundane organic materials can also be dispersed into a dangerous dust cloud, such as grain, flour, starch, sugar, powdered milk, cocoa, coffee, and pollen.
[5] For example, in machining operations downstream of the AM build, excess powder liberated from porosities in the support structures can be exposed to sparks from the cutting interface.
[5] Efforts are underway not only to build this knowledgebase within the industry but also to share it with local fire departments, who do periodic fire-safety inspections of businesses in their districts and who can expect to answer alarms at shops or plants where AM is now part of the production mix.
[8] Similarly, if the fuel to air ratio increases above the upper explosive limit (UEL), there is insufficient oxidant to permit combustion to continue at the necessary rate.
Also, particulate suspensions of compounds with a high oxidative potential, such as peroxides, chlorates, nitrates, perchlorates, and dichromates, can increase risk of an explosion if combustible materials are also present.
For example, a 1 kilogram (2.2 lb) sphere of a combustible material with a density of 1 g/cm3 would be about 12.4 centimetres (4.9 in) in diameter, and have a surface area of 0.048 square metres (0.52 sq ft).
When this mixture of fuel and air is ignited, especially in a confined space such as a warehouse or silo, a significant increase in pressure is created, often more than sufficient to demolish the structure.
Even materials that are traditionally thought of as nonflammable (such as aluminum), or slow burning (such as wood), can produce a powerful explosion when finely divided, and can be ignited by even a small spark.
Good housekeeping practices, such as eliminating build-up of combustible dust deposits that could be disturbed and lead to a secondary explosion, also help mitigate the problem.
