World Library  
Flag as Inappropriate
Email this Article

Dust explosion

Article Id: WHEBN0010473148
Reproduction Date:

Title: Dust explosion  
Author: World Heritage Encyclopedia
Language: English
Subject: List of industrial disasters, Benxihu Colliery, Courrières mine disaster, Hazards, 1942 in China
Collection: Chemical Processes, Explosions, Hazards, Industrial Fires and Explosions
Publisher: World Heritage Encyclopedia

Dust explosion

A dust explosion is the fast combustion of dust particles suspended in the air in an enclosed location. Coal dust explosions are a frequent hazard in underground coal mines, but dust explosions can occur where any powdered combustible material is present in an enclosed atmosphere or, in general, in high enough concentrations of dispersed combustible particles in atmosphere or other suitable gaseous medium such as molecular oxygen.

Dust explosions are also commonly used by special effects artists, filmmakers, and pyrotechnicians, given their ability to be safely contained.


  • Conditions needed 1
    • Sources of dust 1.1
    • Sources of ignition 1.2
    • Concentration 1.3
  • Mechanism 2
  • Terminology 3
  • Protection and mitigation 4
  • Accidents 5
  • See also 6
  • References 7
  • External links 8

Conditions needed

There are five necessary conditions for a dust explosion or deflagration:

  1. A combustible dust
  2. The dust is suspended in the air at a high concentration
  3. The dust cloud is confined
  4. There is an oxidant (typically atmospheric oxygen)
  5. There is an ignition source[1]

Sources of dust

1878 Stereograph rendering of the Great Mill Disaster.

Many materials which are commonly known to oxidise can generate a dust explosion, such as coal, sawdust, and magnesium. However, many otherwise mundane materials can also lead to a dangerous dust cloud such as grain, flour, sugar, powdered milk and pollen. Many powdered metals (such as aluminium and titanium) can form explosive suspensions in air.

The dust can arise from activities such as transporting grain and indeed grain silos do regularly have explosions. Mining of coal leads to coal dust and flour mills likewise have large amounts of flour dust as a result of milling. A gigantic explosion of flour dust destroyed a mill in Minnesota on May 2, 1878, killing 14 workers at the Washburn A Mill, and another 4 in adjacent buildings.[2] A similar problem occurs in saw mills and other places dedicated to carpentry. Thermobaric weapons, depending upon their fuel, are also a potential and intentional source of dust.

Although not strictly a dust, paper particles emitted during processing - especially rolling, unrolling, calendaring/slitting and sheet-cutting - are another known explosion hazard. Enclosed paper mill areas subject to such dangers commonly maintain very high air humidities to reduce the chance of airborne paper dust explosions.

To support combustion, the dust must also consist of very small particles with a high surface area to volume ratio, thereby making the collective or combined surface area of all the particles very large in comparison to a dust of larger particles. Dust is defined as powders with particles less than about 500 micrometres in diameter, but finer dust will present a much greater hazard than coarse particles by virtue of the larger total surface area of all the particles.

In special effects, lycopodium powder and non dairy creamer are two common means of producing safe, controlled fire effects.

Sources of ignition

There are many sources of ignition and a naked flame need not be the only one: over one half of the dust explosions in Germany in 2005 were from non-flame sources.[3] Common sources of ignition include

However it is often difficult to determine the exact source of ignition post-explosion. When a source cannot be found, it will often be cited as static electricity. Static charges can occur by friction at the surfaces of particles as they move against one another, and build up to levels leading to a sudden discharge to earth.


Below a certain value, the lower explosive limit (LEL),[3] there is simply insufficient dust to support the combustion at the rate required for an explosion. A combustible concentration at or below 25% of the LEL is considered safe.[4] Similarly, if the fuel/air ratio increases above the upper explosive limit there is insufficient oxidant to permit combustion to continue at the necessary rate.


Dusts have a very large surface area compared to their mass. Since burning can only occur at the surface of a solid or liquid, where it can react with oxygen, this causes dusts to be much more flammable than bulk materials. For example, a 1 kg sphere of a material with a density of 1g/cm3 would be about 12.4 cm across and have a surface area of 0.048m2. However, if it were broken up into spherical dust particles 50µm in diameter (about the size of flour particles) it would have a surface area of 120 This greatly increased surface area allows the material to burn much faster, and the extremely small mass of each particle allows it to catch on fire with much less energy than the bulk material, as there is no heat loss to conduction within the material. 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.


Dust explosions may be classified as being either primary or secondary in nature. Primary dust explosions occur inside process plant or similar enclosures and are generally controlled by pressure relief through purpose-built ducting to atmosphere. Secondary dust explosions are the result of dust accumulation inside the factory being disturbed and ignited by the primary explosion, resulting in a much more dangerous uncontrolled explosion inside the workplace. Historically, fatalities from dust explosions have largely been the result of secondary dust explosions.

High speed video of a primary dust explosion may be viewed here [1] and a secondary dust explosion may be viewed here [2].

Protection and mitigation

Mount Mulligan mine disaster in Australia 1921. These cable drums were blown 50 feet (15 m) from their foundations following a coal dust explosion.

Much research has been carried out in Europe and elsewhere to understand how to control these dangers, but explosions still occur. The alternatives for making processes and plants safer depend on the industry. In the coal mining industry, a methane explosion can initiate a coal dust explosion, which can then engulf an entire pit working. Stone dust is spread along mine roadways, or suspended from trays in the roof, so as to dilute the coal dust raised ahead of the combustion zone by the shock wave, to the point where it cannot burn. Mines may also be sprayed with water to inhibit ignition. Some industries exclude air from dust-raising processes, known as "inerting". Typically this uses nitrogen, carbon dioxide or argon, which are incombustible gases and so inhibit combustion. The same method is also used in large storage tanks where inflammable vapours can accumulate. Usage of oxygen-free gases however brings a risk of asphyxiation of the workers. Workers who need illumination in enclosed spaces where a dust explosion is a high risk often use lamps designed for divers, as they have no risk of producing an open spark, due to waterproofing.

Good housekeeping practices, namely eliminating the build-up of deposits of combustible dust that may be disturbed and lead to a secondary explosion, also help mitigating the problem.

Best engineering control measures which can be found in the National Fire Protection Association (NFPA) Combustible Dust Standards include:

  • Wet Dust Collection
  • Oxidant Concentration Reduction
  • Deflagration venting
  • Deflagration pressure containment
  • Deflagration suppression
  • Deflagration venting through a dust retention and flame-arresting device


  • May 2, 1878, Minneapolis, Minnesota, grain dust explosion in the Washburn "A" Mill kills 22 people, destroying the largest grain mill in the world and leveling five other mills, effectively reducing the milling capacity of the city by one-third to one-half. The disaster prompts mills throughout the country to install better ventilation systems to prevent dust build-up.
  • 26 April 1942, Benxihu Colliery, coal and gas explosion kills 1,549 Chinese miners, 34% of the miners working that day, making it the worst coal mining accident in history
  • 1977 Westwego, Louisiana grain elevator explosion
  • DeBruce grain elevator explosion
  • January 29, 2003, Kinston, North Carolina, the West Pharmaceutical Services plant suffered an explosion that was blamed on rubber dust.
  • 2008 Georgia sugar refinery explosion

See also


  1. ^ [3]
  2. ^
  3. ^ a b !StaubEx_0805_e.pdf
  4. ^ NFPA 69 8.3.1

External links

For stories about incidents in France and the USA see

  • various completed investigations from the Chemical Safety Board
  • Combustible Dust Policy Institute-ATEX
  • OSHA case studies of dust explosions

For information on how to protect a process plants and grain handling facilities from the risk of dust hazard explosions, see

  • Dust Explosions - The Dangers, and The Precautions Needed To Avoid Them
  • Hazard Monitoring Equipment - Selection, Installation and Maintenance
  • Seminars for Combustible Dust Safety
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.

Copyright © World Library Foundation. All rights reserved. eBooks from World eBook Library are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.