Particle Explosion

In this presentation, you will learn about. . .

• The explosion at the Washburn "A" Mill in 1878 and what caused it
• How flour (and other dust) explosions are caused
• What the 'Fire Triangle' means
• What the 'Dust Pentagon' means
• Why flour and dust explosions are caused
• How to prevent dust explosions

1878, Washburn Mill

• On May 2nd of 1878, a spark ignited in the Washburn A Mill (once the largest industrial building in Minneapolis)
• 18 people were killed
• The explosions caused fire to spread to the other mills, causing even more explosions and deaths
• Minneapolis lost around one-third to a half of their flour producing capacity, impacting the flour industry greatly

The Cause of the Explosion

After the fire was put out in the mill, people began investigating how it had started.

• The manager of the mill, John A. Christian, explained that the flour dust had ignited, causing an intense blast of heat
• S.F. Peckham and Louis W. Peck, two university professors, determined that the flour had ignited due to the millstones rubbing together and creating a spark

“Flour dust that is suspended in air is more explosive than coal dust," - Paul Steinlage

What causes a dust explosion?

The 'Fire Triangle'

Dust explosions occur when combustible/flammable dust particles are present in the air. Dust explosions only occur when there are three things present:

• Combustible dust (as fuel)
• Oxygen
• Heat source (to ignite the explosion)

And in addition, they also need:

• The correct concentration of dust particles (dispersion)
• Confinement of the dust

The 'Dust Pentagon'

Why does the explosion happen?

When dust (e.g. flour, coal, icing sugar, cornstarch, wood, etc.) is released into the air, the particles spread out. This is called dispersion. By dispersing the particles of dust, its surface area increases. This causes the dust to have a higher reaction rate, because the particles are more likely to come in contact with the reactant. The particles collide more, which also increases the reaction rate.

This results in the dust catching fire quickly. The fire spreads through the rest of the airborne dust, causing an intense burst of heat which transfer to other dust clouds and flammable materials.

How to Prevent a Dust Explosion

• Avoid using compressed air or brushes/brooms to clean dusty areas, and instead use a dust vacuum
• Don't let dust accumulate on surfaces
• Inspect and clean facilities regularly
• Make sure dust does not come into close contact with possible ignition sources
• Control all open flames, sparks, wires, and heat sources to make sure they don't ignite the dust
• If dust is leaking from its container, seal the leakage areas immediately
• Keep all equipment in good condition

Bibliography

http://www.friendsofthecemetery.org/history/alley_articles/MillExplosion_March2005.shtml

https://blog.generalmills.com/2012/05/the-explosion-that-changed-milling/

http://www.mnopedia.org/event/washburn-mill-explosion-1878

https://www.wired.com/2008/03/the-explosive-t/

https://www.safetyandhealthmagazine.com/articles/13157-combustible-dust-hazards

http://stellarfoodforthought.net/how-to-prevent-a-dust-explosion-at-your-food-processing-plant/

http://www.hse.gov.uk/food/dustexplosion.htm