Explaining the Risks - Dust Explosions

Dust explosions can be particularly nasty beasts and they can happen anywhere there are flammable materials floating around in the air.

Especially when that air is filled with oxygen; present on our planet in massive amounts and one of the main ingredients you need to make fire.

You cannot create fire without an oxidant.

What is a dust explosion?

There are five fundamental requirements for a dust explosion to happen;

• Fuel,

• Oxidant,

• Dispersion,

• Ignition source,

• Confinement.

Dust explosions are the result of the rapid combustion of thousands of very fine particles suspended in the air.

These explosions most often occur in enclosed spaces, but it's also possible for ignition to occur in non-enclosed areas. It can literally happen anywhere there are high enough concentrations of very fine, combustible particles in the air.

These types of explosions have been a big problem for certain industries over the years. Our coal miners frequently saw dust explosions in underground coal mines, and other industrial environs generally produce a lot of dust which can easily be ignited if not properly controlled.

Grain elevators were especially at risk due to the constant and massive amounts of flour dust in the air.

These fine particles are known as the fuel, and naturally they require an oxidant to ignite.

How do dust explosions happen?

Fire cannot exist without oxygen. In fact, fire is the result of the chemical reaction that occurs when you put an oxidizer, a heat source and a fuel source together. It will never become fire if you don't add that oxidant.

In the case of dust explosions, the oxidant is generally (but not always) oxygen. We need it to live and breathe and it's everywhere. It's not really something we can eliminate.

It is possible for dust explosions to occur even in controlled atmospheres of reduced oxygen. Even though the oxidant levels are reduced, the oxidant is still present and provides enough reaction to ignite the fuel source.

The same is also true in higher pressure atmospheres, if there is sufficient oxidant the fuel source will ignite and an explosion will occur.

Dust must be formed into a cloud

Combustible dusts or particles will not ignite unless they have been dispersed into a floating cloud. Layers of this same dust on the floor cannot actually explode but may catch on fire producing another source of heat and ignition which will increase the risk of explosion.

There is no fire without an ignition

Just like missing an oxidant, the chemical reaction that creates fire won't happen unless there is a source of heat or ignition.

A source of heat or ignition could potentially be a spark or hot spot generated through using tooling or machinery. The only requirement for it to create fire is that it's hot enough to ignite the fuel source in the air.

There are several controlling guidelines to address some ignition sources in electrical and non-electrical equipment, but the sources of heat created by work processes, maintenance and cleaning are more complicated to control.

No explosion without confinement

Confinement could be any constricted area. This could be anything from a sealed and enclosed container, a vented container or a restricted and enclosed location.

If ignition occurs where there is no confinement then the resulting reaction is known as a flash fire. Flash fires are still very dangerous, but less so than dust explosions thanks to the reduced atmospheric pressure present.

In a dust explosion, the area is confined meaning the atmospheric pressure rises rapidly as the fire comes into being creating a massive explosion.

If you're worried that your workplace may not be properly equipped to deal with a dust explosion or flash fire, you can take the new COSHH Risk Assessor Certification™. I will train you how to properly identify, assess and control all risks you will meet on a daily basis.

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