The Hidden Danger of Dust Explosions in Industries
Dust explosions are a critical yet often overlooked subject in various industries, including blasting. Any setting with significant amounts of dust, whether in the air or machinery, holds the potential for explosions.
All dusts can be dangerous.
Even seemingly harmless dust can become explosive in high concentrations. Most dust, when suspended in the air in sufficient amounts, can turn combustible and explosive under specific conditions. Surprisingly, even dust from non-flammable materials like iron, steel, and aluminum can become explosive in a dust form. Industries like sugar or flour mills are particularly susceptible to dust explosions, as witnessed by a series of incidents in the USA that led to loss of life and substantial property damage. Consequently, numerous regulations and safety measures have been implemented to prevent future occurrences.
Minimum Explosible Concentration (MEC).
For a combustible dust explosion, two additional ingredients are required: dust-laden air in a confined space (such as a factory, dust collector, or vessel) and an airborne dust concentration above the lower Minimum Explosible Concentration (MEC) level for that specific dust.
The MEC varies for different dust types, reflecting their explosive potential. For instance, magnesium dust is highly explosive even in small concentrations, while sand dust is less explosive and requires a higher concentration to pose a hazard.
Combustible dust explosions typically happen when a vessel containing dust above its MEC level encounters an ignition source, such as fire, sparks, or electrical faults. The risk lies in a hidden danger – the potential for secondary explosions that can level entire buildings and factories.
Secondary explosion.
The initial explosion may occur in a small piece of equipment, but it sets off a chain reaction. The shock wave from the initial explosion can disturb accumulated dust throughout the facility, creating a confined dust cloud. If the MEC level of the dispersed dust in the cloud is exceeded, the entire building becomes an explosive environment. The resulting explosion, fueled by the initial blast, can be devastating and much larger than the first explosion. Unfortunately, there’s little time to react to prevent a secondary explosion, as it can occur in less than one second.
Blasting abrasives.
In our abrasive blasting industry, where dust is a significant concern, we focus on materials relevant to our field. Abrasive blasting generates large amounts of dust, primarily from the breakdown of abrasives and surfaces being blasted. It’s crucial to consider not just the quantity but also the explosiveness of the dust, where small amounts of highly explosive dust can be as dangerous as or more dangerous than large amounts of less reactive dust, such as garnet sand.
Know your dust.
When evaluating the potential risks of an explosion one of the criteria is to know the explosiveness of the dust being generated. A good source for this is the GETSIS-DUST-EX data based which can be found here http://www.dguv.de/en/index.jsp
This database lists all dusts commonly found in the abrasive blasting industry. Dusts are listed according to their Kst value and classified into 4 categories:
St 0 – Non explosive
St 1 – Weak to moderately explosive
St 2 – Strongly explosive
St 3 – Very strongly explosive
Generally in the blasting industry the explosiveness of the dust will be rated as St 0 – St 1. However there are some notable exceptions of reading St 2 – St 3 when blasting aluminum or zinc items and when blasting with walnut shells.
Bear in mind in a blasting environment there are 2 areas that need to be considered and evaluated, the ventilation dust collector and the blastroom, enclosed area or cabinet in which the blasting is taking place. All of these are confined spaces.
Next post we will discuss the measures that can be taken to totally avoid or mitigate the damage of a combustible dust explosion in a blast cleaning environment.
Further reading.
If you want further reading on this subject a good place to start is OSHA – https://www.osha.gov/dsg/combustibledust/guidance.html
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