In today’s episode of the Dust Safety Science podcast, Michel Vandeweyer, Explosion Safety Consultant from ISMA in Antwerp, Belgium, returns to provide further insight into combustible dust regulations in Belgium. This episode is part two of a two-part series on this subject (you can find part one here).
During the last episode, Michel reviewed his experience in the area, explained how combustible dust safety is approached in terms of regulations and engineering guidelines in Belgium, and provided three steps for applying the ATEX legislation. Today, he provides some example case studies that yield further insights into explosive atmospheres, ignition sources and mitigation of consequences.
Explosive Atmospheres
Zoning and the identification of explosive atmospheres is to ensure the safety of workers. Although there is a European standard with guidelines, it’s quite complex and doesn’t always apply, so most countries have their own rules.
“In the Netherlands, for example, it’s NPR,” Michel said. “In Germany, they have TRGS standards, and so on and so on..”
There is no national guideline or standard in Belgium, but an industry-accredited inspection and certification organization can approve zoning definitions. This minimizes the risk of one’s zoning being challenged by the labour inspectorate. Belgian companies must also have periodic electrical checks from independent organizations, which is another incentive for them to keep everything in order and maintain their zoning.
“Best example is housekeeping,” Michel said. “You can have your zoning drafted when you’ve cleaned everything perfectly and the inspector comes and says, ‘Okay, I agree it’s clean here.’ But if you don’t keep that good housekeeping up and the next electrical inspection comes along, yeah, you do have an issue there because [the inspector] says, ‘Hey, you have dust on non-ATEX equipment- explain this.’ [It’s] more motivation for companies to keep this zoning exercise up and to do what must be done in that regard.”
Ignition Sources
Michel explained that this area is where things often go wrong.
“This should not come (as) a surprise since the ignition source is what causes the explosion. This analysis is most often done per installation part. If you look at one part of an installation, you ask yourself, does it have the possibility of an ignition source?”
However, doing it this way can result in the relationship between different parts being overlooked. Michel provided an example using a dust filter.
“On its own, the dust filter only produces electrostatic discharges. No fast movement occurs in a filter. Standard dust filters do not have heating elements. So actually a dust filter is quite safe on its own. You [add] anti-static filter sleeves and you’re good to go. However, if this filter extracts dust from places with smouldering particles or fast-rotating equipment, you could run into problems.”
In other words, only looking at the filter is not a correct evaluation of ignition sources. When someone is inexperienced or untrained, these evaluations can be difficult.
“For example, electrostatic phenomena are most often not sufficiently understood. If you don’t understand them completely, you cannot evaluate them correctly,” Michel explained. “To give you a specific example, in the food industry, there is a tendency to coat the silos internally with non-conductive coatings. Now they say, ‘Well, propagating brush discharge needs high airflow and high product flow.’ But in a silo where they coat the inside, you don’t have this high speed along the silo wall. So you could say, well, is this such an issue in a silo? The problem is that if you transport products into a silo (for example, pneumatically), the product enters charged. When it is deposited in the silo, there’s a charge compression in the bulk material. All the charges are in the bulk material and they generate a high electric field.”
This electric field is also responsible for cone discharges. However, before cone discharges are formed, Other discharges (e.g. brush) occur. While they aren’t dangerous for dust, the corresponding counter charges are directed along the electric field lines to the earthed silo’s outer wall. They will form a high charge density on the applied coating, and that may lead ultimately to a propagating brush discharge.
“You must use the correct type of FIBCs – flexible intermediate bulk containers- for the same reason,” Michel said. “You should use a type B if you are using flammable bulk material, and this type B must have a breakdown voltage lower than 4 kilovolt just to avoid these propagating brush discharges. And the same applies to the inner coatings of a silo. We did a lot of tests on these coatings since some companies that were concerned about it. These coatings are mostly built from epoxy, and these breakdown voltages should be below 4 kilovolts, but they’re often multiples. I’ve had samples to 20 to 30 kilovolts that did not even have a breakdown then. So it’s probably higher than that. So applying such a coating is actually deliberately putting another ignition source inside of your silo, and you should take that into account in your risk analysis.”
Mitigation of Consequences
Michel said that the consequences of an explosion should be mitigated if the possibility of an ignition source can’t be sufficiently reduced. The problem is that a lot of companies can be creative when it comes to compliance. For example, he has gone into places where explosion venting panels open into areas where people are present.
“A colleague of mine went to a country in East Europe recently and he witnessed two very large filters – they were protected by vent panels. But the vent panels from the two filters gave out directly onto each other – which means if one filter blows up as an explosion, the explosion is vented directly onto the vent panel of the other filter, which most likely will result in an explosion in the second filter.”
He recalled a 2019 incident involving a silo. It was filled with wood waste and experienced a fire. Firefighters covered the product with a foam layer, searched for hotspots and declared that the fire was extinguished. The next day, a cleaning firm started emptying the silo from the bottom. During the emptying, a dust cloud must have formed. When it combined with carbon monoxide from a still-smouldering fire, a hybrid explosion resulted. One person was killed while three others were severely injured.
Conclusion
At the end of the interview, Michel stressed the importance of rewriting the standards to take things like hybrid mixtures and hydrogen explosions into account.
“There’s a lot of research done in this matter, and maybe this will soon be translated into new standards where we also participate. A lot of new things are coming (e.g. biofuels) and we’re really looking forward to it but a lot of new problems will start occurring on larger scales.”
To prevent or mitigate the consequences of such problems, the current standards need to be reviewed. Remaining current on potential dangers as they evolve is key to ensuring safety in at-risk environments.
If you would like to discuss further, leave your thoughts in the comments section below. You can also reach Michel Vandeweyer directly:
Email: [email protected]
Website: https://www.isma.be/
LinkedIn: https://www.linkedin.com/in/michel-vandeweyer-0200071a0/
If you have questions about the contents of this or any other podcast episode, you can go to our ‘Questions from the Community’ page and submit a text message or video recording. We will then bring someone on to answer these questions in a future episode.
Resources mentioned
Dust Safety Science
Combustible Dust Incident Database
Dust Safety Science Podcast
Questions from the Community
Dust Safety Academy
Dust Safety Professionals
Dust Safety Share
Companies
Previous Episodes:
DSS219: Current Status of Combustible Dust Safety in Belgium & Example Case Studies with Michel Vandeweyer – Part 1
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