DSS057: Performing Dust Explosion Risk Assessments with Dr. Russell Ogle

In this episode of the DustSafetyScience Podcast, we interview Dr. Russell Ogle, principal engineer and Practice Director for Thermal Sciences at Exponent based out of Warrenville, Illinois, about performing dust explosion risk assessments.

Russell has over 30 years of experience in incident investigation and explosion hazard evaluation. He is the author of a textbook called [Affiliate] Dust Explosion Dynamics, which focuses on the combustion science of dust explosions and fires. Russell also co-authored Chapter 6, which was about risk assessment, in the book [Affiliate] Methods and Chemical Process Safety Vol. 3 on Dust Explosions.

In this interview, he answers the following questions:

Why should a company have a risk assessment performed at their facility?
How is a dust hazard analysis different?
Why is an evidence-based approach important?
What are some situations that make a risk assessment advisable?
How can DHAs and risk assessments vary from one facility to the next?

Why Should A Company Have A Risk Assessment Performed At Their Facility?

All companies need to recognize the hazards represented by combustible dust, whether it’s a product manufactured for sale or a byproduct that needs to be managed, and answer the following questions:

What are those hazards?
How significant are they?
What can be done to protect workers and property?

Risk assessments are typically regarded as a more sophisticated way of performing a dust hazard analysis. They tend to take a quantitative approach, largely due to the fact that a risk assessment involves a considerable investment of resources.

“We want to make sure that we position our allocated resources to provide the greatest possible risk reduction first,” Russell explained. “And then, as we have additional resources remaining, we can evaluate the less urgent hazards that need to be addressed in our facility.”

One approach for managing combustible dust hazards is to follow the prescriptive safety standards that are available internationally through ISO, the British EN standards, or the National Fire Protection Association (NFPA). These guidelines come with a lot of valuable historical knowledge, although they can be a disadvantage when new technologies, materials, or scenarios are involved.

How Is A Dust Hazard Analysis Different?

While risk assessments and dust hazard analyses have similar objectives, the latter is more of a structured investigation into the hazards. You go from room to room and processing line to processing line and examine each piece of equipment. A dust hazard analysis also involves a risk matrix that evaluates the likelihood and severity of consequences.

“A dust hazard analysis, more often than not, is probably the first place one should consider going,” Russell said. “If you find, though, that you have very little experience that you can draw from, or if there’s very little literature that can guide you on how to manage these particular hazards, then you need to find a way to take a very structured approach to evaluating how hazards arise as the flow of material proceeds through your process… And that’s where risk assessment can come in.”

He said that a risk assessment can complement a dust hazard analysis. If 90% of the hazards at a facility can be adequately addressed via a DHA, a risk assessment can evaluate the remaining 10%. It takes an evidence-based approach that typically involves more detailed sources for estimates of the probability or likelihood of an event as well as the severity of any consequences.

Why Is An Evidence-Based Approach Important?

Some safety decisions are consequence-driven. You can see an opportunity to eliminate a hazard or significantly reduce its severity by using a simple technology that may be relatively inexpensive. Other situations, however, call for difficult decisions in terms of which safeguard to implement.

With dust deflagrations and flame acceleration effects in connected equipment, there can be some tradeoffs between the effectiveness of implementing the technology versus the ability to maintain it and ensure its reliability. You want to base your decision on good evidence and careful consideration of the relative risks and the risk reduction with one general technology versus another.

“The decision-making process and how you implement safeguards is not just about economics,” Russell said. “The cost of a technology, of course, is one important consideration. But we need to also consider its effectiveness and reliability.”

For example, with systems that rely on automated control loops, you want to keep the sensor active and functioning. You also want to confirm that the control loop works. A risk assessment makes you more confident that these factors will work to the desired level of risk reduction and provide some level of evidence to support a decision in one direction versus another.

What Are Some Situations That Make A Risk Assessment Advisable?

According to Russell, there are a number of different methodologies that one can use to do a dust hazard analysis. Some of those methodologies are scenario-based, meaning that you develop a scenario for the hazard that you want to try to design for or control.

Many risk assessments also follow a scenario-based approach, with a specific sequence of events that should be considered. They may be initiated by a malfunction or by some kind of failure. Then the question you’re trying to resolve is: what can happen in this particular piece of equipment?

Dust collectors are a common example. What could happen if there’s an accumulation of self-heating material and smouldering starts inside the unit? What kind of safeguards could you implement for that?

Those considerations will be different if you think about what would happen if a deflagration occurs inside the dust collector. What hazards will arise as a result? What kind of control technologies can you implement to protect workers and the facility from these hazards?

“When we consider the consequences of the deflagration inside a piece of equipment like a dust collector, we think of the ignition event occurring inside the dust collector itself,” Russell pointed out. “That would be your normal or ordinary expected deflagration, but things can change quite a bit if the origin of the deflagration is outside the dust collector and actually travels through a conduit to get to it. That’s where flame acceleration can occur and you get a magnification of the event.”

This scenario implies a different kind of hazard and begs for different controls, which is why coming up with hypothetical dangers is so important. To control the hazard, you need to understand it. This is one of the advantages of the risk assessment: you are forced to be more specific, detailed and intentional about how you think about the hazards and how you address them. After you evaluate the severity of the consequences and identify and analyze the likelihood of those events, you put them together and get the risk.

How Can DHAs And Risk Assessments Vary From One Facility To The Next?

Equipment like dust collectors are used in all sorts of industries, but the application, equipment arrangement, material throughput, and even particle size distribution can vary from one unit to the next. If one dust collector has a shorter distance between it and the processing equipment, the flame acceleration hazard is lower than it would be if there was a wider distance.

Another issue to consider is the dust collector location. An outdoor installation is ideal, but if that’s not possible, you want to consider the risk of a deflagration inside that dust collector, especially if it’s in an area where people regularly work. Even if it is outside, you need to make sure that people are aware of the location and the possible venting field if an incident occurs.

Russell stressed the importance of teamwork in all DHAs and risk assessments. “If you get people from your engineering, operations, and maintenance to help implement this process, there’s a tremendous opportunity to exchange experience and knowledge. And that makes for a stronger safety program at the company that’s performing this analysis.”

Conclusion

When asked if he had any concluding thoughts, Russell came up with ones that we should all remember.

“We need to always realize that this is a process that’s never done and there’s always more work to do. There are always opportunities for improvement. And risk assessment works best when everyone is open to that idea of finding better ways to do things in ways to improve safety at their facility.”

If you would like to discuss further, leave your thoughts in the comments section below. You can also reach Russell Ogle directly:
Email: [email protected]
LinkedIn: https://www.linkedin.com/in/russell-ogle-590554a3/

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.