DSS077: Understanding Hybrid Mixture Explosion Hazards with Dr. Emmanuel Addai

In this episode of the DustSafetyScience Podcast, we are interviewing Dr. Emmanuel Addai about hybrid mixture explosion hazards.

Dr. Addai has a PhD in experimental testing and theoretical modelling of hybrid mixtures. In 2016, he transitioned into industry as a consultant and is currently a senior process safety specialist with Stonehouse Process Safety based out of Houston, Texas. He is also a certified process safety professional and fire and explosion scene investigator.

Dr. Addai’s thesis topic was hybrid mixtures, based on experimental testing and theoretical modeling at industry scale. In today’s interview, he sheds light on a seldom-discussed topic by answering the following questions:

What is a hybrid mixture?
What gaps have you observed in industry?
How do you typically test hybrid mixtures?
How is a hazard analysis different with hybrid mixtures?

What is a hybrid mixture?

Dr. Addai explained that a hybrid mixture is a combination of materials with different states or phases. When it comes to fires or explosions, it means that different materials are involved. For example, combustible dust mixed with flammable gas. This can happen in:

Coal mines, where coal dust can mix with methane gas
Spray dryers that combined dust with drops and flammable vapors
Pharmaceutical applications where solvents are added to the dust in liquid or gas form

When Dr. Addai was pursuing his Masters’, he was involved in a project that mixed flammable solvent with dust, and noted the hazards associated with these kinds of mixtures. He also realized that unlike single phase materials, such as dust and gas, there was very little research into hybrid mixtures.

“I decided to pursue my research to help to understand the explosion behavior of hybrid mixtures, just especially in those areas which have not been touched,” he said.

He focused his thesis research on parameters such as PMax, KST, and explosion likelihood sensitivity (minimum ignition temperature, minimum ignition energy, the minimum explosible concentration and the limited oxygen concentration) of these materials, with the goal of better predicting their explosibility. His findings have since been published in various industry journals and his thesis can be found on Google Books.

What gaps have you observed in the industry?

When Dr. Addai moved into the industry as a process safety consultant, he quickly identified several gaps, one of which was a lack of awareness. People in industrial facilities didn’t understand the consequences of mixing materials.

Another gap was lack of data that could be used to assess the risk of a particular hybrid mixture. Sometimes facility managers would ask him to use the “worst case scenario” but he had to remind them that this approach wouldn’t work because there was no way to accurately assess the risks.

A third issue he regularly encountered was the tendency to ignore the presence of flammable gas or vapor and focus on dust. All the preventive and protective measures will be aimed solely at dust hazards and exclude anything else.

How do you typically test hybrid mixtures?

When testing dust, one can test for the whole concentration range. Hybrid mixtures can have both gas and dust concentrations. Dr. Addai said that depending on the circumstances, he tries to either simulate whatever combustible material is being produced by the facility or run various appropriate tests instead of limiting himself to the worst-case scenario.

In this context, looking at different options makes sense. With a combination of hydrogen gas and non-activated carbon dust, there will be a wide span of KSTs to choose from. It can also be dangerous to design for the worst-case scenario because if a dust explosion occurs, the suppression system could activate so quickly that it all settles out before the dust deflagration gets there. The safest approach is to recommend measures based on a realistic scenario.

How is a hazard analysis different with hybrid mixtures?

When conducting a hazard analysis in a facility where hybrid mixtures are present, Dr. Addai considers the same procedures used for dust, but acknowledges the presence of gas or solvent.

“The first thing that will come to my mind is go back to the drawing board, which is the fire triangle,” he explained. He considers all elements in the mixture to see what could be generated and whether there is additional fuel in the system.

“When a process handles these kinds of mixtures, control of ignition sources is very, very paramount in the operation. One thing we also need to consider is preventing sparks or electric arcs.”

Dr. Addai said that an especially difficult problem is that area classification and equipment rating is different for dust and gas. NFPA 497 for gas and NFPA 499 for dust are not the same. If a piece of equipment is rated specifically for gas and is not dust-tight, any release of dust from the system can go into the motor and cause some kind of short-circuit which can be a source of ignition.

“I recommend that the facilities which handle these kinds of mixtures do proper assessment and performance-based design,” he said.

Conclusion

Dr. Addai acknowledged that hybrid mixtures are rare, but if they ignite, the outcome can be even more devastating than an event involving single components.

“So, we need to be aware of these hazards. We need to ensure that in any process where maybe any additional component could be generated apart from our main component, a detailed hazard assessment is done for this hybrid system.”

If you would like to discuss further, leave your thoughts in the comments section below. You can also reach Dr. Addai directly:
LinkedIn: https://www.linkedin.com/in/emmanuel-k-addai-ph-d-mba-ccpsc-csp-cfei-73574156/

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.