In today’s episode of the Dust Safety Science podcast, we’re talking to Robert Comer, author of the book Explosion Vented Equipment System Protection Guide, about protecting equipment from dust explosions.
This book clarifies a common misconception that merely installing a vent or an explosion protection system is enough to help ensure safety. Instead, it emphasizes that equipment must follow specific structural standards to genuinely mitigate explosion risks. Bob’s publication also stands out for its detailed guidance on conducting assessments to prevent dust explosions, a topic seldom covered in depth in other texts.
Bob Colmer is a licensed professional engineer and a life member of the National Society of Professional Engineers. Hisprofessional journey took a notable turn during his tenure as a site engineering manager for M&M Mars, now Mars Wrigley, where he encountered the practical challenges of managing dust explosions.
An incident involving a minor explosion in a sugar dust collection system underscored the importance of safety measures in industrial settings. The explosion, which occurred in a room designed with explosion relief walls, highlighted the risks associated with dust accumulation and the necessity for proper grounding of equipment to prevent sparks. Drawing on his experience, Bob reinforced the dust collector and implemented additional safety measures, including an explosion relief duct.
This incident paved the way for his subsequent consultancy role with Hazard Research Incorporated, where he has spent the last 25 years analyzing dust collector systems, particularly those that have experienced explosions. His work in this area has had a global impact, with over 200 systems analyzed worldwide. His transition from working on the front lines of explosion prevention to sharing his knowledge through writing reflects his commitment to enhancing safety in industrial environments.
Why Was The Book Written?
“My 25 years of analyzing systems was limited to 100 units,” Bob said. “I felt with the downtime from COVID, it was an opportune time to at least get the information out. Most people don’t know that they have a bomb in their facility. And I think awareness is very important. I think the book will do that.”
He explained that venting systems in industrial settings may appear adequate, but often they’re not designed to withstand the high pressures generated by explosive gases during an explosion. Understanding how explosions occur is fundamental: an ignition source leads to a rapid increase in pressure, potentially exceeding 100 psi without proper venting measures, causing significant destruction.
The minimum burst pressure for many venting elements is around one psi, with a variance of plus or minus a quarter psi. However, when evaluating the structural integrity of dust collectors, which essentially act as poor pressure vessels, the pressure rating is often found to be insufficient. For instance, some systems are rated at plus or minus 20 inches of water, equivalent to 0.723 psi, below the burst pressure of standard venting discs. This discrepancy indicates a need for system reinforcement.
Moreover, the initial one psi rating does not account for the dynamic pressures encountered during an explosion, which can range from 4 to over 10 psi. This mismatch underscores a significant challenge in ensuring the structural resilience of systems against the pressures exerted by explosive gases, necessitating further attention and action to mitigate risks effectively.
An Overview of Structural Assessments
Bob said that In many instances he experienced, the necessary information for assessing the safety of a system against explosions was incomplete. The burst element’s rating was typically available, providing a known factor to work with, including its size and the product associated with it. However, this product often lacked testing for critical safety data, such as the CSD (Chemical Safety Data) or maximum pressure ratings, which are essential for a thorough risk assessment.
To address these gaps, conducting tests on materials became a vital step. Testing is a key service provided by research organizations, enabling the assessment of material properties under specific conditions. With tested materials and the burst element’s data in hand, it was possible to proceed with analyzing the system’s design. This analysis involved understanding the system’s geometry, which, while generally known, often lacked detailed information like wall thickness. Measurements or existing drawings were used to gather the necessary geometric details, allowing for a backward calculation of pressure resilience and other safety parameters.
What Should Facilities Look For in Structural Reinforcements?
When assessing the safety of large, box-like structures subject to pressure, the focus often centers on evaluating flat, thin panels which are critical to the system’s integrity. Using standard formulas for stress and strain found in common engineering texts simplifies this process significantly. By extracting relevant information specifically for flat panels, with permission, this distilled knowledge is made accessible, enabling a straightforward evaluation of whether a panel can withstand expected pressures.
If a panel is found inadequate to handle the pressure, it necessitates subdivision into smaller sections, a process facilitated by adding structural reinforcements such as angles, ribs, channels, or structural tubing based on preference and practicality. These reinforcements can be sized efficiently to manage the panel dimensions effectively, a process detailed comprehensively in the guide.
The reinforcement process is further simplified by the fact that continuous welding is not required; intermittent welds suffice, making it a feasible task for many. The guide elaborates on reinforcing not just the primary container but also specific areas prone to stress, such as the junction between the main body and the cone at the bottom, the roof, and any exiting screw conveyors, which are particularly susceptible to damage from explosions due to their thin construction.
Thus, the guide provides an actionable framework for enhancing the structural resilience of systems against explosive pressures, covering everything from basic panel reinforcement to addressing potential vulnerabilities in the design, making it accessible to a wide audience interested in safeguarding their facilities.
In practical terms, reinforcing a system to withstand explosions has proven effective in real-world applications. There are instances where systems, once reinforced, have experienced explosions without any damage to the structure, demonstrating the success of these enhancements. A specific area of focus includes cylindrical dust collectors, which, while generally robust as pressure vessels, often have flat tops that are susceptible to pressure and therefore require reinforcement to ensure safety.
Additionally, access doors on these collectors, whether on cylindrical or square designs, present a notable weak point. Under normal operations, these doors are held in place by suction, but they are not typically designed to withstand the force of internal pressure from an explosion. The hinges, latches, and bolts that secure these doors tend to be the failure points when subjected to unexpected stress. Therefore, reinforcing these components is essential to prevent failure and maintain the integrity of the system during an explosive event. This approach underscores the importance of anticipating and strengthening potential weak spots to ensure a robust defense against the forces generated by explosions.
Access Hatches as Failure Points
The book provides detailed guidance on reinforcing access panels, including the use of latches, hinges, and destaco toggle clamps. It breaks down the analysis of the door components to ensure they can withstand explosive pressures. It also addresses the forces exerted on the flanges of ducts that vent hot gases outside, highlighting the significant reaction forces these flanges face, which can affect the stability of the dust collector.
An important point covered is the consideration of pressure exceeding 15 psi. At this level, a standard analysis is insufficient, and an ASME code analysis becomes necessary. However, the methodologies described in the book are accessible to any engineer within an organization, regardless of licensing status, for pressures below this threshold.
Additionally, the book discusses dust blast deflectors and their need to endure not only the initial explosive pressure but also the dynamic pressures that can arise from friction against the walls or bends in the ductwork. These factors can increase the pressure burden on the dust collector, highlighting the need for careful consideration in the design and reinforcement of these systems.
Conclusion
Ultimately, the insights shared by Robert Comer are invaluable for industries grappling with the threat of dust explosions. His work underscores the need for diligent assessment, proper material testing, and strategic reinforcement to ensure the safety and integrity of industrial systems. By following the practical guidance outlined in his book, facilities can significantly reduce their risk of dust explosions, safeguarding both their infrastructure and personnel.
If you would like to discuss further, leave your thoughts in the comments section below. You can also reach Robert Comer directly:
Email: [email protected]
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
The resources mentioned in this episode are listed below.
Dust Safety Science
Combustible Dust Incident Database
Dust Safety Science Podcast
Questions from the Community
Books
Explosion Vented Equipment System Protection Guide
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