In this episode of the DustSafetyScience Podcast, we talk to Ric Smith, who has been working in EHS (environmental health and safety) for over 13 years. Much of that time was spent managing combustible dust safety programs at a corn milling facility. An explosion occurred there, and Ric is here to share some lessons learned from that incident.
During this discussion, he answers the following questions:
- How can health and safety managers learn more about combustible dust?
- What happened on the day of the explosion?
- How did you and your team respond?
- What are the lessons learned?
- Do you have any recommendations for facility owners and operators that may be handling combustible dust?
How can health and safety managers learn more about combustible dust?
For EHS managers looking to improve their knowledge about dust hazards, Ric recommended a number of valuable resources, including:
- The NFPA standards
- The American Society for Safety Professionals
- The National Safety Council (NSC)
- The Chemical Safety Board’s investigations section, which reveal the root cause of several events and recommendations for corrective action.
“(Build) upon these factors and see how they apply to operations within each facility,” he advised. “We have to keep in mind that the finer the dust, the more explosive it is (and) control the events.”
What happened on the day of the explosion?
Ric explained that the corn milling facility was undergoing a major transformation. It had always operated using relay logic controls: to start up and stop operations, a series of events had to occur. There were five banks of controllers that would require switching on to get the equipment running.
“We’re trying to automate this process where we have more controls, we have more programmable logic (to) make it more efficient. So we were undergoing a major transformation […], where it took about eight months to go from where it was to automated mode.”
He confirmed that no new equipment was being installed. “It was just the electronics and remapping of electrical controls to the motor switches, etc. Some of the issues we found is that we were using old diagrams that weren’t updated. We also were not having a lot of process safety management of change discussions. (There) wasn’t really a lot of training.”
On the morning of the explosion, there was a sudden power shutdown due to a breaker being overloaded. It was the third time this had happened. There were two main high-voltage breakers set up in an electrical room. They should have been shared 50-50 or 60-40 when the electrical system was being redesigned, but instead, the distribution had been 90-10.
“The 90% overload on the breaker shut down 90 percent of the equipment,” Ric said. “We still had 10% running. So, the way the operations work is there’s a primary fan that acts as a vacuum on one side of it and suspends the product throughout the ductwork. Then there’s the other side that acts as a blower. It sends waste product to the processing equipment that helps dry it out. It gets sent on to be processed in another area.”
The power distribution did not shut down. The flash dryer, which was a natural gas system, also did not shut down the steeping screw that fed corn into a hammer mill, where it would be pulverized. When the power shut down, the flash dryer and the steeping screw were still feeding into the hammer mill.
“We had fine powder being suspended,’ Ric recalled. “A sudden loss of power to the operations then dropped about 5000 pounds an hour of real fine powder from a vertical four stories up and just let that stuff fall down throughout the duct or come back into this hammer mill, overflowing it. But yet we’re still trying to feed stuff into that.”
When the power was shut off, the operator immediately called maintenance. The maintenance staff were familiar with the situation because there had been two other sudden power shutdowns within the previous 24 hours. After they re-engaged the breaker, they radioed the operator and told him to fire back up.
“The previous standard operating procedure said that if you have loss of power or if you have an unexpected shutdown, verify that you don’t have burning embers or burning corn,” Ric said. “The verification was through a visualization port or using the senses to detect the distinct burning corn smell.”
None of that was done. The operator went into the control room and hit the computerized power up sequence. Within seconds, the primary fan that was sucking up the product through the ductwork also brought the embers with it.
Ric recalled, “We had flash fires and a few explosions that were all very minor compared to what we’ve seen in other facilities. They did damage about five pieces of equipment that were vital to the operations. Some inspection ports were blown off from ductwork: if there had been anybody in the area, it could have been potentially fatal. But the integrity of the building stayed intact. There was enough percussion that it blew out windows. And so after that, then we started doing our deep dive analysis.”
How did you and your team respond?
Ric acknowledged that the team had been relatively lucky. The explosion occurred at around 4:30 a.m., when there were fewer people in the building, and no one was in the vicinity. Thanks to external housekeeping practices, fugitive dust was also well-contained. There was a large ball of flame that could be seen by security guards on the other side of the property, but it went away quickly. Fortunately, there were no secondary explosions.
“It did impact about four pieces of vital equipment: knocked them down, shut them down right away. Of course, all the power was shut off,” Ric said.
After making sure that everyone was safe, they called the fire department. Once they determined that there were no continuing flames, the fire department called off. The team continued to make sure that electricity, gas, and water valves were turned off.
“(Then) we started doing our game planning, trying to figure out how we were going to determine the extent of damages and then moving forward, what do we need to do?”
What are the lessons learned?
Ric said that a major lesson learned was the need to refresh emergency action procedures. This included:
- Making sure employees knew where the exit routes were
- Conducting regular fire drills
- Business continuity management
“We also learned about the standard operating procedures. What process failed at that point? The human behavior aspect came into play: people probably didn’t have the right training because of the way the management of change was presented.”
The flash dryer should have been off when the primary fan was off, but that sequence failed because they were not on the same circuit and correctly programmed. The facility added the appropriate programming and installed some fire suppression systems. Other system improvements included proper communication of the startup sequence, so that all employees are clear when the equipment is powered up and adding regular ductwork inspection to the preventative maintenance program.
Do you have any recommendations for facility owners and operators that may be handling combustible dust?
Ric’s first piece of advice was to communicate startup and shutdown information to people in areas that could be impacted. Then he recommended that all emergency action procedures include a worst-case scenario. What are evacuation procedures if the stairwell is gone? What if the lights are off everywhere?
Housekeeping was another important area. “Using compressed air as a primary [dust control method] is illegal. We do not condone that at all. We use the air vacuum. So we have the grounding hoses and the grounding cable and we’ll make sure our folks know how to use those the right way. We also prioritize piles. More explosive materials require the specialized approach to cleaning up.”
He emphasized the importance of training. “This information all begins at the beginning. Make sure your new hires know it and that you have career training throughout the year, whether it’s on baghouse training, motors training, housekeeping, whatever. So we can try to break that chain of these secret events.”
Conclusion
At the conclusion of the interview, Rick said that process safety management for dust should always be in place.
“We know we have to do it for hazardous chemicals. And dust is a chemical. It’s a particulate, but it’s not enforced to the extent that other chemicals are, and I think it needs to get to that point. Possibly it does within certain organizations after they have an event. So, unfortunately, something has to occur and really hit home for things to change. From a proactive standpoint, there’s a heck of a lot we could do before it gets to that.”
If you would like to discuss further, leave your thoughts in the comments section below. You can also reach Ric Smith 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
DustSafetyScience
Combustible Dust Incident Database
DustSafetyScience Podcast
Questions from the Community
DustSafetyAcademy
Companies
Fike
Organizations
American Society for Safety Professionals
National Safety Council
Chemical Safety Board
Standards
NFPA
Thanks for Listening!
To share your thoughts:
- Leave a note in the comment section below
- Ask a question to be answered on the show
- Share this episode on LinkedIn, Twitter or Facebook
To help out the show:
- Subscribe to the podcast on iTunes
- Leave a review and rate our show in iTunes to help the podcast reach more people
Download the Episode
DSS086: Lessons Learned from a Corn Milling Explosion with Ric Smith
