In today’s episode of the Dust Safety Science podcast, Matt Williamson, Director of Engineering at ADF Engineering in Dayton, Ohio, explains strategies for dust hazard control in grain truck load-out bays.
Matt has several years of experience in process engineering, dust hazard analysis, incident investigation, and engineering and design systems. During that time, he has become familiar with dust safety challenges in grain or mill-type load-out bays, such as dust and ignition source control and layout issues.
Tarp Stays and Falling Material Cause Issues With Dust Safety
“Grains are generally loaded into open-top trucks that will be covered with a tarp,” Matt explains. “Across the top are tarp stays, which are little support beams. When the truck goes into the load-out bay, it will be filled from above by spouts that extend down from equipment up in the roof area. One of the problems you run into is that these tarp stays keep the spouts from getting down into the truck, so the material tends to fall a considerable distance.”
Hood tarps are one of the main safety controls in these environments, but the stays can prevent a tarp from extending all the way down and sealing the hood, leaving huge gaps. At the same time, falling material can generate significant dust clouds, which may be exposed to an ignition source.
“If you leave the engine running, there’s a major combustion source right there,” Matt says. “Even if you shut the truck off, you’ve still got the exhaust pipes sticking up and back into the area where you’re loading out. Exhaust pipes can reach 1200 degrees Fahrenheit- more than enough to serve as an ignition source for a dust cloud.”
What are Best Safety Practices in a Grain Truck Load-Out Bay?
Matt recommended the following safety options:
- Dustless spouts
- Regular housekeeping
- Never leaving the engine running
- Address electrical classification issues
- Reduce containment
Dustless Spouts
Dustless spouts come in different designs. The most effective are the so-called dust suppression hoppers being used in certain niches of the grain industry, namely ethanol facilities.
“They work very well when the bulk density of the material that you are loading out is consistent,” Matt says. “They’re designed for a very specific density and if your material varies outside of the range of the design, they cease working. When the density is consistent, they work beautifully.”
The issue with dustless spouts is that they are designed for a specific material and work well when that material is being run. They use the flow of the bulk powder dust to draw back the dust and re-entrain it into the main bulk stream so that clouds don’t arise during filling. Although they work well for specific applications, they are not meant for universal use.
Regular Housekeeping
Truck load-out bays tend to be quickly coated with fugitive dust, which accumulates on top of the hood and gets all over the place.
“It’s very difficult to clean these facilities,” Matt admits. “There are a lot of high places that need to be reached and it needs to be done on a regular basis. One thing you never want to do is try to use air for cleaning. You need to use a vacuum where you can. What I typically see more often now is water-washing, but water is not compatible with every powder out there. If you’re loading starch, you don’t want to be cleaning it with water.”
Never Leaving the Engine Running
“Turn off the truck engine,” Matt says. “Don’t leave the truck running. I know drivers are tempted to run the truck during winter to keep themselves warm, buthey shouldn’t be running the engine when you’re loading out combustible material. It’s just not safe.”
Address Electrical Classification Issues
Matt recommended grounding the truck when dealing with a material that has very low ignition energy.
“The biggest problem that we run into is electrical area classification,” he explained. “In older facilities, you find general-purpose lighting. You’ll even see bug-zappers hanging on the walls in electrically hazardous areas. It can be very expensive to retrofit some of these older facilities when they’ve built general-purpose electrical components, but it needs to be Class 2 Group G.”
In grain handling, the area around the truck itself is typically Division I, which calls for dust-proof ignition equipment. Many truck load-out bays have small control rooms with equipment like computers and ticket printers. According to Matt, this equipment is not electrically-rated, so these rooms need to be segregated from the actual load-out bay with self-sealing doors.
Reduce Containment
Most truck load-out buildings are under roofs. Very rarely are they outside, where an open-top truck is exposed to the weather. To avoid the issue of containment, roll-up doors should be left open whenever possible. Pressure can’t be built up within the building if the bay doors are open at either end.
Conclusion
For Matt, the safest way to load out grain trucks, especially when dealing with different vehicle sizes, is to design for stationary filling of the truck.
“If you are in a facility where you need to move your truck back and forth, you’re probably better off not trying to do that in a truck load-out building. You might want to go and take that outside because you’re creating all of the ingredients necessary for a combustible dust explosion.”
If you would like to discuss further, leave your thoughts in the comments section below. You can also reach Matt Williamson directly:
Email: [email protected]
LinkedIn: https://www.linkedin.com/in/matthew-williamson-6776309/
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
Companies
ADF Engineering
Publications
Effective Dust Control for Grain/Meal Truck Load-Out
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