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Q. What’s the best way to retrofit an existing feed mill facility in order to comply with OSHA’s combustible dust program?

A. A.G.L., OSHA’s Combustible Dust National Emphasis Program was re-issued in March, 2008 following the Georgia sugar plant explosion a month earlier which got a lot of notoriety. Then, later, in 2011, a grain elevator exploded in Atchison, Kansas, killing several people which kept the spotlight on the OSHA program.

It is expected that there will be increased enforcement activities in the future, especially on certain industry groups, like the feed industry.

And so, it’s important to do whatever is necessary in existing facilities to not only meet OSHA’s program but, from a practical perspective, to prevent fugitive dust from creating hazardous accumulations and also to eliminate increased costs associated with material shrink and excessive housekeeping.

Certainly, retrofits may involve restrictions or compromises from ideal due to having to work with existing equipment, available space, and maybe limited available capital. With that said your goals should still include:

• Minimizing the sources of dust emissions.
• Making the system as effective as possible in capturing fugitive dust.
• Facilitating housekeeping.
• Facilitating maintenance.

Here are some specific examples of what you can do:

• Seal and secure conveyor covers.
• Confirm negative air system/air flow volume is at the design volume. Negative air systems are designed for a specific air flow both in air volume and in the resulting air velocity. Which means you need to measure air flow, confirm proper fan operation and condition, adjust air bleed-in gates, and confirm that the ducts are clean.
• Fully enclose the truck receiving pit area and install high-speed curtain driveway doors.
• Install fixed or adjustable baffles in the rail and truck receiving pit grating to minimize the open area.
• Incorporate a plenum into the truck receiving hopper that allows for the installation of a bin vent baghouse and fan to pull air down through the grating.
• Install plastic strips around the rail receiving building openings.
• Install a bin vent baghouse with a fan on a receiving conveyor or conventional turnhead.
• Install an insertable bin vent filter on storage bins.
• Monitor pressure drop across the filter socks and maintain all baghouses and bin vent filters.
• Install an isolation slide gate on the discharge of the micro system discharge conveyor to prevent back pressure and dusting.
• Install properly sized intervent ducts between the major scale, mixer, and mixer discharge surge.
• On loading spouts, minimize the cross-sectional area of the loading spout at the discharge end which will help concentrate the material stream and minimize the loading point drop distance on the discharge.
• Facilitate housekeeping. Which means considering a central vacuum system, providing convenient access, and providing hoist beams or trash spouts to get cleaned-up material out of pits or down from elevated floors.

Through the years, I have observed that any dust control system is no different than any other process system in that it begins with proper design and investment but relies on ongoing maintenance and understanding of the proper operation. And so, the bottom line is that with a focused priority, even in a retrofit situation, on dust control, there is a significant tangible return in:

• Mitigating risk and exposure by minimizing fugitive dust emissions.
• Effectively separating particulate matter from air streams and returning these finds to the process flow.
• Improving the operating efficiency of the various process equipment like hammermills and pellet coolers.

I hope that answers your question completely. If it doesn’t — or if you have questions on another topic — we’re here to help. We’d love to hear from you!

Answered by Tim Lease, P.E., President of WL Port-Land Systems, Inc.