DSS256: Hazard Assessment in Grain Milling, Sifting and Sorting Applications with Matt Williamson

In today’s episode of the Dust Safety Science podcast, Matt Williamson, Director of Engineering at ADF Engineering, returns to talk about common hazards in grain milling, sifting, and sorting applications.

This is the second segment of our two-part discussion on hazards in grain milling operations. In the first segment, we detailed the various risks involved, as highlighted in our previous podcast episode. In this segment, we aim to clarify how to begin assessing these hazards. We will outline the key factors to consider when conducting a hazard assessment or dust hazard analysis for such operations.

How Should You Conduct a Hazard Analysis at a Grain Site?

Matt explained that breaking down the process of conducting a Dust Hazard Analysis (DHA) in grain milling operations requires a systematic approach due to the variety of hazards present and their differing probabilities. The process begins at unloading and continues through milling, storage, and finally to the load-out or packaging stages. Each step, or “node,” such as unloading, storage and drying, dehulling, milling, and screening, is evaluated separately. Additionally, dust collection systems are considered as an independent node.

In a DHA, the likelihood of hazards, such as a dust explosion or fire, is assessed at each node. This assessment considers the combustible dust pentagram, evaluating existing conditions and potential risks introduced by changes or errors. The aim is to prioritize mitigation measures, starting with high-risk areas. Easy and cost-effective measures, like grounding and bonding of equipment to prevent static electricity buildup, are prioritized for immediate implementation.

For a new facility, the initial step involves assessing the combustibility of handled materials. This is critical as grain mills often process a primary grain type but may also handle various other grains occasionally, affecting combustibility profiles. While some combustibility data for common grains are available in resources like NFPA 61, post-milling materials may require specific testing due to differences in processing methods and particle sizes between facilities.

The analysis then moves through each node to identify risks and evaluate the likelihood of hazardous events. This includes identifying missing elements of the combustible dust pentagram and potential ignition sources. The final stage of a DHA often involves a checklist, such as the one provided by NFPA 61, covering aspects like operator training, emergency action plans, and hot work permits, ensuring comprehensive hazard mitigation.

This structured approach ensures a thorough evaluation of risks and the implementation of safety measures throughout the grain milling process, addressing both technical and operational aspects to enhance overall safety.

What About Dust Outside of Equipment?

Matt stated that one of the key areas to focus on outside of equipment maintenance is housekeeping, particularly in managing common leaks and the cleanup of materials during maintenance activities. In grain mills, it’s not unusual to find areas where materials are frequently spilled or diverted to the floor, leading to significant accumulation. This can happen, for example, when there’s a blockage in a chute or spout, and the material is redirected onto the floor, resulting in large piles that may remain unaddressed for some time. Such situations can create a mess, especially in smaller, confined spaces.

Another common issue occurs in the head house atop concrete silos, where conveyors can become clogged if the grain isn’t properly cleaned before storage. The result is often the diversion of grain to the top of silos, where it accumulates. The primary concern in these scenarios is ensuring timely cleanup, ideally within the same shift the spill occurred, to avoid leaving the material for extended periods. Allowing piles to sit not only makes cleanup more challenging but also poses a significant safety risk.

Effective housekeeping practices, including prompt cleanup of spills and maintaining clear areas, are essential in managing these risks and ensuring a safer working environment in grain milling operations.

What Are Best Practices for Dust Collectors?

When managing dust collection in grain milling processes, using a single dust collector for the entire operation is not advisable due to several challenges. Firstly, a single collector would require extensive ductwork to connect various parts of the mill, which can become overly complicated. Such complexity in ductwork makes it difficult to isolate specific sections, increasing the risk of blockages and buildup within the system.

Instead of relying on one large dust collector, it’s more effective to employ multiple collectors throughout the mill, each dedicated to a specific area or function. For instance, the dust collector used for truck load-out operations is typically much larger than others and is designed to handle that task alone. Similarly, separate dust collectors are recommended for unloading, storage, and milling areas. This division is crucial because airflow is especially important in milling operations to prevent heat buildup, which could lead to explosions. Airflow from mills usually leads to a filter receiver, another form of dust collection that plays a critical role in maintaining safety and efficiency.

In a standard dry grain mill, it’s common to find between five to seven dust collectors, depending on the layout and specific needs of the operation. This approach helps manage dust more effectively, reducing the risk of hazards and ensuring that each part of the process is adequately covered without introducing unnecessary complexity.

What About Dust During Truck Loadouts?

Handling dust during truck loadout operations in grain milling is challenging due to the nature of filling an open truck bed. The vast size of these truck beds makes it difficult to efficiently capture dust across their entire length. Moreover, the variability in truck sizes complicates the design of a one-size-fits-all dust collection hood. Attempts to accommodate different truck sizes with adjustable features, like soft plastic flaps, often fall short because they cannot effectively seal the area around every truck type. This mismatch can lead to inefficient dust collection, as air is drawn from unnecessary spaces, requiring larger and more powerful dust collectors.

Another issue arises from the limited number of loading spouts. If there are only one or two spouts available, trucks may need to be moved during loading to fill the entire bed, increasing the risk of ignition from the truck’s engine—a significant hazard given the high temperatures of truck exhausts, which can easily ignite dust particles.

To mitigate these challenges, loadout areas are often designed with open garage doors to facilitate airflow and prevent dust accumulation. However, this solution introduces its own set of problems, as dust can escape and settle on surfaces throughout the facility, including lights and rafters, making daily cleanup a daunting task.

Overall, managing dust during truck loadouts requires careful consideration of equipment design, operational practices, and housekeeping efforts to address the unique challenges presented by this aspect of grain milling operations.

How Do You Handle the Commodity End of the Line?

The production process and the final form of your product significantly influence its dust hazard potential. For instance, when pelletizing corn fiber—a byproduct of the wet milling process where the outer skin of the corn kernel is combined with steepwater to form pellets—these pellets, once produced, might not pose the same dust hazard as their raw materials. This is particularly relevant when the pellets are intended for use in products like pet food, where they can be packaged directly without generating dust.

In the context of evaluating dust hazards, especially on packaging lines, it’s important to test the material in its received state rather than after it has been dried and ground. Drying and grinding almost always result in a combustible dust, but testing the material as it is received can often indicate that it does not pose a dust hazard. This upfront “go” or “no-go” testing can save time and resources by avoiding unnecessary precautions for materials that are not combustible in their intended form.

Even in cases where testing results in a “go,” indicating a potential hazard, the material may still have a low explosion severity (low KST value) and require a high energy for ignition, especially if it consists of larger particles. This scenario significantly affects the approach to mitigation, simplifying the process compared to handling materials that have been processed to be more easily ignitable. Understanding these distinctions helps tailor safety measures more effectively, particularly in packaging operations, by focusing on the specific characteristics of the material in its final form.

Smouldering Fire Response Planning Explained

“I always prioritize discussing bins and storage safety due to my extensive experience in the grains and sugar sectors, where I’ve observed most incidents, such as fires or explosions, occurring within silos,” Matt said. “These events highlight the significant risks and challenges associated with dust hazards in these areas, including the complexities of cleanup efforts post-incident.”

He recommended using the NFPA 61 checklist, especially for its comprehensive approach to safety.This checklist includes an essential section on emergency response, which specifically addresses the management of bin fires. Itt prompts users to ensure their emergency action plans are equipped to handle the possibility of bin fires, underlining the importance of preparedness for such scenarios. This focus stems from witnessing the impact and aftermath of these fires, underscoring the need for targeted preventive measures and response strategies in these critical areas.

“An important aspect we haven’t fully covered is the detection of smoldering fires, especially in areas prone to such hazards,” he said. “Instead of manually searching for the source of a smolder after noticing it, a more proactive approach involves installing detection devices in locations where smoldering is most likely to happen, such as the bins immediately following unloading.”

Carbon monoxide (CO) detectors, for example, can serve as effective indicators of smoldering fires in these areas. Placing these detectors in the headspace or relevant sections of the system can alert you to the presence of smoldering before it escalates. Receiving a CO alarm from a bin during unloading is a clear signal to halt the operation and investigate, as this scenario has been linked to explosions in past incidents. Implementing such detectors can significantly enhance safety by providing early warnings of potential fires.

About Plugging Mills

Plugging primarily occurs in two critical areas of grain processing facilities: conveyors and bucket elevators. While plugging itself does not directly cause explosions, the actions taken to resolve these blockages can lead to significant hazards. For example, when conveyors after elevators become clogged, operators may attempt to clear the blockage by opening up the conveyor and removing the material, often leaving it on the floor. This creates a housekeeping issue, as the accumulated material can become a new source of hazard, potentially leading to external fires.

Another common issue related to plugging is found beneath mills, where screens or airflow can become blocked. If the airflow through a mill is obstructed, the equipment can start to overheat. Overheating is a critical concern because it can lead to explosions within the mills. These incidents are typically the result of blockages, either from screens within the mills or from the material conveying lines immediately following the milling process. Addressing and preventing plugging in these areas is essential to maintaining safety and avoiding the risk of fires or explosions in grain processing facilities.

Conclusion

As we conclude this two-part series, we are reminded of the importance of continuous learning and adaptation in the field of dust safety science. The experiences and knowledge shared by experts like Matt Williamson are invaluable resources for professionals across the grain milling and broader industrial sectors, driving forward improvements in safety practices and hazard mitigation.

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-760111215/
Website: https://www.adfengineering.com/

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.