In today’s episode of the Dust Safety Science podcast, Greg Slavin, President at Clean Air Company, talks about the redesign process for grinding enclosures with metal working applications.
This topic came up through a question from our help desk, where someone was seeking advice on how to improve their grinding enclosure to align with the recommendations of the American Conference of Governmental Industrial Hygienists (ACGIH). Fortunately, Greg is an expert in this area. With over 30 years of experience in industrial ventilation systems and a background in handling combustible dust in industries like woodworking and metalworking, Greg’s insights are sure to be invaluable.
How Do You Assess This Type of System?
Greg explained that when dealing with grinders, he starts by designing a hood for the enclosure. This design helps determine the required airflow. For example, a shop might have a grinder with an eight-inch diameter wheel that is one inch wide, which they’ve used for years. If they switch to a twelve-inch wheel that’s two inches wide, they’ll need more airflow.
The process begins by establishing how much air is needed for the new setup. Next, Greg assesses how much air is currently available. He might use a pitot tube to measure the airflow in the duct. This is crucial because, with metal dust, there is a minimum conveying velocity of 4,000 feet per minute required to prevent the dust from settling in the ductwork. The air must move at this speed to ensure all material is conveyed back to the collector.
This step-by-step approach helps Greg effectively address the changes needed for the grinder’s ventilation system to handle different tools and parts safely and efficiently.
What Are Some Other Reasons for Grinding Enclosures?
Greg noted that the hoods over the grinders can often be damaged by the daily rigors of the workplace. For instance, when employees handle heavy metals, they might accidentally bang into the hoods. These hoods can come loose during routine maintenance, like when changing the grinding wheels, and may need to be disassembled to switch out the discs. Sometimes they are not reassembled correctly, which can lead to improperly sealed ductwork and a loss of air volume.
He emphasized that there is a frequent challenge in how well the equipment is maintained. Ensuring everything is correctly assembled and sealed after maintenance is crucial to prevent these issues and maintain efficient operation.
How Do You Determine How Much Air Is Needed?
Greg explained that the pitot tube traverse is a method used to measure the airflow within ductwork. He described how this measurement is taken: by determining the airflow, then dividing this figure by the area of the duct. This calculation provides the velocity of the air moving through the duct. For the metal working applications, the air velocity needs to reach at least 4,000 feet per minute to be effective. This target is essential for ensuring that the system functions correctly and safely handles the materials involved.
What Are Some of the Challenges With This Application?
Greg pointed out that a common issue stems from a lack of understanding about how blast gates function in duct systems. Many people mistakenly believe that closing one duct will increase airflow to another. However, when they find that this doesn’t achieve the desired effect, they might close additional blast gates. In reality, this approach doesn’t increase airflow to other parts; instead, it adds pressure to the fan and reduces the overall cubic feet per minute (CFM) capacity of the system. This mismanagement often leads to employees frequently adjusting blast gates, which can cause material to settle in the ductwork, creating further complications.
What Are Recommended Fire and Explosion Safety Systems?
Greg explained that many people and companies are still not familiar with NFPA 484, which deals with the safe handling of combustible metals like steel and aluminum. He noted that many facilities have not conducted a dust hazard analysis, leading to unsafe practices such as mixing steel and aluminum in the same collection systems. Greg stressed that hoods should be clearly labeled for either steel or aluminum to ensure that materials are directed to the correct collector without mixing, as mixing can create dangerous conditions.
He also observed that few facilities have an adequate emergency response plan in place for dealing with combustible metal dust. Such plans should include labeling collectors to indicate they contain combustible dust and specifying that water should not be used in case of a fire. Appropriate extinguishing agents should be identified and used instead. Furthermore, t facility maintenance and cleanup are often neglected because they do not directly generate profit. As a result, he frequently sees accumulations of metal chips and dust around machinery, which poses a significant risk.
Additionally, Greg mentioned that wet collectors, often used for metal dust collection, sometimes lack proper venting for hydrogen when dealing with aluminum. He emphasized the necessity of conducting dust hazard analyses and recommends inspecting ductwork at least every six months to prevent material buildup, ensuring a safer working environment.
What Are Some Other Recommendations?
Greg emphasized the importance of understanding the entire ventilation system when making adjustments, such as needing an extra 100 CFM for effective material capture. To find that extra airflow, a comprehensive evaluation of the system is essential. This includes assessing how to decrease the existing pressure on the fan to allow for additional airflow.
He explained that the evaluation might involve examining whether there’s an excessive use of flex hose within the system, checking if the hose is bonded or grounded, or considering modifications to the ductwork to improve balance. In some areas, the airflow might exceed 4000 feet per minute, and increasing the diameter of the duct could reduce the pressure, allowing for the needed extra CFM. Furthermore, adjustments might be needed on a belt-driven fan, possibly by changing the shivs or the fan outlets.
Greg stresses that such a system evaluation is complex and involves a lot of work, even if it’s just for one hood. However, the consequences of not properly managing the system are severe. Inadequate handling can leave combustible material in the ductwork, presenting a significant risk. A single spark from the grinding wheel could ignite this material, leading to a dangerous situation.
Thus, it’s not sufficient to simply change the hood or improve the enclosure; it’s critical to ensure that the entire system can accommodate the increased airflow and pressure changes. This holistic approach is crucial for safety and effectiveness in handling combustible materials in ductwork.
Conclusion
In conclusion, effectively managing airflow in industrial ventilation systems requires a thorough understanding of the entire system’s dynamics, not just individual components. Greg’s insights emphasize the necessity of conducting detailed evaluations and making precise adjustments to ensure safety and efficiency. This approach prevents potential hazards associated with combustible materials and ensures that all parts of the system work cohesively to maintain proper airflow and pressure.
By considering every element from ductwork modifications to fan adjustments, facilities can safeguard against risks while enhancing their operational capabilities. Remember, addressing these challenges comprehensively is not just about improving performance but also about ensuring a safe environment for all employees.
If you would like to discuss further, leave your thoughts in the comments section below. You can also reach Greg Slavin directly:
Website: https://www.cleanairco.com/
LinkedIn: https://www.linkedin.com/in/greg-slavin-73395b12/
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
Companies
Clean Air Company
Standards
NFPA 484
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DSS264: Redesign Process for Grinding Enclosures on a Metal Working Application with Greg Slavin
