If a small amount of cornstarch can produce such an effect, as was demonstrated in Volkman’s class, imagine the effect of plants filled with powdered sugar suspended in the air and set on fire by an ignition source.
Imagine a fire triangle made up of oxygen, fuel and heat, then add to that a confined space and flammable particles dispersed in the air and you get a dust explosion.
Emerson’s ASCO 353 Series Pulse Valves play a vital role in protecting plants from combustible dust explosions. Cleaning the filter bags is critical in a dust collection system. Pulse valves are designed to clean filters with a fast, high flow of air (called peak pressure). The new design increases peak pressure by 14%, resulting in better filter cleaning.
Dustcontrol UK has introduced intelligent controls to its central industrial vacuum systems (the smart panel on the right-hand side of the vacuum cleaner), making them more energy efficient by controlling the motor speed to suit the application. The system will also be able to provide maintenance data.
Pictured is the Volkmann VS200, equipped with an MX series vacuum pump that extracts roasted coffee beans from the roaster without damaging them.
Emerson’s ASCO Series 110 pilot manifolds contain integral direct-acting pilot valves. These pilot boxes are designed for remote operation of pulse valves (ASCO Series 353) used in dust collectors.
Larson Electronics’ GFI EPEXC-GFI-20O-50 explosion-proof cord is certified for Class I Division 1 and Class II Division 1 and allows operators to connect lighting fixtures and appliances to GFCI-protected outlets. The unit comes with a 50-foot 12/3 SOOW cable and is terminated with a 20-amp explosion-proof twist-lock plug.
About 12 years ago, the food and beverage industry suffered perhaps the worst disaster in its history at the Imperial Sugar Refinery near Savannah, Georgia. A fire somewhere in the factory triggered a dust explosion that soon caused several secondary dust explosions that destroyed the entire factory, injuring 38 people and killing 14 workers. As parts of the factory were torn apart like dominoes by successive explosions, workers were left in the dark, without power, and with no way to escape.
Video footage provided by the U.S. Chemical Safety Board shows the investigation and explains why the disaster happened. Sugar was spilling from conveyor belts, and the air was filled with dust. The dust collection system connected to the hammer mill that made the powdered sugar was underpowered, malfunctioning, and not connected to the conveyor system, causing sugar to spill along the way.
”Despite long-standing knowledge of the explosive nature of powdered sugar, insufficient measures were taken to control the hazard,” the CSB said. This was undoubtedly the root cause of the disaster.
“Unfortunately, fires and dust explosions still occur. These incidents continue to cause injuries, deaths, property damage, supply chain disruptions, and permanently change lives,” said Kevin N. Jeffries, CFPS, CEAS, senior process safety specialist at DEKRA Process Safety. “I believe that companies have taken significant steps to reduce the overall risks of combustible dust fires and explosions and are taking life safety very seriously.”
Jeffries adds that the National Combustible Dust Program (OSHA NEP) and other efforts by standards organizations and consulting firms to raise awareness of dust hazards have helped integrate combustible dust safety measures into the traditional compliance and risk mitigation matrix. This makes it easier for organizations to develop, prioritize, and budget for mitigation solutions and strategies.
“Awareness is key,” said Carrie Woehler, PMP, program manager for Black & Veatch NextGen Ag. “Dust areas have been classified as ‘hazardous locations’ since the early 21st century, but following the high-profile incident at the Imperial Sugar plant in 2008, dust fires have become a hot topic in any industry where particulate matter can become airborne.”
“We have seen an increase in awareness of the risks associated with working with dusts and powders,” said Nick Hayes, president of Volkmann. “Risk analysis has now become a more common practice, and the improvements in standards published by NFPA have consequently improved some of the work practices that existed at the time.”
Matthew A. Beyer, senior food and beverage process engineer at CRB, said key factors driving manufacturers to improve dust collection practices include: updated regulations and guidelines, increased compliance audits, insurance requirements, company image, employee safety, investment protection and improved risk management programs.
“With the introduction of NFPA 652 and the new requirement that all facilities conduct a Dust Hazard Analysis (DHA) by September 2020, NFPA has provided greater clarity on dust control regulations and requirements for new and existing facilities,” said Drew Goodall, director of processes at Gray Solutions, a Gray company.
Bell noted that while FSMA is not a dust regulation, it has prompted processors to think seriously about cleaner, safer facilities.
”The implementation of FSMA has resulted in a dramatic change in manufacturing facilities. Increased attention to cleanliness, record keeping, operational training and monitoring programs have had an additional impact on reducing dust levels. Operations crews are better trained, have more accurate records of housekeeping programs and are generally more efficient.”
The latest news focuses on the new NFPA 652 standard and its impact on the industry. Developed in 2015, NFPA 652 simplifies the design and installation requirements for combustible dust equipment by providing a comprehensive standard and a recognized starting point for compliance that applies to all facilities, said Drew Goodall, director of processes for Gray Solutions. Previously, there were five different NFPA standards covering combustible dust, which could cause confusion about their applicability.
Kevin N. Jeffries, senior process safety specialist at DEKRA Process Safety, said NFPA 652, Fundamentals of Combustible Dusts, was developed and published to help organizations better manage combustible dust fire and explosion hazards. The standard reads like an industry-wide OSHA standard, making it easier for health, safety, environment, and health professionals, engineers, and consultants to identify basic risk mitigation methods. NFPA 652 also refers readers to industry and/or product standards such as the Standard for Wood Dust (NFPA 664), the Standard for Metallic Dust (NFPA 484), and the Standard for Agriculture and Food Processing (NFPA 61).
If you manufacture and/or package powdered products, you know the potential problems. Consultants with experience in dust control know all the intricacies of this problem.
“I have worked with a number of food companies to address various combustible dust risks associated with handling and packaging combustible particulates,” said DEKRA’s Jeffries. In most cases, the particulates of concern are sugar, cocoa, milk powder and/or other powdered flavorings. Mixers, dust collectors, silos, bins and conveyors remain the primary sources of concern when it comes to equipment-related hazards.
CRB’s Bell also listed hazards he has personally encountered: corn starch, animal feed, soybean processing, pet food manufacturing, DDG (distillers grains), and corn gluten.
”Add to this list: processing roasted and ground coffee, producing instant coffee, roasting and mixing food powders,” said Stellar project developer F.G. Homolka.
If you run a winery, ethanol plant, or large brewery, you know about the potential dangers of grain dust, but small brewery owners may not.
“A brewery’s grain room can be susceptible to a number of explosive hazards,” said Chris Vigil, PMP, NextGen Ag project manager at Black & Veatch. Proper design of grain bins and associated equipment is critical to preventing explosions.
”With the variety of grains and additives available today, small brewery owners may not be fully aware of the dangers of explosive dust. As these small breweries grow in size, it is important to educate them and support them in terms of design,” Virgil said.
“We specify, supply and install dry ingredient unloading, storage, handling and dosing systems, from large truck/rail haulage to 25kg bag systems,” said Gray’s Goodall. “Each application is unique and requires an understanding of the material properties to know whether explosion suppression (sodium bicarbonate systems), explosion venting (explosion discs/flame suppression) or other system designs should be integrated into the process. For example, this information is needed early in the design process to determine whether storage silos should be located against an external wall to provide explosion venting.
Fortunately, vacuum cleaning and dust collection systems can help reduce indoor dust levels. Pulse valves are part of a dust collection system that can help protect facilities from dust such as peanut dust and soft drink additive powder. “Emerson offers the ASCO Pulse Valve to remove explosive dust from filtration systems, as well as a range of explosion-proof coils and detonation boxes to ensure safe operation in potentially explosive environments,” said Michael Russo, product marketing manager for Emerson/ASCO Dust Collection Systems.
In addition to the equipment, a thorough understanding of the dusty environment is essential. Volkmann, a supplier of ATEX-certified pneumatic vacuum conveyors and pumps for the safe transport of dry products such as coffee beans, emphasizes the importance of education and training. “We believe that risk education is an important factor in risk reduction. Volkmann regularly holds seminars at our factories in Germany on the risks of explosions, or more precisely, how to avoid them,” says Hayes.
For most powder material applications, it is important to understand how to specify the electrical equipment used in these areas. John Phillips, director of electrical engineering at Stellar, says the areas in and around these ingredient handling systems typically contain electrical equipment (such as lighting, power supplies, connections, and sensors) that are rated Class II, Division 1 or Class II, Division 2.
The National Electrical Code (NEC) defines Class II, Division 1 as areas in which combustible dust is present under normal use, and Class II, Division 2 as areas in which combustible dust is not present under normal use.
Examples of Class II, Division 1 spaces include the interior of flour storage silos or areas where flour is pumped into an outdoor mixer. Phillips noted that a Class II, Division 2 space might be the area around a flour delivery line where a ruptured pipe or valve could create a hazardous situation.
Gray’s Goodall said the first step is always to find ways to reduce or eliminate dust at the source. If this is not possible due to the nature of the process or product requirements, a robust dust control system consisting of process equipment and supporting software components should be built into the design to alert operators to abnormalities. The design of walls, structural members, ductwork and utilities, lighting fixtures, equipment platforms, and equipment frames should be designed and configured to prevent dust accumulation and penetration, and to facilitate cleaning and disinfection. This will help reduce the amount of dust that can be dispersed throughout the space.
The design phase will also involve the processor’s safety and operations teams to ensure that the system design complies with standard operating procedures for cleaning and maintenance accessibility for the dust collection system’s Total Productive Maintenance (TPM).
Goodall adds that awareness of dust hazards extends beyond production areas. Clearance design should be reviewed to allow for inspection and maintenance. Ensuring adequate dust penetration through walls and ceilings will help reduce dust migration from production areas into confined spaces or unclassified areas.
The presence of dust can affect the design of mechanical, electrical and process equipment. These systems need to be classified to reduce the risk of fire.
Black & Veatch’s Woehler says a hazard assessment (including materials, particle size, concentration, and Kst value) should be conducted early in the design process to determine the required space classification. Some situations may require housekeeping or limited engineering controls (such as fume hoods) to reduce the hazard, while other situations (or where housekeeping is observed to be lacking) may require significant changes to the environmental design. Class II devices such as enclosures, lighting, or receptacles are expensive but necessary in classified areas. In addition to rigorous safety checks during the design phase, installation validation should be performed to ensure that on-site changes do not disrupt the design process.
Beyer of the CRB says that when working with products that can generate dust, evaluate the room or area where the equipment is located to determine if there are space limitations that could impact the type of dust collection equipment used. Determine the Kst value for the product that will be handled by the equipment to determine the applicable regulations. In general, if possible, try to use equipment that maintains a slight vacuum in the system to reduce the likelihood of dust emissions.
Stellar’s Homolka says architects and engineers familiar with dust-generating environments have experience predicting how dust will form and preventing it from reaching explosive levels. For example:
“To minimize dust generation from certain equipment such as grinders, hammer mills, mixers, screens, vented bins, silos or any other vessel in a powder processing line, the equipment must be designed to control the speed and direction of harmful dust so it does not become vented into the plant air,” says Brian Bernard, president of Gray’s Spec Engineering.
”The key is to control the direction of air flow so that it can be controlled or removed using an active dust collection system. This can be achieved by installing baffles and dust hoods in the equipment to effectively collect dust.”
There are several safety design options for dust collectors, including: (1.) Explosion vents (2.) Chemical suppression (3.) Isolation of deflagration in dirty ducts (4.) Rotating airlocks with a minimum of six vanes and a 0.2 mm clearance between the vanes and the airlock wall. Airlocks must be configured to cease operation in the event of a chemical suppression or explosion safety system being activated. The dust collector must also be designed and installed to withstand the pressure of a deflagration vent or suppression, as well as the associated thrust created by venting and deflagration.
Dust is usually removed from equipment through flexible transition devices. Some hose and fitting manufacturers design their equipment in such a way as to reduce dust emissions. It is also a good idea to install a dust collection system for these systems.
According to Hayes, to avoid an explosion, one of the three elements of the fire triangle (oxygen, ignition source, combustibles) must be eliminated. Volkmann uses compressed air to create the vacuum in its venturi-type vacuum pumps. The only ignition source in a standard system is static electricity. Since all Volkmann systems are grounded and use only static dissipative components, ignition sources are eliminated for all powders with a MEI (minimum ignition energy) > 1 mJ. For volatile chemicals, delivery in an inert atmosphere can eliminate oxygen.
ASCO’s experience in manufacturing explosion-proof enclosures and pulse valves has resulted in a wide range of products worldwide that meet directives for use in dusty and gaseous environments. Russo said the enclosures can meet the needs of all industries. In particular, ASCO’s new 353 Series Pulse Valve is designed to achieve optimum peak pressure, which allows for more efficient cleaning of filter bags in dust collection systems, resulting in improved safety and system efficiency. ASCO offers a complete line of dust collection products, including ATEX-certified pulse valves and UL/CSA explosion-proof solenoid valves, which are essential when designing dust collection systems for potentially explosive atmospheres.
Bernard of Spec Engineering says that a filter can be installed at the outlet to collect dust that would otherwise be released into the air. The idea is to collect fine particles and air and separate them using filters. When the fine particles are collected in the filter, clean air is released. The filter can be cleaned continuously using reverse pulse air.
Finally, don’t forget about maintenance. CRB’s Beyer said that a lack of proper maintenance practices can lead to dust leaks in the system. Failure to reinstall clamps, bolts, or latches on dust-generating equipment after maintenance or cleaning can lead to dust leaks. Another common cause is a leaky gasket that is worn out, damaged beyond repair, replaced with the wrong gasket material, or missing altogether.
Beyer adds that during operation, existing equipment should be assessed to identify leaks or emission points. Systems that are incorrectly sized or deviate from the original design should be carefully inspected. Once gaps are identified, determine the necessary design changes to bring the system into compliance and ensure that additional equipment or processes are available as needed for the project.
Whether you are designing a new facility or upgrading an existing one to make it safer, you can start your journey by seeking advice from experts who have experience working in dust-generating environments.
Post time: Mar-02-2025