Four years has passed since an explosion at Didion Milling Inc. killed five people and injured 14 more. Time marches on, but the incident at the Cambria, Wisconsin, grain mill stands as a stark reminder of the devastation a combustible dust explosion can cause.
It is this type of tragedy the National Fire Protection Association (NFPA) 652 Standard on the Fundamentals of Combustible Dust aims to prevent. The standard contained a deadline of September 7, 2020, for companies to complete a Dust Hazards Analysis (DHA).
But in many companies September 7, 2020, passed with little fanfare and without a DHA, reports Daniel Engling, MS, CIH, of Keramida Inc. As director of Industrial Hygiene Services, Engling handles DHAs. He reports a rush of firms seeking DHAs that started before the deadline and continues today.
“We hit the deadline, and many organizations realized they still needed a DHA,” he says. “Their insurance providers or supply chain partners informed them of the need to get it done. Demand for DHAs has ramped up and hasn’t stopped.”
He adds getting a DHA is not a one-and-done process. Companies must complete DHAs must review/update their DHA every five years and for new processes and facility compartments.
“The standard requires updating the DHA every five years. But is it best practice to abide by the minimum standard?” Engling asks. “No. The best practice is to examine your operation and address changes much sooner than five years—even if the changes happens a month after you completed a DHA. You shouldn’t cruise along for another four years,11 months until the next one.”
What is a DHA?
A DHA is a systemic analytical review of a facility and its processes to identify combustible dust hazards, reports Engling.
The evaluation examines operations, including process equipment, ducts and dust collection systems, to determine if a company must implement administrative or engineering safeguards to reduce risks for combustible dust events. It also examines materials handled, operations performed, all spaces, and potential ignition sources.
The DHA report recommends methods to mitigate the potential for dust cloud ignition. These steps may include dust control measures, ignition control recommendations, and injury and damage control methods, according to an OSHA Fact Sheet titled “Hazard Alert: Combustible Dust Explosions.”
The analysis includes measures that prevent fires and explosions. Engling explains that in the familiar fire triangle of oxygen, heat and fuel, dust particles are the fuel. In sufficient quantity and concentration, dust can cause rapid combustion known as deflagration.
But when confined to a building, room, vessel or process equipment, the deflagration event can cause an explosion. Five factors known as the Dust Explosion Pentagon (oxygen, heat, fuel, dispersion and confinement) must be present for an explosion. “If we remove one or more legs of that Pentagon, we can eliminate explosion risks,” Engling explains.
Proper mitigation also can reduce the potential for catastrophic secondary explosions, which occur when dust builds up over time. Secondary explosions can be more destructive than primary explosions because of the increased quantity and concentration of dispersed combustible dust. In fact, NFPA and OSHA report that a 1/32-inch-thick spread of dust over just 5% of the floor area can pose a combustible dust hazard.
“Poor housekeeping contributes to these explosions,” says Engling. “When companies allow things to accumulate over time on rafters, piping, duct work, electrical conduits and shelving, a small explosion or a small combustion that generates gases, heat, and a little pressure, can knock free accumulated dust to cause a secondary combustion that’s much more explosive and much more violent,” he says.
Who Needs a DHA?
Understanding combustible dust and adopting NFPA 652 into a facility guides a combustible dust strategy that keeps employees safe and safeguards facilities from fire and explosions. It also shows a company’s commitment to protecting employees from combustible dust hazards.
DHAs are for companies producing fine dusts that can explode. OSHA reports the most at-risk industries for combustible dust explosions as: agriculture, chemicals, food, grain, fertilizer, tobacco, plastics, wood, forest, paper, pulp, rubber, furniture, textiles, pesticides, pharmaceuticals, tire and rubber manufacturing, dyes, coal, metal processing, recycling operations, fossil fuel power generation, additive manufacturing and 3D printing.
“Whether you are manufacturing or handling waste as your primary business doesn’t matter,” Engling says. “You just need to produce dust in a fine enough powder that it can burn. Dust only creates an explosion hazard when it’s sufficiently fine.”
Recommended Mitigation Measures
The DHA will evaluate fire, deflagration and explosion hazards then recommend ways to manage these hazards, according to Engling. Recommended action items fall into three basic categories:
- Capture: Dust collection systems that collect dust before it escapes into work areas or other spaces.
- Contain: Contain dust within equipment, systems or rooms designed to handle accumulated combustible dust.
- Clean: Frequent, thorough and approved housekeeping measures to remove dust in work areas, overhead surfaces and concealed spaces.
“The advised remedies will vary by facility,” says Engling. “In some, the best approach may be containment or collecting material before it becomes a hazard. In another facility, the best approach may be ventilation. Or a company may need to add blast panels, explosion relief valves or a suppression system. If you have a fine powder that you cannot do anything about and have no way of collecting it in dust form, perhaps you can suppress it with fog or water to keep it in a physical state that won’t go airborne.”
Engling stresses the DHA may list multiple remedies for a single situation. But companies are not required to do all of them at once. They can pick the ones that make sense for them. “They have to make reasonable progress toward a DHA,” he says. “You may get five or six solutions for the same problem but doing one may suffice. Progress toward implementing solutions must be documented.”
Getting an Analysis Done
A DHA doesn’t take long. The analysis takes one to three days of time onsite and a few additional days to receive recommendations.
However, OSHA requires a qualified person to perform the DHA. OSHA defines this person as someone who, “by possession of a recognized degree, certificate or professional standing, or who by extensive knowledge, training and experience, has successfully demonstrated the ability to solve or resolve problems relating to whatever the subject matter, work or project is.”
A qualified individual must have experience doing DHAs and inside knowledge of the industry and its operations, reports Engling.
“If someone doesn’t understand your business, your processes and the machinery you use, they will struggle to have good outcomes,” he says. “Look for a consultant that understands your industry and dust hazard analysis.”
When a consultant understands the industry, he will tailor recommendations to a company’s operations and processes. “He will not make textbook recommendations that are not feasible in your operation,” he says.
With combustible dust, an ounce of prevention is worth a pound of cure. One needs to look no further than the Didion tragedy. OSHA officials believe the explosion was preventable and attribute it to “Didion’s failures to correct the leakage and accumulation of highly combustible grain dust throughout the facility and to maintain equipment to control ignition sources.” As a result, Didion faces up to $1.8 million in fines.
Companies must understand what combustible dusts exist in their facilities and the associated dangers involved. A DHA keeps employees safe, safeguards facilities, and complies with the NFPA 652 Standard. It avoids tragedies that lead to loss of life and costly fines.
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