Author(s): Scott Sutherland. Published on March 7, 2023.

A Century of Dust

100 Years after the creation of the first combustible dust standard, NFPA committees are approaching another important milestone: the completion of a single comprehensive standard on dust explosion hazards


In 1923, when NFPA published the first standard on combustible dust, the hazards presented by this industrial byproduct had been known for decades. The problem of combustible dust, for example, had been discussed in the aftermath of what became known as “The Great Mill Disaster” of 1878, a catastrophic grain mill explosion in Minneapolis, Minnesota. The blast destroyed the Washburn A Mill, then the world’s largest grain mill, and a handful of adjacent mills, reducing the city’s milling capacity by as much as half. Eighteen people died in the incident, which was blamed on an accumulation of grain dust.

Despite the acknowledged hazard and a growing body of knowledge on how to alleviate it, no national regulations were enacted to address the problem of combustible dust directly—and dust-related explosions and fires, along with loss of life and property, continued to occur. The year 1919 was especially trying. On May 20, a blast at a feed grinding plant in Milwaukee, Wisconsin, destroyed the facility and killed three people. Two days later, in Cedar Rapids, Iowa, an immense explosion—one reportedly felt 30 miles away—leveled the Douglas Starch Works, killing 43 and injuring 30. In September, a large grain elevator in Kansas City, Missouri, exploded, killing 14 and injuring 10. In all of these incidents and many more, dust was identified as the culprit.

The aftermath of a combustible dust explosion at the Imperial Sugar refinery in Port Wentworth, Georgia, in 2008. A series of blasts destroyed much of the facility and killed 14 people. The event added impetus to the effort to create an NFPA document on the fundamentals of combustible dust. AP PHOTO/POOL

The devastation of 1919 provided much of the impetus behind the formation of an NFPA committee on combustible dust hazards in 1922, and for the creation the following year of the first combustible dust standard, which addressed dust explosions in grain terminals and flour mills. That initial standard, the forerunner to NFPA 61, Standard for the Prevention of Fires and Dust Explosions in Agricultural and Food Processing Facilities, eventually led to a host of specialized standards across a range of industries: wood products, agriculture, metals, sugar, plastics, and many more. Over time, documents were consolidated, new standards were published to address new hazards, and further consolidations were undertaken. At the moment, work is proceeding on a new comprehensive dust standard—NFPA 660, Standard for Combustible Dusts, scheduled for release in 2025—that will consolidate six existing NFPA dust standards into a single document.

The effort to produce a new comprehensive standard comes at an encouraging moment in the ongoing fight against dust hazards, says Kevin Kreitman, a former fire chief who is currently city manager of Millersburg, Oregon, and chair of the correlating committee for NFPA 660. “There’s more interest in this problem than ever before from industry, from the public, from just about every sector,” he says. “When I first joined the combustible metals committee, a big committee was one that had maybe eight people on it. Now none of our dust committees have fewer than 35 members, and that’s a good thing—that kind of involvement is one of the biggest changes I’ve seen over the past 20 years. No matter where the members are coming from, they all have a genuine interest in making sure that what’s in the codes is what we need to provide safety for those industries and for the people who work in them.”


Six standards are being consolidated to create the new NFPA 660, Standard for Combustible Dusts:

NFPA 61, Standard for the Prevention of Fires and Dust Explosions in Agricultural and Food Processing Facilities

NFPA 484, Standard for Combustible Metals

NFPA 652, Standard on the Fundamentals of
Combustible Dust

NFPA 654, Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids

NFPA 655, Standard for Prevention of Sulfur Fires and Explosions

NFPA 664, Standard for the Prevention of Fires and Explosions in Wood Processing and Woodworking Facilities

In addition to the Correlating Committee on Combustible Dusts, five technical committees are working on the new NFPA 660:

• Technical Committee on Agricultural Dusts

• Technical Committee on Combustible Metals and Metal Dusts

• Technical Committee on Fundamentals of Combustible Dusts

• Technical Committee on Handling and Conveying of Dusts, Vapors, and Gases

• Technical Committee on Wood and Cellulosic Materials Processing

NFPA 660 is in the fall 2024 revision cycle, with a first edition scheduled in 2025. First draft public input closed in January; the first draft report will be posted by October 26. Second draft public comment closing date is January 4, 2024. The second draft report will be posted by October 3, 2024. —SS

Specialization and Consolidation
Despite that emerging sense of collective responsibility in recent decades, it hasn’t been enough to prevent a steady drumbeat of catastrophic industrial dust explosions. On February 7, 2008, a series of explosions rocked the Imperial Sugar refinery in Port Wentworth, Georgia, destroying much of the facility, killing 14 people and injuring 40. The initial blasts occurred in a basement conveyor area located beneath three large storage silos, producing shock waves that traveled across the entire facility. Poor housekeeping practices had allowed loose sugar to accumulate throughout the plant, and the shock wave from each explosion dispersed new clouds of sugar dust that ignited in turn as subsequent explosions propagated rapidly throughout the complex. A report by the US Chemical Safety Board described the event as “entirely preventable,” findings supported by investigations conducted by other federal agencies, including the Occupational Safety and Health Administration.

Fundamentals like housekeeping haven’t changed that much in the 100 years since the appearance of the first NFPA dust standard, says Tim Myers, chair of the NFPA 61 technical committee on agricultural dusts. Nor have other basic strategies including the prevention of accumulations and releases of dust, minimizing horizontal surfaces where dust can collect, explosion prevention, and control of potential ignition sources like electrical equipment. What has changed over time is the sophistication of the fundamentals. “They’ve become much more quantitative and provide a lot more detail for the design of systems than in the past,” says Myers, principal engineer and office director for Exponent, an engineering consulting firm. “Unfortunately, a lot of the causes of catastrophic incidents come back to those basic requirements like housekeeping.”

Many of the early NFPA dust documents addressed agricultural or food-related processes, from grain handling to cocoa processing; those standards were consolidated into NFPA 61 in 1970. The principles that anchored the original dust document in 1923 were applied to other industries: NFPA 654, Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids, first published in 1943, originally applied exclusively to plastics. Wood products received their own dust standards. A suite of combustible dust standards addressing hazards related to metals emerged in the 1960s and 1970s, starting with NFPA 480, Standard for the Storage, Handling, and Processing of Magnesium Solids and Powders, and NFPA 651, Standard for the Machining and Finishing of Aluminum and the Production and Handling of Aluminum Powders, both in 1967, followed by documents addressing titanium and zirconium and, later, lithium. In 2002, the standards addressing combustible metal dusts were consolidated into NFPA 484, Standard for Combustible Metals, Metal Powders, and Metal Dusts.

“What’s changed a lot is the growth in the types of materials that can become hazardous and the amounts that are used,” says Kreitman. “Fifty years ago, titanium wouldn’t have been the hazard it is today, because the process was so different and nature of the dust was different. We’re seeing much more additive manufacturing, so powders have become a hazard. That goes for a lot of materials: agricultural, wood, plastics, things you wouldn’t normally think of as being a hazard, but if it’s in a small enough form it becomes an explosion and fire hazard.”

Of special concern, Myers says, is the emergence of “nano powders,” super-small dusts typically associated with metals. These micro particles are manufactured as raw materials for 3D printing, powder metallurgy, and other processes used to create components for a range of precision industries: aircraft, medical devices, aerospace, nuclear, automotive, and others. “The smaller the particle size, the higher the specific surface area, so the easier it becomes to ignite and the faster it burns,” says Myers. What that means is that metals historically considered minimally hazardous at a larger particle size—such as Kreitman’s example of titanium—can become much more flammable as those particles shrink. In some cases, nano powders can auto-ignite at close to room temperature, and testing has demonstrated that they can generate an explosion without an outside ignition source.

Compounding the challenge is that many of these metals burn at very high temperatures—zirconium, for example, burns at more than 8,000 degrees Fahrenheit. That’s sufficiently hot to dissociate water and break it into its components of hydrogen and oxygen; put another way, if you attempt to douse burning zirconium with a fire hose, you’ll be met with a tremendous explosion. “You don’t see that with other metals or metal dusts like iron,” Kreitman says. “These are unique. Those characteristics really come into play when you’re trying to figure out how to protect against these hazards.”

The Quest for a Single Standard

And there’s another complicating factor: many facilities don’t face just one dust hazard, but multiple dust hazards. The same facility that produces nano powders from metal processing might also generate dusts from wood or plastic fabrication, and from paint or powder coating equipment. Standards exist to address each hazard, but toggling between multiple documents can be unwieldy and sometimes confusing, since different standards can adopt slightly different methods for addressing the same aspect of a dust hazard.

Harmonizing those requirements and making the documents easier to use have been key elements in consolidation efforts stretching back decades, including the process that combined the ag and food-processing standards into NFPA 61, and the metals standards into NFPA 484. Following the Imperial Sugar disaster, as well as a string of dust-explosion incidents leading up to it, NFPA undertook an ambitious effort to create a fundamentals document that would apply to any industry or process that generated combustible dust. The result was NFPA 652, Standard on the Fundamentals of Combustible Dust, first issued in 2016. The standard included a requirement for dust-generating facilities to conduct a dust hazard analysis, a practice that Myers and Kreitman say boosted the awareness of NFPA dust standards and of dust hazards in general.

An explosion in 1878 in Minneapolis, Minnesota, killed 18 people and leveled the world's largest grain mill, reducing the city's milling capacity by as much as half. Minnesota Historical Society/CORBIS/Corbis via Getty Images

NFPA 652 was also the first step toward a larger goal: the consolidation of the primary NFPA combustible dust standards into a single document [see “660: The Making of a One-Stop Dust Standard,” next page]. “When the Correlating Committee on Combustible Dusts was formed in 2011, the NFPA Standards Council’s vision was to ultimately have just one dust standard,” says Kreitman, who chaired the committee. “The more we looked at the fundamentals that were consistent to all of the dust standards, the more we started to see how much overlap there already was. We started to ask whether we were at the point where we could consider bringing those standards together.”

In 2019, the Standards Council asked the Correlating Committee to explore potential approaches to developing improved, streamlined, and noncontradictory standards addressing hazards of combustible dusts across multiple occupancies and industries, and the work of merging the six documents began in earnest. That included the process of helping the committees get to know one another, which wasn’t always smooth sailing. “People on some of the committees weren’t familiar with other committees, and the initial instinct in some cases was ‘our standard is the best one, and we don’t need to adopt what other people are doing or merge the standards,’” says Myers. “Some thought creating NFPA 652 was enough and that anything else was just needlessly complicating things. But what we found in the development of NFPA 652 is that when people from different committees actually worked together, they realized those other people weren’t as scary or unreasonable as they thought. We’ve purposely developed NFPA 660 slowly to make sure everyone gets to provide their input, and I think that’s resulted in more buy-in. What you see now are people who in the past might have been diametrically opposed to each other’s positions, but then one of them will say, ‘I’m a little concerned that I’m agreeing with you, but I think you’re right.’”

The six committees will remain in place to steer the future development of the standard, Kreitman says. “We don’t want to lose the autonomy of those individual committees,” he says. “That’s one of the things that make the NFPA standards so successful—you have people with specialties in those areas, so you want to ensure you’re putting those documents together by relying on their primary expertise.”
In addition to streamlining the information and providing a one-stop standard for an array of industries, Myers and Kreitman hope the attention around the new NFPA 660 standard can help raise awareness of dust hazards—a challenge that persists even after a century of combustible dust standards, and of notable and often tragic combustible dust explosions. Myers’ company, Exponent, conducts small-scale lab demonstrations of explosive combustible dust explosions and flash fires using nondairy coffee creamer as particulate, and “it’s often surprising to people how large of a fireball you can get from just a teaspoon of nondairy creamer,” he says—and that includes people from industries where dust explosions are a genuine threat.

Myers has also participated in incident investigations involving combustible dust explosions, including one at a facility that happened to make nondairy coffee creamer. “When we do a test in one of our labs and I get that smell, it reminds me of the scene of the explosion, where that same smell permeated the building—it sticks with you,” he says. “I’ve talked to facilities where there’s been a catastrophic dust explosion and they’ll say, ‘We’ve handled this material for 50 years and we didn’t know this could occur.’ The problem isn’t with the standards—the problem is still the lack of awareness. But anything we can do at the standards level to improve that awareness is absolutely essential.” 

SCOTT SUTHERLAND is editor of NFPA Journal. Top image: GETTY