For the past 10 years, the National Fire Protection Association has been working to consolidate several industry-specific standards for combustible dust. In December 2024, the NFPA completed its goal by issuing “NFPA 660–Standard for Combustible Dusts and Particulate Solids.” This new standard combines six existing standards, including NFPA 61 (agricultural dust) and NFPA 664 (wood dust), into a single standard that covers all industries where combustible dust and particulates are generated, used and handled.
Building permitting authorities, code enforcers and fire agencies use the NFPA standards to establish the basis of design and operation for new and existing industrial sites, so it’s important for pellet mill owners and operators to be aware of NFPA requirements, especially for new projects and plant modifications. NFPA 660 covers both administrative and engineering requirements at facilities with combustible dust, and its goal is to minimize fires and explosions, help companies maintain business continuity, and, most importantly, protect workers and the public.
NFPA 664 and NFPA 61 are the standards most often applicable to pellet mills, depending on what material is being processed. Those standards are two of the oldest NFPA standards dealing with combustible dust. NFPA 664 dates back to 1931 when the “Code on Wood Flour Manufacturing” was issued. NFPA 61 is even older, dating to 1923 when standards were first developed to prevent dust explosions in grain terminals and flour mills.
In addition to NFPA 61 and 664, NFPA 660 also incorporates NFPA 484 for combustible metals; NFPA 652, which covers fundamentals of combustible dust; NFPA 654, which is for combustible solids not covered by one of the other commodity standards; as well as NFPA 655 for sulfur. This doesn’t mean that the existing standards will disappear—they are still available at nfpa.org. However, NFPA will no longer revise those six standards, and they will effectively stay frozen in place. Some state and local fire codes are several years old and still reference the legacy dust standards, so there will be times when the old, industry-specific standards apply.
In the past, facilities would start with NFPA 652, which is the standard on the fundamentals of combustible dust. Then, they would need to review the commodity-specific standard that applied to them. This could be burdensome and confusing, requiring users to jump back and forth between multiple standards that sometimes contradicted each other. NFPA 660 does not eliminate the commodity-specific requirements. Instead, the requirements that were in 652 are now chapters 1 through 10 of NFPA 660, and the old commodity standards are separate chapters in 660. So NFPA 61 is chapter 21, NFPA 664 is chapter 24, etc.
The fundamental chapters (1-10) of NFPA 660 apply to everybody handling combustible dust, and the commodity chapters only apply to facilities handling those specific materials. The subchapters of the commodity chapters are aligned with the fundamental chapters. For example, chapter 9.3 covers building design in general, and chapter 24.9.3 covers building design for wood processing facilities. There is a caveat that if there's something in the fundamental chapters that contradicts something in a commodity chapter, the owner of the facility has the option to pick which requirement they want to follow.
The standard includes requirements for hazard identification and analysis, administrative controls, building design, equipment design, and fire and explosion protection. Hazard identification means understanding the combustion and explosion properties of the materials handled. For example, it’s important to know the difference between green wood chips and dry fines when assessing fire and explosion hazards at different stages of the process. Obtaining the material properties may require reading safety data sheets, textbooks and online databases, or it may mean sending dust samples to a combustion testing lab to get more specific data on the dust being generated.
Facilities are required to complete a dust hazard analysis (DHA) for existing operations and as part of the design of any new project. The DHA is a systematic review of the process equipment and buildings to determine where and when a fire, flashfire or explosion hazard might exist. The DHA also needs to evaluate existing or planned safeguards to determine if they are adequate, and if they are not, provide recommendations for additional safeguards. The DHA must be performed by a qualified person who has experience identifying and mitigating hazards related to the specific types of dusts being handled. NFPA requires that the DHA be documented and maintained for the life of the process, and it shall be reviewed and updated at least every five years.
NFPA 660 includes building design requirements such as construction features to limit the accumulation of dust and the need to separate dust fire and explosion hazard areas from other occupancies. The standard addresses life safety (means of egress) as well as when damage-limiting construction may be required. For equipment, the standard covers leak prevention, ignition source control, bonding and grounding, foreign object removal (e.g., magnets and screens), and other safety features. It also identifies where fire and explosion protection are needed in equipment.
The standard outlines the training and preventive maintenance required, covering topics such as inspections, emergency preparedness, incident investigation, management of change and more. Housekeeping is an important focus in the standard, and it provides guidance regarding how to keep dust to manageable levels so that there isn’t potential for secondary explosions.
After many years, “NFPA 660: Standard for Combustible Dusts and Particulate Solids” has finally been published. It does not significantly change many of the requirements that have been in place for decades, but it does make navigating the standards much simpler. It is the one place that pellet mills and other industries can go to understand how to protect against fires and dust explosions in their operations.
