What is NFPA 660 Standard for Combustible Dusts and Particulate Solids?

Chapters 11 through 20 are “reserved” for future fundamental topics. Examples could include a separate Fire Protection chapter, Additive Manufacturing or Nano Materials.

Chapter 21 is the Agricultural and Food Processing chapter. It represents the previous NFPA 61 standard.

Chapter 22 is the chapter on Combustible Metals. It represents the previous NFPA 484 standard.

Chapter 23 is the chapter on Sulfur. It represents the previous NFPA 655 standard (Note: this is covered by the previous NFPA 654 committee).

Chapter 24 is the chapter on Wood Processing and Woodworking. It represents the previous NFPA 664 standard.

Chapter 25 is the chapter on Combustible Dusts and Particulate Solids Not Otherwise Specified. It represents the previous NFPA 654 standard and recognizes that this chapter must cover all other materials not previously covered.

It is important to understand that although the individual fundamental and commodity specific standards no longer exist, the committees for each continue. For example, the Fundamentals committee will be responsible for chapters 1 through 10, while chapter 21 is covered by the Agricultural and Food Processing committee. The NFPA fully recognizes that each commodity chapter and the fundamentals may have differing requirements, hazards, and risks, and those must be recognized.

The Annex Material has been greatly expanded in the new standard. There are now 26 annexes (A through Z). These annexes are “for information only” and are not required, but they represent explanations, additional pertinent information, schematics, etc., to help users understand the requirements of the standard.

Chapters 21 through 25 present additional/augmented and/or revised requirements compared to the fundamentals of Chapters 1 through 10. This is because food processing will always have differing requirements than metals or wood processing or chemicals, etc. 

The following sections provide a general summary of the contents, augmentations, and/or modifications associated with each of the chapters and annexes of the new NFPA 660 standard.

Summary of NFPA 660 fundamentals chapters 

Chapters 1 through 10 represent the “fundamentals” portion of the 660 standard.

Chapter 1 is the Administrative chapter. The scope of the standard “...addresses the fire, flash fire, and explosion hazards of combustible dusts and particulate solids.” The purpose and application sections are similar to the previous 652. The retroactivity section is augmented and clarified and ensures that the special requirements of the previous commodity-specific standards still will apply if the user had applied those previous standards for combustible dust compliance. However, the Authority Having Jurisdiction (AHJ) does have the right to apply any new or revised requirement. If a fundamental requirement is revised or excluded in Chapters 21 through 25, it supersedes the fundamental requirement (but must be justified through the Correlating Committee).

Chapter 2 is the obligatory listing of the references for the standard. This includes all the references used for the requirements chapters.

Chapter 3 is the definitions chapter. All the terms that require definitions are included in this chapter. Fundamental definitions are designated CMD-FUN, while definitions for Chapter 21 (Food) are designated CMD-AGR. The number of definitions is extensive (134) but needed to ensure that users understand the meaning of key terms in the standard. Some new terms are defined, but most have been included in the previous standards.

Chapter 4 is the General Requirements chapter. This includes the Owner/Operator responsibilities and the objectives (or goals) of the standard (these are goals, not standards). One significant change to the section is the use of the word “reasonable” when referring to the objectives/goals of the standard. The objectives are not absolute but represent goals that are to be achieved as fully as is feasible given the limitations and conditions at the subject facility. This recognizes that the requirements for each facility if different. The listed objectives are to be managed according to the requirements of the standard.

Chapter 5 is the chapter on Hazard Identification. Significant improvements have been made to this chapter, which provides the fundamental requirements for determining whether materials involved are combustible or not. If materials are combustible, the characteristics of that combustibility (e.g., Kst, Pmax, MEC and MIE) must be determined. Multiple hazards and testing methods are now included.

Chapter 6 is the Performance Based Design Option chapter. This chapter provides the means and structure for addressing combustible dust hazards that cannot be controlled or mitigated by prescriptive methods (i.e., those designated in the standard). This option is not often used but can be a valid alternative for complex problems or situations where prescriptive solutions are not viable. No significant changes have been made in this chapter.

Chapter 7 is the Dust Hazards Analysis (DHA) chapter. There is no more critical chapter in the 660 standard. Now all the commodity-specific committees recognize that all new and existing facilities must complete a viable DHA. This includes, with limitation, Chapter 21 on Food, (formerly NFPA 61). It is common sense to provide a detailed evaluation of a facility’s combustible dust hazards, then determine the method or methods to eliminate or mitigate or control those hazards and, finally, set a meaningful schedule to complete the necessary solutions. The alternative is to live with the hazards and subsequent disastrous risks and liabilities. The chapter has only been minimally changed to enhance the effectiveness of the DHA.

Chapter 8 is the Management Systems chapter, though I would have preferred the title: “Methods for Managing Combustible Dust Hazards at Minimal Cost.” This chapter provides requirements for managing and limiting combustible dust hazards and risks by methods such as Management of Change (MOC), Housekeeping, PPE, Hotwork, Maintenance, Training, etc. This chapter has been expanded and augmented and includes topics that were previously located in other sections of 652. An example is the inclusion of Operational Readiness Review (ORR), also known as Pre-Start-Up Review. This is critical to ensure that revised or new systems achieve combustible dust compliance before long-term operation. This chapter is retroactive.

Chapter 9 is the Hazard Management: Mitigation and Prevention chapter. This chapter provides requirements and prescriptive methods for mitigation, prevention and/or elimination of combustible dust hazards and their associated risks. This section has been significantly revised with augmentations, modifications, and clarifications. A major effort was made to make the information included truly fundamental to all commodity-specific industries. Examples include:

1. Building Design, which includes the use of separation, segregation, associated Life Safety methods, limiting accumulations, and the use of detachment.
2. Equipment Design is a major portion of this chapter. It covers dust containment methods, pneumatic transfer, dust collection, centralized vacuum cleaning, etc. Various section of this chapter have been reorganized and augmented. 
3. Various equipment items such as mechanical feeding devices, bucket elevators, mixers/blenders, conveyors, dryers, etc., now refer to the commodity specific chapters due to the wide variation of use and hazards for these commodities.
4. There is a significant section on Dust Control without dust collection or containment. This includes the use of dust limiting methods such as large ceiling fans, area fans, etc. Large ceiling fans have a significant listing of requirements and limitations.
5. Subsection six covers fundamental methods of ignition control. Topics include electrostatic discharges, bearings, flexible connectors, FIBCs, lightning, smoking, etc.
6. Subsection eight specifically covers the fundamentals of Explosion Prevention and Protection. The eight-cubic-foot exemption remains. The section refers mostly to NFPA 68 (venting) and 69 (all other methods) regarding specific methods of explosion protection and/or prevention. This section also emphasizes the importance and fundamental requirement for explosion isolation.
7. Subsection nine covers Fire. In the future this will likely become a separate chapter. This section has been significantly reorganized, expanded and revised to emphasize that fire is also a major combustible dust hazard. For true combustible dust compliance, it is also necessary to prevent and/or control fires.

Chapter 10 covers Emergency Planning and Response. This chapter is new and did not exist in the previous NFPA 652 standard. Previously, the information in this section was located in various other sections, but the NFPA combustible dust committees agreed that the need for emergency planning and response is fundamental and required a separate chapter. This chapter covers the need for emergency response planning, the periodic review of that plan, and how to share the plan with appropriate first-responder organizations. 

Chapters 11 through 20 are reserved for future fundamental requirements such as Additive Manufacturing, Nanomaterials, Fire Protection Methods, etc.

Summary of NFPA commodity-specific chapters 

Chapters 21 through 25 provide requirements for specific commodities that are not fundamental to the other commodity-specific standards. Each of these commodity-specific chapters “shall modify and augment the requirements of Chapters 1 through 10” for the commodity covered. 

Chapter 21 is the chapter specifically on Food and Food Processing combustible dust hazards and compliance requirements and represents the NFPA 61 commodity-specific standard. 

One of the major discussions of the (food) committee was whether farms should be included. The committee generally agreed that only those farms (such as those of large corporations) with viable combustible dust hazards should be included and recognized that “family” farms would be exempt. However, further information and study is required. Additionally, the committee recognizes that public food safety must be maintained even when it conflicts with the NFPA 660 standard. 

There were no major disagreements (mainly clarifications) with fundamental Chapters 1 through 6.  However, there were modifications regarding Chapter 7 of the fundamental requirements. A DHA is still required for new and existing systems. However, Chapter 21 requires no DHA when modifications (to a system/process) are less than 25% of replacement cost. I strongly disagree with this limit as even minor changes can result in uncontrolled combustible dust hazards. There are some additional modifications to qualifications, documentation and methodology, including allowing for the use of a “checklist only” for a DHA. I also strongly disagree with this, as no checklist can anticipate all combustible dust hazards and risks for a facility. For example, a Process Hazards Analysis (PHA) using only a checklist would not be acceptable.  

Chapter 21 also has differences associated with Chapter 8 on Management Systems. This includes the allowance of up to 1/8-inch accumulations (5% of the area), a more lenient use of compressed air for housekeeping, additional requirements for portable equipment items (e.g., drills, etc.) associated with hot work. Management of Change (MOC) is slightly more lenient than in the fundamentals chapter but is still required. The Operational Readiness Review (ORR) is still required but modified and less strict in its application. This portion of Chapter 21 also includes information on warning signs and on grain handling facilities. 

Section 9 of Chapter 21 includes multiple modifications to the content of Chapter 9 fundamentals. The Building Design subsections are significantly modified to adjust to food processing requirements. The Ingredient Transfer System exemption has also been improved to clarify what is required to achieve that status and includes additional clarifications in Annex A. Additional modifications were made to the dust collection, centralized vacuum cleaning sections, etc., to reflect the food processing industry. Oddly, the Air-Material Separator (AMS) subsection includes information on dust collection, which needs correction in the future. The section includes extensive information on bins, silos, mechanical feeding devices, bucket elevators (a significant hazard for Agricultural and Food Processing), etc. The extensive Dryer subsections are essentially the same (as previous 61) with minor additions and clarifications. A heat transfer subsection is also provided. A Process Machinery and Equipment subsection is provided and mainly concerns the various unique “food” requirements for unloading barges, spouts, drag and similar conveyors, etc. Starch, which has increased hazards, has a separate subsection. Additional subsections are provided on “point-of-use” dust collectors, ignition source control, electrical systems and engine- and motor-driven equipment. These subsections include modifications and augmentation. 

The Chapter 21 committee also chose to provide its own section, significantly modified, on Explosion Prevention and Protection. The section includes both positive and suspect modifications compared to the fundamental section. It does provide some clarification and considerations applied to food processing requirements. The fire protection section is significantly expanded regarding the standpipe requirements. Section 10 (Emergency Planning and Response) is only modified to reflect specific firefighting requirements related to food processing.

Chapter 22 on combustible metals, replaces the previous NFPA 484 standard. The range of combustible metal dust and particle hazards and risks is complex, immense and continuously changing. Inherently, there are hazards that cannot be addressed properly with only the use of Chapters 1 through 10 of NFPA 660. Anytime combustible metals are involved, Chapter 22 should be thoroughly consulted.              

Sections 22.1 through 22.4 are not basically unmodified when compared with Chapters 1 through 4. However, due to the uniqueness and severity of the hazards associated with combustible metals, Section 22.5 required significant modification. Special considerations may be required when testing certain metal dusts such as the legacy metals (e.g., tantalum, niobium, titanium, etc.). Section 22.6 does not vary from Chapter 6 of the fundamentals. 

Section 22.7 (DHA) augments the fundamentals Chapter 7 to adjust for the unique hazards associated with certain metal dusts and particles. This includes explosion, flash fire, fire, molten metal and special building hazards. This section also allows for the use of Risk Evaluation (assessment) to allow for special requirements, etc. 

The housekeeping subsection (22.8) is modified due to the unique hazards of some combustible metals. Special care and limits are applied to centralized vacuum cleaning systems, the use of compressed air, PPE, inspection and maintenance of explosion prevention equipment and training.              

Section 22.9 (Hazard Management: Mitigation and Protection) has a significantly modified section on Building Design, again associated with the unique hazards of some metals. This includes such topics as floor surfaces, explosion venting, etc.              

The Equipment Design subsection also includes significant modifications for unique hazards of combustible metals, including augmented sections on ductwork and piping, conveying with inert gases, special requirements for Dust Collection, Centralized Vacuum Cleaning and Pneumatic Conveying systems, and metal powder handling and collection. This section also provides extensively revised requirements for various AMS types such as wet, dry, and portable. This also includes special exclusions and limits for legacy metals. 

This subsection also covers cleaned-air exhaust requirements and requirements for equipment items such as bucket elevators, conveyors, feeders, mixers, dryers, etc. Again, the unique hazards involved with combustible metals require augmentation of the fundamental information and requirements in the 22.9 section.              

Fire protection, especially with legacy metals, also requires unique and augmented requirements compared to the fundamental chapter. This includes the use of fire extinguishers, standpipes and sprinkler systems and limits on the use of water, etc.              

Section 22.10 (Emergency Planning and Response) is also significantly augmented and revised to cover such considerations as clothing fires, emergency preparedness for fires (again, especially concerning legacy metals), etc.              

Section 22.14 covers nano-metal powders and is unique to this chapter. Section 22.15 provides an extensive section on Additive Manufacturing (3D printing). Anyone using or considering additive manufacturing should consult this section, regardless of materials used, concerning the hazards and risks of this method of manufacturing. 

Additional sections are provided for Alkaline Metals (22.16), Legacy Metals (22.17), Other Metals (22.18) and Metal Recycling (22.19).

Chapter 23 concerns the combustible dust hazards of Sulfur. This is a little-known standard (formerly NFPA 655) for anyone handling, processing, and/or creating combustible sulfur-related or sulfur-based compounds. This chapter would be a “must-know” for industries involving sulfur creation, the rubber industry, and other industries where sulfur is used in any significant quantity. Overall, only minor differences and enhancements were provided when compared to the previous NFPA 655 standard. The Chapter 25 committee covers this chapter.

Chapter 24 covers Wood Processing and Woodworking Facilities. In general, this chapter differs minimally from the previous NFPA 664 standard. This is also true of differences with the fundamental Chapters 1 through 10. There are no significant changes regarding fundamental Chapters 1 through 4. Section 24.5 (Hazard Identification) is augmented for green wood and other variations, which require special consideration. There is no change from the fundamental Chapter 6 for section 24.6.              

Section 24.7 on DHAs is not significantly changed but is augmented to include additional requirements regarding buildings and compartments.              

Section 24.8 (Management Systems) does include some significant augmentation and modifications. The housekeeping section includes information on sweeping and other related housekeeping activities. Also, there is a “rogue” section on Dust Collection mainly focusing on maintenance issues. Training, hazard awareness, Management of Change, and Document Retention subsections are also modified and augmented.              

Section 24.9 (Hazard Management: Mitigation and Prevention) does include areas of significant modification and augmentation. These changes reflect some of the unique processing requirements for wood products and woodworking. Examples include the building design subsection, equipment design section, etc. The equipment design enhancements mainly involve pneumatic conveying/transfer, dust collection, centralized vacuum cleaning systems, mechanical feeding devices, fans/blowers, ducting, hoods, mixers/blenders, dryers (multiple types) and panel production. The subsection on ignition sources is also modified to include friction and impact sparks and spontaneous ignition. The explosion prevention and protection subsection includes augmentation regarding dust collectors, ducts, silos, size reduction equipment, etc. This also provides an enhancement to address “conveying system isolation.”              

Since Fire is a major combustible dust hazard for wood processing, the 24.10 section is also significantly augmented and revised. This includes detection systems, etc.              

There is no change represented by section 24.11 (Thermal Oil), which was also contained in the previous NFPA 664 standard. Although this is not part of “combustible dust,” it is included as a “grandfather” section. Section 24.12 is also a carryover from NFPA 664.              

Chapter 25 covers Combustible Dust and Particulates Not Otherwise Specified. This odd title is used to make it clear that all combustible materials not previously covered are included in this chapter. This chapter is essentially the content of the previous NFPA 654 standard.              

There are no significant differences for sections 25.1 through 25.6 compared to the fundamentals Chapters 1 through 6.              

Section 25.7 (DHA) is augmented to consider the range of materials that can be considered “other.” The section includes formulas and methods that attempt to determine the mass accumulation that can be allowed before removal. These methods are theoretical and not proven.              

Section 25.8 (Management Systems) includes only minimal differences from fundamentals Chapter 8, but it does include requirements for various equipment items associated with management system methods.              

Section 25.9 (Hazard Management: Mitigation and Prevention) includes significant differences in the building design subsection. The equipment design subsection includes minor additional requirements for pneumatic conveying, dust collection, centralized vacuum cleaning, AMS, duct systems, etc. As required by fundamentals Chapter 9 there are expanded requirements for equipment items such as size reduction, bucket elevators, feeders, etc. There is also a new section on “ultrafine particles” and their, at times, unique combustible dust hazards.              

There are expansive and augmented subsections on standards for Particulate Transport Rates, FIBCs, Friction and Impact Sparks, Electrical Systems, and Process and Comfort Heating.              

There is no significant deviation from the fundamental section on explosion prevention and protection.  Explosion isolation is also required.              

Section 25.10 does not have any significant revision or augmentation. 

Summary of NFPA 660 annexes

NFPA 660 now includes 26 annexes, but users should not be overwhelmed by that number. The annexes, especially Annex A, should be consulted when users are attempting to fully understand and properly achieve the requirements of NFPA 660. It is important to note that annexes are for “informational purposes only” and that the value and veracity of the information presented in some of the annexes is debatable, as I’ve noted in the following summary:

Annex A: This is perhaps the most important and significant annex. It provides additional information designed to explain the standards and clarify possible misconceptions. Use this annex when an asterisk is included with a standard section of 660. The information provided is “should” content rather than “shall” content and is not a requirement. No requirements are provided in the annex, only explanations and examples.

Annex B: An example of a DHA.

Annex C: Information on the effects of dust accumulations at various locations.

Annex D: Additional information regarding fire protection.

Annex E: Additional information regarding fumigation and relationship with combustible dusts.

Annex F: Additional information regarding employee health and safety in relation to combustible dusts.

Annex G: Schematics on Pneumatic Conveying. This annex needs updating and improvement in the future.

Annex H: An example of a DHA using only a checklist. (I strongly oppose using only a checklist for a proper and effective DHA.)

Annex I: Information on electrically conductive floors.

Annex J: Additional information regarding Magnesium.

Annex K: Information on designing for dust concentration control in ductwork. (Use this only with great caution as it can be misleading.)

Annex L: Additional information regarding Tantalum.

Annex M: Additional information regarding Titanium.

Annex N: Additional information regarding Zirconium.

Annex O: Information on agents that should not be used with Lithium fires.

Annex P: Additional information on testing with detailed explanations of some atypical types.

Annex Q: Important information on the various methods of explosion protection. (Needs updating.)

Annex R: Information on spark detection and extinguishing. (Needs updating.)

Annex S: Information on dust layer characterization and prevention. (Use with caution.)

Annex T: Information on explosion isolation methods. (Needs updating.)

Annex U: Information on the use of water as an extinguishing agent.

Annex V: Information on thermal dosing from flash fires, including PPE. (Will likely be augmented in the future.)

Annex W: Information on explosion isolation of conveying systems but limited to detection and extinguishing, not true explosion isolation.

Annex X: Information on dryer water deluging systems.

Annex Y: Extensive listings of explosibility characteristics of many types of combustible dusts. This is historical data and should only be used as a guide or with great caution. This is an important annex.

Annex Z: Information on the references used.