Frequently Asked Questions

NFPA 660 is a consolidation and replacement of the general and industry/commodity specific NFPA standards for combustible dusts.

The 2025 edition was published on November 16, 2024 with an effective date of December 6, 2024. The next Edition will be 2028.

The first 10 chapters are essentially the fundamental explosion protection requirements taken from NFPA 652. Chapters 11 through 20 are reserved for future use. Chapter 21 – 25 are dedicated to the Industry or commodity specific NFPA standards being replaced. These are:

• NFPA 61 which is now Chapter 21 Agricultural and Food Processing
• NFPA 484 which is now Chapter 22 Combustible Metals
• NFPA 655 which is now Chapter 23 Sulfur
• NFPA 664 which is now Chapter 24 Wood Processing and Woodworking Facilities
• NFPA 654 which is now Chapter 25 Combustible Dusts and Particulate Solids Not Otherwise Specified

These two standards, which cover explosion protection methods for flammable gases, vapors, mists, dusts, or hybrid mixtures, remain unchanged as separate standards outside of NFPA 660. The next editions are 2028 for NFPA 68 and 2029 for NFPA 69.

Note and follow the requirements of Chapter 1 through 10 which detail the fundamental requirements for explosion protection, then modify or augment these requirements with the relevant industry or commodity specific requirements in Chapters 21-25, according to your industry or commodity. Chapter 1 provides some helpful flow diagrams to take you through the process.

A hard copy of NFPA 660 can be ordered from https://www.nfpa.org/. Subscribers to NFPA LiNK® can view the standard online. Additionally, by registering on the NFPA.org website anyone can use NFPA’s Free Access feature to view individual NFPA standards online.

Conflicts within NFPA 660 (Section 1.6) are handled in a similar way, as they were in NFPA 652.

• Where a requirement in chapters 1-10 is prohibited within a commodity specific chapter. The commodity specific requirement shall be applied.
• It is permitted to apply a fundamental requirement in a commodity specific chapter where it differs from Chapters 1-10.
• The requirements of chapters 1-10 shall be applied where they are neither prohibited nor required by the commodity specific chapter.

Yes, where specified, the requirements of NFPA 660 are retroactive to existing and new facilities and processes. The following chapters and the corresponding sections in commodity specific chapters are retroactive:

• Chapter 7 Dust Hazard Analysis (DHA)
• Chapter 8 Management Systems
• Chapter 10 Emergency Planning and Response

Any new facilities or processes or changes, modifications or additions to an existing facility are subject to the requirements of this standard.

While the large majority of the source materials remain unchanged, changes have been introduced to both the explosion protection fundamentals and the industry specific source materials. A partial list of changes is detailed on pages 1 and 2 of the standard.

Equipment having a dust explosion hazard and a containing volume greater than 8ft3 (0.2M3) shall incorporate one of the following protection methods per NFPA 68 and NFPA 69:

• Oxidant concentration reduction
• Deflagration venting
• Deflagration pressure containment
• Deflagration suppression
• Rendering the dust non-combustible by dilution with a non-combustible dust

The deadline originally set by NFPA 652 of September 7, 2020 has passed. A DHA must be completed for all new and existing processes and thereafter every 5 years. Any change to the process or material being handled shall trigger the need to update the DHA.

In the USA states either Adopt NFPA standards directly or indirectly by reference to the International Fire Code, making NFPA 660 an enforceable Standard. Internationally, the NFPA codes are widely recognized as best engineering practices.

This standard which covers explosion protection methods for flammable gases, vapors, mists, dusts, or hybrid mixtures, remain unchanged as a separate standard outside of NFPA 660. The next edition is 2028 for NFPA 68. BS&B offers deflagration explosion relief vent panels, flame arresting, flameless and building vent devices in accordance with NFPA 68, 2023.

This standard which covers explosion prevention system remains unchanged as a separate standard outside of NFPA 660. The next edition is 2029 for NFPA 69. BS&B offers explosion prevention protection strategies: deflagration suppression, chemical isolation, active mechanical isolation and passive isolation devices in accordance with NFPA 69, 2024.