NFPA 484 Is Now NFPA 660: What It Means for Combustible Metal Facilities

By DHA Report Group · Updated October 20, 2026

If your plant grinds, cuts, or finishes aluminum, magnesium, titanium, zirconium, or other combustible metals, NFPA 484 was the standard that governed your metal dust. It has been folded into NFPA 660. The metals requirements now live in Chapter 22, Combustible Metals, applied along with the fundamentals that cover every combustible dust facility.

Where NFPA 484 went

NFPA 484 was the combustible metals standard. In NFPA 660, its content sits in Chapter 22. The fundamentals that used to come from NFPA 652, including the dust hazard analysis (DHA) requirement, sit in Chapters 1 through 10 of the same document.

Metals have always needed more than the general rules, and that has not changed. Not every metal dust is combustible, which is why testing matters. The ones that are can behave very differently from wood or food dust, and the right approach depends on which metal you have and how it is produced.

Who this applies to

• Grinding, polishing, and finishing of combustible metals such as aluminum, magnesium, titanium, and zirconium
• Welding, laser cutting, and plasma cutting. NFPA 660 keeps these in Chapter 22 unless the collected fumes are shown to meet its exclusion criteria, so do not assume welding fume is out of scope until it has been tested out.
• Any process that collects combustible metal dust

For more on metals specifically, see DHA for metal dust.

What NFPA 660 says about collecting metal dust

This is where the most overstated claims show up, so here is how the standard actually frames it:

• Two recognized methods. A wet-type collector located indoors near the point of generation, or a dry-type collector located outdoors as close as possible to the point of generation.
• Wet is the preferred default for most combustible metal dust, but it is not a blanket mandate for every metal. An indoor dry-type collector is allowed only where wet or outdoor dry is not feasible, and then with added protection.
• Dry-type is not recommended for niobium or tantalum.
• Wet does not mean no hazard. Wetted metal dust that is not kept submerged can be highly flammable, and water reacting with metal produces hydrogen. A wet system still needs hydrogen venting, water-level monitoring, and sludge management.

Your DHA is where the right approach for your metal and your process gets decided. DHA Report Group does not sell equipment.

The step most metal facilities skip

Published values for metal dust are for screening, not design. Particle size, moisture, and composition change how a dust behaves, so protection design needs lab testing of your actual dust. See combustible dust testing for what the tests tell you.

What carried over

• A DHA is required, performed or led by a qualified person. NFPA 660 notes that a person can be qualified for one dust type and not another, which matters a great deal with metals.
• The DHA is reviewed at least every five years and whenever your process changes.

What to do with a DHA written to NFPA 484

NFPA 660 ties DHA reviews to two triggers: at least every five years, and whenever your process changes.

• When your next review is due, by either trigger, write it to NFPA 660.
• Old section references to NFPA 484 will not match NFPA 660, so updating them belongs in that review.
• No DHA yet: start with one written to NFPA 660.

Keep reading

• Dust Collector Explosion Protection: Venting, Isolation, and Suppression Explained
• Is My Dust Combustible? How to Find Out Before Your DHA

Questions about NFPA 484 and NFPA 660

Is NFPA 484 still a separate standard?

No. NFPA 484 was consolidated into NFPA 660. Its combustible metals requirements now sit in Chapter 22.

Which chapter of NFPA 660 covers combustible metals?

Chapter 22, Combustible Metals, applied along with the fundamentals in Chapters 1 through 10, including the DHA requirement.

Does NFPA 660 require wet collectors for all metal dust?

No. NFPA 660 treats wet collection as the preferred method for most combustible metal dust, with an outdoor dry-type collector as the recognized alternative. Indoor dry-type is a last resort with added protection.

Is welding fume covered by NFPA 660?

Welding, laser cutting, and plasma cutting are within Chapter 22 unless the collected fumes are shown to meet the standard’s exclusion criteria.

Do I need a new DHA because NFPA 484 was replaced?

NFPA 660 ties DHA reviews to two triggers: at least every five years, and whenever your process changes. When your next review is due, write it to NFPA 660 and update the old section references.