40 CFR 63 Subpart 6X: EPA Metal Fabrication

Regulatory citation: 40 CFR Part 63, Subpart XXXXXX, National Emission Standards for Hazardous Air Pollutants Area Source Standards for Nine Metal Fabrication and Finishing Source Categories

What Is the 6X Rule?

Subpart XXXXXX, known as the 6X rule, is an area source air toxics standard for metal fabrication and finishing shops. It applies to facilities primarily engaged in one of nine source categories, meaning at least 50% of production over the previous 12 months:

• Electrical and electronic equipment finishing
• Fabricated metal products
• Fabricated plate work (boiler shops)
• Fabricated structural metal
• Heating equipment, except electric
• Industrial machinery and equipment finishing
• Iron and steel forging
• Primary metal products
• Valves and pipe fittings

The rule only applies where a covered process uses materials containing metal fabrication or finishing hazardous air pollutants (MFHAP). These are compounds of cadmium, chromium, lead, manganese or nickel, or the elemental forms of those metals other than lead. A material contains MFHAP if it has at least 0.1% by weight of cadmium, chromium, lead or nickel, or at least 1.0% manganese, based on supplier data such as a safety data sheet.

Why the 6X Rule Matters

Welding fume, blasting dust and paint overspray can carry toxic metals out of the building. Simple practices such as capture, filtration and trained painters cut those emissions.

Core Requirements

1. Identify Covered Processes (63.11514)

The rule covers dry abrasive blasting, machining, dry grinding and polishing with machines, spray painting and welding that use MFHAP-containing materials. Research labs, tool and equipment repair, facility maintenance and quality control are excluded. The rule does not by itself require a Title V permit.

2. Control Dry Abrasive Blasting (63.11516(a))

In totally enclosed, unvented blast chambers, minimize dust and follow the manufacturer's instructions. In vented enclosures, capture emissions and send them to a filtration control device. Objects over 8 feet in any dimension may be blasted outside an enclosure using alternative practices, such as minimizing dust, enclosing abrasive storage and running Method 22 visual checks.

3. Control Machining and Grinding (63.11516(b) and (c))

For machining, minimize excess dust and follow the manufacturer's instructions. Dry grinding and polishing emissions must be captured and sent to a filtration control device.

4. Meet Spray Painting Standards (63.11516(d))

Spray painting with MFHAP paints must be done in an enclosed booth with filters that capture at least 98% of MFHAP, or a waterwash booth achieving the same. Fabricated structural metal facilities, and objects over 15 feet that are not painted in booths, are exempt from the booth requirement. Paint must be applied with HVLP, electrostatic, airless or air-assisted airless guns, or an approved equivalent. Guns must be cleaned with non-HAP solvent or without atomizing solvent outside a collection container. Painters must be trained and certified within 180 days of hire, with refresher training every 5 years.

5. Follow Welding Practices (63.11516(f))

Welding equipment must be run to the manufacturer's instructions, and shops must use one or more of five practices: lower-fume processes, fume-reducing process variations, lower-fume filler metals, optimized process variables, or fume capture and control.

6. Run Visible Emissions Checks at 2,000 Pounds of Rod a Year (63.11516(f)(3) to (8) and 63.11517)

Shops using 2,000 pounds or more of MFHAP welding rod a year, on a rolling 12-month basis, follow a tiered approach. Tier 1 is Method 22 visual checks at building vents, starting daily and stepping down to quarterly after clean results. If visible emissions are seen more than once in 12 months, Tier 2 requires a Method 9 opacity reading within 24 hours and corrective action. Opacity above 20% is Tier 3: report it as an exceedance and prepare a site-specific welding emissions management plan within 30 days.

7. Submit Notifications and Annual Reports (63.11519)

Covered sources submit an Initial Notification and a Notification of Compliance Status. An Annual Certification and Compliance Report covering January 1 to December 31 is due by January 31 each year, with any exceedances included.

8. Keep Records for 5 Years (63.11519(c))

Keep notifications and reports, Method 22 and Method 9 results, control device and filter documentation, spray gun documentation, painter training certificates, any welding plan, and welding rod usage records. Records must be kept for 5 years, with at least 2 years on site.

Common Compliance Approaches

Screen Materials With SDSs

Check welding rod, abrasives and paint safety data sheets for chromium, nickel, manganese, lead and cadmium before adding them to stock.

Track Welding Rod Use

Log purchases or issues of MFHAP rod each month so you know when the 12-month total nears 2,000 pounds.

Keep a Painter Training Roster

Record each painter's training date and the next 5-year refresher.

Example: 6X Compliance in Practice

A structural steel fabricator uses stainless and manganese-bearing welding wire and about 3,500 pounds of wire a year. It switches some joints to a lower-fume process and adds fume extraction at fixed welding stations. A trained employee runs daily Method 22 checks at the roof vents, which step down to quarterly after a run of clean results. The shop logs wire usage monthly, keeps the check records and files its annual certification report each January.

Related regulations: EPA 6H paint stripping and coating, OSHA hexavalent chromium, OSHA welding and hot work.

Note: Subpart XXXXXX was last amended in 2020 and 2021, and no changes had been proposed as of October 2026. State and local air agencies may add stricter requirements. Always check the current regulation text.

Frequently Asked Questions

What is MFHAP?

Metal fabrication or finishing hazardous air pollutants: compounds of cadmium, chromium, lead, manganese or nickel, or those metals in elemental form other than lead. A material counts if it contains at least 0.1% cadmium, chromium, lead or nickel, or 1.0% manganese.

Does 6X apply if my shop is not in one of the nine categories?

No. The facility must be primarily engaged in one of the nine listed source categories. Spray coating at other shops may fall under the separate 6H rule.

Do I need to run Method 22 checks for welding?

Only if you use 2,000 pounds or more of MFHAP welding rod a year on a rolling 12-month basis. Smaller users follow the welding management practices.