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NESHAP Subpart IIII surface coating (major source)

If you're a tier-1 or tier-2 supplier finishing parts for an OEM assembly plant, Ford, GM, Stellantis, Honda, Nissan, Toyota, VW, and your facility exceeds the major-source threshold, you're under NESHAP Subpart IIII. Major-source rules carry more rigor than the area-source rules that cover most independent collision shops. The OEM customer's engineering specification usually drives more of the operational requirement than the federal rule itself, but the federal rule sets the floor.

Quick answer

NESHAP Subpart IIII covers major-source surface coating operations for automobiles and light-duty trucks, OEM assembly plants and tier-supplier facilities exceeding the major-source threshold. Major-source rules are more rigorous than area-source rules: stricter emission limits, mandatory source testing, and more detailed maintenance logs. Filter selection and recordkeeping align with the customer OEM's engineering specifications.

By Ben Kurtz · Filter Fitment Lead, 20+ years in paint-booth service · Updated May 9, 2026
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What this means for filter selection

Subpart IIII facilities run booth filtration sized to the customer's engineering specification. The filter selection isn't a catalog decision, Ford GMS, GM SOR, Stellantis MS, Honda HES, Nissan NES specifications each prescribe specific media classes and replacement cadences for the booth lines on their supplier programs. The federal rule's emission-limit floor is the regulatory baseline; the OEM customer's spec is what the shop actually orders against.

Capture-test documentation ships with every filter shipment, formatted for the OEM's recordkeeping requirements. Source-test data (periodic measurement of actual emissions vs rated capture) is required at the federal level and typically more frequently at the OEM customer's contract level. Maintenance logs track filter changes per shift and any abnormal conditions.

Cycle math for Subpart IIII facilities is much tighter than collision-shop cycles, production-line throughput drives shorter intervals. Intake-side cycles often run 14-21 days; exhaust-side 45-75 days; AMU pre-filter 30-45 days. The customer-spec'd cadence supersedes any catalog default.

Regulatory landscape

Subpart IIII facilities face more rigorous EPA inspection cadence than area-source shops, plus the OEM customer's audit cadence on top. The OEM audit is often more demanding than the federal inspection. Documentation that satisfies the OEM customer typically exceeds the federal floor. Subscription delivery records covering the engineering-spec cadence document the maintenance log piece by default.

Who needs to know this

Subpart IIII applicability concentrates in OEM assembly plants (Ford, GM, Stellantis, Honda, Nissan, Toyota, VW, Hyundai, Kia, Subaru, plus the EV transition entrants), the tier-1 supplier base finishing exterior body parts and certain interior components, and tier-2 supplier facilities exceeding the major-source threshold for the specific finishing work they do. The bulk of the Subpart IIII installed base is in the Detroit metro area, the I-65 corridor through Ohio/Kentucky/Tennessee, the Southeast (Alabama, Georgia, South Carolina), and emerging EV manufacturing clusters.

NESHAP Subpart IIII surface coating (major source) FAQs

What's the difference between Subpart IIII and Subpart HHHHHH (6H)?

Subpart IIII is major-source automotive surface coating; Subpart HHHHHH (6H) is area-source paint stripping and miscellaneous surface coating. Major-source thresholds are higher emissions volumes; smaller shops fall under the area-source rules. Subpart IIII has more rigorous requirements proportional to the higher emissions impact.

Am I under Subpart IIII or 6H?

Depends on the facility's emissions volume relative to the major-source threshold. Most independent collision shops are 6H. Tier-supplier finishing operations may be either depending on size and coating mix. Your state DEQ or AQMD makes the final classification.

Can I use the same filter brand across both rules?

The filter brand isn't the regulatory question, the filter spec is. Subpart IIII facilities require filtration meeting the customer OEM's spec, which typically exceeds 6H requirements. Don't assume a 6H-compliant kit satisfies a Subpart IIII requirement.

How do source tests work?

Periodic measurement of actual emissions leaving the facility, typically a stack test with calibrated instruments measuring captured vs released particulate. The result is compared against the rated capture of the installed filtration. Subpart IIII requires source tests at federally-specified frequency; OEM customers may require additional tests.

What happens if a source test fails?

The facility goes into corrective-action status: identify the failure cause, restore capture to the rated specification, retest. Failed source tests typically trace to filter degradation or operational drift. Subscription delivery on the customer-spec cadence is the prevention path.

Do EV manufacturers have different requirements?

EV assembly plants face the same Subpart IIII framework but the coating mix is different (less solvent-based primer, more waterborne) which changes the emissions profile. Tier-supplier facilities for EV programs face the same federal requirements as ICE-vehicle suppliers; the OEM customer's spec varies by program.

Sources

Primary references cited on this page.

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