# EPA NESHAP — National Emission Standards for Hazardous Air Pollutants

The National Emission Standards for Hazardous Air Pollutants NESHAP, codified at 40 CFR Part 63, are EPA's technology-based emission standards for 187 toxic air pollutants — chemicals like benzene, me

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## Facts
- Domain: Environment
- Category: Air Quality & Climate
- Page type: topic
- U.S. Code anchor: none
- Last verified: 2026-11-01

## Article

The **National Emission Standards for Hazardous Air Pollutants (NESHAP)**, codified at **40 CFR Part 63**, are EPA's technology-based emission standards for 187 toxic air pollutants — chemicals like benzene, mercury, vinyl chloride, and dioxins that cause cancer, neurological damage, or reproductive harm even at concentrations below criteria pollutant thresholds. Congress listed these **Hazardous Air Pollutants (HAPs)** in the 1990 Clean Air Act Amendments and directed EPA to set **Maximum Achievable Control Technology (MACT)** standards for each industrial source category that emits them. Part 63 now contains hundreds of industry-specific MACT subparts covering petroleum refineries, chemical plants, paint strippers, dry cleaners, hospital sterilizers, and dozens more.

## Current Rule (2026)

| Parameter | Value |
|-----------|-------|
| Citation | 40 CFR Part 63 (source category MACT standards); 40 CFR Part 61 (pre-1990 standards) |
| Issuing agency | EPA Office of Air Quality Planning and Standards |
| Statutory authority | 42 U.S.C. § 7412 (Clean Air Act § 112) |
| Source categories covered | Hundreds of major and area source categories across industry |
| HAP list | 187 listed hazardous air pollutants (as of 2026) |
| Standard basis | Maximum Achievable Control Technology (MACT) for major sources; Generally Achievable Control Technology (GACT) for area sources |
| Last major framework amendment | 1990 Clean Air Act Amendments (Pub. L. 101-549) |

## What This Rule Does

Not all air pollution is treated equally. The six "criteria pollutants" — particulate matter, ozone, carbon monoxide, nitrogen dioxide, sulfur dioxide, and lead — are regulated through the National Ambient Air Quality Standards (NAAQS) framework, targeting safe concentration levels in outdoor air. **Hazardous Air Pollutants (HAPs)** are a different category: 187 toxic chemicals that cause cancer, neurological damage, reproductive harm, or other serious health effects even at levels below criteria pollutant thresholds. Congress listed these HAPs in 1990 and directed EPA to set **Maximum Achievable Control Technology (MACT) standards** for industrial categories that emit them — resulting in **40 CFR Part 63**, one of the most extensive regulatory programs in U.S. environmental law.

Part 63 currently contains hundreds of industry-specific subparts — each a stand-alone MACT rule for a particular source category — covering facilities from petroleum refineries and chemical plants to paint stripping operations, chromium electroplating shops, dry cleaners, hospital sterilizers, and rubber tire manufacturing. When EPA promulgates a MACT standard for a source category, every major source in that category must meet the standard's emission limits, work practice requirements, equipment specifications, monitoring requirements, recordkeeping obligations, and reporting deadlines. MACT standards are technology-based, not health-based: they require sources to match the best-performing 12% of existing sources in the category (the "MACT floor"), then allow EPA to set more stringent standards if technically feasible.

After a MACT standard has been in place for at least eight years, EPA must conduct a **Risk and Technology Review (RTR)** — an assessment of residual cancer and non-cancer risks to the public from sources complying with the MACT floor. If residual risks remain above acceptable levels (generally, more than 1-in-10,000 excess cancer risk in the most-exposed population), EPA must strengthen the standards. This RTR process drives ongoing revisions to existing Part 63 subparts as EPA works through its backlog of reviews.

## How It Works

The NESHAP framework divides emission sources into two tiers. A **major source** — any facility that emits 10 tons or more per year of any single HAP, or 25 tons or more of all HAPs combined — must meet **Maximum Achievable Control Technology (MACT)** standards. EPA sets MACT at no less than the **MACT floor**: the average emission level achieved by the best-performing 12% of existing sources in each category. EPA may then set standards "beyond the floor" if further reductions are economically and technically feasible. An **area source** (any source below the major thresholds) must meet **Generally Achievable Control Technology (GACT)** standards, which are typically less stringent. When EPA promulgates a new standard, existing sources generally get three years to comply from the rule's effective date; new sources must comply immediately on startup.

Each regulated source category gets its own subpart within **40 CFR Part 63**, identified by a letter or letter combination. Subpart A contains the general provisions that all other subparts incorporate by reference: the applicability determination process (§ 63.1), recordkeeping and reporting (§ 63.10), control device requirements (§ 63.11), and definitions (§ 63.2). A facility covered by NESHAP must therefore understand both its source-category subpart — which sets the emission limits, work practice standards, and monitoring requirements specific to its industry — and the general provisions, which govern how those requirements are demonstrated and documented. States that have received delegation from EPA may administer NESHAP programs directly, but must apply standards at least as stringent as the federal requirements.

## How It Affects You

**If you operate an industrial facility**: Your first task is determining which Part 63 subparts apply to your operations. Applicability depends on whether your facility qualifies as a major or area source, what processes you operate, and which source categories EPA has listed. EPA's website provides applicability tools, but the threshold question — major or area source — depends on your actual potential to emit each HAP, which requires a careful analysis of your equipment and operational limits. Operating below the major source threshold (often done through a "synthetic minor" permit limiting your allowable emissions) keeps you in the less stringent area source tier.

**If you are in a regulated industry category**: Once your applicable subpart is identified, the compliance path is clear — you must meet the emission limits or work practice standards in your subpart. Many MACT standards specify control technology (continuous emission monitors, thermal oxidizers, carbon adsorbers, enclosures) that you must install and maintain. The monitoring and recordkeeping obligations are extensive: Part 63 requires documenting equipment performance, maintaining deviation reports, and submitting semi-annual compliance reports. Continuous Emission Monitoring Systems (CEMS) are required for many major source categories.

**If you are near a facility regulated under Part 63**: MACT standards reduce HAP emissions from industrial sources by requiring the best available technology — but the "residual risk" that remains after MACT controls may still present health risks in communities adjacent to facilities. EPA's Residual Risk and Technology Review process is intended to address this, but many reviews have been delayed. EPA's AirToxScreen tool provides community-level cancer risk estimates from air toxics, allowing residents to understand the cumulative HAP exposure in their area.

**If you operate a small or area source** (dry cleaner, auto body shop, chromium plater, commercial sterilizer): EPA has promulgated area source MACT and GACT standards for many categories affecting small businesses. Work practice standards — how you manage chemicals, store solvents, conduct equipment inspections — rather than continuous monitoring often define compliance for area sources. Check whether your industry is a listed source category and what the applicable standard requires.

## Statutory Authority

This rule implements:
- **42 U.S.C. § 7412** (Clean Air Act § 112) — Establishes the 187-HAP list; directs EPA to list all major source categories emitting HAPs; requires promulgation of MACT standards for listed categories; requires Risk and Technology Review no less than every 8 years; authorizes area source GACT standards; provides for state delegation of NESHAP implementation

## Recent Developments

- **Trump deregulatory rollbacks (2025-2026)**: EPA rescinded or proposed to rescind MACT standards for integrated iron and steel manufacturing, proposed to reconsider the 2024 ethylene oxide sterilization NESHAP that required significant emission reductions at commercial hospital sterilizers, and extended compliance deadlines for oil and gas sector NESHAPs. These rollbacks represent a significant departure from the Obama and Biden-era approach of tightening MACT floors through RTR reviews.
- **RTR backlog**: EPA maintains a large backlog of required Risk and Technology Reviews. Courts have held that EPA must complete RTRs for overdue source categories; litigation over RTR delays has produced court-ordered schedules for several source categories.
- **Part 61 legacy standards**: The earlier 40 CFR Part 61 contains NESHAP promulgated before 1990, covering categories such as asbestos (Subpart A), benzene (Subpart F), and vinyl chloride (Subpart F). These pre-1990 standards are health-based (not MACT-based) and apply to specific source types independently of the Part 63 framework.
- **Electronic reporting**: EPA has transitioned Part 63 compliance reports to electronic submission through the Compliance and Emissions Data Reporting Interface (CEDRI) in EPA's WebFIRE system; most Part 63 subparts now require electronic submission of compliance certifications and deviation reports.

In December 2025, EPA rescinded a July 8, 2025 interim final rule (IFR) that had extended compliance deadlines for the Coke Ovens NESHAP (covering Pushing, Quenching, and Battery Stacks and Coke Oven Batteries source categories), which had been revised by a 2024 final rule following a Residual Risk and Technology Review. EPA concluded, after public comment and a public hearing, that available information did not support a finding that regulated parties would face significant immediate compliance challenges meeting the MACT standards and leak limits for doors, lids, and offtakes without the deadline extensions. The rescission reinstates the original compliance deadlines established in the July 5, 2024 final rule for the coke ovens source category. [(Federal Register, 2025-22034)](https://www.federalregister.gov/documents/full_text/html/2025/12/05/2025-22034.html)

In late 2025, EPA finalized a rule extending multiple compliance deadlines for the Integrated Iron and Steel (II&S) Manufacturing NESHAP, originally revised by a 2024 final rule following a Technology Review. EPA extended deadlines to April 3, 2027 for several standards established in the 2024 rule, including opacity limits for planned bleeder valve openings, work practice standards for bell leaks, opacity monitoring frequency for blast furnaces, work practice standards and operational limits for unplanned bleeder valve openings, work practices for beaching, opacity limits for slag processing activities, and fenceline monitoring requirements. EPA had previously conducted mandatory reconsideration under CAA § 307(d)(7)(B) of four specific standards and administratively stayed the April 3, 2025 compliance deadlines until July 1, 2025 pending that review. EPA reaffirmed that the targeted deadline extensions were necessary and appropriate while maintaining that the 2020 residual risk review had found existing II&S NESHAP provided an ample margin of safety to protect public health. [(Federal Register, 2025-21787)](https://www.federalregister.gov/d/2025-21787)

In November 2025, the Trump EPA finalized a rule locking in an 18-month delay of Biden-era methane emission standards for the oil and gas sector, converting an earlier interim final rule into a permanent compliance deadline extension. The final rule also extends timelines for states to develop plans for cutting methane emissions from existing oil and gas operations. EPA Administrator Lee Zeldin framed the action as necessary to protect U.S. energy production, while environmental groups argued the delay would expose millions of Americans to additional pollution. The Trump administration has separately placed the underlying methane rule on a broader list of regulations under reconsideration. [(The Hill, 2025)](https://thehill.com/policy/energy-environment/5624445-epa-methane-oil-gas-biden-trump/)

EPA proposed on June 17, 2025 to repeal most amendments made by a 2024 final rule updating the NESHAP for coal- and oil-fired electric utility steam generating units (EGUs), as part of the Trump administration's broader deregulatory review of Biden-era MACT standards. A subsequent Federal Register action on this matter was published on February 24, 2026. The coal- and oil-fired EGU NESHAP governs hazardous air pollutant emissions — including mercury, acid gases, and particulate matter — from power plants, making it one of the most significant source-category rules under Part 63. [Federal Register, 2026-03638](https://www.federalregister.gov/documents/2026/02/24/2026-03638/national-emission-standards-for-hazardous-air-pollutants-coal--and-oil-fired-electric-utility-steam)

On February 18, 2026, OIRA completed its review of the proposed repeal of amendments to the NESHAP for coal- and oil-fired electric utility steam generating units (RIN 2060-AW68), issuing a "Consistent with Change" decision and classifying the rule as "Major." OIRA received the rule from EPA on December 23, 2025, indicating the repeal advanced through interagency review following EPA's June 2025 proposal. The "Consistent with Change" decision signals that OIRA required modifications to the rule before clearing it for publication. This OIRA clearance is a procedural milestone confirming the repeal is moving toward finalization, though it does not itself constitute a final rule. [(OIRA Completed Review, 2026-02-18)](https://www.reginfo.gov/public/Forward?SearchTarget=RegReview&textfield=2060-AW68)

On March 11, 2026, OIRA completed its review of EPA's proposed reconsideration of the NESHAP for ethylene oxide emissions from sterilization facilities (RIN 2060-AW79), issuing a "Consistent with Change" decision and classifying the rule as "Major." OIRA received the proposed rule from EPA on March 4, 2026, indicating the reconsideration advanced rapidly through interagency review. The "Consistent with Change" decision signals that OIRA required modifications before clearing the proposal for publication, but does not itself constitute a final or proposed rule. This procedural milestone confirms that EPA's reconsideration of the 2024 ethylene oxide sterilization NESHAP — which had required significant emission reductions at commercial hospital sterilizer facilities — is moving toward formal proposal. [(OIRA Completed Review, 2026-03-11)](https://www.reginfo.gov/public/Forward?SearchTarget=RegReview&textfield=2060-AW79)

## Pending Action

The Trump EPA's deregulatory agenda has targeted multiple Part 63 MACT standards for reconsideration, including the 2024 ethylene oxide sterilization rule (which required significant emission reductions at commercial hospital sterilizer facilities), integrated iron and steel MACT standards, and several oil and gas sector NESHAPs. Litigation from both industry (challenging tighter MACT floors from Biden-era RTR reviews) and environmental groups (challenging delayed RTR schedules and deregulatory rollbacks) is proceeding in the D.C. Circuit. Watch for EPA action on court-ordered RTR completion schedules for source categories where EPA has missed statutory deadlines.

## Sources
- [EPA NESHAP — National Emission Standards for Hazardous Air Pollutants on PolicyRisk](https://policyrisk.com/wiki/epa-neshap-hazardous-air-pollutants)

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Source: PRIA, https://policyrisk.com/wiki/epa-neshap-hazardous-air-pollutants (as of 2026-11-01).