Ethylene Oxide Provisions Deferred from Final Rule
On March 28, 2026, EPA Administrator Lee Zeldin signed the final amendments to the National Emission Standards for Hazardous Air Pollutants for Chemical Manufacturing Area Sources (CMAS NESHAP, 40 CFR Part 63, Subpart VVVVVV). The final rule completes EPA’s technology review obligations under Clean Air Act (CAA) Section 112(d)(6) and satisfies a consent decree originally requiring action by September 2025, later extended to March 31, 2026.
Trinity Consultants previously summarized the proposed amendments in a January 2025 article on EPA’s proposed CMAS technology review. This article covers what’s changed and what hasn’t, between the proposed and final rule.
Ethylene Oxide Provisions Deferred
The most closely watched part of the proposed rule was the creation of a new “Chemical Manufacturing with Ethylene Oxide (EtO)” area source category. This would have added approximately 29 new facilities and imposed stringent EtO-specific standards, including 99.9% process vent control, fenceline monitoring with public data reporting, and monthly EtO LDAR.
None of these provisions were finalized. Instead, EPA has deferred all EtO related provisions, stating that it needs more time to consider public comments and coordinate an area source EtO regulation with its ongoing major source EtO rulemakings. The agency also pointed out that EtO was not part of the original CMAS Urban Air Toxics listing, so the consent decree did not compel action on EtO. Facilities that had been preparing for new EtO requirements should continue to monitor the rulemaking docket for future action.
New Method 21 LDAR Program
The most operationally significant change for existing CMAS facilities is the introduction of an annual instrument monitoring program for equipment leaks. Under the current rule, facilities were only required to follow management practices with no instrument monitoring. The final rule now requires annual EPA Method 21 monitoring of pumps in light liquid service and valves and connectors in gas/vapor and light liquid service, with a 10,000 ppmv leak definition. Additional language surrounding first repair attempt, full repair and delay-of-repair provisions were also included in the rule. Equipment in vacuum service is excluded from these LDAR requirements.
The final rule also incorporates several HON Subpart H LDAR requirements for compressors, sampling connections, open-ended valves and lines, heavy liquid service equipment, closed vent systems, and agitators. These updates further demonstrate EPA’s recent focus on fugitive emissions.
EPA evaluated but rejected more advanced monitoring alternatives. Optical gas imaging (OGI) and leak detection sensor networks were of the rejected alternatives due to questions of effectiveness and available data for facilities subject to the rule.
Pressure Vessel PRD Standards, and Bypasses
The final rule introduces first-time standards for pressure vessels and pressure relief devices (PRDs). Pressure vessels must meet a no-detectable-emissions (NDE) standard of less than 500 ppmv, with initial and annual monitoring using Method 21. Organic HAP must be routed through a closed vent system to an air pollution control device (APCD).
One change from the proposal worth highlighting: EPA revised the pressure vessel provisions to clarify that the unsafe-to-monitor (UTM) and difficult-to-monitor (DTM) exemptions already available in the general LDAR program also apply to pressure vessel components. This revision came in response to public comments.
The final rule also establishes closed vent system bypass requirements. Any use of a bypass line to divert emissions to atmosphere or to a non-compliant control device is a deviation.
Heat Exchange System Monitoring & Process Vent Changes
For heat exchange systems with a cooling water flow rate of 8,000 gallons per minute (gpm) or greater, the final rule requires the Modified El Paso Method. Systems below 8,000 gpm must comply with a regular inspection plan. An alternative compliance path is available for systems where at least 99% of the organics are water soluble and have a Henry’s Law Constant a specified value.
Additionally, EPA is removing the 50 ppmv threshold for metal HAP process vents. This threshold was added in 2012, and its removal means all metal HAP process vents will be included in the threshold and control requirements three years after the April 1st, 2026 publication date.
The rule now requires performance testing every five years for non-flare control devices and certain exemptions for certain high-concentration wastewater streams were removed.
Affirmative Defense & Compliance Timeline
The final rule removes the affirmative defense provisions consistent with the D.C. Circuit’s decision in NRDC v. EPA, 749 F.3d 1055 (2014). Facilities can no longer assert an affirmative defense to civil penalties for emissions exceeding standards during malfunctions.
Existing sources and sources that were new under the previous CMAS NESHAP (construction or reconstruction commenced after October 6, 2008 and on or before January 22, 2025) have 3 years from the date of Federal Register publication to comply with the new LDAR, heat exchange, pressure vessel, and PRD requirements. New sources commencing construction after January 22, 2025 must comply by April 1, 2026 or upon startup, whichever is later.
