Final rule adds EtO emission limits to polyether polyol production
The Environmental Protection Agency (EPA) finalized major changes to the National Emission Standards for Hazardous Air Pollutants (NESHAP) for Polyether Polyols (PEPO) Production (PEPO NESHAP).
Who’s impacted?
The final rule applies to facilities that produce polyether polyols and are subject to the regulations at 40 CFR 63 Subpart PPP.
What are the changes?
EPA’s final rule establishes ethylene oxide (EtO) standards, updates maximum achievable control technology (MACT) requirements, and revises other provisions for the PEPO NESHAP.
EtO standards
The final rule adds EtO emission standards for:
- Equipment leaks,
- Heat exchange systems,
- Process vents,
- Storage vessels, and
- Wastewater.
The standards set emission limits and add requirements for monitoring and leak repairs.
MACT standards
Further, the final rule:
- Requires heat exchange systems to use the more sensitive Modified El Paso Method (also known as the Air Stripping Method) for quarterly monitoring and a leak definition of 6.2 parts per million by volume of total strippable hydrocarbon concentration (as methane) in the stripping gas,
- Lowers the MACT control thresholds for batch process vents and storage vessels,
- Updates the requirements for internal floating roof storage vessels,
- Lowers the threshold for equipment leaks for valves in gas/vapor service or light liquid service, and
- Requires transfer operations with loading operations that exceed a certain threshold to use a vapor balance system or reduce emissions.
Other standards
EPA’s final rule also:
- Requires 5-year performance testing for process vent control devices;
- Revises flare monitoring and operational requirements to ensure they meet the MACT standards at all times when controlling hazardous air pollutant (HAP) emissions;
- Adds new monitoring requirements for pressure vessels to verify that no detectable emissions exist;
- Clarifies that any bypass of a pollution control device for closed vent systems is a violation;
- Aligns the requirements for surge control vessels and bottoms receivers with the process vent standards;
- Adds butylene oxide to the definition of “epoxide” and the HAPs list;
- Expands “affected source” to cover specific post-reaction processes; and
- Finalizes work practice standards for maintenance vents and equipment openings, storage vessel degassing, and routine storage vessel maintenance.
However, EPA didn’t finalize the 2024 proposed rule’s addition of a fenceline monitoring program for EtO or its changes to the continuous process vent standard.
What’s the compliance timeline?
Facilities subject to the PEPO NESHAP must comply with the changes by March 18, 2029, or upon startup, whichever is later.
Key to remember: EPA’s final rule for polyether polyol emissions makes significant changes, such as establishing EtO limits and revising MACT standards.


























































