Finalized Amendments to NESHAP for Commercial Sterilization Facilities

The U.S. Environmental Protection Agency (U.S. EPA) has finalized revisions to 40 CFR Part 63, Subpart O – Ethylene Oxide Emissions Standards for Sterilization Facilities (Subpart O) following its residual risk and technology review (RTR). Amendments were initially proposed on April 13, 2023. The final rule was signed on March 1, 2024 and published in the Federal Register on April 5, 2024. This article provides a summary of the significant changes to Subpart O as described in the final rule.

Title V Permitting Obligation

Subpart O applies to both major and area sources of hazardous air pollutant (HAP) emissions. In the April 13, 2023 Federal Register notice, U.S. EPA proposed that facilities subject to Subpart O be required to obtain a Title V operating permit, regardless of whether they are a major source or area source of HAPs. U.S. EPA did not finalize this requirement, citing the lack of other Federal requirements that apply to commercial sterilization facilities and the robust requirements of finalized Subpart O. Area sources of HAP emissions remain exempt from the obligation to obtain a Title V operating permit under Subpart O.

Revision of Emissions Standards for Affected Sources

The amended rule contains new ethylene oxide (EtO) emissions reduction standards for sterilization chamber vents (SCVs) and aeration room vents (ARVs). Previously, facilities using less than 10 tons per year (tpy) of EtO were not required to control EtO emissions from ARVs, and facilities using less than 1 tpy of EtO were not required to control EtO emissions from SCVs. Under the amended rule, all sterilization facilities are subject to EtO emissions reduction standards for SCVs and ARVs. Emissions standards for SCVs and existing ARVs have changed slightly from the proposed rule, with standards being more stringent in the final rule for facilities using greater than 30 tpy of EtO.

Previously under Subpart O, facilities using greater than 10 tpy of EtO had the option of complying with a maximum outlet concentration standard of 1 part per million (ppm) of EtO from ARVs. This option has been removed in the final rule, and all emissions standards for ARVs are on an emissions reduction basis. An affected source with a low inlet EtO concentration at the inlet to its control device might struggle to meet an emissions reduction standard individually. However, the final rule contains provisions allowing for calculation of compliance with standards for combined streams or a site-wide emissions limitation.

The amended rule also adds emissions standards for chamber exhaust vents (CEVs). The proposed hourly mass emissions rate standard for CEVs at facilities using greater than 10 tpy of EtO was not incorporated into the final rule. All CEV emissions standards are on an emissions reduction basis.

U.S. EPA has defined Group 1 room air emissions and Group 2 room air emissions as two additional affected sources under Subpart O. Group 1 room air emissions consist of emissions from indoor EtO storage, EtO dispensing, vacuum pump operations, and pre-aeration handling of sterilized material. Group 2 room air emissions are defined as emissions from post-aeration handling of sterilized material. Both Group 1 and Group 2 room air emissions are subject to emissions standards under the final rule. The proposed hourly mass emissions rate standards for room air emissions were not incorporated into the final rule, in favor of emissions reduction standards or limits on sterilization chamber EtO concentration before the chamber can be opened.

Removal of Startup, Shutdown, and Malfunction Exemptions

U.S. EPA has removed exemptions from certain provisions of Subpart O during periods of startup, shutdown, and malfunction (SSM). The removal of the SSM exemptions is consistent with U.S. EPA’s broader stance that standards under Section 112 of the Clean Air Act are required to apply continuously. U.S. EPA has not established alternate standards for periods of SSM in the final rule.

Addition of Continuous Emissions Monitoring System Requirements

The final rule adds a requirement for facilities subject to Subpart O to demonstrate continuous compliance with applicable emissions reduction standards using an EtO continuous emissions monitoring system (CEMS). While U.S. EPA initially proposed that facilities could demonstrate compliance using either an annual compliance demonstration and operating limits or EtO CEMS, the EtO CEMS requirement under the final rule applies to all commercial sterilization facilities except those using less than 100 pounds per year (lb/yr) of EtO. For additional information on the requirements for EtO CEMS, please look out for an upcoming ALL4 article by Matt Carideo.

Alternative Compliance Demonstration Requirements for Very Small Commercial Sterilization Facilities

Facilities using less than 100 lb/yr of EtO may demonstrate compliance with applicable Subpart O emissions standards by establishing operating limits for control devices based on performance testing and subsequent parametric monitoring, in lieu of the use of EtO CEMS. The amended rule adds provisions for establishing operating limits for gas/solid reactors and demonstrating compliance via pressure drop monitoring and weekly media analysis. For acid-water scrubbers, scrubbing liquor pH monitoring has been added as a compliance option. Manufacturer-recommended temperatures are no longer acceptable for establishing operating limits for thermal or catalytic oxidizers – facilities must establish minimum oxidation temperatures through performance testing.

Addition of Permanent Total Enclosure Requirements

Under the final rule, U.S. EPA has established requirements for certain operations to be conducted within a permanent total enclosure (PTE). Group 1 room air emissions at all facilities and Group 2 room air emissions at facilities using greater than 4 tpy of EtO must operate in a PTE that meets the criteria of Method 204 of Appendix M to 40 CFR Part 51 and that is routed to a control device.

Next Steps for Facilities Subject to Subpart O

Commercial sterilization facilities constructed on or before April 13, 2023 must comply with the amended Subpart O within two to three years following publication in the Federal Register, depending on facility size and major source status. While this is longer than the 18-month compliance period that U.S. EPA initially proposed, it is important for facilities to consider these questions as soon as possible to allow for any changes needed to control and monitoring equipment:

• Are my control devices capable of achieving the applicable emissions reduction standards?
• Do I have EtO CEMS or parametric monitoring that meets the requirements of the revised rule?
• Do I have a PTE for my room air emissions that meets the requirements of Method 204?

If your facility needs assistance in answering these questions or proceeding with permitting that will likely be required for installing controls and the PTE, please contact me at jmartin@all4inc.com or Lindsey Kroos at lkroos@all4inc.com.