The Clock is Ticking to Get Ethylene Oxide CEMS Installed & Certified

The U.S. Environmental Protection Agency (U.S. EPA) 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). The final rule was published in the Federal Register on April 5, 2024. ALL4 summarized the significant changes to Subpart O here. This article provides details on the rigorous continuous emissions monitoring systems (CEMS) requirements within the final rule.

The Subpart O revisions require facilities to demonstrate continuous compliance with the applicable ethylene oxide (EtO) emissions reduction standards using an EtO CEMS, except for those commercial sterilization facilities that use less than 100 pounds per year (lb/yr) of EtO. To demonstrate compliance with the emissions reduction standards, facilities must install and operate an EtO CEMS on each inlet to, and outlet of the control system, in accordance with the requirements of 40 CFR Part 63, Subpart O, Appendix A (Appendix A). Appendix A requires that EtO CEMS be installed, operated, and certified in accordance with 40 CFR Part 60, Appendix B, Performance Specification 19 (PS-19) and quality assured thereafter in accordance with 40 CFR Part 60, Appendix F, Procedure 7 (P7). Some of the key requirements within PS-19 and P7 include:

PS-19 Installation and Initial Certification:

• Regarding installation, the EtO CEMS probe must be located within 0.5 equivalent diameters of the flow sensor used to express EtO emissions in units of mass (i.e., lb/hr).
• The following performance testing must be completed at the time of installation or soon after:
  • Interference test (PS-19,11.1) – to demonstrate the EtO CEMS measures EtO accurately in the presence of common interferences from commercial sterilizers. This must be performed in a controlled environment (e.g., laboratory or manufacturer’s facility).
  • Level of detection determination (PS-19,11.2) – to determine the minimum amount of EtO that can be detected above background. Subpart O requires that for outlet streams, instrumentation must have a method detection limit an order of magnitude below concentration equivalent of the emissions limit. This determination must also be performed in a controlled environment.
  • Response time test (PS-19,11.3) – to quantify the time it takes for the measurement system, while operating normally at its target sample flow rate, dilution ratio, or data collection rate to respond to a known step change in gas concentration.
  • Measurement error (ME) test (PS-19,11.4) – to quantify the difference between the concentration measured by the entire EtO CEMS and the known concentration of a reference gas standard. The ME is performed at the same time as the calibration drift test when the system is being placed in service.
  • Seven-day calibration drift (CD) test (PS-19,11.5) – to determine the difference between the EtO CEMS output response and an upscale reference gas or a zero-level gas daily, over a 7-day period during which no unscheduled adjustments, maintenance or repairs took place.
  • Relative Accuracy Test (PS-19,11.6) – to determine the difference between the gas concentration or the emissions rate measured by the EtO CEMS and the measurements made using U.S. EPA Reference Methods. This activity will most likely require a third-party stack testing firm.

• Stack gas flow rate monitoring systems required to express concentrations as mass rate (i.e., lb/hr) must be certified in accordance with 40 CFR Part 75.

P7 Ongoing Quality Assurance (QA):

Once the installation and certification under PS-7 is complete, you must develop and complete systems and activities for the ongoing QA of the EtO CEMS. These include:

• Develop and implement a Quality Control (QC) program including written procedures which describe in detail, complete, step-by-step procedures for each of the following:
  • Daily CD checks
  • Routine and preventative maintenance of EtO CEMS
  • Accuracy audit procedures for:
    • Quarterly relative accuracy audit (RAA), cylinder gas audit (CGA), or dynamic spiking audit (DSA)
    • Annual relative accuracy test audit (RATA)
  • Program of corrective action for malfunctioning CEMS

• Anytime the measured concentration of EtO exceeds 200% of span for two consecutive one-hour averages, conduct an “above span” response check, as follows:
  • Within a period of 24 hours (before or after) the “above span” period, introduce a higher “above span” reference gas standard to the EtO CEMS, at a target concentration level between 75% and 125% of the highest hourly concentration measured during the period of measurements above span, or 5 part per million by volume (ppmv), whichever is greater. Record and report results of the “above span” check as done for a daily CD check.
  • The “above span” concentration may not exceed the analyzer full scale range.
  • The “above span” response check passes if the results are within 20% of the certified reference gas.
  • If the “above span” response check fails, the one-hour average stack gas values measured during the 24-hour period preceding or following the check must be normalized using Eq. 7-1 in P7.

In addition to what is required by PS-19 and P7, Appendix A of Subpart OOOO has additional requirements that commercial sterilization facilities must be aware of:

• An EtO CEMS is out-of-control (OOC) and data from the system cannot be reported when any of the acceptance criteria for a QA test are not met, OR when a required QA test is not performed on schedule or within an allotted grace period.
• To minimize data loss, data is considered “conditionally valid” following EtO CEMS recertification and diagnostic testing in accordance with provisions of 40 CFR §75.20(b)(3)(ii) through (b)(3)(ix).
• Any process operating hour for which quality-assured EtO concentration data are not obtained is counted as an hour of monitoring system downtime – data substitution for missing data must not be utilized.
• Within the written QA procedures required by P7, the facility must explain how each component of the EtO CEMS will be adjusted to provide correct responses to calibration gases after routine maintenance, repairs, or corrective actions.
• An electronic and hardcopy monitoring plan (MP) must be maintained for the EtO CEMS and other monitoring systems needed to convert concentrations to units of the applicable emissions standard. The monitoring plan must contain the information specified in Sections 10.1.1.2.1 and 10.1.1.2.2 of Appendix A. The electronic monitoring plan must be submitted via the U.S. EPA Compliance and Emissions Data Reporting Interface (CEDRI).
• Use CEDRI to electronically submit quarterly reports and the results of ALL required certification, recertification, quality-assurance, and diagnostic tests of the EtO CEMS. This includes daily CD checks, seven-day CD tests for recertification, RATAs, ME tests, interference tests, LOD tests, quarterly RAA, CGA, and DSA. The information required to be submitted for each test is specified in Appendix A Section 11.4.1 through 11.4.9.

If you’ve made it this far, you can see that the newly promulgated EtO CEMS requirements are quite thorough and will require a great deal of resources to design, install, operate, and maintain. Commercial sterilization facilities constructed on or before April 13, 2023 must comply with the amended Subpart O within two to three years of its publication in the Federal Register on April 5, 2024, depending on facility size and major source status [see 40 CFR §63.360(j)(1) through (17) for source-specific compliance dates]. Considering that it could take several years to design, procure, install, certify, and develop workflows around EtO CEMS, your facility should be working on this now. If your facility needs assistance with anything related to these new EtO CEMS requirements, please contact me at mcarideo@all4inc.com.