Sterigenics Emissions Investigation in Ontario

South Coast AQMD is conducting special air monitoring in the City of Ontario to assess Ethylene Oxide emissions

Recent Activity

On May 27, 2024, the Sterigenics facility in Ontario voluntarily shut down its EtO operations to conduct routine maintenance and to upgrade existing air pollution control equipment.

Amended Early Action Reduction Plan:


South Coast AQMD has an ongoing investigation into emissions of EtO from facilities within our jurisdiction. For more information on the overall initiative please visit:

Sterigenics conducts sterilization of medical equipment using a gas called Ethylene Oxide (EtO) and operates a facility in Ontario in an industrial area. The nearest residential area is about 1.4 miles away and the nearest school is about 1.2 miles.

Based on sampling around the facility, elevated levels of EtO have been discovered, and South Coast AQMD is taking immediate actions to identify sources and reduce emissions as quickly as possible including:

  • Air monitoring efforts at the facility

  • Proposition 65 Notice

  • A complete investigation into the facilities’ equipment and compliance with South Coast AQMD rules, regulations and permit requirements.

  • Evaluation of immediate actions to be taken by the facilities to reduce leaks or fugitive emissions, including leak and source testing.

Ongoing Investigation

South Coast AQMD has conducted numerous on-site inspections and has responded to breakdowns reported by the facility.  On June 30, 2022, Notices of Violation were issued to Sterigenics Ontario relating to equipment breakdowns. Following an investigation, inspectors determined that the facility failed to maintain equipment in good operating condition, did not report equipment breakdowns in a timely manner, submitted incomplete breakdown reports, failed to operate equipment as specified in the permit equipment description.

South Coast AQMD’s investigation is ongoing.

AB 2588 Air Toxic “Hot Spots” program

On September 29, 2022, the Sterigenics facility (687 Wanamaker Avenue, Ontario) was designated as a Potentially High Risk Level Facility, requiring a reduction of toxic emissions from operations as well reports on potential health risks. A facility is designated a Potentially High Risk Level Facility when emissions data show either a potential to exceed or that emissions have already exceeded cancer risk thresholds (greater than 100 in a million). As a Potentially High Risk Level Facility, Sterigenics was required to develop an Early Action Reduction Plan that includes measures that can be taken immediately to reduce health risks. In addition, the facility was required to submit an air toxics emissions inventory report (ATIR), conduct a Health Risk Assessment (HRA), and submit a Risk Reduction Plan (RRP). As of early March 2023, these documents have all been submitted by the facility and are under various stages of review and approval. 

South Coast AQMD staff identified deficiencies and rejected the ATIR on March 29, 2023. Sterigenics did not submit a revised ATIR, therefore South Coast AQMD modified the ATIR to fix the deficiencies and approved it on October 5, 2023. Staff also identified deficiencies with the HRA and rejected it on October 31, 2023. A revised HRA was received on January 2, 2024, and is currently under review.

Amended Early Action Reduction Plan:


The Amended Early Action Reduction Plan set a temporary threshold for EtO emissions from the facility of 10 parts per billion (ppb) over a 24-hour period (see below). These temporary thresholds ensures that the facility does not reverse any emission reductions that have been achieved recently while more permanent engineering controls are put into place. If air monitoring results near the facility show an exceedance at the designated threshold or higher, the facility must initiate curtailment of its operations. Repeated exceedances of the threshold within a rolling 15-day period may result in a temporary shutdown of the facility.

Early Action Reduction Plan Thresholds and Actions:

EtO Level ≥ 10 ppb but < 16 ppb


 EtO Level ≥ 16 ppb


First Sample

20% Curtailment of Operations (maximum 2,000 lbs of EtO usage per day)

First Sample

40% Curtailment of Operations (maximum 1,500 lbs of EtO usage per day)

Second Sample

40% Curtailment of Operations (maximum 1,500 lbs of EtO usage per day)

Second Sample

80% Curtailment of Operation (maximum 500 lbs of EtO usage per day)

Third Sample

60% Curtailment of Operations (maximum 1,000 lbs of EtO usage per day)

Third Sample

100% Curtailment of Operation

Fourth Sample

80% Curtailment of Operations (maximum 500 lbs of EtO usage per day)



Fifth Sample

100% Curtailment of Operations



Curtailment begins after South Coast AQMD is notified of an exceedance of the threshold. Laboratory analysis can take many days to complete. Sterigenics must provide results within 10 days of collecting the sample. Sterigenics must also provide sample data within three hours of receiving results from their laboratory analysis when levels are above curtailment thresholds.

Sterigenics may resume normal operations once monitored EtO levels are below the thresholds set under the plan.

Sterigenics Ontario Curtailment

EtO Sample Level That Required Curtailment

Curtailment Sample Date

Monitor Location


Curtailment Start Date**

EtO Sample to End Curtailment

Date of Sample

Curtailment End Date

33.6 ppb*

24.3 ppb

39.8 ppb




Site #1B

100% Curtailment


1.7 ppb




13 ppbv


 Site #A2

 20% Curtailment


4.6 ppbv



 11.0 ppbv

 5/24/24 - 5/25/24

Site #A5 

20% Curtailment 


.37 ppbb 

5/27/24- 5/28/24


*The results from these three samples were validated by the laboratory on the same day. 
** Curtailment start and end date is based on when analysis has been made available from the laboratory.

Air Monitoring Efforts

From April 2023 through April 2024, South Coast AQMD conducted local air sampling to determine levels of EtO near the facility and in the surrounding area. Early in this investigation mobile monitoring was conducted to collect data on volatile organic compounds (VOCs) around the facility and the surrounding area. VOC signals associated with EtO were elevated near the facility; concentrations decreased to near background levels approximately 1,000 ft. downwind. Individual grab samples (an air sample collected at one location at one point in time) were taken to confirm ethylene oxide levels (Figure 1), and a monitor was placed nearby to collect 24-hour samples beginning June 16, 2022 (Figures 2 and 3).  Sampling conducted adjacent to the facility to evaluate levels of EtO concluded April 18, 2024.

South Coast AQMD worked with Sterigenics’ Ontario facility operator to identify potential sources of EtO from their operations and the facility implemented actions to reduce EtO emissions. As part of the facilities Early Action Reduction Plan, the facility installed air monitors around the facility adjacent to agency monitors and data collected was compared to ensure accuracy. The facility monitors, along with the strengthened requirements on the facility under the recently amended Rule 1405, led to South Coast AQMD concluding its sampling activities. Sterigenics is responsible for continuing to collect and analyze 24-hour samples near their Ontario facility and provide that data to South Coast AQMD. The agency will occasionally collect 24-hour samples at one or more of these locations for quality assurance and quality control purposes.

The agency will continue to work with Sterigenics Ontario as needed to identify the source(s) of EtO and determine measures to reduce EtO emissions.


Figure 1: Map of grab samples. Concentrations are in parts per billion volume (ppbv).

Ontario Sampling Locations
Figure 2:  Map of 24-hour sampling locations

This plot is interactive, individual data points can be viewed with a mouse hover. The view can be reset by selecting the circular arrows to the right of the plot.  


Figure 3: Plot of 24-hour time integrated sample concentrations 

South Coast AQMD air monitoring data can be found here (PDF).

Facility Air Monitoring

As part of the facility’s Early Action Reduction Plan the facility has installed three air monitors around the facility (see figure 4) and provides that data to South Coast AQMD.

Data from the air monitors operated by the facility can be found here. (PDF)

Ramboll Sampling Sites
Ramboll Sampling Sites - Ontario
Figure 4. Map of Early Action Reduction Plan

Health Impacts

South Coast AQMD is required to use methodologies developed by OEHHA in its health risk programs. Based on preliminary monitoring data, the primary concern is off-site worker exposure. Air monitoring efforts for a more extensive evaluation are continuing in the community. Health impacts will be assessed when more data measuring the level of exposure to the community is available.

A Proposition 65 notice was issued on July 1, 2022 notifying the San Bernardino County Board of Supervisors and the Health Officer for the San Bernardino Department of Public Health of the illegal discharge likely to impact public health or safety.


The Ontario facility currently has active permits for nine EtO sterilization chambers, two EtO aeration rooms, and air pollution control equipment which includes one wet scrubber and two catalytic oxidizers.  Products are loaded into sealed sterilization chambers where EtO is injected. Chambers are required to have strict requirements to capture the EtO gas and prevent 99.9% of emissions.  When the sterilization cycle is complete the chamber is opened, and the chamber is vented through additional vents to control equipment called catalytic oxidizers. The catalytic oxidizer is required to further reduce EtO emissions by 95%. The products are then moved to aeration rooms which are also vented to the catalytic oxidizers.  

On October 31, 2023, the facility submitted three permit applications to modify their existing control equipment to include a PTE with negative air.  Once installed, the PTE will be required to control at least 95% of EtO emissions from operations within the facility.  Additionally, it will require the facility to maintain negative air pressure to prevent fugitive EtO emissions from escaping the building. The additional layer of controls will result in higher control efficiencies, which will be verified through Source Tests.

The facilities’ permits can be accessed through South Coast AQMD’s Facility Information Detail (F.I.N.D.) using the facility address or ID number (126060).


EtO sterilization and aeration facilities are subject to local, state, and federal regulations. South Coast AQMD Rule 1405 (PDF) - Control of Ethylene Oxide Emissions from Sterilization and Related Operations.
During South Coast AQMD's monitoring efforts at several commercial EtO sterilization facilities, the agency became aware of fugitive emissions from sources that were not previously known. South Coast AQMD’s investigation has identified that existing pollution controls will need to be upgraded and measures will be needed to reduce fugitive emissions. Rule 1405 was amended on December 1, 2023 to strengthen requirements for sterilization and storage facilities. The updated rule applies to 15 sterilization facilities which are required to upgrade existing or add new pollution controls and implement measures to monitor and minimize stack and fugitive emissions. Additionally, storage facilities that receive products sterilized by EtO may also be required to monitor emissions at the fenceline. More details related to Rule 1405 requirements can be found on the Rule 1405 webpage

More information


Newsletter Sign Up
Periodic newsletter updates via Email on a variety of air quality-related topics

South Coast Air Quality Management District

21865 Copley Dr, Diamond Bar, CA 91765


© 2024 South Coast Air Quality Management District