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

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, 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 the equipment breakdowns in a timely manner, and submitted incomplete breakdown reports. 

South Coast AQMD’s investigation is ongoing.

AB 2588 Air Toxic “Hot Spots” program

On September 29, 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, conduct a Health Risk Assessment (HRA), and submit a Risk Reduction Plan (RRP).

Early Action Reduction Plan:


The approved Early Action Reduction Plan set a temporary threshold for EtO emissions from the facility of 8 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 30-day period will result in a temporary shutdown of the facility.

Early Action Reduction Plan Thresholds and Actions:

EtO Level ≥ 8 ppb but <12 ppb


EtO Level ≥ 12 ppb


Second Sample

20% Curtailment of Operations

First Sample

20% Curtailment of Operations

Third Sample

50% Curtailment of Operations

Second Sample

50% Curtailment of Operation

Fourth Sample

100% Curtailment of Operations

Third Sample

100% Curtailment of Operation

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 14 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



*The results from these three samples were validated by the laboratory on the same day. 


Air Monitoring Efforts

South Coast AQMD is conducting local air sampling to determine levels of EtO near the facility and in the surrounding area. 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 from June 16 to June 28 (Figures 3 and 4).  The agency will continue to work with Sterigenics Ontario to identify the source(s) of EtO and 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 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 is permitted for multiple EtO sterilization chambers, aeration rooms and associated air pollution control equipment.  Products are loaded into sealed sterilization chambers where EtO is injected. The chamber is required to have equipment 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.  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 and Chlorofluorocarbon Emissions from Sterilization or Fumigation Processes reduces emissions of EtO from sterilization 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. We are working on amending Rule 1405 to strengthen requirements to address fugitive emissions, as well as provisions to further reduce EtO emissions from operations at these facilities. The rulemaking process, including Working Group meetings are ongoing and open to the public. Upcoming meeting dates can be found at the Proposed Amended Rule 1405 page. 

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


© 2023 South Coast Air Quality Management District