Investigators with the Los Angeles County District Attorney’s Office converged this week on a Carson company that sterilizes medical equipment amid a criminal probe alleging it failed to protect employees from prolonged exposure to the cancer-causing chemical ethylene oxide.

More than 20 members of the DA’s Bureau of Investigation, in coordination with the Los Angeles County Fire Department and the California Department of Toxic Substances Control, executed a search warrant at Parter Medical Products Inc., which does business as Parter Sterilization Services.

“No employer should risk the safety of their workers by exposing them to toxic substances and then turn a blind eye,” District Attorney Nathan Hochman said in a prepared statement. “Ethylene oxide can silently poison people over time, causing cancer, damaging organs, and cutting lives short. We remain steadfast in our commitment to follow the evidence wherever it leads and will not hesitate to hold accountable any individual or organization that puts profits over public health.”

Officials with Parter could not be reached for comment.

Chronic exposure to ethylene oxide is associated with cancer, reproductive effects and neurotoxicity, resulting in damage to the brain or peripheral nervous system. The chemical’s odor is undetectable to humans until its concentration exceeds hazardous levels.

More than half of the medical equipment in the United States — approximately 20 billion devices — is sterilized with ethylene oxide because of the chemical’s ability to penetrate plastics and other materials to destroy bacteria without melting or weakening the device.

Although the company was aware that some employees were exposed to elevated levels of the chemical, Parter is accused of failing to take adequate steps to mitigate the danger.

In March 2023, the California Division of Occupational Safety and Health issued 18 citations and fines totaling $838,000 to Parter for failing to protect employees from overexposure to ethylene oxide. A half-dozen of the citations were for willful and intentional violations.

“Our inspection showed this was not an isolated incident of chemical overexposure to workers,” Cal/OSHA Chief Jeff Killip said at the time the citations were issued. “The employer failed to take action to protect employees even after it knew that some of them were exposed to dangerous levels of ethylene oxide.”

The toxicity of ethylene oxide has been debated nationally for decades, but critics say federal regulators have moved at a glacial pace to restrict its use. A draft assessment from the U.S. Environmental Protection Agency in 2006 determined the chemical was significantly more carcinogenic than previously believed, according to ProPublica. Yet the final assessment wasn’t published until a decade later.

Cal/OSHA’s Process Safety Management Unit, which is responsible for inspecting refineries and chemical plants that handle large quantities of toxic and flammable materials, inspected the Parter facility in August 2022 following an investigation by the South Coast Air Quality Management District.

Parter, situated near Avalon Boulevard and the 91 Freeway just north of Cal State Dominguez Hills, is within 700 feet of a residential neighborhood and 2,000 feet away from a school. However, information was not immediately available regarding how far the emissions might have traveled.

Although Parter shut down its facility in August 2022 for several months while it made modifications to reduce outdoor ethylene oxide emissions, it did not resolve employee exposure issues indoors, Cal/OSHA said.

When Cal/OSHA resumed its inspection in December 2022, it found that one employee was overexposed to ethylene oxide his entire shift.

Although Cal/OSHA regulations state that the permissible exposure limit for eight hours is no more than 1 part per million, the employee’s exposure averaged 5 ppm during the shift and averaged 9 ppm during a 3 1/2-hour period. Additionally, tests show that Parter employees were exposed to ethylene oxide above the permissible limit from 2019 until 2022, Cal/OSHA said.

Parter also failed to implement effective safety and respiratory protection plans and didn’t monitor employee exposure or notify workers of exposure over the permissible limit for ethylene oxide, according to Cal/OSHA.