WEST VALLEY CITY, Utah (ABC4) — The two employees who were found unconscious in West Valley in January this year reportedly died after oxygen displacement from argon gas, according to police reports.

In January, two men, identified as Ken Tran, 48, and Jonathan Steinke, 24, were found unconscious at the Northrop Grumman facility. West Valley Fire Department first responders attempted life-saving measures and both Tran and Steinke were taken to the hospital where they were pronounced dead.

According to police documents obtained by ABC4 through a GRAMA request, an autopsy ruled both deaths as “an accident.”

The doctor wrote in his opinion, “In consideration of the known circumstances surrounding this death, the available medical history, and the examination of the remains, the cause of death is suffocation (oxygen displacement by argon gas).”

According to the Occupational Safety and Health Administration, the normal oxygen concentration in breathing air is 21%. Anything below 19.5% is considered hazardous. Argon gas, which is used in some industrial processes, can displace oxygen in the air. OSHA said since argon is denser than air, it can become deadly in confined spaces.

OSHA issued 13 citations as a result of Tran’s and Steinke’s deaths, fining Northrop Grumman over $172,000. Three of the 13 citations found Northrop Grumman at fault for “respiratory protections,” while the other 10 cited the company for “permit-required confined spaces” violations.

OSHA records show Northrop Grumman contested the fines in August and the citations remain contested as of Monday. ABC4 reached out to Northrop Grumman regarding the citations but the company did not immediately respond to the request for comment.

The facility in West Valley is reportedly a manufacturing plant for guided missiles and space vehicle propulsion units and parts, according to OSHA.