SAFTENG Comment:
A basement is NOT by definition a “confined space”. That does not mean that a basement cannot have a hazardous atmosphere. Argon is 1.38 times heavier than air and with NO ventilation designed to remove this gas from a basement, it will displace the Oxygen leading to this horrific event. So many failures in this event to learn from.
On January 30, 2023, at approximately 5:30 p.m., argon gas was released at a facility. Exposure to the argon gas fatally injured two employees, who asphyxiated.
The facility treated carbon fiber blocks. As part of the treatment, a specialized vessel (autoclave) containing carbon fiber blocks was pressurized with argon gas. On the day of the incident, two employees were working to locate argon leaks and troubleshoot the vessel’s pressure control system. During this work, the autoclave did not contain carbon fiber blocks. Throughout the workday, the vessel was pressurized with argon gas several times, but the task was not completed by the end of the employees’ shift.
The employees changed out of their work clothes and removed their personal oxygen monitors. However, before meeting with the oncoming shift workers, the two employees returned to the basement. The crew arriving for the next shift found their two coworkers unconscious in the basement’s stairway.
Emergency responders transported the two employees to the hospital, where they were declared deceased.
The company’s investigation found that argon had leaked through the seals of the pressurized vessel while the basement’s ventilation system was off, which allowed the basement (about 4,500 cubic feet) to begin to fill with argon and create an oxygen-deficient atmosphere. The company’s investigation did not determine why the two employees returned to the basement at the end of their shift, however.
After the incident, the company classified the basement as a confined space and installed an oxygen monitoring system. The company also implemented safeguards to prevent entry into the basement when the oxygen concentration is unsafe, the exhaust ventilation fan is off, or the vessel is pressurized.
Probable Cause
Based on the company’s investigation, the CSB determined that the probable cause of the incident was the release of argon gas from the autoclave into a confined area. The two workers were fatally injured when they entered this oxygen-deficient environment. The lack of effective engineering controls, such as forced air ventilation and continual oxygen monitoring, contributed to the severity of the incident.
Source: https://www.csb.gov/assets/1/6/incident_reports_volume_4_2026-02-18.pdf