Abstract: At 7:15 a.m. on June 18, 2021, an employee was working as a maintenance technician for a firm that provided maintenance and repair services for land-based and airborne gas turbine engines for civilian and military clients. He and other workers in the maintenance department were replacing metal bars at the bottom of a pit furnace, the "H2 furnace," located in an outdoor area of the facility. Using a stepladder, the employee entered the pit furnace to remove the old metal bars. He was working alone, as his partner/supervisor was working in the production area. A worker from the metal preparation department went down to the furnace area to see if there were any completed parts. He noticed the ladder sticking out of the furnace. He went over and saw the employee at the bottom of the furnace, unresponsive. He saw that the switch on the furnace control panel for argon gas was in the ON position. He shut it off and went to look for help. In the shop next door, he found the maintenance supervisor, who immediately ran over to the furnace and began rescue procedures to remove the employee from the furnace with an overhead crane. The employee had been in the space for ten to fifteen minutes. The employee was retrieved and transported to the hospital. He died from asphyxiation as a result of exposure to the argon. The San Diego fire department reported the serious injury accident to DOSH San Diego at approximately 9:00 a.m. The firm reported the fatality at approximately 10:00 a.m. Both reports were made within the 8-hour requirement. Investigators from DOSH San Diego arrived at the site at approximately 11:00 a.m. The H2 furnace was identified as a permit required confined space. Maintenance department employees did not obtain a confined space permit and did not follow lockout/tagout procedures for the argon gas system prior to entering the furnace. The employer was cited for a Serious Accident-Related violation of 8 CCR 5157(d) for unauthorized entry into a confined space.