Abstract: Employee #1 was assigned to purge a pipe that was to be welded with argon gas. Argon was coming through the pipe and a spray nozzle, and Employee #1 entered the steam generator compartment to tape off the spray nozzle at the bottom of the compartment. A coworker heard him tear off some tape, after which he became unresponsive. Employee #1 had died after suffering a heart attack. The only opening to the compartment was a 16 inch diameter manway; all other openings were sealed. The only source of air was a hose hooked to a compressor. The inert argon gas may or may not have contributed to Employee #1's death.