Abstract: Employees #1 and #2, plant security guards, descended a stairway to the basement underneath a cold rolling mill to reset a carbon dioxide extinguishing system. The system had been triggered when a small fire at the mill had broken out six hours earlier. These two employees knew there was a known concentration of carbon dioxide in the basement but left their self contained breathing apparatus units in their vehicle and took one self rescuer with them. They were discovered 30 minutes later at the bottom of the stairway and all efforts to revive them failed. Employee #1 and #2 were pronounced dead at Jackson General Hospital.