Abstract: On February 3, 2004, Employees #1 and #2 were working inside a refinery's reactor vessel that was cleared previously by the site employer for a planned turnaround. Employee #1 and #2 were part of a specialist contractor, assigned to remove spent catalyst from the vessel's beds. Outdoor conditions were cold, between 55 and 65 degrees Fahrenheit, with mild humidity. Employee #1 and #2 were dressed in multiple clothing layers, including a Tyvek suit for winter conditions. The temperature inside the vessel was over 100 degrees Fahrenheit. The ventilation of the space was lacking. Employee #1 was unable to maneuver the cable ladder to rescue himself from the lengthy vertical ascent, once he became affected by the heat stress. Employee #2, who was not working so long in this confined space, sustained heat stress symptoms but was able to exit. Rescue time for Employee #1 was extended, and he showed no signs of life when he was removed from the processed vessel.