Abstract: On July 16, 1999, Employee #1, an operations trainee, was descending the inside surface of an earthen dike that surrounded some tanks in the sulfur plant area. This dike was north of tank #775 and had an oiled, asphalt-like surface that was pitched at an approximately 31 degree angle. There were stairs for access to the diked area, but going over the top was a more direct route. As he was moving down the surface, Employee #1's left foot slipped then caught again with his ankle twisted. He fractured both his tibia and fibula in his lower left leg, for which he was hospitalized. The refinery had had a rule against walking on dikes and Employee #1 had always seen coworkers use the access stairways when entering or leaving diked areas. After the accident, the refinery found that at some point this provision had been deleted from its safety rules.