Abstract: On February 23, 1999, two employees, Employee #1 and Employee #2, died of burns sustained from a fire at Tosco refinery. The fire occurred at the Fractionator tower in the 50 crude oil processing unit at Tosco "Avon" refinery in Martinez, California. Employee #1 and #2 were engaged in a maintenance activity to remove and eventually replace the naphtha draw piping which had developed a leak. Tosco decided to fix the repair while the process unit remained in operation. The highly flammable gasoline-like, benzene-containing hydrocarbon flowed through openings into the line and onto hot surfaces in the operating unit. The naphtha piping ignited, causing a fire near the bottom of the tower, which continued to spread up and down the tower. The fire killed two workers and seriously injuring another contractor. The contractor was hired by Tosco to erect scaffold for the removal and replacement of the naphtha piping. Three additional contractor employees also assisted Tosco maintenance employees while the pipeline was being cut. Employee #1 and #2 died of burns sustained during the fire. They were unable to escape. The surviving contractor employee had been sent to another assignment and location in the refinery after lunch when the fire occurred. Investigators determined that Tosco failed to isolate or to drain the naphtha piping from the operating process prior to cutting into the line.