Abstract: At 3:37 a.m. on May 5, 1988, an explosion occurred in the catalytic cracking unit (CCU) of an oil and gas refinery. The explosion apparently was the result of corrosion of an 8-inch vapor line. This vapor line, under 270 psi pressure, ran from a 10-inch header that originated as the main overhead vapor line from the depropanizer column. The apparent instantaneous line failure released approximately 17,000 pounds of hydrocarbon vapor for approximately 30 seconds. A possible ignition source could have been the unit's superheater furnace. The damage pattern indicated that the explosion was probably an aerial explosion with an epicenter located in the area between the depropanizer and the CCU control room. Employees #1, #2, #4, #5, and #7 were found fatally injured inside the CCU control room as a direct result of the blast. Employee #3 was found fatally injured approximately 30 feet outside the west side of the CCU control room as a direct result of the blast. Employee #6 was fatally injured while he was exiting the GO-1 South control room. The negative pressure wave of the explosion apparently created a vacuum that caused the east brick wall of GO-1 South to be "sucked" toward the CCU and then to fall on Employee #6. Employee #8 was on the northwest side of the reactor-regenerator vessels in the CCU and was critically injured as a result of the blast. The rest of the employees, #9 through #26, were in different units in the refinery at the time of the explosion. All received varying injuries to different degrees as a direct result of the explosion.