Abstract: At approximately 7:05 p.m. on January 19, 2000, Employees #1 through #4 were in the naphtha unifiner area of the refinery when a 26 in. diameter by approximately 20 ft long heat exchanger, designated as 55-EX-02B, ruptured, resulting in a fire and a catastrophic release of hydrocarbons. The break occurred approximately 10 1/2 ft from the front of the channel, releasing light hydrocarbons at 300 psi and at temperatures between 130 and 140 degrees F. Employee #1 sustained severe burns and was transported to the LSU burn unit in Shreveport, LA; Employees #2 through #4 suffered from smoke inhalation and other injuries, and were admitted to area hospitals. The 55-EX-02B heat exchanger was a type AEU (or U-tube type exchanger), constructed to ASME code (section VIII, 1968 edition), and inspected using the requirements of API 510/RP572 and NB-23. During normal operations, light hydrocarbons, such as naphtha and benzene, were circulated through the exchangers from the hydrotreater and reactor to the pressure separator. Hydrocarbon vapors from the hydrotreater went into the reactor. From the reactor, the vapors entered a series of heat exchangers, 55-EX-01A through E and 55-EX-02A through B, where the vapor was transformed into a two-phase product (vapor and liquid) by cooling within the exchangers. The product continued on to the pressure separator, where the two states were separated out, along with the wash water. Wash water was injected into the flow before the 55-EX-01D and after the 55-EX-01E exchangers to remove organic and inorganic material that might have been in the naphtha flow. The wash water system had been down for maintenance since the beginning of the month. The temperature of the naphtha when it left the reactor was over 250 degrees F. The temperature at the time the flow entered the 55-EX-02B exchanger was approximately 130 to 140 degrees F. When the flow exited the 55-EX-02A exchanger, the temperature was approximately 90 degrees F. The heat exchanger was manufactured in 1971 by Heat Exchanger Service of Dutchtown, LA.