(40az) Tesoro Refinery Fatal Fire and Explosion

On April 2, 2010, at the Tesoro Anacortes Refinery in Anacortes, Washington, Tesoro workers were completing the final stages of starting up a bank of three parallel heat exchangers located in the Naphtha Hydrotreater unit (NHT unit) section of the petroleum refinery plant. The heat exchangers were constructed from carbon steel, which left the machines susceptible to high temperature hydrogen attack (HTHA). HTHA occurs in high temperature environments where carbon steel is exposed to hydrogen, and it can lead to formation of fissures and cracking in the carbon steel. During startup, one of the heat exchangers experienced catastrophic failure as a result of HTHA, releasing highly flammable hot hydrogen and naphtha. The release of the hot chemicals led to an explosion and an intense fire which killed seven Tesoro employees working near the unit (Chemical Safety Board, 2010).

Investigation revealed that the bank of heat exchangers had a long history of occasional fires and leaks during startup. It was also determined that the process was operating well above the autoignition temperature of the naphtha (500˚F), and therefore the explosion and resulting fire were likely a result of autoignition. Further investigation into the accident revealed that the plant, like many other petroleum refineries, relied on the Nelson curves published by the American Petroleum Institute (API) to determine a safe operating range for carbon steel heat exchangers to protect against HTHA damage. After detailed process simulations were performed by the Chemical Safety Board (CBS) investigation team, however, the process was determined to have been operating in a range of temperature and pressure predicted to be safe by the API recommendations. Further review of previous accidents revealed eight other incidents that occurred at operating conditions that were in a zone that industry guidance considered safe . Based on these findings, the CSB report recommended that the API revise their recommendations to prohibit the use of carbon steel equipment where there is a risk of HTHA and require verification of safe operating conditions (Chemical Safety Board, 2010).

Another contributing factor to the eventual disaster was the fact that the heat exchangers were well known to leak during startup, yet nothing was done to examine the cause of the leak. Based on this oversight, the CSB also recommended changes in the legislation surrounding MOC procedures (Chemical Safety Board, 2010). Although they are not mentioned in the CSB report, further recommendations for Tesoro include regular safety trainings, the implementation of a stop work order, and the use of metrics to promote better safety culture. An additional recommendation not included in the CSB report is the implementation of a process safety review when an accident happens at a similar plant. For example, when a disaster happens at a refinery, this should trigger safety reviews to occur at petrochemical plants across the country and across companies. Refineries should use the findings from CSB investigations to prevent the same type of accidents from recurring across different companies.