The U.S. Chemical Safety Board (CSB; www.csb.gov) has released a case study on the 2008 heat-exchanger rupture and ammonia release at the Goodyear Tire and Rubber Co. in Houston that identifies gaps in facility emergency response training and calls for increased adherence to existing industry codes.
The accident occurred on June 11, 2008, when an overpressure in a heat exchanger led to a violent rupture of the exchanger, hurtling debris that struck and killed an employee walking through the area. The heat exchanger contained pressurized anhydrous ammonia, a colorless, toxic chemical, used as a coolant in the production of synthetic rubber; five workers were exposed to ammonia released by the rupture. On the day prior to the accident, maintenance work required closing several valves on the heat exchanger. CSB investigators found that workers closed a valve that isolated the exchanger from a relief valve, to replace a burst rupture disk located below the relief valve. Unaware that the isolation valve was closed, the next day, an operator closed another valve — this one blocking a second, automatic pressure control valve — to begin cleaning the process line with steam. This left no means of relieving excess pressure in the exchanger, and pressure continued to increase until the heat exchanger exploded violently.
Although the plant was evacuated, CSB investigators found that on the day of the accident the employee tracking system was not operating properly, making it difficult to quickly account for all employees. The CSB case study notes that because the fatally injured employee had been a member of the emergency response team, her absence from the evacuation muster point was not considered unusual.
The CSB’s final report outlines several lessons learned including the need to adhere to existing American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code. CSB investigations supervisor Robert Hall said, “We found the accident likely would not have happened had operators followed the ASME code. It’s crucial that workers continuously monitor an isolated pressure relief system throughout the course of a repair and reopen blocked valves immediately after the work is completed.” The CSB’s report notes that the ASME code states that “Overpressure protections shall be continually provided…whenever there is a possibility that the vessel can be over-pressurized by a pressure source.”
The CSB is an independent federal agency charged with investigating serious chemical accidents. The Board makes safety recommendations to plants, industry organizations, labor groups, and regulatory agencies such as OSHA and EPA. CSB’s final report can be viewed at www.csb.gov.