On January 27, the U.S. Chemical Safety Board (CSB) released a case study examining the causes of a heat exchanger rupture and ammonia release at the Goodyear Tire and Rubber Plant in Houston in 2008. Use these lessons learned to check your employee tracking system and to determine whether your plant has installed valves that violate the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code.
The CSB event summary begins by noting that the accident occurred on June 11, 2008, when an overpressure in a heat exchanger led to a violent rupture of the exchanger that hurled debris, which struck and killed a Goodyear 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 (Figure 7).
|7. Tragic event. On June 11, 2008, one worker was killed and seven others were injured when, during a maintenance operation on a heat exchanger, ammonia overpressured the exchanger, causing it to rupture. The cause of the accident was attributed to failure to follow the requirements of the ASME Boiler and Pressure Vessel Code. Employee training lapses also were found to be the cause of a slow accounting of all missing employees. Source: Chemical Safety Board|
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.
The next day, at about 7:30 a.m., an operator closed another valve—this one blocking a second, automatic pressure control valve—to begin cleaning the process line with steam. The operator was unaware that the isolation valve was also closed, thus leaving no means of relieving excess pressure in the exchanger. As a result, pressure continued to increase until the heat exchanger exploded violently.
Employee Training Lapses
Managers ordered the plant evacuated. However, 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 found that a malfunction in the computerized electronic employee badge-tracking system delayed supervisors in immediately retrieving the list of personnel in their area; that required handwritten lists to be generated. At about 1:20 p.m. an operations supervisor assessing the damage to the incident area discovered a fatally injured employee buried in rubble in a dimly lit area. 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.
CSB Chairperson Rafael Moure-Eraso said, “The absence of this worker had not been noted due to the lack of training and drills on worker headcounts. Plant personnel were not provided with the proper training to effectively manage this emergency. Company procedures called for routine evacuation and shelter-in-place drills four times a year, but such drills were not held for several years prior to the incident. Management’s adherence to company procedures should have allowed for effective communication between all members of the workforce and a more robust emergency response structure.”
The report further notes that maintenance work activity was not properly communicated between maintenance and operations personnel, resulting in a subsequent shift not being notified of the isolation of the pressure relief line.
Plant Design Mistakes
The CSB’s final report outlines several lessons learned, including the need to adhere to the existing 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 complete final report can be downloaded from http://www.csb.gov.
—Edited by Dr. Robert Peltier, PE.