CSB to Investigate Fatal Heat Exchanger Rupture
The accident occurred on June 11 during a maintenance operation on a heat exchanger that used pressurized, liquid ammonia to cool chemicals that are later processed to make synthetic rubber. The rubber-making chemicals were pumped through steel tubes inside the heat exchanger, while ammonia flowed through a cylindrical steel shell that surrounded the tubes.
The day prior to the accident, the process was shut down for cleaning. During the shutdown, an isolation valve was closed between the heat exchanger and a pressure-relief device designed to protect the heat exchanger from possible overpressure.
On the morning of the accident, an operator used steam to clean out process piping; the steam also flowed through the heat exchanger tubes. The steam heated the liquid ammonia remaining in the exchanger shell, which caused the pressure to build. With the path to the pressure-relief device blocked, the heat exchanger ruptured catastrophically.
An operations supervisor who was not involved in the maintenance work but was working in the area was killed by the explosion. Her body, which was covered with explosion debris, was not discovered until several hours after the emergency had been declared over.
Since the accident, CSB investigators have completed two week-long visits to the plant conducting interviews and gathering other evidence.
"This tragic accident is but the latest example of the destruction that can result from a lack of effective pressure relief systems and practices," said CSB Chairman John Bresland, who personally visited the accident site on June 12. "Companies should be vigilant to ensure that pressure-relief systems are adequate and are properly maintained and operated to continuously protect equipment from overpressure."
Chairman Bresland said the CSB investigation would likely focus on the company's practices for managing, inspecting, and maintaining relief systems; training operators; and accounting for workers during emergencies. A case study report is expected at the end of 2008.