So far, the CSB has found the June 11 blast at the Houston plant happened during maintenance on a heat exchanger, which used pressurized, liquid ammonia to cool the chemicals used to make synthetic rubber. A day before the explosion, the system was shut down for cleaning. During that time, an isolation valve between the heat exchanger and a pressure-relief device was closed, officials said.
On the day of the blast, an operator used steam to clean piping. The steam also flowed through the heat exchanger tubes and heated the remaining liquid ammonia, causing pressure to build. Since the path to the pressure-relief device had been blocked a day earlier, the heat exchanger ruptured, the CSB said.
"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. "Companies should be vigilant to ensure that pressure-relief systems are adequate and are properly maintained and operated to continuously protect equipment from over-pressure."
Hours after the morning blast, the debris-covered body of production supervisor Gloria McInnis was found. Some seven others were injured, including contract workers who were exposed to hazardous anhydrous ammonia.
Officials have finished conducting interviews at the plant and gathering other evidence. A report on the explosion is expected at the end of the year, the CSB said in a news release.
While the board does not issue citations or fines, it make safety recommendations to plants and regulatory agencies such as OSHA and the EPA.
A message left Wednesday for Goodyear officials was not immediately returned.
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