20 August 2008 16:48 [Source: ICIS news]
HOUSTON (ICIS news)--The US Chemical Safety Board (CSB) has pinned the likely cause of a fatal 11 June explosion on a build up of pressure in a heat exchanger at a Goodyear synthetic rubber plant in Houston, it said on Wednesday.
However, the board has not closed the investigation, as it will determine - among other things - how Goodyear overlooked the accident's sole fatality, the board said.
Goodyear did not discover the fatality until several hours after the emergency was declared over, the board said. The blast also injured seven others.
The explosion occurred during maintenance on a heat exchanger, which is used to pressurise liquid ammonia, the board said.
The ammonia is used to cool chemicals that are processed to make styrene-butadiene rubber (SBR).
The chemicals flowed through steel tubes inside of the heat exchanger, the board said. The ammonia flowed through a cylinder-shaped shell that surrounded the tubes.
A day before the accident, the process was shut down for cleaning, the board said.
During the shutdown, an isolation valve was closed between the heat exchanger and a pressure-relief device, the board said.
On the morning of the accident, an operator used steam to clean out the process piping, the board said. The steam also flowed through the heat-exchanger tubes.
The steam heated up ammonia that had remained in the exchanger shell, causing pressure to build up, the board said. Because the isolation valve was closed in the relief device, pressure built up.
The heat exchanger then ruptured from the build-up, the board 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," according to a statement by John Bresland, board chairman. "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.'
The board will investigate Goodyear's practices for managing, inspecting and maintaining relief systems as well as its practices for training operators, the agency said.
The CSB should complete a case study of the accident by the end of the year, it said.
The Goodyear plant, near the Houston Ship Channel, produces styrene-butadiene rubber (SBR), with a capacity of 265,000 tonnes/year.
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