In the minutes leading up to the fatal explosion at the Kleen Energy Systems LLC power plant project in Middletown, CT, last month, there was enough natural gas released into the atmosphere to fill an entire pro-basketball arena from floor to ceiling, the Chemical Safety Board's (CSB) lead investigator into the blast said last Thursday.
"Initial calculations by CSB investigators reveal that approximately 400,000 standard cubic feet of gas were released to the atmosphere near the building in the final 10 minutes before the blast," said CSB lead investigator Don Holmstrom.
"This gas was released into a congested area next to the power block building. This congested area likely slowed the dispersion of the gas. The gas built up above the lower explosive limit of approximately 4% in air and was ignited by an undetermined ignition source," he said. "There were potential ignition sources present in the surrounding area, including inside the power plant building."
The explosion at the natural gas-fired plant under construction ultimately resulted in six fatalities (see NGI, Feb. 15). The blast is believed to have occurred while natural gas lines were being purged in a procedure commonly referred to as "blow down." The 620 MW combined-cycle baseload plant had been expected to begin operation this summer.
A major focus of the CSB investigation is to determine what regulations, codes and good practices might apply to these gas blows, Holmstrom said, adding that no specific codes have been identified as yet. However, the National Fire Protection Association (NFPA) took a step in the right direction last week when it supported the CSB's new recommendations on purging practices.
"In the meantime, we strongly caution natural gas power plants and other industries against the venting of high-pressure natural gas in or near work sites. This practice, although common, is inherently unsafe," he said.
Just three days prior to the explosion at the Kleen Energy facility the CSB recommended changes to the National Fuel Gas Code to prevent explosions involving gas purging, according to Holmstrom. At a meeting in San Francisco last Wednesday, a panel of the NFPA responsible for the fuel gas code voted to move forward with the CSB's recommendations to make purging practices safer at work sites. "These provisions will apply at hundreds of thousands of facilities, once fully adopted" by the NFPA, he said.
"The type of purging described in that code is different from the gas blows used in the power industry, and power plants remain exempt from the national fuel gas code. However, gas purging as defined in the code has certain similarities to gas blows, in that gas is applied at one end of a pipe and gas is intentionally vented at the other end to the atmosphere," Holmstrom said.
"We encourage the gas power industry to closely study the very positive actions recommended by the NFPA and the American Gas Association committees [last Wednesday]," he said. "The safety issues raised by this accident are not limited to Connecticut. These issues are larger than any particular company, facility or individual."
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