02.25.2010: Middletown, CT - During a press conference, Don Holmstrom, the Chemical Safety Board Lead Investigator of the Kleen Energy power plant explosion, uses a photograph made on the morning of the event to show how natural gas, which is mostly methane, was used to clean debris from natural gas pipes at the plant. According to a statement he read, "To remove debris, workers used natural gas at a high pressure of approximately 650 pounds per square inch. The high velocity of the natural gas flow was intended to remove any debris in the new piping. At pre-determined locations, this gas was vented to the atmosphere through open pipe ends, which were located less than 20 feet off the ground. These vents were adjacent to the main power generation building and along the south wall. The open pipe ends are visible here in the photographs." "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 ten minutes of the blast." "That is enough natural gas to fill the entire volume of a pro-basketball arena with an explosive natural gas-air mixture, from the floor to the ceiling." "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.