On Sunday, February 7, 2010, Kleen Energy, a combined-cycle natural gas fueled power plant under construction in Middletown, Conn., experienced a catastrophic natural gas explosion that caused six deaths and at least 50 injuries.

The accident occurred during the planned cleaning of fuel gas piping, part of the commissioning and startup phase of construction. At the time of the accident, workers were conducting a “gas blow,” whereby natural gas is forced through the piping at a high velocity and pressure to remove any debris within the piping. The gas and debris were subsequently released directly to atmosphere. A spark ignited the vented gases, causing the explosion.

At the Kleen Energy construction site, workers used natural gas at a pressure of approximately 650 psig to clean gas pipes. A total of 15 natural gas blows were completed intermittently over approximately four hours through a number of open pipe ends that were located less than 20' off the ground.

According to reports from those at the Kleen Energy site on the day of the blast, efforts were made to eliminate or control potential ignition sources outside the power generation building. However, many ignition sources existed inside the building: electrical power to the building was on, welders were actively working, and diesel-fueled heaters were running.

Initial calculations by CSB investigators reveal that approximately 400,000 scf of natural gas were released to the atmosphere near the building in the final 10 minutes before the blast. Just over 2 million scf of gas were released in total over the course of the morning. At approximately 11:15 a.m., the released natural gas found an ignition source and exploded.