CSB sheds light on fatal Kleen Energy explosion
02 March 2010
The Kleen Energy accident occurred during a planned work activity to clean debris from natural gas pipes at the plant. To remove the 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.
This cleaning practice is known within the natural gas power industry as a “gas blow.” Industry personnel have indicated to CSB investigators that gas blows are a common practice during the commissioning of new or modified gas pipes at their facilities.
CSB investigators have reviewed gas utility records for the morning of the accident. These records together with written pipe cleaning procedures and witness testimony confirm that the gas blows occurred intermittently over the course of the morning. At the same time that gas blows were underway, there were potential ignition sources present in the surrounding area, including inside the power plant building. There were many construction-related activities underway inside the building.
Determining the exact ignition source is not a major focus of our investigation at this point. In most industrial worksites, ignition sources are abundant and efforts at accident prevention focus first and foremost on avoiding or controlling the release of flammable gas or vapour.
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 before 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.
In the days since the accident, companies and safety regulators from around the world have contacted the CSB asking about the circumstances of this devastating accident. Some companies, including a power plant here in the region, indicated that they themselves have been planning similar gas blows as part of commissioning pipes in the very near future.
A major focus of the CSB investigation is to determine what regulations, codes, and good practices might apply to these gas blows. To this point, no specific codes have been identified, but we are continuing our research.
In the meantime, the CSB 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.
The CSB is investigating possible alternatives to this practice, including the use of air, steam, nitrogen, or water or the use of combustion devices to safely destroy the gas. Combustion devices like flares can safely burn up flammable gas or vapor, preventing the possibility of an explosion.
Recommending safer alternatives will be a primary focus of the CSB investigation as we move forward.
Just three days prior to this tragic accident, the Chemical Safety Board recommended changes to the National Fuel Gas Code to prevent disastrous explosions involving gas purging. At a meeting in San Francisco recently, the NFPA panel responsible for the fuel gas code voted to move forward with the CSB’s recommendations to make purging practices safer at work sites across America. These provisions will apply at hundreds of thousands of facilities, once fully adopted.
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.
There is an underlying common theme among the tragic accidents at Kleen Energy, the ConAgra Slim Jim plant in North Carolina, the Ford River Rouge power plant in Michigan, the Hilton Hotel in San Diego, and many other purging-related accidents. Companies must ensure that flammable gases are not vented into close proximity with ignition sources and workers. That is a vital safety message from all these tragedies.
The CSB encourage the gas power industry to closely study the very positive actions recommended by the NFPA and the American Gas Association committees. The CSB investigation will focus on determining what permanent changes in standards or practices are needed to prevent future accidents involving gas blows.