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U.S. Chemical Safety Board (CSB) member Mark Griffon on September 21 called on the American Society of Mechanical Engineers (ASME) to adopt a CSB recommendation calling for natural gas blows to be prohibited during power plant construction.
The recommendation was one of 18 urgent recommendations issued in June 2010 following a CSB investigation into a powerful natural gas explosion that killed six workers and injured dozens of others at the Kleen Energy plant in Middletown, Conn., on February 7, 2010, which was under construction. Workers used hundreds of thousands of cubic feet of natural gas to clean debris from gas pipes used to fuel electricity-producing turbines. The gas accumulated in and around the buildings, was ignited by an unknown ignition source, and exploded.
Speaking to a meeting of ASME members in Phoenix who are considering changes to the ASME Code for Pressure Piping Systems, Griffon said, “The CSB believes that using natural gas or other flammable gases to clean fuel gas piping is inherently unsafe and should be prohibited.” He cited other accidents to show that explosions resulting from flammable gas blows have the potential of causing death, serious injuries, and costly property damage.
Griffon noted that the practice of using gas blows, or forcing large volumes of flammable gas through piping to clear out debris, was common in construction of electric generating facilities. The CSB investigation of Kleen Energy, resulting in 18 urgent recommendations, states “From a fire and explosion perspective, releasing large volumes of natural gas in the vicinity of workers or ignition sources is inherently unsafe.”
In remarks prepared for the ASME, which is considering the CSB recommendation to prohibit gas blows and use inherently safer methodologies to clean piping, board member Griffon said, “It has been argued that the gas blow at Kleen Energy was not conducted properly to ensure the dispersion of the released natural gas and to prevent the gas from encountering ignition sources. This point overlooks the simple fact that cleaning piping with flammable gases presents an inherent explosion hazard. Cleaning piping with flammable gases presents an explosion hazard that cannot be wholly eliminated.”
Even if every effort is made to eliminate ignition sources, such as welding, or electrical equipment not rated for a hazardous environment, he noted, the friction of the gas flowing through the piping can cause an accumulation of static electricity and cause ignition; in addition, sparks from impacts of metal debris striking surfaces when the gas exits the piping can also ignite the gas.
Griffon noted the CSB investigation found ample alternatives to gas blows which are safer. These methods include blowing air or nitrogen through piping, or by “pigging,” in which a cleaning device is propelled through the pipe using air.
Griffon noted that that some in industry have already eliminated gas blows. He said that a representative of General Electric, a major gas turbine manufacturer, stated at the CSB public meeting in June that his company greatly discourages gas blows and did not know of any situation where using gas to clean pipes was necessary. The company official said GE wants to “make gas blows something that will not happen again under GE’s watch.” GE also expressly prohibits its own employees from being on site if one of its customers chooses to conduct a blow with natural gas.
Since the public meeting, several other major turbine manufacturers also have reported to the CSB that they already have, or intend to soon develop, guidance that strongly advises their clients away from the practice of natural gas blows.
The CSB has also made recommendations to OSHA to promulgate a standard that prohibits gas blows to the atmosphere for the purpose of cleaning fuel gas piping, and to the National Fire Protection Association (NFPA) to similarly modify their standards.
The CSB is an independent federal agency charged with investigating industrial chemical accidents. The agency's board members are appointed by the president and confirmed by the Senate. CSB investigations look into all aspects of chemical accidents, including physical causes such as equipment failure as well as inadequacies in regulations, industry standards, and safety management systems.
The board does not issue citations or fines but does make safety recommendations to plants, industry organizations, labor groups, and regulatory agencies such as OSHA and EPA. Visit the CSB Web site at www.csb.gov.