NTSB Would Expand Use of Excess Flow Valves
The National Transportation Safety Board (NTSB) last week recommended that excess flow valves be installed in all new and renewed gas utility service lines, where feasible, as the result of an investigation of a gas explosion in a home that killed one member of a Loudoun County, VA, family and injured three others.
An investigation of the blast, which occurred in 1998, revealed that heat coming from a failed underground electrical line weakened a nearby gas line owned by Washington Gas Light, which was supplying the home, causing it to rupture and fill the basement with gas, which then exploded. The NTSB said that if an excess flow valve had been installed, it would have closed when the line ruptured, making an explosion unlikely. Also, if the gas and electric lines had been placed farther apart, the electric line failure would not have affected the gas line. The insulation on the electrical line was damaged either during its installation or when the gas line was put in.
The NTSB has also recommended that "gas utility operators be required to maintain a specified minimum separation distance, sufficient to protect against both thermal and mechanical damage, between plastic gas service lines and underground electrical facilities whenever they install a new gas service line or perform maintenance on existing lines."
The board's recommendation regarding excess flow valves was that they be installed "regardless of a customer's classification, when the operating conditions are compatible with readily available valves." Recommendations of the NTSB must be acted on by the Research and Special Programs Administration (RSPA) of the Department of Transportation.
Washington Gas "doesn't necessarily disagree with the NTSB finding --- if the flow of gas was sufficient to trigger such a valve," WGL spokesman Tim Sargeant said. But "it's really a series of things that prevent accidents and damage." Safety measures should include separation of electric and gas lines, adequate inspections and auditing, worker training, injection of odorant and the reduction of third party damage. "We've been installing excess flow valves since January 1999 on all new and replaced residential service at no charge," he added. The company will install valves on other existing customer lines for a charge.
The American Gas Association noted that the RSPA's Office of Pipeline Safety "coincidentally issued two final rules on excess flow valves" just after the Loudoun County explosion. "In compliance with the RSPA regulation, gas customers are advised by the gas utility of the availability of excess flow valves for installation, and the valves are installed at the customer's request."
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