National Transportation Safety Board
Office of Public Affairs
WASHINGTON, D.C. - The National Transportation Safety Board today determined that the probable cause of a July 7, 1998 South Riding, Virginia explosion was the failure of the gas service line and the resulting release of natural gas into the basement of a home.
The investigation discovered the presence of corrosion and subsequent overheating and arcing at a splice in one of the conductors of the nearby triplex electrical service line. This led to the Board's determination that inadequate separation between the electrical conductors and the gas service line contributed to the accident. Additionally, damage done to the electrical service line during installation of the gas service line and/or during subsequent excavation of the electrical line was also a contributing factor to the accident.
As a result of the accident, which claimed one fatality, the Safety Board recommended that gas utility operators be required to maintain a specified minimum separation distance between plastic gas service lines and underground electrical facilities when installing new gas service lines or performing maintenance on existing lines.
The Safety Board concluded that, "had the gas and electrical service lines involved in this accident been adequately separated, the heat from the arcing electrical failure would probably not have damaged the gas service line, and the accident would not have occurred."
The Safety Board also recommended that excess flow valves be installed in all new and renewed gas service lines when the operating conditions are compatible with readily available valves.
"An excess flow valve would have closed after the hole in the pipeline developed and the explosion likely would not have occurred," the Safety Board concluded. "Although 50 percent of the of the gas distribution companies have begun to voluntarily install excess flow valves since the accident, it is important that more providers install these devices on new and renewed gas service lines," the Board stated.
A copy of the report, which was adopted on June 12, 2001, will be available on our website at <http://www.ntsb.gov>. Paper copies of the report, when available, can be purchased from the National Technical Information Service (800) 533-NTIS.
NTSB Media Contact:
Terry N. Williams
The National Transportation Safety Board (NTSB) is an independent federal agency charged with determining the probable cause
of transportation accidents, promoting transportation safety, and assisting victims of transportation accidents and their families.