South Riding, Virginia
July 7, 1998
NTSB Number: PAR-01/01
NTIS Number: PB2001-916501
Adopted June 12, 2001
About 12:25 a.m. on July 7, 1998, a natural gas explosion and fire destroyed a newly constructed residence in the South Riding community in Loudoun County, Virginia. A family consisting of a husband and wife and their two children were spending their first night in their new home at the time of the explosion. As a result of the accident, the wife was killed, the husband was seriously injured, and the two children received minor injuries. Five other homes and two vehicles were damaged.
The National Transportation Safety Board determines that the probable cause of the accident in South Riding, Virginia, was the corrosion and subsequent overheating and arcing at a splice in one of the conductors of the triplex electrical service line, which, because of inadequate separation between the electrical conductors and the gas service line, led to the failure of the gas service line and the subsequent uncontrolled release of natural gas that accumulated in the basement and was subsequently ignited. Precipitating the electrical service line failure was damage done to the electrical service line during installation of the gas service line and/or during subsequent excavation of the electrical line.
The safety issues identified during this investigation were (1) the adequacy of standards for minimum separation distances between gas service lines and electrical service lines and (2) the lack of a requirement for the installation of excess flow valves. As a result of this investigation, the Safety Board issues two recommendations to the Research and Special Programs Administration (RSPA) and one recommendation each to the Edison Electric Institute, the National Rural Electric Cooperative Association, the American Power Association, and the U.S. Department of Agriculture's Rural Utilities Service.
As a result of its investigation of the South Riding, Virginia, accident, the National Transportation Safety Board makes the following safety recommendations:
To the Research and Special Programs Administration:
Require gas utility operators 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. (P-01-1)
Require that excess flow valves be installed in all new and renewed gas service lines, regardless of a customer's classification, when the operating conditions are compatible with readily available valves. (P-01-2)
To the Edison Electric Institute:
To the National Rural Electric Cooperative Association:
To the American Public Power Association:
Inform your member utilities of the circumstances surrounding the July 7, 1998, explosion and fire in South Riding, Virginia, and of the need to ensure that underground electrical facilities are installed and maintained with separation between those facilities and plastic gas pipelines in accordance with the National Electrical Safety Code. (P-01-3)
To the U.S. Rural Utilities Service:
Inform your participating rural utilities of the circumstances surrounding the July 7, 1998, explosion and fire in South Riding, Virginia, and of the need to ensure that underground electrical facilities are installed and maintained with separation between plastic gas pipelines in accordance with the National Electrical Safety Code. (P-01-4)