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Progress Made In Crossbore Avoidance, Discovery
Dealing With Crossbores
Crossbores continue to spark concern and controversy among utility providers and contractors engaged in underground utility construction. While no immediate solution to safety issues related to crossbores is in sight, clearly progress is being made.
Efforts of the Cross Bore Safety Association (CBSA) are gathering momentum to educate the industry and the varied organizations and agencies with a stake in eliminating crossbore accidents, and the association’s work is showing results.
On the regulatory front, in May the Minnesota Office of Pipeline Safety issued an alert notice to state pipeline operators setting forth guidelines aimed at eliminating the risk of installing gas lines through sewer service laterals. The action has been described as the first definitive step taken by a regulatory agency to prevent crossbores and verify that none was created at the conclusion of gas line installations. It has been suggested the alert notice should serve as a model for other agencies (for details, see sidebar).
Technically a crossbore is defined as an intersection of two or more underground utilities. However, the major concern is unknowingly boring through a sanitary sewer lateral by horizontal directional drilling or a piercing tool and placing a natural gas line through the sewer pipe.
A crossbored gas line may remain in place for months or years before a blockage develops in the sewer line and the gas line is punctured by a plumber’s power drain auger or “snake” being used to clear the sewer line. The result can be a deadly explosion destroying property and claiming lives. If the crossbore involves a power cable, the operator of the sewer cleaning machine faces serious injury or death from electrocution. Hitting a crossbored communications cable cuts off telephone and internet service.
There are two basic crossbore issues:
• How to prevent crossbores on current and future projects; and
• Developing realistic plans for dealing with “legacy” crossbores (unknown crossbores that have occurred basically since horizontal directional drilling became an accepted method of installing natural gas pipes, roughly since the early 1990s).
A National Transportation Safety Board’s (NTSB) 1976 investigation of an explosion resulting in death was the first crossbore of a gas line in a sewer documented in the U.S., said Mark Bruce, CBSA president. Numerous explosions, injuries and deaths have continued to occur because of crossbores.