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Pepco Files Report of Georgetown Manhole Investigation

Monday, March 20, 2000

For Immediate Release
March 20, 2000

Potomac Electric Power Company filed a 47-page report today with the District of Columbia Public Service Commission regarding last month`s manhole fire and explosion in Georgetown. The report followed a month-long investigation by Pepco engineers and outside forensic experts.

In its report on the Georgetown fire, forensic and technical experts hired by Pepco ruled out the presence of either natural gas or sewer gas, damage to the cable during installation, manufacturing defects, chemical attack, premature aging and the presence of water in the manholes. Forensic experts subjected the undamaged ends of the cable close to the fire to numerous chemical, electric, mechanical and metallurgical tests as well as visual examination.

The report concluded: "System maintenance practices cannot be faulted for the incident since protective devices in the electrical system operated the way they were designed and there is no evidence that the responsible cable was deteriorated or overloaded. The cause was likely from external physical damage to the cable."

In checking records for any construction activities in the 3100 block of M Street and the surrounding areas, Pepco investigators found that Washington Gas dispatched an emergency crew to 3111 M Street after midnight on Feb. 4 to investigate a possible gas leak. According to the report, "the most likely cause" was cable failure from insulation damaged Feb. 4 "by a Washington Gas crew driving a bar into the ground in the tree box in front of 3111 M Street and directly above Pepco`s duct bank, and nicking the secondary cables."

"This caused a fault in the cable that smoldered over time, producing combustible gases which finally ignited into a fire and explosion," the report said. Forensic experts identified the cable directly under the tree box as "where the cable failed and started the fire."

The report also included an investigation of five unrelated and less severe manhole cable failures in the District. The report listed that three resulted from failed Pepco cable splices and the fourth was caused by insulation failure in a secondary cable that caught fire and burned an adjacent primary cable. The fifth fire on March 16 was caused by a contractor for Washington Gas who cut through an electric cable while digging a trench.

As a result of these incidents, Pepco said it is undertaking a two-part mitigation plan.

  • Enhancing Underground Equipment Inspections.

Enhancing inspections of 660 manholes in Georgetown and immediately correcting any problems; enhancing a system-wide underground inspection program begun in March 1999 to increase the number of underground structures to be inspected by year`s end.

  • Installing Vented Manhole Covers.

Venting and tethering selected manhole covers in high traffic areas to further reduce threats to public safety from displaced manhole covers.

"Pepco is committed to doing everything we can to provide our customers with reliable service in a way that assures their continued safety and safeguards their property," said Bob Grantley, Group Vice President, Customer Service and Power Distribution. "While there is no way to totally prevent manhole fires, our enhanced inspection program and other measures we`re putting into effect will help mitigate the problem in areas with heavy pedestrian and vehicle traffic."

Grantley called the Georgetown fire "an extraordinary event," and said the means to prevent a repeat occurrence are already in place, including the strict observance by third parties of requirements to prevent digging without first properly identifying and marking utility lines.

Pepco`s report cited and included a published Washington Post photograph showing smoke "coming from a hole in this tree box space--an indication that there was a direct passage from the origin of the smoke and fire to the hole in the tree box space."

Point of Contact:
Robert Dobkin