Excavation Damage Resulting in Explosion and Fire in Delaware

National Transportation Safety Board, Apr 30, 2007

Wilmington, Delaware: Quickform Concrete Company was hired by the city of Wilmington, Delaware, to replace sidewalk and curbing dug into an unmarked natural gas service line with a backhoe. Although the service line did not leak where it was struck, the contact resulted in a break in the line inside the basement of 1816 West 3rd Street, where gas began to accumulate. A manager for the contractor said that he did not smell gas and therefore did not believe there was imminent danger and that he called an employee of the gas company and left a voice mail message. A resulting explosion destroyed two residences and damaged two others to the extent that they had to be demolished. Other nearby residences sustained some damage, and the residents on the block were displaced from their homes for about a week. Three contractor employees sustained serious injuries. Eleven additional people sustained minor injuries.

The contract also required Quickform to have the underground utilities marked out before beginning excavation. A Quickform manager called Miss Utility to have underground utilities marked for 1820 West 3rd Street, but the manager inadvertently called in an incorrect address: 820 West 3rd Street.

Conectiv Power Delivery provided gas through its pipeline distribution network to the residences on this block. A Conectiv employee placed yellow paint marks on the ground in front of 1818, 1820, and 1822 West 3rd Street to mark the location of its underground service lines to those addresses. The Conectiv employee said that although the Miss Utility information noted planned excavation at 820, he determined that the request for 820 was in error, and he proceeded to mark the correct 1820 address and the additional addresses of 1818 and 1822 to provide a further safety margin.

A Quickform backhoe contacted and pulled up an unmarked 1-1/4 inch steel service line serving 1816 West 3rd Street. Contractor employees estimated that the damage to the service line occurred at about 1:30 p.m. The crew was not aware that the action of pulling the service line outside resulted in a break to the line inside the basement at 1816 West 3rd Street. Natural gas then began to accumulate in the residence. The Quickform crew said when they saw the damage, they stopped excavation activities and notified the Quickform manager when he arrived on site a few minutes after the service line was contacted.

A resident of 1816 West 3rd Street said that she smelled a strong odor in her house shortly thereafter. She and her two children left the house, but she did not tell anyone about the odor. Eight other residents who lived on the block told investigators that they smelled a gas odor before the explosion. Except for Quickform's voice mail to Conectiv, no calls were placed to Conectiv or the fire department about the damaged line or a leak before the explosion.

The National Transportation Safety Board determines that the probable cause of the natural gas explosion in Wilmington, Delaware, was the failure of Quickform to verify that all underground facilities were marked within the proposed dig site before beginning excavation. Contributing to the accident was the failure of Tech Consultants and Quickform to effectively communicate about the project scope. Contributing to the severity of the accident was the failure of Quickform employees to immediately notify the utility owner and emergency authorities when they realized they had struck and pulled up a gas service line.