NTSB Safety Recommendation Letter P-95-028

Page 1Official PDFNational Transportation Safety Board Washington, D.C. 20594 lliafety Recommendation Date: May 10, 1995 In Reply Refer To: P-95-28 Mr. James J . Howard Chief Executive Officer Northern States Power Company 414 Nicollet Mall Minneapolis, Minnesota 55404 About 8:30 a.m. on July 22, 1993, a city of St. Paul Department of Public Works (DPW) backhoe hooked and pulled apart a Northern States Power Company (NSP) high-pressure gas service line.' The 1-inch plastic line pulled apart approximately 12 feet from where the backhoe hooked the line and just outside an elbow that was within 1 foot of the stone foundation wall of a building. A sidewalk extended from the street to the foundation wall and hindered the gas from rising. However, the foundation wall had many holes and loose, permeable mortar, enabling natural gas to flow quickly into the building, which contained three ground-floor businesses and eight upstairs residential apartments. An explosion and natural gas-fueled fire resulted about 20 minutes after the backhoe hooked the service line. The explosion force caused part of the building to land on and flatten an automobile traveling southwest on East Third Street, and the driver died instantly. The explosion and ensuing fire also killed an apartment occupant and a person outside the building and injured 12 people. A St. Paul DPW crew, consisting of a crew leader, a backhoe operator, and two sewer services (SS) workers, had been repairing a sewer junction structure on the northeast corner of East Third Street and Maria Avenue before the accident. Their work included repairs to an adjoining sewer catch basin that ran along Maria Avenue, and the crew needed to excavate both the junction structure and the catch basin to complete the work. On July 16, 1993, the St. Paul DPW contacted the one-call system, which notified all buried-facility operators, including the NSP, about the work planned for July 21 and 22. The 'The accident is also discussed in Pipeline Accident Brief DCA-93-MP-011. 6536 7 ,#

Page 2n L NSP painted a yellow markout on the street surface on July 20 to indicate the gas main and service line to 679 East Third Street. The St. Paul DPW crew removed the old junction structure at the north comer of East Third Street and Maria Avenue and dug into a small concrete portion of Maria Avenue on July 21. That morning, when an NSP meter reader performed her monthly reading of the 679 East Third Street meter, she did not smell the odor of natural gas (mercaptan). About 7 a.m. on July 22, the DPW crew used a pneumatic hammer on an older backhoe to fracture the concrete above the planned excavation area, which was directly above the gas service line to 679 East Third Street. A newer, conventionally equipped backhoe was moved into place after the concrete had been fractured. According to the DPW crewmember interviews, an SS worker then shoveled by hand to find the gas service pipeline. He had dug about 1 112 feet when the crew leader asked him whether he had found anything, and the SS worker replied, "No." (The gas service line should have been visible because its casing surface was 1 1/2 feet below the concrete, which was about 6 inches thick.) The crew leader then instmcted the backhoe operator to "take back the concrete." About 8:30 a m . , the conventionally equipped DPW backhoe hooked a 3-inch (nominal diameter) steel casing with an inserted 1 U4-inch plastic pipe. The SS worker told the crew leader that he smelled gas. The crew leader then told the backhoe operator to shut down the backhoe, and the operator did so. Investigators found the damaged 3-inch steel casing after the accident about 1 foot north of a yellow markout on the concrete surface. Both the 3-inch steel casing and the inserted 1 114- inch plastic pipe were about 2 inches above the dirt surface. The soil-filled backhoe bucket was underneath the casing at a 90-degree angle to the backhoe arm. The DPW crew leader used his truck radio to contact his office to inform the NSP about the backhoe striking the gas line, A sewer maintenance DPW dispatcher called the NSP gas service dispatch center between 8:30 and 8:35 a.m., and the NSP entered the gas service hit at 679 East Thrd Street into the crew dispatch computer system at 8:39 a.m. An NSP serviceman was dispatched to the site at 8:42 a.m., and others were dispatched less than 10 minutes later. After the DPW crew leader made his radio call, a store owner came from the building and said that he could smell gas in his store. The four crewmembers went through the ground floor main entrance into the building. One SS worker and the store owner went upstairs to alert any apartment occupants; the two knocked on doors but received no response. After returning to the main entrance, they learned that all residents may not have exited. The same SS worker and the crew leader then went upstairs to alert any remaining residents. After these trips to the upstairs apartments, the SS worker, crew leader, and backhoe operator went in different directions outside the building to divert pedestrians from the intersection of East Third Street and Maria Avenue. The gas inside the building exploded about 8:50 a.m. The St. Paul Fire Department received a 911 call at 8 5 2 a.m. from a local citizen, who reported an explosion and fire in the building at the northeast comer of East Third Street and#

Page 33 Maria Avenue. Emergency response units were dispatched at 8:53 a.m. from the closest fire station, about 1/2 mile from the accident site. (The St. Paul Fire Department had perfornied a disaster drill that simulated a building collapse involving 45 injuries about 2 months before this accident.) If the St. Paul DPW dispatcher had called 91 1 after being notified that a gas pipeline had been struck and the odor of gas was present, the fire department would have had an opportunity to initiate an evacuation o€ the area and to close roads adjacent to the accident site before the explosion occurred. At the time of the accident, St. Paul DPW policy was to call the gas company. After the accident, the St. Paul DPW changed its policy and now requires that its dispatchers call both the fire department, using 911, and the gas company when a gas pipeline has been struck. Excavation-caused pipeline damage is a serious problem in the city of St. Paul and is the primary cause of pipeline accidents in the State of Minnesota. The NSP had 243 and 976 pipeline strikes, respectively, in its St. Paul and Minnesota operations during 1993. Most of these pipeline strikes were not reported to the Minnesota Office of Pipeline Safety (MNOPS) or to the Occupational Safety and Health Division of the Minnesota Department of Labor and Industry (MNOSHA). The U.S. Department of Transportation (DOT) only requires natural gas pipeline operators to report an incident that involves a release of gas from a pipeline if it involves "(i) a death, or personal injury necessitating in-patient hospitalization; or (ii) estimated property damage, including cost of gas lost, of the operator or others, or both, of $50,000 or more. In this accident, the St Paul DPW did not comply with the labor and transportation regulations in effect to prevent excavation-caused pipeline damage. The MNOSHA is responsible for enforcing the labor regulations Title 29 Code of Federal Regulations 1926.651@)(3) states: When excavation operations approach estimated location of underground installations, the exact location of the installations shall be determined by safe and acceptable means The Minnesota one-call transportation regulations state: The excavator or land suiveyor shall determine the precise location of the underground facility, without damage, before excavating within 2 feet of a marked location of the underground facility. St Paul DPW officials stated that the DPW has no written procedures to prevent damage to underground facilities by excavation activities and that their excavators follow the Minnesota regulations The one-call system has published guidelines that state:#

Page 44 If excavation is required within 2 feet horizontally of any marking, the i excavation should be performed very carefully with hand tools and without damage. These guidelines are similar to those developed at a recent workshop on excavation damage prevention sponsored by the Safety Board and the DOT. Workshop participants concluded that excavators should "use nonmechanized hand tools or tools specifically designed to safely expose an underground facility to determine its exact location. " The DPW should train its excavators in procedures that incorporate these safe excavation guidelines. MNOSHA and MNOPS enforce similar laws to prevent excavation-caused pipeline damage. However, many pipeline strikes are reported to only one of these organizations. Additionally, underground facility operators are aware of strikes to pipelines that may not meet reporting criteria and therefore are not reported to either MNOSHA or MNOPS. The Board believes that sharing excavation-caused pipeline damage data, including information about strikes to pipelines that may not meet reporting criteria, would provide a better understanding of the extent of the problem, help to focus programs to reduce excavation-caused pipeline damage, and enhance the protection of workers and buried facilities. Therefore, the National Transportation Safety Board recommends that the Northern States Power Company: Develop and implement written procedures for gathering and exchanging with the Minnesota Office of Pipeline Safety and the Occupational Safety and Health Division of the Minnesota Department of Labor and Industry information about excavation- caused pipeline damage, including information about strikes to pipelines that may not meet reporting criteria. (Class II, Priority Action) (P-95-28) Also, the Safety Board issued Safety Recommendations P-95-30 to b e Minnesota Department of Labor and Industry, P-95-29 to the Minnesota Office of Pipeline Safety, P-95-26 and -27 to the St. Paul Department of Public Works, and P-95-24 and -25 to the American Public Works Association. The National Transportation Safety Board is an independent Federal agency with the statutory responsibility "to promote transportation safety by conducting independent accident investigations and by foImulating safety improvement recommendations" (Public Law 93-633). The Safety Board is vitally interested in any action taken as a result of its safety recommendations. Therefore, it would appreciate a response from you regarding action taken or contemplated with respect to the recommendation in this letter. Please refer to Safety Recommendation P-95-28 in your reply. If you need additional information, you may call (202) 382-0670 7 ,#

Page 5Chairman concurred in this 5 HALL, Vice Chairman recommendation. FRANCIS. and Member HAMMERSCI-IMIDT By :#