NTSB Safety Recommendation Letter P-81-011 through P-81-012

Page 1Official PDFNATIONAL TRANSPORTATION SAFETY BOARD WASHINGTON, D.C. American Gas Association 1515 Wilson Boulevard Arlington, Virginia 22209 SAFETY RECOMMENDAT I O N ( S ) P-81-11 and -12 About 11:55 a.m., on October 9, 1980, a 2-inch-diameter compression coupling located on the upstream side of a gas meter set assembly in the boilerroom of the Simon Kenton High School in Independence, Kentucky, pulled out of its connection with a 2-inch-diameter gas service line. Natural gas at 165-psig pressure escaped through the 2-inch-diameter opening and, seconds later, exploded and burned. A basement wall was blown down, an adjacent classroom was damaged, and one student was killed. About 30 minutes later, a second explosion occurred, which injured 37 persons and extensively damaged the school. The gas service line was connected to a 4-inch-diameter gas main owned by the IJnion Light, Heat and Power Company (gas company), which was uprating the gas main by controlled pressure increases at the time of the accident. IJ The gas main's operating pressure was being increased from 60 psig t o 200 psig in increments of approximately 35 psig. The gas main had many customer service lines connected to it. In preparation for the line uprating, the gas company's pressure crew, using microfiche customer connection records, had replaced the single regulators at the gas meter set assemblies on all of the known service line connections to the gas main with double-regulator systems as mandated by 49 CFR 192.195 to protect against accidental overpressure. The double regulators were designed t o handle the anticipated 200-psig line test pressure; the single regulators were not. Because the gas company's records showed that the school's service line was connected to a 2-inch-diameter gas main that ran parallel and adjacent to the 4-inch-diameter gas main, the school's single regulator was not replaced. When the pressure crew increased the gas main's pressure to 165 psig, the 2-inch-diameter compression coupling located on t h e upstream side of the school's gas meter set assembly disconnected from its lower nipple, allowing natural gas to be released at an initial pressure of 165 psig into the school's boilerroom. Approximately 5 seconds later, at about 11:55 a.m., the gas exploded, demolishing a wall that separated the boilerroom from a classroom. The cement blocks blown from this wall by the force of the explosion struck and fatally injured a student who was in the classroom. The teacher and the other students in the classroom escaped unharmed; - 11 For more detailed information read "Pipeline Accident Report-Union Light, Heat fnd Power Company Natural Gas Explosion and Fire, Simon Kenton High School, ndependence, Kentucky, October 9, 1980" (NTSB-PAR-81-1). 3096A#

Page 2-2- however, t h e classroom was heavily damaged by the explosion and an ensuing fire. About 12:25 p.m., another gas explosion occurred, injuring 37 persons, mostly firefighters. This explosion, described by witnesses as 1 0 times greater than the first explosion, damaged floors, doorways, and walls in the building. Gas company employees arrived at the accident site within minutes of the first explosion. They immediately began searching for the lid on the curb box containing the valve that controlled the gas supply to the school's service line. However, they were unsuccessful in locating it visually or with electronic detectors and spotting bars. After the second explosion, the search for the curb box continued. The lid was finally located 8 inches below the ground surface. Gas company employees removed the lid and turned off the curb valve with a wrench, stopping the flow of natural gas to the school. The fire in the boilerroom went out a t 1:40 p.m., 1 hour 45 minutes after the first explosion. If gas company employees had been able to locate and close the curb valve rapidly, the second explosion with its large number of injuries and heavy damage to the school might not have occurred. Title 49 CFR 192.365 requires that each service line have a shutoff valve in a readily accessible location, but these regulations did not become effective until after the installation of the service line involved in this accident. However, the industry code ASA B31.8-1963, which was in effect at the time of the installation, regarding the location and accessibility of service line valves, states the following: 849.13, Location of Service Shut-Offs. Service shut-offs shall be installed on all new services (including replacements) in a readily accessible location. Shut-offs shall be located upstream of the meter if there is no regulator, or upstream of the regulator, if there is one. All gas services operating at a pressure greater than 10 psig, and all services 2 inches in diameter or larger, shall be equipped with a shut-off located on the service line outside of the building, except that whenever gas is supplied to a theater, church, school, factory or other building where large numbers of persons assemble, an outside shut-off in such case will be required regardless of t h e size of the service or of the service pressure. Underground shut-off shall be located in a covered durable curb box or standpipe, which is designed to permit ready operation of the valve. The curb box or standpipe shall be supported independently of the gas service line. Kentucw Energy Regulatory Commission (KERC) regulations, under Section 22, Subsection 4(a)3, require that all curb valves be inspected annually for accessibility. The KERC also requires, under Section 22 of 807 Kentucky Administrative Regulation (KAR) 50:015, General Rules, that "at intervals not to exceed one (1) year . . . the curb box on service shall be inspected for accessibility."#

Page 3-3- The gas company stated that it conducts an annual public building inspection of all schools and churches in its service area. Company records indicated that t h e Simon Kenton High School was last inspected on December 3, 1979. The inspection record shown to Safety Board investigators was a computer readout sheet with minimal information on it. Nothing was provided on the inspection form to indicate that accessibility to the curb shutoff valve was checked as part of this annual inspection. The inspection form of December 3, 1979, indicated that no irregularities were found. Gas company officials said that the accessibility to the curb valve was checked during the annual inspection of the school on December 3, 1979. However, since there is no provision on the inspection form for checking accessibility to curb valves, and since no activity that would have caused the curb box lid to become covered with 8 inches of earth was reported in the area after t h e inspection, the Safety Board concludes that the curb valve box had been inaccessible for some time before the December 3, 1979, inspection. Title 49 CFR 192.615(a) requires that each operator establish written procedures to minimize hazards resulting from a gas pipeline emergency. Subsection 192.615(8)(6) requires that an emergency shutdown procedure be a part of these written procedures. The subject regulations were applicable to the uprating of the gas main, but the gas company did not have such written procedures. The gas company believes that a complete shutdown is a dangerous practice. It maintains that there is a possibility of forming a gas-air mixture with a potential for explosion. The gas company believes that air could enter a shutdown gas system by way of open home appliances and, to avoid this entry of air, it is necessary to maintain a positive pressure in the system. The Safety Board reviewed its pipeline accident reports and found no reports indicating that an explosion had occurred as a result of a complete pipeline. shutdown. The Safety Board believes that under certain conditions when a complete shutdown is performed, there is more of an economic burden to the gas companies than a potential danger to the public, because gas company employees have to shut off the gas to each customer individually, which is a major task when part of a city or town is involved. Afterwards, when service is restored, gas company personnel have to purge the lines and restore the natural gas.service to each customer. The Safety Board is aware of some companies' objections to complete shutdown, but it believes that in this case the decision to shut down would have been t h e better one because damage to the school and injuries to persons could have been far greater if the second explosion had occurred later and involved more gas. Therefore, the National Transportation Safety Board recommends that the American Gas Association: Advise its member companies of the circumstances of this accident, and urge them to include in their training programs information for their own personnel and local firefighting personnel regarding the hazards of secondary explosions or fire which may exist if the gas supply is not shut down. (Class 11, Priority Action) (P-81-11)#

Page 4-4- Advise its member companies to check unrestrained compression couplings on gas meter set assemblies in buildings for conformance with t h e manufacturer's installation recommendations and industry standards. (Class 11, Priority Action) (P-81-12) KING, Chairman, DRIVER, Vice Chairman, and McADAMS, GOLDMAN, andBURSLEY, Members, concurred in these recommendations.#