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From:
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NTSB
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To:
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FRA
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Date:
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7/18/2008
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Response:
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Notation 8027: The National Transportation Safety Board has reviewed the Pipeline and Hazardous Materials Safety Administration’s (PHMSA’s) notice of proposed rulemaking (NPRM), “Hazardous Materials: Improving the Safety of Railroad Tank Car Transportation of Hazardous Materials,” that was published at 73 Federal Register 17818 on April 1, 2008. The NPRM requested comments on proposed enhanced railroad tank car performance standards and operating restrictions that are designed to minimize the loss of lading from railroad tank cars transporting liquefied gases that are poisonous by inhalation (PIH), especially chlorine and anhydrous ammonia, in the event of an accident. These proposals include enhanced tank car performance standards for head and shell impacts, operational restrictions for trains hauling tank cars containing PIH materials, interim operational restrictions for trains hauling tank cars not meeting the enhanced performance standards, and an allowance to increase the gross weight of tank cars that meet the enhanced performance standards. This proposed rulemaking does not establish enhanced tank car performance standards for all pressure tank cars. For example, pressure tank cars transporting liquefied flammable gases, such as propane, would not be subject to the proposed improved performance standards.
Overview
Between 2002 and 2005, the Safety Board investigated three accidents that involved the failure of railroad tank cars and the release of PIH materials: (1) the January 18, 2002, derailment of a Canadian Pacific Railway freight train near Minot, North Dakota; (2) the June 28, 2004, collision of a Union Pacific Railroad freight train and a BNSF freight train in Macdona, Texas; and (3) the January 6, 2005, collision of a Norfolk Southern freight train with a standing local
train in Graniteville, South Carolina. As a result of the Minot investigation, the Board issued the following four safety recommendations to the Federal Railroad Administration (FRA):
R-04-4
Conduct a comprehensive analysis to determine the impact resistance of the steels in the shells of pressure tank cars constructed before 1989. At a minimum, the safety analysis should include the results of dynamic fracture toughness tests and/or the results of nondestructive testing techniques that provide information on material ductility and fracture toughness. The data should come from samples of steel from the tank shells from original manufacturing or from a statistically representative sampling of shells of the pre-1989 pressure tank car fleet.
R-04-5
Based on the results of the Federal Railroad Administration’s comprehensive analysis to determine the impact resistance of the steels in shells of pressure tank cars constructed before 1989, as addressed in Safety Recommendation R-04-4, establish a program to rank those cars according to their risk of catastrophic fracture and separation and implement measures to eliminate or mitigate this risk. This ranking should take into consideration operating temperatures, pressures, and maximum train speeds.
R-04-6
Validate the predictive model the Federal Railroad Administration is developing to quantify the maximum dynamic forces acting on railroad tank cars under accident conditions.
R-04-7
Develop and implement tank car design-specific fracture toughness standards, such as minimum average Charpy value, for steels and other materials of construction for pressure tank cars used for the transportation of U.S. Department of Transportation class 2 hazardous materials, including those in low-temperature service. The performance criteria must apply to the material orientation with the minimum impact resistance and take into account the entire range of operating temperatures of the tank car.
As a result of the Graniteville investigation, the Safety Board issued the following two safety recommendations to the FRA:
R-05-15
Require railroads, in non-signaled territory and in the absence of switch position indicator lights or other automated systems that provide train crews with advance notice of switch positions, to operate those trains at speeds that will allow them to be safely stopped in advance of misaligned switches.
R-05-16
Require railroads to implement operating measures, such as positioning tank cars toward the rear of trains and reducing speeds through populated areas, to minimize impact forces from accidents and reduce the vulnerability of tank cars transporting chlorine, anhydrous ammonia, and other liquefied gases designated as poisonous by inhalation.
As a result of the Macdona accident, the Safety Board reiterated Safety Recommendations R-04-4 through -7 and R-05-16.
The Safety Board supports the stated goals of the NPRM to improve the crashworthiness protection of railroad tank cars designed to transport PIH materials and believes that many of the proposed standards in the NPRM, when implemented, will significantly improve the safety of transporting PIH gases in railroad tank cars. The Safety Board notes that the NPRM will not apply to all pressure tank cars, such as those used to transport flammable gases like propane. The Board believes that the NPRM can be improved in several areas that we address below.
Proposed Performance Standards for the Structural Integrity of Tank Cars
The NPRM proposes that for a tank car transporting PIH gases, the standard for tank head puncture resistance will be increased from an 18-mph strike with a coupler to a 30-mph strike by a loaded freight car with a 6-inch-square cross-section ramming device that has the outer dimensions of a coupler with its knuckle removed. In addition, the NPRM also includes a proposed standard for tank shell puncture resistance that would require that the tank shell be capable of sustaining the impact of a 25-mph strike by a loaded freight car with a 6-inch-square cross-section ramming device. The current regulations do not include any standards addressing tank shell puncture resistance. These proposed performance standards for tank cars used for the transportation of PIH gases will improve the integrity and performance of the puncture resistance of such tank cars and thereby reduce the likelihood of a subsequent release of the PIH cargoes.
However, the Safety Board does have concerns about the technical basis of these performance standards. The Board understands that the test speed chosen for the performance standard is based on the assumption that the impact speed of a freight car striking a tank car will be less than the speed of the train. The FRA said that Volpe National Transportation Systems Center (Volpe) research concluded that the speed at which freight cars hit after an accident’s initiation is about 50 percent of the train speed at the time of the accident. Therefore, a maximum 25-mph impact speed for secondary rail cars involved in an accident was proposed. The Board
does not believe that 50 percent is applicable to all derailment conditions. In the Volpe research, a simple two-dimensional model of a train with an artificially triggered motion and induced motions of a derailment was used. Volpe could have used other initial conditions that replicate derailment triggers, which would have shown car-to-car impacts at greater than 50 percent of the train speed. More important, this accident modeling approach did not take into consideration many of the three-dimensional, highly nonlinear dynamic responses that occur in derailments. Consequently, the Board believes that while establishing tank car puncture resistance at 25 mph is an improvement that will enhance tank car safety, it does not represent a standard for ensuring safety in 50-mph derailments. The Safety Board believes that more technically rigorous models should be developed and validated.
In Safety Recommendations R-04-6 and -7, the Safety Board urged the FRA to validate a predictive model for quantifying the relevant dynamic forces acting on railroad ta
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