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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 tank cars during an accident and to initiate rulemaking to develop and implement appropriate design standards for pressurized tank cars. Safety Board staff evaluated the tank car failures in the Minot accident by utilizing the dynamic fracture toughness data for TC-128B steel developed through FRA-funded research conducted at the Southwest Research Institute. Based on the data, Safety Board staff determined that these tank cars failed from structural loads caused by high-speed impacts with frozen ground. No sign of a puncture in the tank car walls (that is, by impacting objects such as couplers) was found in the tank cars. Many previous tank car failures have been caused by impacts not only with couplers and drawbars, but also with other objects of varying size and shape, such as side-to-side and localized impacts with other freight cars, the ground, rails, and wheel sets. Tank car failures have also occurred following severe crushing damage and/or denting.
In the preamble of the NPRM, PHMSA states the following:
[The U.S. Department of Transportation’s] tank car research has shown that the rupture of tank cars and loss of lading are principally associated with the car-to-car impacts that occur as a result of derailments and train-to-train collisions.
The Safety Board does not disagree with this statement but is concerned that the proposed rule defines only a puncture-resistance standard for tank cars. Although this is an important aspect of tank car safety enhancement, the proposed standard falls short of meeting the goal of ensuring that tank cars can withstand the spectrum of loads from a variety of impacts that are known to have occurred during past derailments. The Board intentionally worded Safety Recommendation R-04-06 to include the different types of critical-loading conditions observed in derailments. Again, the Safety Board believes that additional modeling and testing of various loading scenarios is needed to address this concern.
The proposed rule also states that because the data from FRA-funded research show that measured values of fracture toughness for tank car steels vary by a factor of four, criteria based on fracture toughness cannot be developed for tank car steels. However, the Safety Board has an alternate interpretation and notes that the variation in fracture toughness values occurred over a wide temperature range (from about -50° F to about 72° F). The FRA research values do demonstrate that at any given temperature, the variation of fracture toughness is generally bounded by a factor of two or less. Such a variation is common to this class of steels and has been used in other applications to define fracture-based criteria. Additionally, as shown in the evaluation by Safety Board staff, through use of a statistically valid estimate of the lower bound for measured fracture toughness, one can show reliable estimates of crack sizes necessary to generate ruptures from impact-generated cracks. Fracture toughness determines the critical size of an impact-generated crack that can be sustained in a given tank car design without a structural failure under specified operating conditions. Fracture toughness also determines whether a tank car that sustains localized structural failures from impact loads can resist catastrophic rupture. Therefore, the Safety Board believes that requirements for fracture toughness also should be part of the design specifications. In evaluating the safety of new tank car designs, a standard for required fracture toughness of construction materials should be included as recommended in Safety Recommendation R-04-7.
The Safety Board also is concerned that the proposed standards would allow new designs to be approved based solely on computational analysis. As part of the Next Generation Rail Tank Car Project (NGRTCP), Dow Chemical Company has funded three tank car impact tests at Transportation Technology Center, Inc. Although the initial computational simulations of these tests have shown a good correlation with the overall test results, a reliable capability to accurately predict material failure and resultant puncture of the tank walls solely from computational simulations has not been demonstrated. Therefore, we believe that computational simulations, until demonstrated to reliably predict material and structural failures, must be complemented by a well-designed and comprehensive testing program to qualify tank car designs.
The Safety Board reviewed the proposed qualification tests for simulating punctures in Appendix C. The three tests already conducted in the NGRTCP have demonstrated that tank car body motion under impact conditions can have a significant influence on the degree of damage done to a tank car. To ensure that the test protocols described in Appendix C of the NPRM accurately simulate puncture resistance, the rigid body motion should be constrained.
Operational Restrictions
The Safety Board supports, in principle, the implementation of the proposed speed restrictions for trains with tank cars transporting PIH gases, as addressed in Safety Recommendation R-05-16. The Board also notes that, in response to Safety Recommendation
R-05-15, the NPRM further proposes additional speed restrictions through non-signal territory for trains with tank cars that transport PIH gases and that do not meet the enhanced performance standards. However, the Board does not believe that the operating restrictions being proposed in the NPRM fully address Safety Recommendations R-05-15 and -16.
In the NPRM, the proposed interim standard would reduce the speed of trains transporting PIH materials in tank cars that do not meet the proposed performance standards for structural integrity. These trains could not exceed 30 mph in non-signal territory. PHMSA states that this speed restriction is in response to Safety Recommendations R-05-15 and -16, which were issued as a result of the Graniteville investigation. The Safety Board notes that Safety Recommendation R-05-15 applies to any train operating in non-signal territory and in the absence of switch position indicator lights or other automated systems that provide train crews with advance notice of switch positions. Because the NPRM does not address speed restrictions for any train operating in territory without switch indicator lights or automated systems to provide switch positions, the NPRM does not fully address Safety Recommendation R-05-15.
Similarly, the NPRM does not fully address Safety Recommendation R-05-16 because the NPRM does not include operating measures to minimize impact forces from accidents and reduce the vulnerability of tank cars transporting PIH materials, as stated in the recommendation. Positioning of tank cars toward the rear of trains and reducing speeds through populated areas were specifically suggested in the recommendation text as examples of the operational measures that should be considered.
Further, the NPRM states that the Safety Board classified Safety Recommendations
R-05-15 and -16 as “Open—Response Received” but fails to mention that the Safety Board classified the two recommendations respectively as “Closed—Unacceptable Action” and “Open—Unacceptable Response” on June 7, 2007. In its June 7 letter regarding Safety Recommendation R-05-15, the Safety Board noted the FRA’s response, which stated that the recommendation was not feasible for operational and economic reasons and that the FRA had given its final response. The Safety Board also stated its concern that the FRA had neither fully acknowledged that there was a problem that needed to be addressed nor offered an alternate course of action. Regarding Safety Recommendation R-05-16, the Safety Board acknowledged the FRA’s concern that train-handling measures must be taken into consideration when positioning tank cars in freight trains. The Board also expressed its disappointment that the FRA neither pursued the placement of tank cars in trains and speed restrictions nor suggested other positive alternatives.
Implementation Schedule
The Safety Board supports the proposed implementation schedule for the design, construction, and deployment of a new enhanced tank car that meets the proposed performance standards. The planned schedule is very aggressive: design approval and commencement of construction of the higher performance tank cars within 2 years of the adoption of the final rule, replacement of 50 percent of the PIH fleet within 5 years, and replacement of 100 percent of the fleet within 8 years. The FRA has indicated that the proposed implementation schedule will also accelerate the retirement of pre-1989 pressure tank cars and the transfer of post-1989 pressure tank cars currently in PIH service to transporting less dangerous materials. The Board commends the FRA and PHMSA for the proposal to accelerate this transition.
In closing, the Safety Board supports the stated goals of the NPRM but believes that it can be improved and strengthened as noted in this letter. The Safety Board appreciates the opportunity to comment on the notice.
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