Hazard Assessment for Pressure Tank Cars involved in Accidents

In the event of an accident or derailment involving a freight train, various personnel must respond to clear the rightof-way, repair the tracks, and remove the damaged rail cars. If the train contains pressure tank cars, the potential hazard needs to be assessed and safe handling procedures need to be followed. Since 1985, the Association of American Railroads, Transportation Technology Center (AAR/TTC) and other organizations have used a set of guidelines developed in the late 1970s to teach emergency response personnel how to make judgments in the field as to the severity of damage to tank cars involved in accidents. The severity of the damage then determines the appropriate course of action regarding rerailing, unloading, or moving the tank cars. Unfortunately, the Guidelines were developed by a few individuals who are no longer available to substantiate them. Thus, the guidelines lack validation beyond their reliable 15-year history and their level of conservatism is unknown. Fortunately, only very few catastrophic delayed ruptures have occurred, and those ruptures occurred in cases where the damage to the tank cars would not have passed the guidelines’ rules. A research program was begun to establish the validity of the Guidelines. The research program first focused on evaluating the technical foundation for the guidelines and the degree to which they have been validated. A program of experiments and analyses was then performed to validate the Guidelines and estimate their margins of safety. The experimental effort used small laboratory specimens to provide material property data as well as validation for the analyses. The structural and fracture mechanics analysis parts of the proposed research were accomplished by combining nonlinear finite element simulations with advanced elasto-plastic fracture and local fracture theories to quantify the severity of various types of tank car damage. The results of this research are being used to reformulate the Guidelines in more precise and quantitative terms, so that their use will contribute to increased safety at derailment sites. This paper describes the results of this program.