[en] Over the past several years, there have been ongoing discussions about the attempt to compare the thermal hypothetical accident environment in the Nuclear Regulatory Commission (NRC) regulations for the packaging and transportation of radioactive materials and the thermal qualification test conditions in the Department of Transportation's (DOT) thermal insulation specifications for tank cars. This paper discusses the purposes and differences of each test environment and shows the relative magnitude of error that can occur when applying these regulations inappropriately. The purpose of the NRC regulations governing the packaging and transportation of radioactive materials is to assure that the transportation cask is designed safely and will protect the public in the event of an accident. Radiological criteria, such as radioactivity release and radiation levels external to the cask, are specified. Contained in these regulations are severe performance standards which outline sequential mechanical and thermal loads that the package must be designed to withstand. The sequential nature of the tests are an important consideration. By the time a package is subjected to the thermal environment, it may already have sustained a significant amount of structural damage. The regulations do not define allowable structural or thermal damage to the package; instead the cask integrity must maintain stringent containment, shielding, and criticality specifications. 10 refs., 4 figs