This International Standard describes a method for relating permissible activity release rates of the radioactive contents carried within a containment system to equivalent gas leakage rates under specified test conditions. This approach is called gas leakage test methodology. However, in this International Standard it is recognized that other methodologies might be acceptable.When other methodologies are to be used, it shall be shown that the methodology demonstrates that any release of the radioactive contents will not exceed the regulatory requirements. The use of any alternative methodology shall be by agreement with the competent authority.This International Standard provides both overall and detailed guidance on the complex relationships between an equivalent gas leakage test and a permissible activity release rate. Whereas the overall guidance is universally agreed upon, the use of the detailed guidance shall be agreed upon with the competent authority during the Type B package certification process.It should be noted that, for a given package, demonstration of compliance is not a single methodology.While this International Standard does not require particular gas leakage test procedures, it goes present minimum requirements for any test that is to be used. It is the responsibility of the package designer or consignor to estimate or determine the maximum permissible release rate of radioactivity to the environment and to select appropriate leakage test procedures that have adequate sensivity.This International Standard pertains specifically to Type B packages for which the regulatory containment requirements are specified explicitly.