Some changes to the leak impact factor (LIF), relative to the first and second editions of this text, are recommended. The elements of the LIF have not changed, but the protocol by which these ingredients are mathematically combined has been made more transparent and realistic in this discussion. Additional scoring approaches are also presented. Given the increasing role of risk evaluations in many regulatory and highly scrutinized applications, there is often the need to consider increasing detail in risk assessment, especially consequence quantification. There is no universally agreed upon method to do this. This edition of this book seeks to provide the risk assessor with an understanding of the sometimes complex underlying concepts and then some ideas on how an optimum risk assessment model can be created. The final complexity and comprehensiveness of the model will be a matter of choice for the designer, in consideration of factors such as intended application, required accuracy, and resources that can be applied to the effort.