Abstract ISO/TS 16732:2005 provides the conceptual basis for fire risk assessment by stating the principles underlying the quantification and interpretation of fire-related risk. These fire risk principles apply to all fire-related phenomena and all end-use configurations, which means these principles can be applied to all types of fire scenarios. ISO/TS 16732:2005 is designed as a guide for future documents that provide formal procedures for the implementation of the risk assessment principles for specific applications, e.g., situations in which only certain types of fire scenarios are possible. Those future documents will complete the process of full standardization begun by ISO/TS 16732:2005, which not only specifies the steps to be followed in fire risk assessment but also provides guidance for use in determining whether the specific approach used for quantification falls within an acceptable range. Principles underlying the quantification of risk are presented in ISO/TS 16732:2005 in terms of the steps to be taken in conducting a fire risk assessment. These quantification steps are initially placed in the context of the overall management of fire risk and then explained within the context of fire safety engineering, as discussed in ISO/TR 13387. The use of scenarios and the characterization of probability and consequence are then described as steps in fire risk estimation, leading to the quantification of combined fire risk. Guidance is also provided on the use of the information generated, i.e., on the interpretation of fire risk. Finally, there is an examination of uncertainty in the quantification and interpretation of the fire risk estimates obtained following the procedures in this document.