In ISO/TR 15656:2003, the term model includes all calculation procedures that are based on physical models. These mechanistic-based or physical models encompass all the physical, mathematical and numerical assumptions and approximations that are employed to describe the behaviour of structural members and assemblies when subjected to a fire. In general, such physical models are implemented as a computer code on a digital computer. The application and extension of results from calculation methods are generally limited to performance resulting from standard tests. Aspects of ISO/TR 15656:2003 are applicable to calculation procedures not based on physical models. Mechanistic-based models can often be used to calculate the behaviour of structures in non-standard fire exposures.
The process of model evaluation is critical in establishing both the acceptable uses and limitations of fire models. It is not possible to evaluate a model in total; instead, ISO/TR 15656:2003 is intended to provide methodologies for evaluating the predictive capabilities for specific uses. Documentation of suitability for certain applications or scenarios does not imply validation for other scenarios.