Currently, the scope of the methodology of risk analysis continues to expand. With regard to the emergency (fire in particular) it's more correct to speak about security analysis and quantitative risk assessment (QRA). Accidental risk metric that describes a probability and accident damage, it should express the scalar number. There are four most important issues of this methodologies today: • imperfection of the existing methodological framework; • staffing (human resources); • absence of federal criteria of acceptable risk; • presence of uncertainty on all stages of the QRA. Despite the fact that around the world the presence of uncertainty and methods of its quantitative assessment in the performance of the QRA has long been widely studied, this problem is ignored in Russia. Uncertainty has two aspects - quantitative and qualitative. Analyzing the sources of uncertainty, it decided to allocate the following types: terminological, parametric and model. The latter, in turn, are subdivided into scenario, conceptual and approximating. One can cite a few concrete examples of the different types sources of uncertainty of fire risk. According to the analysis, the greatest uncertainty is accompanied assessing the likelihood of events and stage assessment of the damage. In the latter case it is possible to allocate uncertainty of qualitative and quantitative type.