This paper presents a new methodology for determining the thermal radiation of dynamic fireballs considering the presence of obstructions (i.e. safety barrier, topographic elevation). The specific type of obstruction considered is a flat wall. The key feature of the methodology is that, due to the presence of a barrier, the dynamic fireball evolves through different stages of relative visibility (i.e. null, partial or complete) during its transitional regime. A set of equations defining the boundaries of each region has been developed, which are required to calculate the configuration factor for each transient position of the fireball. According to the relative visibility, analytical or numerical methods must be used to determine the configuration factor between the fireball and the receiver. This methodology aims to achieve a more realistic modeling of the fireball elevation mechanism, enabling safety engineers to better estimate the fraction of thermal radiation received in common scenarios in the process industry and to improve the design of safety barriers to minimise the impact of radiation on vulnerable elements or critical infrastructures. The study is of particular interest for land use planning and plant location. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.