Organic peroxides are highly reactive and unstable substances that can undergo self-accelerating decomposition and develop sequential fireballs during storage and transportation. The available semi-empirical equations for the assessment of physical and radiative properties of organic peroxides and liquid hydrocarbon fireballs are based on a fixed mass of substance with an assumption of single fireball formation. However, the involvement of variable fuel mass in sequential fireballs developed in an overlapping and individual manner requires further modifications to the existing equations. Considering the complexities involved in large-scale experiments, Computational Fluid Dynamics (CFD) based open-source code Fire Dynamics Simulator (FDS) has been used in the present study to estimate the characteristics of such sequential fireballs. The existing equations are modified based on visible diameter of the overlapped fireballs. The safety distances are calculated and compared using different models viz. TDU, TNT equivalence and irradiation. Results indicated that the predicted Surface Emissive Power (SEP) for the overlapped fireballs are 9–27% higher compared to the individual fireballs. Moreover, the predicted safety distances as per NFPA 49CFR (5 kW/m2) for overlapped fireballs were ranging from 60 to 70 m compared to 15–25 m for the individually generated ones.