Accounting for fire scenarios is critical when analyzing pressure-relieving and depressuring systems. This is particularly true in systems such as oil refineries, petrochemical facilities, gas plants, and oil and gas production facilities where the flowing fluids are highly flammable. Because operating safely is of paramount importance in these industries, standards and recommended practices have been developed by trade associations such as the American Petroleum Institute Standard 521 (API 521) to aid in the analysis of the system. In the case of fire scenarios, the traditional recommendation of API 521 has been an empirical model based on the wetted area of the vessel. However, in the most recent 6th edition released in 2014, the standard added an analytical equation based on the Stefan-Boltzmann law that can be used for modeling the dynamic response of pressurized vessels in fire scenarios. Using BLOWDOWN (TM) Technology in Aspen HYSYS, this analytical fire equation was validated with available experimental data and compared with the traditional wetted area model. This also included evaluating the effects of the parameters in the analytical equation such as surface emissivity of the equipment wall and external heat transfer coefficient, which have significant uncertainties. As plant fires can impact a wide area, this study further investigated using the analytical equation to model fire on a detailed geometry of a pressurized vessel with associated piping. (C) 2017 Elsevier Ltd. All rights reserved.