PresentationThe purpose of this study is to compare calculated sizes of explosion venting fireballs to correlations for a range of gas explosions in enclosures fitted with an explosion vent. Explosion vents are commonly used to protect process equipment containing flammable gases. When properly designed, an explosion vent can reduce the peak overpressure inside the enclosure so that the enclosure does not permanently deform or fail catastrophically. The fuel and combustion products that exit the vent, however, create an external fireball hazard. Deflectors can be used to reduce the extent of that external fireball, but their effectiveness has not been rigorously tested for vessels larger than 20 m3Recently, there have been questions about the accuracy of correlations to predict fireball dimensions from explosion vents and the effects of deflectors on those dimensions. The fireball size during venting is crucial in determining the thermal hazard area around the protected enclosure. The National Fire Protection Association standard NFPA 68 and International Standard EN14994 provide correlations for calculating the extent of the expected fireball during explosion venting scenarios. The formulas for gas-explosion fireball-sizes are empirical and based on data from a limited number of experiments. In this study, explosion-venting scenarios are modelled numerically using FLACS v10. FLACS is a Computational Fluid Dynamics (CFD) software widely used in the oil and gas industry to perform explosion consequence modelling (Gexcon 2015). The CFD model was used to evaluate the fireball extent and temperature. The model results provide the fireball shape and size for different scenarios including scenarios with deflectors. A number of parameters are varied, including: Enclosure size Type of fuel Presence of a deflagration deflector plate The study elucidates the relative importance of each of these parameters on the explosion fireball size. This can assist in designing future testing programs to examine fireball size and identifying parameters for use in improved fireball size correlations