Venting systems are useful for the mitigation of accidental explosions. Vent ducts should be used if equipment is located indoors, as NFPA 68 (2007) suggests, for discharging combustion products to safe location. However, the presence of a duct is likely to increase the severity of the explosion with respect to simply vented vessels. Up to now, no reliable correlations are available for the sizing of ducted vented systems. The only cord relation available was developed by Bartknecht in 1993 for gas explosion, also acknowledged by NFPA 68. In this study, we propose an engineering correlation based on semi-empirical engineering methodologies, which is able to quantify the relations between geometric properties and the peak pressure occurring in the combustion chamber in the presence of a duct fitted on the vent panel. To this aim, we have regressed all the available experimental data on gas explosion in ducted-vented vessels. (c) 2007 American Institute of Chemical Engineers.