According to the process safety glossary of CCPS, the deflagration explosion of a flammable mixture that occupies only a part of the total volume of a vessel or of a confined compartment is known as a Partial Volume Deflagration (PVD). Such events are characterized by overpressure values much lower than those observed in deflagration involving a compartment or a vessel completely filled by a flammable mixture, but still significantly higher than threshold values for building and process equipment damage. After a concise discussion of the main features of PVDs, the author review the methods for calculating the PVDs overpressure already available in the literature. Then the author presents a thermodynamic method based on the coupling between isobaric chemical equilibrium calculation and isentropic compression of the non reactive volume, that can be used to calculate overpressures in unvented PVD. Comparison with experimental data and CFD predictions relevant to a wide range of applications where PVDs are expected is satisfactorily. The present method can be satisfactorily used for engineering purposes. (C) 2016 Elsevier Ltd. All rights reserved.