In the chemical industry, most reactors are equipped with an emergency relief vent to prevent bursting in case of accidental overpressure. The physical nature of the vent release (gas phase or two-phase liquid-gas) strongly influences the necessary vent size. To know that nature is critical for vent sizing. The objective of my thesis is to develop a methodology to predict the nature of the vent release at industrial scale based on thermodynamic and physicochemical data of the reacting system, the size of the vent, its actuation set pressure..., whatever the reactive system.Joint DIERS Meeting 2015 in Dusseldorf is an opportunity to communicate among the <i>European and US DIERS Users’ Group</i> who work on emergency relief system design. The members are industrialists, consultants and academics who are working in the field of process and plant safety. The presentation allows showing my thesis study to the European and US communities. Their advices and comments are very useful to verify the current and further works.