Polymerisation process

A process for the polymerisation of monomer in a polymerisation system having at least one component attached thereto which is flushed with a flush medium which enters the polymerisation system, wherein initially said component is flushed with a first flush medium, and subsequently said component is flushed with a second flush medium which second flush medium differs in composition from the first flush medium, the flow of flush medium being used to keep polymer and/or polymer reaction medium away from the component, wherein the at least one component is attached on a polymerisation reactor is selected from pressure relief valves, withdrawal lines, inlet lines, and instrument tappings, and wherein stand-by or unused withdrawal and inlet lines are maintained with a manual or control valve closed and the stagnant zone between the reactor and the valve is flushed.