Dynamic modelling and simulation of a chemical process in emergency conditions is considered. Such modelling and simulation often requires rapid implementation of model changes by the process engineer followed by simulation runs. A simulator with an open architecture structure is presented where the model components (equations) an stored in an object-oriented form in a database, enabling rapid and easy modification of the model. A general-purpose numerical solver is used for solving the model and plotting the pertinent results. An example is presented, where the use of the proposed simulator enables a rapid identification of the right strategy to prevent development of runaway temperature conditions in a reactor.