This invention relates to a method of monitoring a fluid processing network having a plurality of fluid processing regions including the steps of: receiving measured current parameter values at known points of the network; determining from the measured current parameter values regions of the network that are active, all other regions being deemed inactive; subtracting inactive regions of the network from a model of the fluid processing network to provide a current active network model; determining current parameter values of the current active network at least at points remote from the known points, the parameter values at said remote points being determined using the measured current parameter values and the current active network model; based on the current parameter values, determining if one or more pre-specified boundaries are breached; and performing a predetermined action if one or more said boundaries are breached.