A method for generating data indicating a degree of change within an installation, the change being indicated by increased release of a contaminant. The method comprises receiving as input a plurality of dose data items, each dose data item indicating a dose of the contaminant to which an individual has been exposed while carrying out a predetermined task at a time specified by that dose data item, and processing said dose data items to generate output data indicative of a degree of change occurring within the installation between times specified by the dose data items.
