In spaces with emission hazards, such as warehouses containing chemicals or technical process plants, an emission source of unknown intensity may start at any point in time in any location. Hence the need for a method allowing the location, intensity, and onset of an emission to be determined by means of spatially distributed measurements of concentrations of the substance emitted at various points of measurement. For this purpose, first the concentration is determined and then its rise, its constant level, or its decrease as derived from the sensors. The flow rate of the emission is measured in terms of amount and direction. In this way, solutions of the propagation equation are used which contain the quantities to be determined, i.e. location, intensity, and onset of action of the emission source, as parameters. On the basis of these solutions, the method then builds up and solves a new multi-step problem of parameter assessment. The method requires only a small number of measuring points. For instance, four measuring points are sufficient to cover three-dimensional emission propagation, and the method works even when the diffusion coefficient of the system is unknown.