In a method of operating an irradiation system (10) for irradiating layers of a raw material powder with electromagnetic or particle radiation in order to produce a three-dimensional work piece (110) it is determined whether a region of a raw material powder layer (11) to be selectively irradiated with electromagnetic or particle radiation in accordance with a geometry of a corresponding layer of the work piece (110) to be produced is affected or substantially unaffected by particulate impurities. Upon selectively irradiating the region of the raw material powder layer (11) with electromagnetic or particle radiation, an energy density applied to the region of the raw material powder layer (11) by a radiation beam (14a, 14b) is controlled in such a manner that the energy density is higher in case it is determined that the region of the raw material powder layer (11) is affected by particulate impurities than in case it is determined that the region of the raw material powder layer (11) is substantially unaffected by particulate impurities.