Laboratory investigations have been carried out to study the influence of process failure modes on organics emission during the incineration of hazardous sludge. The thermal, temporal and fuel-oxidant mixing failure modes were tested. They were simulated by holding the first combustion temperature at 400°C and varying the after-burning one between 600 and 1100°C, the after-burning residence time between 1 and 3 s and the excess air between 30 and 160%. Results showed that the thermal failure mode is the most important factor controlling the number and concentration of emitted organics leading to the formation of over 70 compounds at after-burning temperature of 600°C. At higher after-burning temperatures emissions are controlled by the fuel-oxidant mixing failure mode and, only when the after-burning is 800°C and the oxygen is 160% over the stoichiometric value, by the temporal failure mode. Based on results obtained some suggestions for reducing emissions of toxic organics in full-scale incinerators are given.