Thermogravimetry, differential thermal analysis and Fourier transform infrared spectroscopy were used to determine the thermal behaviour of the electric are furnace dust from stainless steel and carbon steel operations. The dust is classified as environmentally hazardous waste in most regions of North America and Europe because of its relatively high levels of lead, cadmium and chromium. The results indicated that, thermally, the two types of dust are still somewhat active and that there are apparent differences in their thermal behaviour. A thermal process for the stabilization of the dust by vitrifying with clay has been developed at the Environment Laboratory of the Canada Centre for Mineral and Energy Technology in Canada. The vitrification product (clinkers) of both types of dust were also examined and were found to be thermally stable at least up to 1000 degrees C.