In addition to heat, the combustion in the incinerator releases a number of harmful substances. It goes without saying that the flue gases are thoroughly cleaned before we allow them to be released into the outside air through the chimney. The first step in the purification process is the electrofilter. The electrofilters are the large shiny boxes set up beside the chimney, one for each furnace line. The dust particles from the cooled flue gases are trapped in this filter.