Elemental chlorine free (ECF) is a technique that uses chlorine dioxide for the bleaching of wood pulp. It does not use elemental chlorine gas during the bleaching process and prevents the formation of dioxins and dioxin-like compounds, carcinogens. The traditional ECF sequence is DEopDEpD:14 using the common letter symbols for bleaching stages, though many improved sequences are available.:15
Totally chlorine free (TCF) is paper that does not use any chlorine compounds for wood pulp bleaching.