Abstract: This invention relates to a process for thermally cracking waste polymer(s) comprising chlorinated polymers in a reactor in the presence of a fluidizing gas and a fluidized bed of solid, particulate fluidizable material at a temperature from 350.degree.-600.degree. C. to cracked products comprising a mixed vapor of lower hydrocarbons which have a chlorine content of less than 50 ppm. In the process, the cracked products emerging from the fluidized bed are passed through one or more guard beds comprising calcium oxide or a compound capable of giving rise to calcium oxide under the reaction conditions maintained at a temperature in the range from 400.degree.-600.degree. C. in such a way that the chlorine content of the product is less than 50 ppm.