AbstractLow‐density polyethylene, with and without an antimony–bromine synergistic fire retardant or aluminium hydroxide, was subjected to standard fire tests and to experiments which determined the smoke and harmful fumes emitted on overheating. Both additives improved most fire properties but the fire retardant increased the smoke generated by intense radiant heat. The onset of smoke, flammable gas, carbon monoxide and acids was generally delayed by the additives. The total amounts and maximum values of these volatiles were lessened. Sample weight and form affect the results of these experiments. Observations during heating show that the additives reduce spreading of the melt, thus reducing the surface area available for oxidat