Gas outlets (6) are located at each end of the chamber. [0058]FIG. 1AC is a diagrammatic end view representation of a pyrolysis reactor of the invention similar to that shown in FIG. 1AA or 1AB but having a gas outlet (6) located below the localised heating zone (8). [0059] In operation, the reactor shown in FIGS. 1AA to 1AC is flushed with an inert gas such as N2 or Ar, or is evacuated by means o