2. No fuel is to be used other than:
Untreated dry wood but excluding any such wood which contains halogenated organic compounds or heavy metals as a result of treatment with wood-preservatives or coatings;
Peat or peat briquettes with, in either case, less than 25% moisture;
Union Coal Briketts, manufactured by Rheinbraun AG of Germany comprising lignite compressed into briquettes of approx. 15cm in length with square ends and with a sulphur content not exceeding 1% of the total weight;
CPL wildfire, manufactured by Coal Products Ltd, Immingham, which comprise bituminous coal with a volatile content of 32—36% (as to approximately 96% of the total weight) and a cold cure resin binder (as to the remaining weight) are manufactured from these constituents by a process involving roll pressing, have an average weight of either 80— 90 grams or 160—170 grams, and have a sulphur content not exceeding 1.8% of the total weight