Sch 1 para 33 Explosive atmospheres caused by air and dust mixtures
(1) Equipment must be so designed and constructed that ignition of air and dust mixtures does not occur even in the event of rare incidents relating to equipment. (2) It must be equipped with means of protection such that— (a) either, in the event of failure of one means of protection, at least an independent second means provides the requisite level of protection; or (b) the requisite level of protection is ensured in the event of two faults occurring independently of each other. (3) Where necessary, equipment must be so designed that dust can enter or escape from the equipment only at specifically designated points. (4) The requirement in sub-paragraph (3) must also be met by cable entries and connecting pieces. (5) The surface temperatures of equipment parts must be kept well below the ignition temperature of the foreseeable air and dust mixtures in order to prevent the ignition of suspended dust. (6) With regard to the safe opening of equipment parts, sub-paragraph 32(5) applies.