Sch 1 para 37 Explosive atmospheres caused by air and dust mixtures
(1) Equipment must be so designed and constructed that air and dust mixtures cannot be ignited by foreseeable ignition sources likely to exist during normal operation. (2) With regard to surface temperatures, sub-paragraph 33(5) applies. (3) Equipment, including cable entries and connecting pieces, must be so constructed that, taking into account the size of its particles, dust can neither develop explosive mixtures with air nor form dangerous accumulations inside the equipment.