Explosive atmospheres caused by air/dust mixtures
2.1.2.1 Equipment must be so designed and constructed that ignition of air/dust mixtures does not occur even in the event of rare incidents relating to equipment.
It must be equipped with means of protection such that:
either, in the event of failure of one means of protection, at least an independent second means provides the requisite level of protection,
or, the requisite level of protection is ensured in the event of two faults occurring independently of each other.