IEC
IEC 60079-7
Explosive Atmospheres — Equipment Protection by Increased Safety 'e'
Increased safety works by excluding the arc, spark and hot surface in the first place, through creepage and clearance distances, terminal quality, temperature limits and conductor fill. That makes the installed condition the whole of the protection, which is why an Ex e terminal box is the enclosure most often found non-compliant on inspection: one conductor too many in a terminal, a mixed conductor size, a missing barrier, or a gasket that has been reused. The standard also sets the tE time that determines how a motor's overload protection must be selected.
This is an explanation, not the standard. PipingInspector is not affiliated with IEC and reproduces no part of the document. Always work to the current edition of the standard itself and to your project specification.