Zones and Categories
A hazardous areas is classified into Zones (0, 1 or 2 for gasses and vapors, 20, 21 or 22 for dust).
According to the directive equipment is divided into 2 groups, which are sub-divided into categories. The categories correspond with a certain Zone where it may be used.
Example: II 1 G/D means the apparatus is not certified for use in mines and suitable for Zone 0 (gas) and Zone 20 (dust).
In the US the National Electric code is in force. The NEC500 divides a hazardous area into Division, with Division I approximately matching Zone 0 and Zone 1 together. Division 2 approximately matches Zone 2.
Suitable types of protection are often "Explosion Proof" (~ Ex d) and Intrinsic Safety (~Ex ia). There are no equivalents of Ex m and Ex e under this code.
De NEC505 divides the hazardous area in to Zones as does ATEX, and allows virtually identical types of protection.