For equipment intended for use in hazardous areas the regulations vary per country. In the European Union however these regulation have been harmonized since the ATEX directive is in force. In the US the NEC500 and the more recent NEC505 are mandatory.
For background information on explosion safety go here.
Since 1 July 2003 the ATEX directive is in force in the whole European Union . 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 categories of protection, that correspond to the Zones where it may be used. Behind the category classification follows the type of protection.
Example: II 1 G EEx ia IIC T4 means the apparatus is certified for use in surface industries and has a very high degree of protection which makes it suitable for use in Zone 0 (gasses). The protection is bases on intrinsic safety for gasses and vapors with an ignition energy higher then 40 µJ and an ignition temperature higher then 135 °C (275 °F).
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 Zone as does ATEX, and allows virtually identical types of protection.
Ex and the rest of the world
Equipment that complies with ATEX and FM regulations must be certified separately in other countries. However, this normally does not create additional technical difficulties. It will however take additional time and expenses.