Areas classified into Zones must be protected from effective sources of ignition. The directive distinguishes between two types of explosive atmospheres, which are dust and gas. Each of these explosive atmospheres are categorically subdivided into three sub-zones. For gas, vapor, and mist the zone classifications would be 0, 1, and 2. For dust, the zones would be 20, 21, and 22. As is logical, the protection levels and testing for products that meet Zone 0 and Zone 20 are much more restrictive than those that meet Zone 2 and Zone 22.