Warning signs are safety signs intended to draw attention to objects and issues to warn of possible dangers. Self-adhesive zone floor markings made of PVC foil serve for the practical zone classification and are intended for use in potentially explosive areas of all zones.
The classification of Ex zones depends on the atmosphere of the respective zone. A distinction is made between gas and dust explosion hazard zones and these are divided into three zones each.
Zone zero to two concern gases, mists or vapors. In zone 0, there is a permanent explosion hazard. Zone 1 designates areas in which an explosive atmosphere may occasionally form during normal operation. In Zone 2, it can be assumed that no explosive atmosphere is present or occurs only briefly during normal operation.
The zone classification for dust explosions corresponds to that for gases. In zone 20, a permanently explosive atmosphere is present due to flammable substances in the air. In zone 21, explosive atmospheres are expected to occur only occasionally during normal operation, and in zone 22, explosive atmospheres are not present or are present only for a short time. Terms such as "normal operation" or "short-term" are not clearly defined by the European Union. These are defined in national regulations, which may result in differences in categorization in different countries.