Explosive zone - a space in a room or around an outdoor installation in which explosive mixtures are or may be formed.
An area within 5 m horizontally and vertically from the equipment from which flammable gases or vapors of flammable liquids (flammable liquids) can be released is considered explosive in the room.
Gaseous and vapor-explosive atmospheres form explosive zones of classes 0, 1, 2, and dust-air - explosive zones of classes 20, 21, 22.
Class 0 explosive zone - a space in which an explosive atmosphere is present constantly or for a long time. Class 0 explosive zone may only take place within the process equipment enclosures.
Example of an explosive zone of class 0: a tank in which PPE is stored, for example, gasoline.
Class 1 explosive zone - a space in which an explosive atmosphere may be formed during normal operation (normal operation - a situation where the installation operates in accordance with its design parameters).
Example of an explosive zone of class 1: sludge settler of acetylene station.
Class 2 explosive zone - a space in which an explosive atmosphere under normal operating conditions is absent, and if it occurs, it is rare and short-lived. In these cases, possible accidents of catastrophic proportions (rupture of high-pressure pipelines or tanks of large capacity) should not be considered when designing electrical installations.
The frequency and duration of explosive gas-air environment is determined by the rules (regulations) of the relevant industries.
Example of an explosive zone of class 2: painting room in the presence of main and backup ventilation units.
Class 20 explosive zone - a space in which during normal operation explosive dust in the form of a cloud is present constantly or often in an amount sufficient to form a dangerous concentration of air mixture, and (or) a space where dust layers of unforeseen or excessive thickness may form. This usually takes place inside the equipment, where dust can form explosive mixtures frequently and for a long time.
Example of an explosive zone of class 20: machines used in the technological process of obtaining flour (for example, sieve).
Class 21 explosive zone - a space in which during normal operation, the appearance of dust in the form of clouds in an amount sufficient to form a mixture with air of explosive concentration is likely.
This area may include the space near the place of powder filling or settling and the space where dust layers are likely to appear during normal operation, which may form a dangerous concentration of explosive dust-air mixture.
An example of a Class 21 explosive zone: a room for crushing coal in the absence of spare units of the aspiration system.
Class 22 explosive zone is a space in which explosive dust in a suspended state may occur infrequently and short-lived, or in which layers of explosive dust may exist and form explosive mixtures in the event of an accident. This area may include a space near the equipment containing dust, which can be released by leakage and form dust formations.
Example of an explosive zone of class 22: production facilities of the mill.