Section 7. Electrical equipment of special installations

Electrical installations in hazardous areas. Definitions

Encyclopedia of radio electronics and electrical engineering / Rules for the installation of electrical installations (PUE)

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7.3.2. An explosion is a rapid transformation of substances (explosive combustion), accompanied by the release of energy and the formation of compressed gases capable of doing work.

7.3.3. Flash - rapid combustion of a combustible mixture, not accompanied by the formation of compressed gases.

7.3.4. Smoldering - burning without glow, usually identifiable by the appearance of smoke.

7.3.5. Electrical sparking - spark, arc and glowing electrical discharges.

7.3.6. Intrinsically Safe Electrical Circuit - An electrical circuit designed such that an electrical discharge or heating of the circuit cannot ignite an explosive atmosphere under prescribed test conditions.

7.3.7. Flash point - the lowest (under special test conditions) temperature of a combustible substance at which vapors and gases are formed above its surface that can flare up from an ignition source, but the rate of their formation is still insufficient for subsequent combustion.

7.3.8. Ignition temperature - the temperature of a combustible substance at which it releases flammable vapors or gases at such a rate that, after igniting them from an ignition source, stable combustion occurs.

7.3.9. The autoignition temperature is the lowest temperature of a combustible substance at which a sharp increase in the rate of exothermic reactions occurs, ending in the occurrence of fiery combustion.

7.3.10. The smoldering temperature is the lowest temperature of a substance (materials, mixture) at which there is a sharp increase in the rate of exothermic reactions, ending with the onset of smoldering.

7.3.11. A flammable liquid (hereinafter FL) is a liquid capable of burning independently after the ignition source is removed and having a flash point not higher than 61 ºС.

Flammable liquids are explosive, in which the flash point does not exceed 61 ºС, and the vapor pressure at a temperature of 20 ºС is less than 100 kPa (about 1 atm).

7.3.12. Combustible liquid - a liquid capable of burning on its own after the ignition source is removed and having a flash point above 61 ºС.

Combustible liquids with a flash point above 61 ºС are classified as flammable, but heated under production conditions to a flash point and above, they are classified as explosive.

7.3.13. Light gas - a gas that at an ambient temperature of 20 ºС and a pressure of 100 kPa has a density of 0,8 or less relative to the density of air.

7.3.14. A heavy gas is a gas which, under the same conditions as in 7.3.13, has a density greater than 0,8 relative to that of air.

7.3.15. Liquefied gas is a gas that, at an ambient temperature below 20 ºС, or a pressure above 100 kPa, or under the combined action of both of these conditions, turns into a liquid.

7.3.16. Combustible gases are explosive at any ambient temperature.

7.3.17. Combustible dust and fibers are classified as explosive if their lower concentration limit of ignition does not exceed 65 g/m3.

7.3.18. Explosive mixture - a mixture with air of combustible gases, flammable liquid vapors, combustible dust or fibers with a lower concentration limit of ignition of not more than 65 g / m3 when they pass into a suspended state, which, at a certain concentration, is capable of exploding when a source of initiation of an explosion occurs.

Explosive also includes a mixture of combustible gases and vapors of flammable liquids with oxygen or another oxidizing agent (for example, chlorine).

The concentration of combustible gases and vapors of flammable liquids in the air is taken as a percentage of the air volume, the concentration of dust and fibers - in grams per cubic meter to the air volume.

7.3.19. The upper and lower concentration limits of ignition are, respectively, the maximum and minimum concentrations of combustible gases, flammable liquid vapors, dust or fibers in the air, above and below which an explosion will not occur even if an explosion initiation source occurs.

7.3.20. Premises - a space enclosed on all sides by walls (including windows and doors), with a coating (overlapping) and a floor. The space under the canopy and the space limited by mesh or lattice enclosing structures are not premises.

7.3.21. Outdoor installation - installation located outdoors (outside) openly or under a canopy or behind mesh or lattice enclosing structures.

7.3.22. Explosive zone - a room or a limited space in a room or outdoor installation in which explosive mixtures are present or may form.

7.3.23. Explosion-proof electrical equipment - electrical equipment, which provides for constructive measures to eliminate or hinder the possibility of ignition of the explosive environment surrounding it as a result of the operation of this electrical equipment.

7.3.24. General-purpose electrical equipment - electrical equipment made without taking into account the requirements specific to a particular purpose, certain operating conditions.

7.3.25. Safe experimental maximum gap (BEMZ) - the maximum gap between the flanges of the shell, through which the transfer of an explosion from the shell to the environment does not pass at any concentration of the mixture in air.

See other articles Section Rules for the installation of electrical installations (PUE).

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