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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
Section 7. Electrical equipment of special installations Electrical installations in hazardous areas. Classification of hazardous areas
Encyclopedia of radio electronics and electrical engineering / Rules for the installation of electrical installations (PUE) 7.3.38. The classification of hazardous areas is given in 7.3.40 to 7.3.46. The class of the explosive zone, in accordance with which the choice of electrical equipment is made, is determined by the technologists together with the electricians of the design or operating organization. 1) 1. The volumes of explosive gas and vapor-air mixtures, as well as the time of formation of a vapor-air mixture are determined in accordance with the "Instructions for determining the category of production for explosive, explosive and fire hazards", approved in the prescribed manner. 2. In premises with industries of categories A, B and E, electrical equipment must meet the requirements of Ch. 7.3 to electrical installations in hazardous areas of the corresponding classes. 7.3.39. When defining explosive zones, it is assumed that a) the explosive zone in the room occupies the entire volume of the room if the volume of the explosive mixture exceeds 5% of the free volume of the room; b) an explosive zone is considered to be a zone in a room within a range of up to 5 m horizontally and vertically from the process apparatus, from which combustible gases or vapors of flammable liquids can be released, if the volume of the explosive mixture is equal to or less than 5% of the free volume of the room (see also 7.3.42, item 2). A room outside the explosive zone should be considered non-explosive if there are no other factors that create an explosion hazard in it; c) the explosive zone of outdoor explosive installations is limited to the dimensions determined in 7.3.44. 7.3.40. Zones of class B-I - zones located in rooms in which combustible gases or vapors of flammable liquids are released in such quantity and with such properties that they can form explosive mixtures with air under normal operating conditions, for example, when loading or unloading process equipment, storage or transfusion of flammable liquids in open containers, etc. 7.3.41. Class B-Ia zones - zones located in rooms in which, during normal operation, explosive mixtures of combustible gases (regardless of the lower concentration limit of ignition) or flammable liquid vapors with air are not formed, but are possible only as a result of accidents or malfunctions. 7.3.42. Zones of class V-Ib - zones located in rooms in which, during normal operation, explosive mixtures of combustible gases or vapors of flammable liquids with air are not formed, but are possible only as a result of accidents or malfunctions and which differ in one of the following features: 1. Combustible gases in these areas have a high lower concentration limit of ignition (15% or more) and a pungent odor at maximum permissible concentrations in accordance with GOST 12.1.005-88 (for example, machine rooms of ammonia compressor and refrigeration absorption plants). 2. Premises of industries associated with the circulation of gaseous hydrogen, in which, according to the conditions of the technological process, the formation of an explosive mixture in a volume exceeding 5% of the free volume of the premises is excluded, have an explosive zone only in the upper part of the premises. The explosive zone is conditionally taken from the mark of 0,75 of the total height of the room, counting from the floor level, but not higher than the crane runway, if any (for example, water electrolysis rooms, charging stations for traction and stator batteries). Clause 2 does not apply to electrical machine rooms with hydrogen-cooled turbogenerators, provided that the electrical machine room is provided with natural exhaust ventilation; these electrical machine rooms have a normal environment. Class C-IB also includes areas of laboratory and other premises in which combustible gases and flammable liquids are present in small quantities, insufficient to create an explosive mixture in a volume exceeding 5% of the free volume of the room, and in which work with combustible gases and flammable liquids is carried out without open flame applications. These zones are not explosive if work with combustible gases and flammable liquids is carried out in fume hoods or under fume hoods. 7.3.43. Zones of class B-Ig - spaces near outdoor installations: process installations containing flammable gases or flammable gases (with the exception of outdoor ammonia compressor installations, the choice of electrical equipment for which is made in accordance with 7.3.64), above-ground and underground tanks with flammable liquids or flammable gases (gas holders) , racks for unloading and loading of flammable liquids, open oil traps, settling ponds with a floating oil film, etc. The zones of class B-Ig also include: spaces at openings behind the external enclosing structures of rooms with explosive zones of classes B-I, B-Ia and B-II (with the exception of window openings filled with glass blocks); spaces near external enclosing structures, if they are equipped with devices for ejection of air from exhaust ventilation systems of premises with explosive zones of any class or if they are located within the outer explosive zone; spaces at safety and breathing valves of containers and technological apparatuses with combustible gases and flammable liquids. 7.3.44. For outdoor explosive installations, the explosive zone of class B-Ig is considered to be up to: a) 0,5 m horizontally and vertically from openings behind the outer enclosing structures of rooms with explosive zones of classes B-I, B-Ia, B-II; b) 3 m horizontally and vertically from a closed technological apparatus containing combustible gases or flammable liquids; from an exhaust fan installed outside (on the street) and serving rooms with explosive zones of any class; c) 5 m horizontally and vertically from devices for ejection from safety and breathing valves of containers and technological apparatus with combustible gases or flammable liquids, from devices located on building envelopes for ejection of air from exhaust ventilation systems of rooms with explosive zones of any class; d) 8 m horizontally and vertically from tanks with flammable liquids or combustible gases (gas holders); in the presence of embankment - within the entire area inside the embankment; e) 20 m horizontally and vertically from the place of open discharge and filling for overpasses with open discharge and loading of flammable liquids. Overpasses with closed loading and unloading devices, overpasses and supports for pipelines for combustible gases and flammable liquids are not classified as explosive, with the exception of zones within 3 m horizontally and vertically from shutoff valves and flange connections of pipelines, within which electrical equipment must be explosion-proof for the corresponding category and group of explosive mixture. 7.3.45. Zones of class B-II - zones located in rooms in which combustible dusts or fibers passing into suspension are emitted in such quantity and with such properties that they are capable of forming explosive mixtures with air under normal operating conditions (for example, during loading and unloading technological devices). 7.3.46. Zones of class B-IIa - zones located in rooms in which the hazardous conditions specified in 7.3.45 do not occur during normal operation, but are possible only as a result of accidents or malfunctions. 7.3.47. Zones in rooms and zones of outdoor installations within a horizontal and vertical range of up to 5 m from the apparatus in which explosive mixtures are present or may occur, but the technological process is carried out using open fire, hot parts, or technological apparatuses have surfaces heated to the self-ignition temperature of combustibles gases, vapors of flammable liquids, combustible dusts or fibers, are not classified as explosive in terms of their electrical equipment. The classification of an indoor environment or an outdoor installation environment outside the specified 5-meter zone should be determined depending on the technological processes used in this environment. Zones in rooms and zones of outdoor installations, in which solid, liquid and gaseous combustible substances are burned as fuel or disposed of by combustion, are not classified as explosive in terms of their electrical equipment. 7.3.48. In the premises of heating boiler houses built into buildings and designed to operate on gaseous fuels or liquid fuels with a flash point of 61 ° C and below, it is required to provide the necessary minimum of explosion-proof lamps that are turned on before the start of the boiler installation. Light switches are installed outside the boiler room. Electric motors of fans switched on before the start of operation of the boiler plant, and their starters, switches, etc., if they are located inside the premises of boiler plants, must be explosion-proof and correspond to the category and group of an explosive mixture. Wiring to ventilation electrical equipment and lamps must comply with the class of the explosive zone. 7.3.49. When used for painting materials that can form explosive mixtures, when painting and drying chambers are located in the general process flow of production, subject to the requirements of GOST 12.3.005-75, the zone is classified as explosive within up to 5 m horizontally and vertically from the open openings of the chambers , if the total area of these chambers does not exceed 200 m2 with a total area of the premises up to 2000 m2 or 10% with a total area of the premises over 2000 m2. In case of tubeless painting of products in the general process flow in open areas, subject to the requirements of GOST 12.3.005-75, the zone is classified as explosive within up to 5 m horizontally and vertically from the edge of the grating and from the products being painted, if the area of the gratings does not exceed 200 m2 at the total area of the premises is up to 2000 m2 or 10% if the total area of the premises is more than 2000 m2. If the total area of the painting and drying chambers or grates exceeds 200 m2 with a total area of the room up to 2000 m2 or 10% with a total area of the room more than 2000 m2, the size of the explosive zone is determined depending on the volume of the explosive mixture in accordance with 7.3.39. The explosive class of zones is determined according to 7.3.40 - 7.3.42. A room outside the explosive zone should be considered non-explosive if there are no other factors that create an explosion hazard in it. The areas inside the painting and drying chambers should be equated with the areas located inside the technological apparatus. The requirements of this paragraph do not apply to these zones. 7.3.50. Zones in rooms of exhaust fans serving explosive zones of any class are classified as explosive zones of the same class as the zones served by them. For fans installed behind external enclosing structures and serving explosive zones of classes B-I, B-Ia, B-II, electric motors are used both for an explosive zone of class B-Ig, and for fans serving explosive zones of classes B-Ib and B- IIa, - according to the table. 7.3.10 for these classes. 7.3.51. Zones in supply fan rooms serving explosive zones of any class are not classified as explosive if the supply air ducts are equipped with self-closing check valves that prevent the penetration of explosive mixtures into the supply fan rooms when the air supply is interrupted. In the absence of non-return valves, the premises of supply fans have explosive zones of the same class as the zones served by them. 7.3.52. Explosive zones containing light non-liquefied combustible gases or flammable liquids, if there are signs of class B-I, may be classified as class B-Ia, provided that the following measures are taken: a) devices of the ventilation system with the installation of several ventilation units. In the event of an emergency stop of one of them, the remaining units must fully ensure the required performance of the ventilation system, as well as sufficient uniformity of ventilation throughout the entire volume of the room, including basements, channels and their turns; b) an automatic alarm device that operates when a concentration of combustible gases or flammable liquid vapors occurs at any point in the room, not exceeding 20% of the lower concentration limit of ignition, and for harmful explosive gases - also when their concentration approaches the maximum allowable in accordance with GOST 12.1.005-88 . The number of alarm devices, their location, as well as their redundancy system should ensure the failure-free operation of the alarm. 7.3.53. In industrial premises without an explosive zone, separated by walls (with or without openings) from the explosive zone of adjacent premises, an explosive zone should be taken, the class of which is determined in accordance with Table. 7.3.9, the size of the zone is up to 5 m horizontally and vertically from the door opening. Tab. 7.3.9. do not apply to switchgear, transformer substations, switchgear and instrumentation installations located in premises adjacent to explosive zones of premises. The location of switchgear, transformer substations, switchgears and instrumentation and automation installations in premises adjacent to explosive zones of premises and in external explosive zones is provided in accordance with the section "Switchgear, transformer and converter substations" (see 7.3.78 - 7.3.91) Table 7.3.9. Zone class of a room adjacent to the hazardous area of another room
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