Classification of hazardous areas according to PUE. The purpose of the classification of fire and explosive zones

Dangerous, from the point of view of the occurrence of an explosion and fire, the zone represents the location of a production or storage facility. Here under standard operating conditions in the atmosphere there is an admixture of flammable gases or vapors. Special classification of hazardous areas allows you to determine the type of electrical and other equipment. And also choose the degree of protection to reduce the risk of contact of a combustible air mixture with sparks of machines and devices. These comprehensive protection measures are only relevant for operation under normal conditions. If we talk about the occurrence of an emergency, then the primary methods of precaution lose their meaning.

Key hazard indicators

In most cases, ignition results from the interaction of three key substances:

• fuel present in the consistency of steam, dust or gas;
• oxygen in the air;
• igniter arising in the production process.

The purpose of the classification of fire and explosive zones is to distinguish between the concentration limits of the lower and upper ignition limits. In addition, divide the premises according to the degree of danger, which is characterized by certain indicators. These include:

1. Temperature threshold sufficient for ignition.
2. The rate of burning and flame propagation.
3. The smallest amount of oxygen leading to ignition.
4. The sensitivity of the components present to friction and vibration loads.

As a result of the accident, the force of the explosion and the shock action on the wave front arise. Fire spreads and, depending on speed, destroys communications, structures, electrical lines. The forces of destruction contribute to the appearance and scattering of fragments dangerous to human life, the release of harmful and toxic substances that pollute the environment.

Category concept

The classification of the explosive areas of the premises into categories expresses the readiness of the atmosphere for an explosion from contact with a spark or arc. Hazardous areas in it are considered as potentially explosive mixtures in a single space with a set of accompanying production conditions. In this case, a separate temperature classification takes into account the effect of ignition from contact with a hot surface. Each gas, steam or dust of a combustible substance has its own temperature limit for spontaneous combustion. Upon its achievement, a flame occurs.

Fire hazard classification

Fire hazard zones are divided into the following classes:

• Objects PI. They are determined in places with a concentration of flammable liquid substances with an indicator of the boundary flash point of more than 61 º.
• Zone P-II. They are isolated in rooms with a high fiber content in the air and technological dust of a combustible nature.
• Territories P-IIa. Their classification of hazardous areas describes as places where solid combustible materials with a specific fire pressure of more than 1 mJ per 1 m2 are contained.
• Zone P-III. They are located behind the wall of the premises with combustible solid materials, fluid liquids and explosive gaseous mixtures stored in them.

Classification of hazardous areas according to FZ-123

This type of classification is made depending on the duration of the presence of the hazardous mixture in the room and the frequency of occurrence of such concentrations:

1. Zero class. It examines rooms with the constant appearance of a combustible mixture for one hour.
2. First grade. It includes places with the release of easily flammable vapors and gases, which form hazardous compounds with air, in the normal process.
3. Second class. It marks areas without the release of hazardous gases, vapors and solid dust clouds in a standard production process. But there is a danger of their hazardous concentrations resulting from an accident.
4. Twentieth class of premises. Provides a constant small concentration of hazardous impurities in air with a low ignition limit.
5. Twenty first grade. Here are described the premises with the release in the production process of suspended dust or fibrous particles in explosive quantities.

Methods for determining normative indicators for determining the class of a room are regulated in documents and technical specifications for fire safety.

Division of zones according to PUE

Classification of hazardous areas according to the rules of electrical installations provides for the following separation of premises:

• Class B-1. Describes the areas of the premises where the release of combustible components in such quantities that the formation of explosive mixtures occurs in the air during a normal production process. For example, when cleaning equipment or changing raw materials.
• Class B-1a. In the premises during the normal production cycle, no dangerous combustible components are released. Their appearance is associated only with the occurrence of an emergency.
• Class B-1b. It combines areas located in rooms where hazardous substances are released only as a result of an accident. Moreover, they have a pungent odor, low ignition limit, and are concentrated in the upper part of the workshop.
• Class B-1g. Lists premises outside the zone. Ammonia compressors with a specific equipment selection are not included in this category.
• Class B-II. Lists rooms with emissions during the production of large quantities of combustible fibers and dust, capable of forming mixtures with air, leading to an explosion.
• Class B-IIa. Describes areas in which the explosion hazard conditions described in the previous class do not arise during normal operation of the equipment. Their release is possible only in the event of an accident or damage to appliances.

Zones five meters from the machine or device horizontally and vertically in which there are areas that are dangerous from the point of view of fire or explosion, while production requires open fire or hot parts, the classification of explosive and fire hazard zones according to the EMP is not considered as emergency rooms. Their grouping is engaged in the classification of premises depending on the technology used at this stage of production. Zones in the workshops and outside the premises, in which gaseous, liquid and solid materials are used for heating and burned in boilers or disposed of by burning, are not classified as dangerous places. And the classification of explosive zones according to PUE is not related to them.

NBA Zone Separation

Hazardous areas, which the classification of fire and explosive zones refers to group "A", are characterized by the use of liquids and gases with a fire limit of not higher than 28 ° C or their emission. The wave pressure does not exceed 5 kPa. This applies to workshops in which explosive components are located. They cause flashes in contact with air masses.

The premises belonging to group B are distinguished by the use of combustible substances in the production or by the technological emission of dust particles and fibers. Their spontaneous combustion occurs at temperatures above 28 ° C. The shock pressure index of the wave in such cases exceeds 5 kPa.

Ways to eliminate or reduce the explosion hazard of areas

Classification of hazardous areas according to the EMP and GOST as initiators of an emergency considers individual substances, such as steam, gas, dust formulations in contact with air masses or interacting with one another in the complex. The class or category of a room depends on the type of glowing or flaming components, the possibility of electric discharges, heat generated during chemical reactions, mechanical vibration and shock, a beam of scattering sparks, solar radiation, and various types of radiation.

Special organizational measures of a technical nature have been developed to reduce the possibility of explosions and fires at work. Their application is based on the scientific method of studying the behavior of materials and substances in the process of flash and burning. To reduce hazards, the following activities are carried out in production halls, warehouses and other areas:

1. Analyzes are regularly taken to determine the chemical composition of the surrounding space.
2. For work, equipment is selected taking into account the sealing, its protection is carried out.
3. Combustible atmospheric components are removed by forced ventilation.
4. The hazardous composition of substances is diverted from the area of ​​potential ignition.

Explosion-proof equipment marking according to GOST

Many devices operate in conditions where some substances capable of ignition are in the atmosphere surrounding the device. To prevent the accident of the apparatus as a result of sparking contacts, heating of parts and structures, they create a certain degree of protection. Classification of hazardous areas and marking of explosion-proof equipment make it possible in the complex to ensure the correct operation of machine tools, devices, furnaces and other equipment in rooms of varying degrees of danger.

Explosion-proof electrical equipment groups

Group 1 includes equipment used in mines underground, mines, buildings on the surface of the earth, working with hazardous gas or combustible dust masses. Group II includes electrical equipment with protection for working indoors or outdoors. It works in a potentially hazardous environment, but not in the conditions described for the devices of the first group. This category includes general industrial equipment.

The requirements for the protection of devices and equipment from explosions are regulated in GOST R.51330.9-99. Classification of hazardous areas determines the type of machine tools and devices and devices for each room. The requirements are spelled out in relation to the material of manufacture of the case, the type of cable water, docking and fastening elements, seals and interlocks. Marking in accordance with a certain category is applied on a visually visible part of the body. The paint is durable and resistant to chemical destruction.

Types of labeling on equipment

For the installation of machines in hazardous areas, they are marked with:

• The degree of protection of the electrical device from explosion.
• Compliance of the installed device with the international standard.
• What type of protection does the equipment include (i, o, n, q, d, s, e, etc.). For category i, a subspecies (ia, ib, ic) must be indicated.
• Class of accessories by temperature.
• One of the letters is put - X or U. They mean, respectively, the creation of special conditions or the use of the Ex-component.

Requirements for the selection of electrical equipment

Electrical equipment, especially with sparkling parts and blocks, as the classification of hazardous areas predetermines, is mounted outside of dangerous places, if this does not entail unjustified and excessive costs, it does not cause difficulties. If such devices are intended for operation in explosive workshops, then additional requirements are imposed on their installation and selection. In a dangerous situation in a working production area, the use of various electrical appliances, lamps is limited to cases where their use in this place is necessary.

Equipment located in the zone of increased aggressive influence of dust masses, gas, moisture, is protected, as the classification of explosive zones according to PUEs, from these active initiators of the emergency. Equipment mounted in outdoor conditions should be protected from atmospheric influences, moisture, and glaciation. If the electric machine is assigned protection with the designation “e”, then it is allowed to be installed only on equipment where it will not experience vibration and overloads. Such electrical appliances are protected by installing a relay with shutdown when overheating.

Electrical equipment designed to work in a certain environment can be installed in a room with precisely such parameters or with lower performance. You can not mount it in more aggressive places. If the requirement for the installation of equipment is to provide a purge of the casing with pressure, then a ventilation system with control devices is arranged. At the same time, installation is done in accordance with the requirements of GOST specifically for this machine:

1. When creating foundation pits for foundations, they should not have blind areas with combustible volatile substances without the possibility of blowing.
2. Gas pipelines supplying flowing air masses to the fan are mounted outside of dangerous premises.
3. Similar gas pipelines are conducted under the floor if their design is protected from the ingress of combustible substances.
4. When the ventilation device is used only devices of the type specified in the installation instructions, the use of other types is not allowed.

Electric machines, inside of which the work of oily liquids is provided and there are elements with the passage of current, can be set in the absence of mechanical and vibration shocks that allow splashing of oil.

Indicators for choosing electric cars

Classification of hazardous areas, according to the rules for installing electrical appliances in a hazardous area, the voltage limit provides 10 kW. And the level of protection against flammability, in accordance with GOST 17494-1987, seems to be higher according to standards. If the individual structural components of the equipment have different protection indicators, then the standards are determined in accordance with the tables.

When installing equipment in the zone of categories B-I a, B-I, B-II, the classification of explosive zones according to GOST regulates the installation of electric motors outside the hazardous area, behind a blank wall and fireproof coating with a fire resistance not exceeding 0.75 hours. The room is provided emergency exit and exhaust ventilation was performed with the capacity of distillation of the volume of air in the room five times per working hour. The drive is routed through the wall through a seal with a seal.

In conclusion, it should be noted that work in fire hazardous and explosive rooms becomes less harmful and does not cause emergency situations if the organization’s management is worried about observing all the norms and rules for installing equipment during installation in such categories of zones. First of all, the fulfillment of conditions becomes a priority for extending the life and preserving the health of workers in workshops and enterprises.