Classification of explosive areas by EMP. The purpose of classification of fire-hazardous and explosive areas

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

Basic hazard indicators

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

• The presence of fuel in the consistency of steam, dust or gas;
• Contained in the air oxygen;
• An igniter that occurs during the production process.

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

1. Temperature threshold, sufficient for ignition.
2. Speed of combustion and flame propagation.
3. The least amount of oxygen that leads to inflammation.
4. The sensitivity of the components present to friction and vibration loads.

As a result of the accident, there is an explosion force and a shock action on the wave front. The fire spreads and, depending on the speed, destroys communications, structures, electric lines. Forces of destruction contribute to the appearance and scattering of fragments, dangerous for human life, the release of harmful and poisonous substances that pollute the environment.

Concept of category

Classification of explosive areas of the premises by category 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 conditions of a separate 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 the heated surface. Each gas, vapor or dust of a combustible substance has its own temperature limit for spontaneous combustion. By its attainment, a flame appears.

Classification of fire hazard zones

Dangerous zones for fire fighting are divided into the following classes:

• Objects P-I. Determined in places having a concentration of combustible liquid substances with an index of the boundary flash point of more than 61 ° C.
• Zones P-II. They are isolated in rooms with a high content of fibers in the air and a technological dust of a combustible nature.
• Territories P-IIa. Their classification of explosive areas describes how to place solid combustible materials with a specific fire pressure of more than 1 mJ per m2.
• Zones P-III. Are located behind a wall of premises with stored in them combustible solid materials, fluid fluids and explosive gaseous mixtures.

Classification of explosive zones according to FZ-123

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

1. Zero class. Considers rooms with a constant appearance of a combustible mixture for one hour.
2. First grade. It includes places with the release during the process in the normal mode of easily flammable vapors and gases, which form dangerous compounds with air.
3. Second class. It identifies areas without the release of hazardous gases, vapors and hard dust clouds in a standard production process. But there is a danger of obtaining their dangerous concentrations as a result of the accident.
4. The twentieth class of premises. Provides for a constant low concentration of hazardous impurities in air with a low ignition limit.
5. Twenty-first class. Here are described the premises with the release during the production of suspended dust or fibrous particles in explosive quantities.

The methods for determining the normative indices for determining the class of a room are regulated in documents and technical specifications for fire safety.

Separation of zones by PUE

The classification of explosive zones according to the rules for the installation of electrical installations provides for the following division of premises:

• Class B-1. Describes the zones of rooms where the combustible components are released in such a quantity that explosive mixtures form in the air during the normal production process. For example, when cleaning equipment or changing raw materials.
• Class B-1a. In rooms in the normal production cycle, no hazardous combustible components are released. Their appearance is associated only with the emergence of an emergency situation.
• Class B-1b. It unites zones located in premises where dangerous substances are allocated only as a result of an accident. In this case they have a sharp odor, a low limit of ignition, they concentrate in the upper part of the shop.
• Class B-1d. Contains a list of rooms outside the zone. This category does not include ammonia compressors with a specific choice of equipment.
• Class B-II. Enumerates rooms with the release in the process of 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 ejection is possible only in case of an accident or damage to instruments.

Zones in five meters from the machine or device horizontally and vertically, which are dangerous from the point of view of the occurrence of a fire or explosion area, while the production requires open flames or incandescent parts, the classification of explosive and fire hazardous areas according to the PUE does not consider as an emergency room. Their grouping deals with the classification of premises, depending on the technology used at this stage of production. Zones in shops and outside the premises in which gaseous, liquid and solid materials are used for heating and burned in boilers or disposed of by incineration are not considered dangerous places. And the classification of explosive zones according to the PUE to them has nothing to do.

Separation of zones by NBA

Hazardous premises that classify fire-hazardous and explosive zones as group "A" are distinguished by the use of liquids and gases with an ignition limit of no higher than 28 ° C or their release. The wave pressure does not exceed 5 KPa. This applies to workshops where explosive components are located. They cause flares in contact with air masses.

Premises belonging to group "B" differ in the use of combustible substances in the production or in the technological emission of particles of dust and fibers. Their self-ignition occurs at temperatures above 28 ° C. The index of the shock wave pressure in such cases exceeds 5 KPa.

Methods for eliminating or reducing the explosiveness of zones

Classification of explosive areas by PUE 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 the room depends on the type of incandescent or flame-affected components, the possibility of the appearance of electrical discharges, the evolving heat in chemical reactions, mechanical vibration and shock, a beam of sparks, solar radiation, various types of radiation.

Special organizational measures of a technical nature have been developed to reduce the possibility of explosions and fires in production. Their application is based on the scientific method of studying the behavior of materials and substances in the process of flare and combustion. To reduce hazardous factors, the following activities are carried out in production workshops, warehouses and other areas:

1. Regularly taken tests to determine the chemical composition of the surrounding space.
2. For work the equipment is chosen taking into account the sealing, its protection is carried out.
3. The combustible components of the atmosphere are removed by forced ventilation.
4. A dangerous composition of substances is diverted from the area of possible ignition.

Marking of equipment protected from explosion by GOST

Many devices operate under conditions where some substances that are capable of ignition are in the atmosphere surrounding the device. To prevent a car accident due to the sparking of contacts, the heating of parts and structures, they create a certain degree of protection. The classification of explosive areas and the marking of explosion-proof equipment make it possible in the complex to ensure the correct operation of machines, instruments, furnaces and other equipment in premises of varying degrees of danger.

Explosion-proof electrical equipment groups

The first group includes equipment used in underground mines, mines, structures on the surface of the earth, working with dangerous gas or combustible dust masses. Group II includes electrical equipment with protection for indoor or outdoor operation. Works in a potentially dangerous environment, but not under the conditions described for devices in the first group. This category includes industrial equipment of general purpose.

Requirements for the protection of devices and equipment from explosions are regulated in GOST R.51330.9-99. The classification of explosive zones determines the type of machines and devices and devices for each room. The requirements are spelled out in relation to the material of the housing, the type of water of the cable, docking and fastening elements, seals and blocking devices. The marking in accordance with a certain category is applied to the visually prominent section of the body. The paint is durable and resistant to chemical damage.

Types of marking on equipment

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

• The degree of protection of an electrical device from an explosion.
• The conformity of the device to the international standard.
• What type of protection is the equipment (i, o, n, q, d, s, e, etc.). For category i, a subspecies (ia, ib, ic) is mandatory.
• Class accessories by temperature.
• One of the letters X or U is put. They denote, respectively, the creation of special conditions or the application of the Ex component.

Requirements for the selection of electrical equipment

Electrical equipment, especially with sparking parts and blocks, as predetermines the classification of explosive areas, is mounted outside hazardous locations, if it does not entail unjustified and overstated costs, does not cause difficulties. If such devices are intended for use in explosive workshops, additional requirements are required for their installation and selection. In a hazardous situation in the working production area, the use of various electrical appliances and fixtures is limited to cases when their use in this place is conditioned by necessity.

The equipment located in the zone of increased aggressive influence of dust masses, gas, moisture, is protected, as the classification of explosive zones by PUE states, from these active initiators of the emergency situation. The equipment installed in outdoor conditions must be protected from atmospheric influences, moisture, glaciation. If an electric machine is assigned a protection with the designation "e", then it can only be installed on equipment where it will not experience vibration and overloads. Such electrical devices are protected by relay installation with shutdown in case of overheating.

Electrical equipment intended for operation in a particular environment can be installed in a room with these parameters or with less parameters. You can not mount it in more aggressive places. If the requirement to install the tool is to ensure the blowdown of the shell with pressure, then a ventilation system with control devices is arranged. In this case, the installation is done in accordance with the requirements of GOST for this machine:

1. When creating foundation pits for foundations, they should not create dull areas with combustible volatile substances without the possibility of blowing.
2. Gas pipelines supplying flowing air masses to the fan are installed outside hazardous areas.
3. Similar gas pipelines are conducted under the floor, if their construction is protected from the ingress of combustible substances into them.
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 which oil oils work and there are elements with current passing, are allowed to be installed in the absence of mechanical and vibration shocks that allow splashing oil.

Indicators for the selection of electrical machines

Classification of explosive zones, according to the rules for the installation of electrical appliances in the hazardous production zone, the voltage limit provides 10 kW. And the level of protection against flammability, in accordance with GOST 17494-1987, is represented by the higher standards. If the individual structural units of the equipment have different protection indicators, then the specifications are determined in accordance with the tables.

When installing equipment in the category B-1a, B-I, B-II categories, the classification of hazardous areas according to GOST specifies the installation of electric motors outside the hazardous room, behind a blind wall and a fireproof coating with a fire resistance limit of not more than 0.75 hours. A reserve evacuation exit and exhaust ventilation with a capacity of distillation of the air volume in the room five times per working hour. Through the wall drive is laid through the gland with a seal.

In conclusion, it should be noted that work in fire-hazardous and explosive areas becomes less harmful and does not cause emergency situations, if the management of the organization worries about compliance with all norms and rules for installing equipment for installation in such categories of zones. First of all, the fulfillment of the conditions becomes a priority task for prolonging life and preserving the health of the workers of the workshops and enterprises.