Explosion-proof equipment and measuring instruments: basic design principles

They are based on IEC recommendations and remain identical for all manufacturing units and equipment worldwide. Explosion safety standards are especially in demand at gas production enterprises, chemical manufacturing and petroleum refining companies, as well as in the mining industry.

Equipment with enhanced explosion protection is installed in areas where fires and explosions are possible due to process failures or accidents, where a potentially explosive atmosphere is constantly present. These can be flammable vapors, gases, liquids, dust, oxidizers of air or oxygen mixtures, the presence of thermal or electrical energy that can lead to ignition. Usually, these factors work in combination: for example, a gas-air mixture can ignite and explode due to a sparking contact.

In Russia, explosive zones are classified by classes:

• B-1: combustible gases, vapors of flammable liquids creating explosive mixtures when in contact with air;
• B-1a: the occurrence of explosive mixtures (vapors, gases) is possible only after breakdowns and accidents;
• B-1b: more typical for laboratories, since in this case gases have a strong odor and a high lower flammability limit;
• B-1c: used for areas located near potentially explosive outdoor installations (tanks, storage facilities, process vessels, settling tanks, including petrochemical plants);
• B-2: the technological process involves the supply of explosive gases into the working area air or the formation of explosive dust mixtures during normal material processing;
• B-2a: safe under standard operating conditions but unsafe during emergency equipment failures.

All explosion-proof equipment is marked Ex, confirming its compliance with the GOST R 51330 standard.

Types of Explosion Protection

There are three possible causes leading to an explosion: the presence of an oxidizer, fuel, or explosion energy. Without at least one of these factors, an emergency situation is impossible. Accordingly, there are also three methods to prevent such emergencies: containment, event prevention, or object isolation. Here are their main features:

1. Containment: an explosion may occur but only within a specific controlled zone. This method is characterized by explosion protection in the form of an impermeable equipment enclosure.
2. Isolation involves separating sources of fuel and energy (for example, electrical elements or heated surfaces are physically separated from heated mixtures). This category of explosion protection includes methods such as increased pressure, sealing, or immersion of electrical components in an oil mixture. These methods are more often used for stationary equipment. Additionally, isolation can be achieved by filling with powdered substances.
3. Prevention is based on the use of an intrinsically safe electrical network. In this case, energy is limited in such a way that the occurrence of sparks or electric arcs is completely excluded.

According to current regulations, there are several marking methods. They determine which type of explosion protection is used in a particular industrial equipment:

• Explosion-proof enclosure (marked as d). In this case, the equipment may contain ignition devices, explosive mixtures, and sparking components. But the enclosure protecting the internal structure is so strong that it easily withstands internal explosions and prevents energy from spreading outside the housing and causing an external explosion. For this, all joints, grooves, gaps, and holes on the cover are specially sealed (the degree and reliability of the seal must be regularly checked).
• The equipment uses components that cannot spark or cause temperature increases under normal operating conditions (marked as e). This usually applies to equipment operating at a maximum voltage of 11kV. Reliable insulation is used to ensure safe electrical connections. Additionally, the equipment housing itself must be reliably protected from external influences: categories not lower than IP6x for dust and IP54 for gas or vapor. Such types of protection are used for control posts and cabinets, distribution devices, terminal and junction boxes, lighting fixtures, and signal devices.
• Creation of an intrinsically safe electrical circuit (designated as i, includes two main subgroups — Ex ia and Ex ib). The principle is that materials with low spark potential are used (as a result, ignition of the explosive mixture becomes impossible). Equipment marked Ex ia is considered more reliable because it can be used in zones with maximum explosion hazard and withstands 2 faults. To enhance protection, they can be placed in an insulated enclosure.             
• Filling the enclosure with excess pressure (defined as P). In this case, positive static pressure is created inside the housing and a constant supply of air or inert gas is ensured. Thus, if an explosive mixture does enter the enclosure, it is pushed out. To ensure explosion protection of equipment by this principle, it is necessary to strictly follow the purging schedule and constantly monitor the process. This method can protect analyzers, distribution devices, control sensors, electric motors.
• Oil-filled enclosure (O). Equipment with this type of protection can only be used where the likelihood of explosive gas accumulation is low. It is also the optimal choice for networks where equipment with sparking components is immersed in oil (for example, transformers or switching equipment).
• Quartz-filled enclosure (or q) using sand or powder filler where sparking or electric arc passage is possible. Often used for internal components of equipment, such as starters, transformers, fuses, and fluorescent lamps.
• Sealing with compound (or n). In this case, components or equipment are encapsulated, i.e., filled with compound, preventing explosive mixtures from reaching the spark area. This protects various sensors and indicators.
• Equipment without ignition capability (protection type n) can be used where the explosion risk is minimal. There are several categories here as well. For example, components that do not produce arcs or are fully insulated, sealed, airtight, with limited air movement are used. This protection is not applied to switching devices.

Principles

The principles of explosion protection organization for equipment are directly related to the types and methods of such protection. Four groups stand out as the most commonly used:

1. Equipment is protected by minimizing the possibility of spark occurrence. Developers initially use design solutions that prevent temperature exceedances characteristic of normal operation. Additionally, special insulating materials are used for circuit sealing: it is placed in an enclosure impermeable to dust and moisture and absorbing explosive substances.
2. In this case, all electrical circuits are isolated from the explosive environment by a contour or enclosure. Protection may use mineral oils, compound, quartz sand, or explosion-proof gas under pressure.
3. This protection is based on explosion containment methods. Usually, it involves using an enclosure around electrical circuits that restrains excess pressure at the moment of explosion and prevents its spread. The type of enclosure is selected depending on the penetrating ability of the explosive gas.
4. Here, the power of the spark capable of causing ignition and explosion is limited. Many electrical circuits are protected by this principle, making it universal.

Areas of Application

Explosion-proof equipment (including measuring equipment) is necessary for chemical, mining, oil refining enterprises, as well as any production workshops and sites where explosive atmospheres may accumulate in the working area.

If flammable liquids, vapors, and gases, oxidizers in the form of oxygen or air mixtures, as well as thermal or electrical energy capable of "triggering" an explosion, are present at an industrial site, the use of special equipment or measures to protect existing equipment is mandatory.

Explosion-Proof Measuring Equipment

The company "Izmerkon" offers explosion-proof pressure gauges, digital pressure measuring instruments (the obtained data is displayed on an LCD). The offered equipment operates with high accuracy.

The catalog features KELLER pressure gauges corresponding to explosion protection type Ei (intrinsically safe circuit). Oxygen-type or food industry versions with special oil filling are available. They can operate over wide value ranges. To purchase a suitable model, simply submit a selection request or order a callback.