3.3. Lightning protection and protection

from static electricity

3.3.1. Technological equipment, buildings and structures depending on their purpose, explosive class and fire hazardous areas must be equipped with lightning protection, protection against static electricity and secondary manifestations of lightning in accordance with the requirements regulatory documents on the design and installation of lightning protection of buildings and structures and protection against static electricity.

3.3.2. Devices and measures that meet the requirements for lightning protection of buildings and structures must be included in the project and schedule for the construction or reconstruction of an oil depot (individual technological facilities, tank farm) in such a way that lightning protection occurs simultaneously with the main construction and installation work.

3.3.3. Tank farms with flammable liquids and gas liquids with a total capacity of 100 thousand m3 or more, as well as tank farms of oil depots located in residential areas, must be protected by separate lightning rods.

3.3.4. Tank farms with a total capacity of less than 100 thousand m3 must be protected from direct lightning strikes as follows:

Tank bodies with a roof metal thickness of less than 4 mm - with free-standing lightning rods or installed on the tank itself;

Tank bodies with a thickness of 4 mm or more, as well as individual tanks with a unit capacity of less than 200 m3, regardless of the thickness of the roof metal, are connected to grounding conductors.

3.3.5. The breathing fittings of tanks with flammable liquids and the space above it, as well as the space above the cut of the neck of tanks with flammable liquids, limited by a zone 2.5 m high with a diameter of 3 m, must be protected from direct lightning strikes.

3.3.6. Protection against secondary manifestations of lightning is ensured through the following measures:

Metal structures and housings of all equipment and devices located in the protected building must be connected to the grounding device of electrical installations or to the reinforced concrete foundation of the building, provided that continuous electrical communication is ensured through their fittings and connected to embedded parts by welding;

In connections of pipeline elements or other extended metal objects, transition resistances of no more than 0.03 Ohm per contact must be provided.

3.3.7. Grounded metal equipment covered with paints and varnishes is considered electrostatically grounded if the resistance of any point on its internal and external surface relative to the grounding line does not exceed 10 Ohms. Measurements of this resistance should be carried out at a relative humidity of ambient air no higher than 60%, and the area of ​​contact of the measuring electrode with the surface of the equipment should not exceed 20 cm2, and during measurements the electrode should be located at points on the surface of the equipment most distant from the points of contact of this surface with grounded metal elements, parts, fittings.

3.3.8. Connections of lightning rods with down conductors and down conductors with grounding conductors must, as a rule, be made by welding, and if hot work is prohibited, bolted connections with a transient resistance of no more than 0.05 Ohm are allowed, with mandatory annual monitoring of the latter before the start of the thunderstorm season.

3.3.9. Grounding conductors and down conductors are subject to periodic inspection once every five years. Every year, 20% of the total number of grounding conductors and down conductors must be opened and checked for corrosion damage. If more than 25% of the cross-sectional area is affected, then such grounding conductors are replaced.

The results of the checks and inspections carried out are entered into the lightning protection device passport and the lightning protection device status log.

3.3.10. Buildings and structures where explosive or fire-hazardous concentrations of petroleum product vapors may form must be protected against the accumulation of static electricity.

3.3.11. To prevent dangerous manifestations of static electricity, it is necessary to eliminate the possibility of accumulation of static electricity charges on equipment and petroleum products by grounding metal equipment and pipelines, reducing the speed of movement of petroleum products in the pipeline and preventing splashing of petroleum products or reducing the concentration of petroleum product vapors to safe limits.

3.3.12. In order to protect against static electricity, the following are subject to grounding:

Ground tanks for flammable liquids and gases and other liquids that are dielectrics and capable of creating explosive mixtures of vapors and air upon evaporation;

Ground pipelines every 200 m and additionally on each branch with the connection of each branch to a ground electrode;

Metal heads and hose pipes;

Mobile means of refueling and pumping fuel - during their operation;

Railway rails of unloading areas, electrically connected to each other, as well as metal structures of unloading overpasses on both sides along the length;

Metal structures of auto-filling devices;

All mechanisms and equipment of pumping stations for pumping petroleum products;

Metal structures of sea and river berths in places where oil products are unloaded (loaded);

Metal air ducts and thermal insulation casings in explosive areas every 40 - 50 m.

3.3.13. The grounding device for static electricity protection should generally be combined with the grounding devices for electrical equipment protection and lightning protection. The resistance of a grounding device intended only for protection against static electricity must be no more than 100 ohms.

3.3.14. All metallic and electrically conductive non-metallic parts technological equipment must be grounded regardless of the use of other ESD protection measures.

3.3.15. The connection between fixed metal structures (tanks, pipelines, etc.), as well as their connection to grounding conductors, is made using strip steel with a cross-section of at least 48 mm2 or round steel with a diameter of more than 6 mm by welding or using bolts.

3.3.16. Spiral rubber-fabric hoses (RSH) are grounded by connecting (soldering) a stranded copper wire with a cross-section of more than 6 mm2 to a ruff and a metal winding, and smooth hoses (RBG) - by passing the same wire inside the hose and connecting it to the ruffs.

3.3.17. Protection against electrostatic induction must be ensured by connecting all equipment and devices located in buildings, structures and installations to protective grounding.

3.3.18. Buildings should be protected from electrostatic induction by covering non-metallic roofing with a mesh of steel wire with a diameter of 6 - 8 mm, with a cell side of no more than 10 cm, the mesh nodes must be boiled. Down conductors from the wall must be laid along the outer walls of the structure (with a distance between them of no more than 25 m) and connected to the ground electrode. Metal structures of the building, equipment housings and apparatus must also be connected to the specified grounding electrode.

3.3.19. To protect against electromagnetic induction between pipelines and other extended metal objects (structure frame, cable sheaths) laid inside a building and structure, in places where they are mutually close at a distance of 10 cm or less, every 20 m of length it is necessary to weld or solder metal jumpers so that Avoid the formation of closed loops. In connections between pipeline elements and other extended metal objects located in the protected structure, it is necessary to install jumpers made of steel wire with a diameter of at least 5 mm or steel tape with a cross-section of at least 24 mm2.

3.3.20. To protect against the drift of high potentials through underground metal communications (pipelines, cables, including those laid in channels and tunnels), when entering the structure, it is necessary to connect the communications to the grounding electrodes for protection against electrostatic induction or to the protective grounding of the equipment.

3.3.21. All measures to protect buildings and structures from secondary manifestations of lightning discharge coincide with measures to protect against static electricity. Therefore, devices designed for secondary manifestations of secondary lightning discharge should be used to protect buildings and structures from static electricity.

According to the current rules, protection against static electricity discharges should be carried out in explosive and fire hazardous industries in the presence of zones of classes B-I, B-Ia, B-II, B-IIa, P-I and P-II, in which substances with specific volumetric electrical resistance Ohm∙m.

In other cases, protection is provided only when static electricity poses a danger to operating personnel or negatively affects the technological process or product quality.

The main ways to eliminate the danger from static electricity are (slide):

1) grounding of equipment, communications, devices and vessels, as well as ensuring constant electrical contact with the grounding of the human body;

2) reducing specific volumetric and surface electrical resistance by increasing air humidity or using antistatic impurities;

3) ionization of air or environment, in particular, in the interior of an apparatus, vessel, etc.

In addition to these methods, they use: preventing the formation of explosive concentrations, limiting the speed of liquid movement, replacing flammable liquids with non-flammable solvents, etc. The practical method for eliminating static electricity hazards is selected based on efficiency and economic feasibility.

Let us dwell in more detail on the above methods of eliminating the danger from static electricity.

Grounding (18 min)– the most commonly used measure of protection against static electricity. Its purpose is to eliminate the risk of electrical discharges from conductive parts of equipment. Therefore, all conductive parts of equipment and electrically conductive non-metallic objects must be grounded, regardless of whether other methods of protection against static electricity are used. It is necessary to ground not only those parts of the equipment that are involved in the generation of static electricity, but also all other parts of the above properties, since they can be charged according to the law of electrostatic induction.

In cases where equipment is made of electrically conductive materials, grounding is the main and almost always sufficient method of protection.

If deposits of non-conducting substances (resins, films, sediments) form on the external surface or internal walls of metal devices, tanks and pipelines, grounding becomes ineffective. Grounding does not eliminate the danger when using devices with enameled or other non-conductive coatings.

Non-metallic equipment is considered electrostatically grounded if there is resistance to current flow to the ground from any point on its outer and inner surface Ohm at relative humidity. Such resistance provides the required value of the relaxation time constant within a tenth of a second in a non-explosive environment and thousandths of a second in an explosive environment. The relaxation time constant is related to resistance R grounding of the device or equipment and its capacity C ratio τ = R∙ C.

Pipelines of external installations (on overpasses or in channels), equipment and pipelines located in workshops must provide an electrical circuit throughout their entire length and be connected to grounding devices. It is believed that the electrical conductivity of flange connections of pipelines and apparatus, connections of covers with apparatus bodies, etc. high enough that no special parallel jumpers are required.

Each system of apparatus and pipelines within the workshop must be grounded in at least two places. All tanks and containers with a capacity of more than 50 m 3 and a diameter of more than 2.5 m are grounded at at least two opposite points. There should be no floating objects on the surface of flammable liquids in tanks.

The loading risers of trestles for filling railway tanks and the rails of railway tracks within the loading front must be electrically connected to each other and reliably grounded. Tankers, tankers, aircraft under loading (unloading) of flammable liquids and liquefied gases, must also be grounded. Contact devices (without explosion protection) for connecting grounding conductors must be installed outside the explosive zone (at least 5 m from the filling or draining point, PUE). In this case, the conductors are first connected to the body of the grounding object, and then to the grounding device.

It should be noted that the grounding conductors still used for grounding tank trucks do not provide the required level of fire and explosion safety for the technology of loading or unloading fuel and other flammable liquids. Therefore, at present, special grounding devices for tank trucks (UZA) of the UZA-2MI, UZA-2MK and UZA-2MK-03 types have been developed and are mass-produced, which comply with the requirements of GOSTs and can be installed in explosive zones of class B-Ig.

When grounding is used to protect conductive, non-metallic, conductively lined equipment from static electricity, the same requirements apply as for grounding metallic equipment. For example, grounding of a pipeline made of dielectric material, but with a conductive coating (paint, varnish), can be done by connecting it to the grounding loop using metal clamps and conductors after 20÷30 m.

But grounding does not solve the problem of protecting a reservoir filled with electrified liquid from static electricity; it only eliminates the accumulation of charge (flowing from the liquid volume) on its walls, but does not accelerate the process of charge dissipation in the liquid. This is explained by the fact that the rate of relaxation of static electricity charges in the volume of dielectric liquid of petroleum products is determined by the relaxation time constant. Consequently, in a reservoir filled with electrified products, during the entire time of liquid injection and for approximately the same time after its completion, an electric field of charges exists, regardless of whether this reservoir is filled or not. It is during this period of time that there may be a danger of ignition of the steam-air mixture of petroleum products in the tank by discharges of static electricity.

Given the above, there is a significant danger in taking samples from a tank immediately after it has been filled. But after a period of time approximately equal to , after filling the grounded tank, the charges of static electricity in it practically disappear and taking liquid samples becomes safe.

For light petroleum products with low electrical conductivity (at Ohm∙m), required time The waiting time after filling the tank, ensuring the safety of further operations, must be at least 10 minutes.

Grounding the tank and waiting the required time after filling will not give the desired safety effect if the tank contains insulated objects floating on the surface of the liquid, which can acquire a charge of static electricity when filling the tank and retain it for a period of time significantly exceeding. In this case, when a floating object comes into contact with a grounded conductive body, a dangerous spark may occur.

Decrease in volumetric and surface electrical resistivity (8 min).

This increases electrical conductivity and ensures the ability of the dielectric to remove static electricity charges. Eliminating the danger of static electrification of dielectrics by this method is very effective and can be achieved by increasing air humidity, chemical surface treatment, and the use of electrically conductive coatings and antistatic substances (additives).

A. Increase in relative air humidity.

Most fires caused by static electricity sparks usually occur in winter, when the relative humidity is high. At a relative humidity of 65÷70%, as research and practice show, the number of outbreaks and fires becomes insignificant.

The acceleration of the drainage of electrostatic charges from dielectrics at high humidity is explained by the fact that a thin film of moisture is adsorbed on the surface of hydrophilic dielectrics, usually containing a large number of ions from contaminants and dissolved substances, due to which sufficient surface electrical conductivity of an electrolytic nature is ensured.

However, if the material is at a temperature higher than that at which the film can be held on the surface, said surface may not become conductive even at very high air humidity. The effect will also not be achieved if the charged surface of the dielectric is hydrophobic (non-wettable: sulfur, paraffin, oils and other hydrocarbons) or the speed of its movement is greater than the speed of formation of the surface film.

An increase in humidity is achieved by spraying water vapor or water, circulating moist air, and sometimes by free evaporation from the surface of the water or by cooling the electrifying surface 10 o C below the temperature environment.

B. Chemical surface treatment, electrically conductive coatings.

A decrease in the specific surface resistance of polymer materials can be achieved by chemically treating their surface with acids (for example, sulfuric or chlorosulfonic acid). As a result, the surfaces of the polymer (polystyrene, polyethylene and polyester films) are oxidized or sulfonated and the resistivity decreases to 10 6 Ohms at a relative humidity of 75%.

A positive effect is also achieved when processing products made of polystyrene and polyolefins by immersing samples in petroleum ether while simultaneously exposed to ultrasound. Chemical treatment methods are effective, but require strict adherence to technological conditions.

Sometimes the desired effect is achieved by applying a surface conductive film to the dielectric, for example, a thin metal film, obtained by spraying, spraying, evaporating in a vacuum, or gluing metal foil. Carbon-based films are produced by sputtering carbon in a liquid medium or powder with particles smaller than 1 micron.

B. Use of antistatic substances.

Most flammable and flammable liquids are characterized by high electrical resistivity. Therefore, during some operations, for example with petroleum products, static electricity charges accumulate, which prevents the intensification of technological operations, and also serves as a source of explosions and fires in oil refineries and petrochemical enterprises.

The movement of liquid hydrocarbons relative to a solid, liquid or gaseous medium can lead to the separation of electrical charges at the contact surface. When a liquid moves through a pipe, a layer of charges located on the surface of the liquid is carried away by its flow, and charges of the opposite sign remain on the surface of the pipe in contact with the liquid and, if the metal pipe is grounded, flow into the ground. If the metal pipeline is insulated or made of dielectric materials, then it acquires a positive charge, and the liquid acquires a negative charge.

The degree of electrification of petroleum products depends on the composition and concentration of active impurities contained in them, the physico-chemical composition of petroleum products, the condition of the internal surface of the pipeline or technological apparatus (presence of corrosion, roughness, etc.), dielectric properties, viscosity and density of the liquid, as well as speed fluid movement, diameter and length of the pipeline. For example, the presence of 0.001% of mechanical impurities transforms an inert hydrocarbon fuel into an electrified fuel to dangerous levels.

One of the most effective ways to eliminate electrification of petroleum products is the introduction of special antistatic substances. Adding them in thousandths or ten-thousandths of a percent makes it possible to reduce the resistivity of petroleum products by several orders of magnitude and make operations with them safer. Such antistatic substances include: oleates and naphthenates of chromium and cobalt, chromium salts based on synthetic fatty acids, the Sigbal additive and others. So, an additive based oleic acid Chromium oleate reduces ρ v of B-70 gasoline by 1.2 ∙ 10 4 times. The additives “Ankor-1” and ASP-1 have found wide application in parts washing operations.

To obtain “safe” electrical conductivity of petroleum products under any conditions, it is necessary to introduce 0.001÷0.005% additives. They usually do not affect the physicochemical properties of petroleum products.

To obtain conductive solutions of polymers (adhesives), antistatic additives soluble in them are also used, for example, metal salts of variable valence, higher carboxylic and synthetic acids.

Positive results are achieved when using antistatic substances in synthetic fiber processing plants, since they have the ability to increase their ionic conductivity and thereby reduce the electrical resistance of the fibers and materials obtained from them.

To prepare antistatic substances that affect the electrical properties of fibers, the following are used: paraffin hydrocarbons, fats, oils, hygroscopic substances, surfactants

Antistatic agents are used in the polymer industry, for example in the processing of polystyrene and polymethyl methacrylate. The treatment of polymers with antistatic additives is carried out both by surface application and by introduction into the molten mass. For example, surfactants are used as such additives. When applying surfactants on the surface, the ρ s of polymers decreases by 5–8 orders of magnitude, but the effective action period is short

(up to one month). The introduction of surfactants orally is more promising because the antistatic properties of polymers remain for several years, polymers become less susceptible to solvents, abrasion, etc. For each dielectric, the optimal surfactant concentrations are different and range from 0.05 to 3.0%.

Currently, pipes made of semiconducting polymer compositions with fillers: acetylene black, aluminum powder are widely used. graphite, zinc dust. The best filler is acetylene black, which reduces resistance by 10–11 orders of magnitude even at 20% by weight of the polymer. Its optimal mass concentration for creating an electrically conductive polymer is 25%.

To obtain electrically conductive or antistatic rubber, fillers are introduced into it: powdered graphite, various carbon blacks, and fine metals. The specific resistance ρ v of such rubber reaches 5 ∙10 2 Ohm∙m, and up to 10 6 Ohm∙m for ordinary rubber.

Antistatic rubbers of the KR-388, KR-245 brands are used in explosive industries, covering floors, work tables, equipment parts and wheels of intra-shop transport. This coating quickly removes emerging charges and reduces electrification of people to a safe level.

Recently, oil and petrol resistant electrically conductive rubber has been developed using nitral butadiene and polychloroprene rubbers, which is widely used for the manufacture of pressure hoses and hoses for pumping flammable liquids. Such hoses significantly reduce the risk of ignition when draining and filling flammable liquids into road and railway tanks and other containers, and eliminate the use of special devices for grounding filling funnels and tips.

Effective reduction of the potential of belt drives and belt conveyors made of materials with ρ s =10 5 Ohm∙m is achieved by increasing the surface conductivity of the belt and mandatory grounding of the installation. To increase the surface conductivity of the belt, its inner surface is coated with an antistatic lubricant, renewed at least once a week.

Air ionization (9 min).

The essence of this method is to neutralize or compensate surface electrical charges with ions of different signs, which are created by special devices - neutralizers. Ions having a polarity opposite to the polarity of the charges of electrified materials, under the influence of the electric field created by the charges of such materials, settle on their surfaces and neutralize the charges.

Air ionization by a high-intensity electric field is carried out using two types of neutralizers: induction and high-voltage.

Induction neutralizers come with tips (Fig. 2, a) and wire (Fig. 2, b). In a neutralizer with tips, grounded tips, thin wires or foil are fixed in a wooden or metal rod. A wire neutralizer uses a thin steel wire stretched across a moving charged material. They work as follows. Under the influence of a strong electric field of an electrified body, impact ionization occurs near the tip or wire, as a result of which ions of both signs are formed. To increase the efficiency of neutralizers, they strive to reduce the distance between the tips of the needles or wire and the neutralized surface to 5÷20 mm. Such neutralizers have a high ionization ability, especially neutralizers with tips.

Rice. 2. Induction neutralizer circuit (slide):

a- with points; b- wire; 1- points; 1" - wire; 2 - charged surface.

Their disadvantages are that they operate if the potential of the electrified body reaches several kV.

Their advantages: simplicity of design, low cost, low operating costs, do not require a power source.

High-voltage neutralizers (Fig. 3) operate on alternating, direct and high-frequency current. They consist of a high output voltage transformer and a needle arrester. In the neutralizer on DC A high-voltage rectifier is also included. Their operating principle is based on high voltage ionization of air. The maximum distance between the discharge electrode and the neutralized material, while the neutralizer is still effective, for such neutralizers can reach 600 mm, but usually the working distance is taken equal to 200÷300 mm. The advantage of high-voltage neutralizers is their sufficient ionizing effect even at a low potential of the electrified dielectric material. Their disadvantage is the high energy of the resulting sparks, which can ignite any explosive mixtures, so for hazardous areas they can only be used in explosion-proof versions.

Fig. 3 Diagram of a high-voltage neutralizer (slide).

To protect service personnel from high voltage, protective resistances are included in the high-voltage circuit, which limit the current to a value 50÷100 times less than the life-threatening current.

Radioisotope neutralizers are very simple in design and do not require a power source. Quite effective and safe when used in explosive environments. They are widely used in various industries. When using such neutralizers, it is necessary to ensure reliable protection of people, equipment and products from the harmful effects of radioactive radiation.

Radioisotope neutralizers most often take the form of long plates or small disks. One side contains a radioactive substance that creates radioactive radiation that ionizes the air. In order not to pollute the air, products and equipment, the radioactive substance is covered with a thin protective layer of special enamel or foil. To protect against mechanical damage, the ionizer is placed in a metal casing, which simultaneously creates the desired direction of ionized air. Table 3 shows data on the radioactive substances used in radioisotope neutralizers.

Data on radioactive substances of radioisotope neutralizers (slide).

Table 3

Radioactive substances with α-particles are the most effective and safe. The penetrating ability of α-particles in air is up to 10 cm, and in more dense environments significantly less. For example, a sheet of ordinary clean paper completely absorbs it.

Neutralizers with such radiation are suitable for local ionization of air and neutralization of charges at the point of their formation. To neutralize electrical charges in devices with a large volume, β-emitters are used.

A radioactive substance with γ-study is not used in neutralizers due to its high penetrating ability and danger to people.

The main disadvantage of radioisotope neutralizers is the low ionization current compared to other neutralizers.

To neutralize electrical charges, combined neutralizers, for example, radioactive-induction, can be used. Such neutralizers are produced by industry and have improved performance characteristics. The performance characteristics express the dependence of the discharging ionization current on the potential of the charged body.

Additional ways to reduce the danger from static electricity (3 min, slide No. 13).

The danger of static electrification of flammable liquids and flammable liquids can be significantly reduced or even eliminated by reducing the flow rate v. Therefore the following speed is recommended v dielectric liquids:

At ρ ≤ 10 5 Ohm∙m accept v≤ 10 m/s;

At ρ > 10 5 Ohm∙m accept v≤ 5 m/s.

For liquids with ρ > 10 9 Ohm∙m transport and flow rates are set separately for each liquid. A movement or flow speed of 1.2 m/s is usually safe for such liquids.

For transporting liquids with ρ > 10 11 -10 12 Ohm∙m with speed v≥ 1.5 m/s it is recommended to use relaxers (for example, horizontal pipe sections of increased diameter) directly at the entrance to the receiving tank. Required diameter D R,m of this section is determined by the formula

D R =1.4 D T ∙ . (7)

Relaxer length L p determined by the formula

L p ≥ 2.2 ∙ 10 -11 ξρ, (8)

where ξ is the relative dielectric constant of the liquid;

ρ – specific volumetric resistance of the liquid Ohm∙m.

When filling the reservoir with liquid ρ >10 5 Ohm∙m until the loading pipe is flooded, it is recommended to supply liquids at a speed v ≤ 1 m/s, and then at the specified speed v ≤ 5 m/s.

Sometimes it is necessary to increase the speed of liquids in the pipeline to 4÷5 m/s.

The diameter of the relaxer, calculated using formula (7), turns out to be prohibitively large in this case. Therefore, to increase the effectiveness of the relaxer, it is recommended to use them with strings or needles. In the first case, grounded strings are stretched inside the relaxer and along its axis, which reduces the electrification current by more than 50%, and in the second, grounded needles are introduced into the liquid flow to remove charges from the liquid flow.

The maximum permissible and safe (with regard to the possibility of ignition of liquid vapors in an industrial tank) modes of transporting petroleum products through long pipes with a diameter of 100÷250 mm can be assessed by the ratio

v T 2 D T ≤ 0.64 , (9)

Where v T– linear velocity of the liquid in the pipe m/s, D T– pipe diameter, m.

When operations with bulk and finely dispersed materials, reducing the danger from static electrification can be achieved by the following measures: when transporting them pneumatically, use pipes made of polyethylene or the same material (or a composition similar to the transported substance); the relative humidity of the air at the outlet of the pneumatic transport must be at least 65% (if this is unacceptable, it is recommended to ionize the air or use an inert gas).

The formation of flammable dust-air mixtures should be avoided and dust should not be allowed to fall, become swirled or swirl. It is necessary to clean the equipment and building structures from settled dust.

When operating with flammable gases, it is necessary to ensure their cleanliness and the absence of ungrounded parts of equipment or devices along the paths of their movement.

A good effect in terms of fire and explosion safety from sparks of static electricity and all other ignition sources is achieved by replacing organic solvents and flammable liquids with non-flammable ones if such replacement does not disrupt the technological process and is economically feasible.

4.4.1. To prevent the occurrence of spark discharges from the surface of equipment, oil and petroleum products, as well as from the human body, it is necessary to provide, taking into account the specifics of production, the following measures to ensure the drainage of the resulting charge of static electricity:

• reducing the intensity of generation of static electricity charge;
• grounding equipment for tanks and communications, as well as ensuring constant contact of the human body with grounding;
• reduction of specific volume and surface electrical resistance;
• use of radioisotope, induction and other neutralizers.

4.4.2. Grounding devices for protection against static electricity should generally be combined with grounding devices for electrical equipment. Such grounding devices must be made in accordance with the requirements of PUE-85, GOST 21130-75 SN 102-76, Instructions for the installation of grounding networks. The resistance of a grounding device intended solely for protection against static electricity is allowed to be no higher than 100 ohms.

All metallic and electrically conductive nonmetallic parts of tank equipment must be grounded, regardless of whether other ESD protection measures are in place.

Paint coating applied to grounded metal equipment, internal and external walls of tanks is considered electrostatic grounding if the resistance of the outer surface of the coating relative to the grounded equipment does not exceed 10 ohms.

4.4.3 Tanks with a capacity of more than 50 m3 (except for vertical diameters up to 2.5 m) must be connected to grounding conductors using at least two grounding conductors at diametrically opposite points.

4.4.4. Petroleum products must be pumped into tanks without splashing, atomizing or violent mixing. Filling of petroleum products with a free-falling jet is not permitted.

The distance from the end of the loading pipe to the bottom of the tank should not exceed 200 mm, and if possible, the jet should be directed along the wall. In this case, the shape of the pipe end and the rate of supply of the petroleum product must be selected in such a way as to prevent splashing.

4.4.5. The speed of movement of petroleum products through pipelines must be limited in such a way that the charge brought into the reservoir with the flow of petroleum product cannot cause a spark discharge from its surface, the energy of which is sufficient to ignite the environment. The permissible speeds of liquid movement through pipelines and their flow into tanks depend on the following conditions affecting the relaxation of charges: type of filling, properties of the petroleum product, content and size of insoluble impurities, properties of the material of the walls of the pipeline and tank.

4.4.6. For petroleum products with a specific volumetric electrical resistance of no more than 10 9 Ohms. m, movement and outflow speeds are allowed up to 5 m/s.

For petroleum products with a specific volumetric electrical resistance of more than 10 9 Ohm.m, permissible transportation and outflow rates are established for each petroleum product separately.

To reduce the charge density in a flow of liquid having a specific volumetric electrical resistance of more than 10 9 Ohm.m to a safe value, if it is necessary to transport them through pipelines at a speed exceeding the safe one, special charge removal devices should be used.

A device for removing charges from a liquid product must be installed on the loading pipeline directly at the entrance to the tank being filled so that, at the maximum transport speed used, the time the product moves through the loading pipe after leaving the device before flowing into the apparatus does not exceed 0.1 of the charge relaxation time constant in liquid.

If this condition cannot be fulfilled structurally, then the removal of the charge arising in the loading pipe must be ensured inside the tank being filled before the charged flow reaches the surface of the liquid in the tank.

Notes. Neutralizers with strings can be used as devices for removing charge from a liquid product, the rules for the selection, design, installation and operation of which are set out in RTM 6.28-008-78 Devices for removing charge from a liquid flow with extended discharge electrodes (neutralizers with strings).

Cages made of a grounded metal mesh can be used as charge removal devices inside the filled tank, covering a certain volume at the end of the loading pipe so that the charged flow from the pipe enters the cell. In this case, the volume of the cell must be at least V = Q τ /3600, where V is the volume of the cell, m 3 ; Q—petroleum product pumping speed, m 3 /h; τ is the charge relaxation time constant in the oil product, s.

4.4.7. Data on the electrical parameters of light petroleum products and nomograms for determining permissible pumping speeds are given in the Recommendations for the prevention of dangerous electrification of petroleum products when loading into vertical and horizontal tanks, road and rail tanks, approved on November 12, 1985 by the State Oil Product Committee of the RSFSR.

4.4.8. Petroleum products must enter the tank below the level of the remaining petroleum product in it.

When filling an empty tank, oil products must be fed into it at a speed of no more than 1 m/s until the end of the receiving and dispensing pipe is flooded.

For further filling, the speed should be selected taking into account the requirements of clause 4.4.6.

4.4.9. To prevent the risk of spark discharges, there should be no ungrounded electrically conductive floating objects on the surface of oil products.

4.4.10. Pontoons made of electrically conductive materials, designed to reduce losses of petroleum products from evaporation, must be grounded using at least two flexible grounding conductors with a cross-sectional area of ​​at least 6 mm 2 connected to the pontoon at diametrically opposite points.

4.4.11. Pontoons made of non-electrically conductive materials must have electrostatic protection.

4.4.12. Manual sampling of petroleum products from tanks is allowed no earlier than 10 minutes after the movement of the petroleum product ceases.

> POT R M-021-2002 Interindustry rules for labor protection during the operation of oil depots, fuel depots, stationary and mobile gas stations (contents)

5.4. Fighting static electricity

5.4.1. Protection of buildings and structures of oil depots, fuel and lubricant warehouses, gas stations, gas stations from static electricity must be carried out in accordance with the requirements of the current state standards.
5.4.2. The resistance of a grounding device intended solely for protection against static electricity should not exceed 100 ohms.
5.4.3. All metallic and electrically conductive nonmetallic parts of tank equipment must be grounded, regardless of whether other ESD protection measures are in place.
5.4.4. Paint coating applied to grounded metal equipment, internal and external walls of tanks is considered electrostatic grounding if the resistance of the outer surface of the coating relative to grounded equipment does not exceed 10 Ohms.
5.4.5. Tanks with a capacity of more than 50 m3 (except for vertical ones with a diameter of up to 2.5 m) must be connected to grounding switches using at least two conductors at diametrically opposite points.
5.4.6. The capacity of filling and emptying the tank should not exceed the total capacity of the breathing, safety valves and ventilation devices installed on the tank.
Filling the tank should be done without splashing or vigorously mixing the liquid.
5.4.7. Maximum speeds the movement of petroleum products to ensure safety from electrification must be determined in accordance with the requirements of current state standards, Rules for protection against static electricity in the chemical, petrochemical and oil refining industries to prevent dangerous electrification of petroleum products when loading into vertical and horizontal tanks, automobile and railway tanks, depending on type of petroleum product, pipeline material and diameter, tank dimensions and other indicators.
5.4.8. To protect against static electricity, it is necessary to ground metal equipment, tanks, oil product pipelines, and unloading devices intended for transportation, storage and dispensing of flammable and combustible liquids. The grounding system must represent a continuous electrical circuit throughout.
5.4.9. To avoid the danger of spark discharges, the presence of ungrounded electrically conductive floating objects on the surface of oil products is not allowed.
On float or buoy level gauges used, the floats and buoys must be made of electrically conductive material and reliably grounded.
When operating tanks with metal or synthetic pontoons, the electrically conductive elements of the pontoons must be reliably grounded.
5.4.10. To dissipate static electricity, the bottom surface of the polyurethane foam pontoon and its shutter are coated with electrically conductive latex or other similar coatings.
The resistance is measured after polymerization and hardening of the latex (about a day) at any point on the pontoon in relation to the tank wall.
5.4.11. Tankers, as well as tankers, during unloading and loading operations of flammable and combustible petroleum products must be connected to grounding conductors using an automatic grounding control device with an intrinsically safe contact device or directly to a grounding device.
As a grounding device, it is necessary to use a flexible (multi-core) copper wire with a cross-section of at least 6 mm2. The tip of the grounding device must be made of metal that does not produce sparks upon impact.
5.4.12. It is prohibited to disconnect or connect grounding cables during loading operations.
5.4.13. The rails of railway tracks within the filling front must be electrically connected to passing pipelines every 200 - 300 m and have reliable grounding at both ends.
5.4.14. Inspection and ongoing repair of grounding devices must be carried out simultaneously with the inspection and ongoing repair of process equipment, electrical equipment and electrical wiring.
5.4.15. Installation of contact connections of technological equipment and connection of grounding and grounding networks to them is carried out in accordance with the working drawings.
The locations of contact connections and branches from them must be accessible for inspection.
5.4.16. The transition electrical resistance in contact connections of technological equipment should be no more than 0.03 Ohm per contact.
The contact resistance of contact connections should be measured with explosion-proof instruments.
5.4.17. Workers conducting an inspection of lightning protection devices must draw up an inspection and inspection report indicating any damage or malfunctions found.
The results of the audit of lightning protection devices, verification tests of grounding devices, and repairs performed should be recorded in a special journal.
5.4.20. The chief power engineer's service is responsible for the condition of static electricity and lightning protection devices. Responsible employees are required to ensure the operation and repair of static electricity and lightning protection devices in accordance with current regulations.

Static electricity refers to electrical charges in a state of relative rest, distributed on the surface or volume of a dielectric or on the surface of an insulated conductor.

The contact potential difference is different and depends on the dielectric properties of the contacting materials, their physical state, the pressure with which the surfaces are pressed against each other, the speed of movement, humidity and ambient temperature, etc.

Electrification of solids is possible during the movement of belt drives and conveyor belts.

As studies have shown, intense electrification is observed when particles collide with the surface of pipelines during pneumatic transportation of dusty materials, deformation, crushing (splashing) of substances, relative movement of two bodies in contact, layers of liquid or bulk materials, during intense movement, mixing, crystallization and evaporation of substances.

In addition, electrification of liquids with low electrical conductivity is possible, including during loading, draining and pumping of toluene, gasoline and other petroleum products from ungrounded reservoirs, tanks, barrels; when transporting liquids in ungrounded containers; when filtering them through porous partitions and meshes, etc. The danger of static electricity is mainly due to the possibility of spark discharge, which can lead to explosion, fire and, consequently, injury to people.

A discharge of static electricity occurs when the electrostatic field strength reaches a breakdown (critical) value. For air, the breakdown voltage is approximately 30 kV/cm.

The physiological effect of static electricity on the human body depends on the amount released during discharge electrical energy. A person may experience mild, moderate, or severe punctures or shocks. Injections and shocks are not life-threatening, since the current strength is negligible. However, reflex movements are possible, leading to a fall from a height, contact with unguarded rotating parts of machines, etc.

On railway transport Of the variety of technological processes that lead to the appearance of static electricity, the main ones are the transportation of various liquids in tanks and the pumping of petroleum products on loading and unloading racks.

Let's consider the process of electrification of liquid. The mechanism of electrification of a liquid moving through a pipe is explained by the mechanical destruction of the double electrical layer that appears at the boundary with the solid phase. Since any dielectric liquid always contains a certain amount of carriers electric charge, at the interface between the liquid and solid phases, the formation of a double electrical layer occurs.

In this case, charges of the same sign, deposited on the surface of the solid wall, are neutralized, and charges of the opposite sign, located in the volume of the liquid, are carried away by the flow and enter the receiving tank. If there is a flammable vapor-air mixture in the tank above the surface of the liquid, then the possibility of an explosion and fire due to a discharge of static electricity between the surface of the electrified liquid and the walls of the tank or other grounded structural elements cannot be ruled out.

The formation of static electricity charges also occurs when filling tanks with a freely falling stream, with splashing.

In this case, small and large drops acquire charges of opposite signs. A cloud of small drops is formed, creating an electric field with a high gradient above the surface of the liquid. As a result of these phenomena, electrostatic discharges occur.

The main factors determining the intensity of electrification of petroleum products, the purity of petroleum products and their electrical resistance; speed and nature of movement (continuous stream or splashing); metal material of pipelines, tanks and other devices through which petroleum products move, as well as the condition of their internal surface. Petroleum products are especially intensively electrified during their filtration.

It has been established that gasoline, flowing through pipes, is charged negatively, and the pipeline is charged positively.

The amount of total charge transferred by the electrified product to the receiving tank:

where: -- product charge, k/l;

Amount of product pumped, l.

Data on the minimum ignition energy of steam and gas-air mixtures (at a pressure of 0.1 MPa and a temperature of 200C) are given in Table 11.1

Table 11.1

To prevent the possibility of dangerous spark discharges from the surface of equipment, processed substances, as well as from the human body, the following measures are provided (taking into account the specifics of production) to ensure that the resulting charges of static electricity drain off:

Removal of charges by reducing specific volumetric and surface electrical resistances;

Neutralization of charges using induction neutralizers, etc.;

Discharge of charges using a grounding device for equipment and communications.

Among the measures to protect against static electricity, the most widely used for the removal of electrostatic charges is grounding, which is used in conjunction with the measures discussed above. Loading risers of trestles for filling tanks and rails within the front of draining and loading operations are subject to grounding. Grounding devices for protection against static electricity are combined with protective or lightning protection grounding devices. In this case, the maximum permissible resistance of a grounding device intended solely for the removal of static electricity should be no more than 100 Ohms. Non-metallic equipment will be electrically grounded if the resistance of any point relative to the ground loop does not exceed 107 ohms.

With a small capacitance C, the current spreading resistance of the grounding device can be higher than 107 Ohms.

Let's consider in what case safety will be ensured from possible discharges of static electricity when filling into an insulated tank with a capacity of M = 1000 liters. gasoline at a speed v = 100 l/min. The rate of electrification of gasoline = 1.1·10-8 A·s/l.

Let's determine the potential on the tank at the end of filling. The total charge transferred by electrified gasoline to the tank will be.