Explosive limits of liquefied gases. Explosive concentration of natural gas. Rules for the use of gas at home
If the concentration of a combustible substance in the mixture is less than the lower limit of flame propagation, such a mixture cannot burn and explode, since the heat released near the ignition source is not enough to heat the mixture to the ignition temperature. If the concentration of a combustible substance in the mixture is between the lower and upper limits of flame propagation, the ignited mixture ignites and burns both near the ignition source and when it is removed. This mixture is explosive. The wider the range of flame propagation limits (also called flammability limits and explosive limits) and the lower the lower limit, the more explosive the gas. If the concentration of a combustible substance in the mixture exceeds the upper limit of flame propagation, then the amount of oxidizing agent in the mixture is insufficient for complete combustion of the combustible substance.
The range of values of the graph of the dependence of the KPRP in the "combustible gas - oxidizer" system, corresponding to the ability of the mixture to ignite, forms the ignition region.
The following factors influence the values of NKPRP and VKPRP:
- Properties of reacting substances;
- Pressure (usually an increase in pressure does not affect the LKPR, but the VKPR can increase greatly);
- Temperature (an increase in temperature expands the CRRP due to an increase in the activation energy);
- Non-flammable additives - phlegmatizers;
The dimension of the KPRP can be expressed in volume percent or in g/m³.
The introduction of a phlegmatizer into the mixture lowers the value of VKPRP almost in proportion to its concentration up to the point of phlegmatization, where the upper and lower limits coincide. At the same time, NKPP rises slightly. To assess the ignitability of the "Fuel + Oxidizer + Phlegmatizer" system, a so-called fire triangle- a diagram, where each vertex of the triangle corresponds to one hundred percent content of one of the substances, decreasing to the opposite side. Inside the triangle, the area of \u200b\u200bignition of the system is distinguished. In the fire triangle, a line of minimum oxygen concentration (MCC) is marked, corresponding to such a value of the oxidant content in the system, below which the mixture does not ignite. Evaluation and control of the ICC is important for systems operating under vacuum, where atmospheric air can be sucked through leaks in process equipment.
With regard to liquid media, the temperature limits of flame propagation (TPRP) are also applicable - such temperatures of the liquid and its vapors in the oxidizer medium at which its saturated vapors form concentrations corresponding to the CPRP.
KPRP is determined by calculation or found experimentally.
A mixture of natural gas with air can explode at a gas concentration in air of 5-15%.
A mixture of liquefied gas in air explodes at a concentration of 1.5-9.5%.
For an explosion, 3 conditions must be present simultaneously:
The gas-air mixture must be in a closed volume. In the open air, the mixture does not explode, but flares up.
The amount of gas in the natural mixture should be 5-15% for natural gas and 1.5-9.5% for liquefied gas. At a higher concentration, the sweep will light up and when the limit is reached, it will explode.
The mixture should be heated at one point to the flash point.
5 First aid for a victim of carbon monoxide poisoning
Symptoms:
There is muscle weakness
Dizziness
Noise in ears
Drowsiness
hallucinations
Loss of consciousness
convulsions
Assistance:
Stop the flow of carbon monoxide
Remove victim to fresh air
If the victim is conscious, lay down and provide rest and continuous access to fresh air
If there is no consciousness, it is necessary to start a closed heart massage and artificial respiration before the arrival of an ambulance or before regaining consciousness.
Ticket number 10
5 First aid for a burn victim
Thermal caused by fire, steam, hot objects and in-you. If the victim's clothes caught fire, you need to quickly throw on a coat, any dense fabric, or knock down the flame with water. You can not run in burning clothes, as the wind will fan the flames. When providing assistance in order to avoid infection, you should not touch the burned areas of the skin with your hands or lubricate with fats, oils, petroleum jelly, sprinkle with baking soda. It is necessary to apply a sterile bandage to the burnt area of the skin. If pieces of clothing are stuck, then a bandage should follow over them, you can not tear it off.
Ticket number 11
5 Contents of the work permit for gas hazardous work.
Written permission, indicating the period of its validity, the start time of work, the end of work, their safety conditions, the composition of the team and persons responsible. for safety works. ND approved ch. engineer. List of persons entitled to issue ND approved. by order under predp. ND is issued in two copies. for one work foreman with one team; for one workplace. One copy is transferred to the manufacturer, the other remains with the person who issued the outfit. Accounting for ND is carried out according to the registration book; they enter: serial number, summary, position; FULL NAME. resp. guides; signature.
Ticket number 12
5 first aid to the victim of suffocation with natural gas
Remove victim to fresh air
In case of absence of consciousness and pulse on the carotid artery, proceed to the resuscitation complex
In case of loss of consciousness for more than 4 minutes - turn over on the stomach and apply cold to the head
In all cases, call an ambulance
Ticket number 13
1 classification of gas pipelines by pressure.
I- low (0-500 mm water column); (0.05 kg * s / cm 2)
II-medium (500-30,000 mm water column); (0.05-3 kg * s / cm 2)
Ticket number 14
3 requirement for lighting, ventilation and heating in hydraulic fracturing.
The need for heating the hydraulic fracturing room should be determined depending on climatic conditions.
In the premises of the GTP, natural and (or) artificial lighting and natural permanent ventilation should be provided, providing at least three air exchanges per hour.
For rooms with a volume of more than 200 m3, air exchange is carried out according to the calculation, but not less than a single air exchange in 1 hour.
The placement of equipment, gas pipelines, fittings and instruments should ensure their convenient maintenance and repair.
The width of the main passage in the premises should be at least 0.8 m.
Explosive limits of gas-air mixtures
Excluding the formation of explosive gas-air concentrations, as well as the appearance of sources of ignition of this mixture (flames, sparks) is always the main task of the maintenance personnel of compressor stations. During the explosion of the gas-air mixture, the pressure in the explosion zone rises sharply, leading to the destruction of building structures, and the flame propagation speed reaches hundreds of meters per second. For example, the auto-ignition temperature of a methane-air mixture is at the level of 700 °C, and methane is the main component of natural gas. Its content in gas fields fluctuates in the range of 92-98%.
During the explosion of a gas-air mixture under a pressure of 0.1 MPa, a pressure of about 0.80 MPa develops. The gas-air mixture explodes if it contains 5-15% methane; 2-10% propane; 2-9% butane, etc. With an increase in the pressure of the gas-air mixture, the explosive limits narrow. It should be noted that the admixture of oxygen in the gas increases the risk of explosion.
The limits and range of explosiveness of gases in a mixture with air at a temperature of 20 ° C and a pressure of 0.1 MPa are given in Table. 1.4.
Table 1.4
Limits and range of explosion of gases in a mixture with air at a temperature of 20 ° C and a pressure of 0.1 MPa
|
Explosive limits, % by volume |
Explosive interval, % by volume |
||
|
Acetylene | |||
|
Oilfield. gas | |||
|
carbon monoxide | |||
|
Natural gas | |||
|
Propylene | |||
1.2. Laws of ideal gases. Areas of their application
Ideal gases are considered to be gases that obey the Clapeyron equation (). At the same time, ideal gases mean gases in which there are no forces of intermolecular interaction, and the volume of the molecules themselves is zero. At present, it can be argued that none of the real gases obeys these gas laws. Nevertheless, these specific gas laws are widely used in technical calculations. These laws are simple and quite well characterize the behavior of real gases at low pressures and not very low temperatures, far from saturation regions and critical points of matter. The laws of Boyle-Mariotte, Gay-Lussac, Avogadro and, based on them, the Clapeyron-Mendeleev equation received the greatest practical distribution.
Boyle-Mariotge's law states that at constant temperature ( 
= const) the product of absolute pressure and specific volume of an ideal gas remains constant ( 
= const), i.e. The product of absolute pressure and specific volume depends only on temperature. Where at 
= const we have:
.
(1.27)
Gay-Lussac's law states that at constant pressure ( 
= const) the volume of an ideal gas changes in direct proportion to the temperature increase:
,
(1.28)
where 
- specific volume of gas at temperature 
°С and pressure 
- specific volume of gas at temperature 
= 0 °С and the same pressure 
;
- temperature coefficient of volume expansion of ideal gases at 0 ° C, which remains the same value at all pressures and is the same for all ideal gases:
.
(1.29)
Thus, the content of the Gay-Lussac law is reduced to the following statement: the volumetric expansion of ideal gases with a change in temperature and with 
= const is linear, and the temperature coefficient of volume expansion 
is the universal constant of ideal gases.
Comparison of the laws of Boyle-Mariotte and Gay-Lussac leads to the equation of state for ideal gases:
,
(1.30)
where 
- specific volume of gas; 
- absolute gas pressure; 
- specific gas constant of an ideal gas; 
is the absolute temperature of an ideal gas:
.
(1.31)
The physical meaning of the specific gas constant 
is specific work in progress 
= const when the temperature changes by one degree.
Avogadro's law states that the volume of one mole of an ideal gas 
does not depend on the nature of the gas and is completely determined by the pressure and temperature of the substance ( 
). On this basis, it is argued that the volumes of moles of different gases, taken at the same pressures and temperatures, are equal to each other. If a 
is the specific volume of gas, and 
- molar mass, then the volume of a mole (molar volume) is equal to 
. At equal pressures and temperatures for different gases, we have:
Since the specific molar volume of gas 
depends in the general case only on pressure and temperature, then the product 
in equation (1.32) - there is a value that is the same for all gases and therefore is called the universal gas constant:
, J/kmol K. (1.33)
From equation (1.33) it follows that the specific gas constants of individual gases 
are determined in terms of their molar masses. For example, for nitrogen ( 
) the specific gas constant will be
= 8314/28 = 297 J/(kg K). (1.34)
For 
kg of gas, taking into account the fact that 
, the Clapeyron equation is written as:
,
(1.35)
where 
- amount of substance in moles 
. For 1 kmole of gas:
.
(1.36)
The last equation obtained by the Russian scientist D.I. Mendeleev is often called the Clapeyron-Mendeleev equation.
The value of the molar volume of ideal gases under normal physical conditions ( 
= 0 °С and 
= 101.1 kPa) will be:
= 22.4 m 
/kmol. (1.37)
The equation of state of real gases is often written on the basis of the Clapeyron equation with the introduction of a correction into it 
, which takes into account the deviation of the real gas from the ideal
,
(1.38)
where 
- compressibility factor, determined by special nomograms or from the relevant tables. On fig. 1.1 shows a nomogram for determining the numerical values of the quantity 
natural gas depending on pressure 
, relative density of gas in air 
and its temperature 
. In the scientific literature, the compressibility factor 
usually determined depending on the so-called reduced parameters (pressure and temperature) of the gas:
;
,
(1.39)
where 
,
and 
- respectively reduced, absolute and critical gas pressure; 
,
and 
are the reduced, absolute and critical gas temperatures, respectively.
Rice. 1.1. Calculation nomogram 
depending on the 
,
,
Critical pressure is the pressure at which, and above which, no increase in temperature can any longer turn the liquid into vapor.
The critical temperature is the temperature at which and above which no vapor can be condensed under any increase in pressure.
Numerical values of critical parameters for some gases are given in Table. 1.5.
Table 1.5
Methane, or firedamp, natural gas is colorless and odorless. The chemical formula is CH 4 . In November 2011, coal-bed methane was recognized as an independent mineral and included in the All-Russian Classifier of Minerals and Groundwater.
Methane is contained in various forms (from free to bound) in coal and host rocks and was formed there at the stage of coalification of organic remains and metamorphization of coals. In workings, methane is released mainly from coal (there are deposits where the relative methane release exceeds 45 m³ of methane per ton of coal, there have also been cases of methane release of the order of 100 m³ / t), mainly in the process of its destruction (breaking), less often - from natural cavities - tanks.
In mines, methane accumulates in voids among rocks, mainly under the roof of workings, and can create explosive methane-air mixtures. For an explosion, it is necessary that the concentration of methane in the mine atmosphere be from 5 to 16%; the most explosive concentration is 9.5%. At a concentration of more than 16%, methane simply burns, without an explosion (in the presence of an influx of oxygen); up to 5-6% - burns in the presence of a heat source. In the presence of suspended coal dust in the air, it can explode even at a concentration less than 4-5%.
The cause of the explosion can be an open fire, a hot spark. In the old days, miners took a cage with a canary into the mine, and as long as the birds were singing, they could work calmly: there is no methane in the mine. If the canary fell silent for a long time, and even worse - forever, then death is near. At the beginning of the 19th century, the famous chemist H. Davy invented a safe miner's lamp, then it was replaced by electricity, but explosions in coal mines continued.
Currently, the concentration of methane in the mine atmosphere is controlled by automatic gas protection systems. In gas-bearing formations, measures are taken for degassing and an isolated gas outlet.
The media often use the phrases “the miners were poisoned by methane”, etc. There is an illiterate interpretation of the facts of suffocation caused by a decrease in the concentration of oxygen in an atmosphere saturated with methane. The methane itself non-toxic.
In media reports, fiction, and even experienced miners, methane is erroneously referred to as "explosive gas". In fact, explosive gas is a mixture of hydrogen and oxygen. When ignited, they connect almost instantly, a strong explosion occurs. And methane from time immemorial was called "mine" (or "swamp", if we are not talking about a mine) gas.
Methane is combustible, which makes it possible to use it as a fuel. It is possible to use methane for refueling vehicles, as well as at thermal power plants. In the chemical industry, methane is used as a hydrocarbon raw material.
Most domestic mines emit methane into the atmosphere, and only a few have introduced or are implementing installations for its disposal. Abroad, the situation is reversed. Moreover, well projects for the production of reservoir methane are being actively implemented, including as part of the preliminary degassing of mine fields.
Explosive concentration of natural gas
Methane, or firedamp, is a natural gas that is colorless and odorless. The chemical formula is CH 4 . In November 2011, coal-bed methane was recognized as an independent mineral and included in
Dangerous properties of natural gas
Dangerous properties of natural gas.
Toxicity (hazardous properties of natural gas). A dangerous property of natural gases is their toxicity, which depends on the composition of gases, their ability, when combined with air, to form explosive mixtures that ignite from an electric spark, flame and other sources of fire.
Pure methane and ethane are not poisonous, but with a lack of oxygen in the air they cause asphyxiation.
Explosiveness (hazardous properties of natural gas). Natural gases, when combined with oxygen and air, form a combustible mixture, which, in the presence of a fire source (flame, spark, hot objects), can explode with great force. The ignition temperature of natural gases is the lower, the higher the molecular weight. The strength of the explosion increases in proportion to the pressure of the gas-air mixture.
Natural gases can explode only at certain limits of gas concentration in the gas-air mixture: from a certain minimum (lower explosive limit) to a certain maximum (higher explosive limit).
The lower explosive limit of a gas corresponds to such a gas content in the gas-air mixture at which a further decrease in it makes the mixture non-explosive. The lower limit is characterized by the amount of gas sufficient for the normal course of the combustion reaction.
The highest explosive limit corresponds to such a gas content in the gas-air mixture at which its further increase makes the mixture non-explosive. The highest limit is characterized by the content of air (oxygen), insufficient for the normal course of the combustion reaction.
With an increase in the pressure of the mixture, the limits of its explosiveness increase significantly. With the content of inert gases (nitrogen, etc.), the flammability limits of mixtures also increase.
Combustion and explosion are chemical processes of the same type, but differ sharply in the intensity of the reaction. During an explosion, the reaction in a closed space (without air access to the ignition source of an explosive gas-air mixture) occurs very quickly.
The propagation speed of the detonation combustion wave during an explosion (900-3000 m/s) is several times higher than the speed of sound in air at room temperature.
The strength of the explosion is maximum when the air content in the mixture approaches the amount theoretically required for complete combustion.
If the concentration of gas in the air is within the flammable range and in the presence of an ignition source, an explosion will occur; if the gas in the air is less than the lower limit or more than the upper limit of ignition, then the mixture is not capable of exploding. A jet of a gas mixture with a gas concentration above the upper flammability limit, entering the air volume and mixing with it, burns out with a calm flame. The propagation velocity of the combustion wave front at atmospheric pressure is about 0.3-2.4 m/s. The lower speed value is for natural gases, the upper one is for hydrogen.
Detonation properties of paraffinic hydrocarbons . Detonation properties are manifested from methane to hexane, the octane number of which depends both on the molecular weight and the structure of the molecules themselves. The lower the molecular weight of the hydrocarbon, the lower its detonation properties, the higher its octane number.
Properties of individual constituents of natural gas (consider the detailed composition of natural gas)
Methane(Cp) is a colorless, odorless gas, lighter than air. Flammable, but still it can be stored with sufficient ease.
Ethane(C2p) is a colorless, odorless and colorless gas, slightly heavier than air. Also combustible, but not used as a fuel.
Propane(C3H8) is a colorless, odorless gas, poisonous. It has a useful property: propane liquefies at low pressure, which makes it easy to separate it from impurities and transport it.
Butane(C4h20) - similar in properties to propane, but has a higher density. Twice as heavy as air.
Carbon dioxide(CO2) is a colorless, odorless gas with a sour taste. Unlike the other components of natural gas (with the exception of helium), carbon dioxide does not burn. Carbon dioxide is one of the least toxic gases.
Helium(He) - colorless, very light (the second of the lightest gases, after hydrogen) without color and odor. Extremely inert, under normal conditions does not react with any of the substances. Does not burn. It is not toxic, but at elevated pressure it can cause anesthesia, like other inert gases.
hydrogen sulfide(h3S) is a colorless heavy gas with a smell of rotten eggs. Very poisonous, even at very low concentrations it causes paralysis of the olfactory nerve.
Properties of certain other gases that are not part of natural gas but have uses similar to those of natural gas
Ethylene(C2p) A colorless gas with a pleasant smell. It is similar in properties to ethane, but differs from it in lower density and flammability.
Acetylene(C2h3) is an extremely flammable and explosive colorless gas. With strong compression, it can explode. It is not used in everyday life due to the very high risk of fire or explosion. The main application is in welding work.
Methane used as fuel in gas stoves. propane and butane as fuel in some vehicles. Lighters are also filled with liquefied propane. Ethane it is rarely used as a fuel, its main use is the production of ethylene. Ethylene is one of the most produced organic substances in the world. It is a raw material for the production of polyethylene. Acetylene used to create a very high temperature in metallurgy (reconciliation and cutting of metals). Acetylene it is very combustible, therefore it is not used as a fuel in cars, and even without this, the conditions for its storage must be strictly observed. hydrogen sulfide, despite its toxicity, is used in small quantities in the so-called. sulfide baths. They use some of the antiseptic properties of hydrogen sulfide.
The main useful property helium is its very low density (7 times lighter than air). Helium fill balloons and airships. Hydrogen is even lighter than helium, but at the same time combustible. Helium balloons are very popular among children.
All hydrocarbons, when fully oxidized (excess oxygen), release carbon dioxide and water. For example:
Cp + 3O2 = CO2 + 2h3O
With incomplete (lack of oxygen) - carbon monoxide and water:
2Cp + 6O2 = 2CO + 4h3O
With an even smaller amount of oxygen, finely dispersed carbon (soot) is released:
Cp + O2 = C + 2h3O.
Methane burns with a blue flame, ethane - almost colorless, like alcohol, propane and butane - yellow, ethylene - luminous, carbon monoxide - light blue. Acetylene - yellowish, strongly smokes. If you have a gas stove at home and instead of the usual blue flame you see yellow, you should know that methane is diluted with propane.
Helium, unlike any other gas, does not exist in a solid state.
Laughing gas is the trivial name for nitrous oxide N2O.
Dangerous properties of natural gas
Dangerous properties of natural gas. Toxicity (hazardous properties of natural gas). Explosiveness (hazardous properties of natural gas).
CIB Controls LLC
Explosive limits (LEL and ERW)
What are the lower and upper explosive limits (LEL and ULL)?
For the formation of an explosive atmosphere, the presence of a flammable substance in a certain concentration is necessary.
Basically, all gases and vapors require oxygen to ignite. With an excess of oxygen and its lack, the mixture will not ignite. The only exception is acetylene, which does not require oxygen to ignite. The low and high concentrations are called the “explosive limit”.
- Lower Explosive Limit (LEL): The concentration limit of a gas-air mixture below which a gas-air mixture cannot ignite.
- Upper Explosive Limit (UEL): The concentration limit of a gas-air mixture above which a gas-air mixture cannot ignite.
Explosive limits for explosive atmosphere:
If the concentration of a substance in the air is too low (lean mixture) or too high (saturated mixture), then an explosion will not occur, and most likely a slow combustion reaction may occur or it will not occur at all.
An ignition reaction followed by an explosion reaction will occur in the range between the lower (LEL) and upper (URL) explosive limits.
Explosive limits depend on the pressure of the surrounding atmosphere and the concentration of oxygen in the air.
Examples of lower and upper explosive limits for various gases and vapors:
Dust is also explosive at certain concentrations:
- Lower explosion limit of dust: in the range of approximately 20 to 60 g/m3 of air.
- Upper explosion limit of dust: within the range of approximately 2 to 6 kg/m3 of air.
These parameters may vary for different types of dust. Highly flammable dusts may form a flammable mixture at substance concentrations below 15 g/m3.
There are three subcategories of category II: IIA, IIB, IIC. Each subsequent subcategory includes (can replace) the previous one, that is, subcategory C is the highest and meets the requirements of all categories - A, B and C. Thus, it is the most "strict".
There are three categories in the IECEx system: I, II and III.
From category II, dust was separated into category III. (Category II for gases, category III for dusts.)
The NEC and CEC system provides a more advanced classification of explosive mixtures of gases and dusts to ensure greater safety by classes and subgroups (Class I Group A; Class I Group B; Class I Group C; Class I Group D; Class I Group E; Class II Group F Class II Group G). For example, for coal mines it is produced with double marking: Class I Group D (for methane); Class II Group F (for coal dust).
Characteristics of explosive mixtures
For many common explosive mixtures, so-called ignition characteristics have been built experimentally. For each fuel, there is a minimum ignition energy (MEI) that corresponds to the ideal proportion of fuel and air in which the mixture is most easily ignited. Below the MEP, ignition is impossible at any concentration. For a concentration lower than the value corresponding to the MEP, the amount of energy required to ignite the mixture is increased until the concentration value becomes less than the value at which the mixture cannot ignite due to the small amount of fuel. This value is called the lower limit of the explosion (LEB). Similarly, as the concentration increases, the amount of energy required for ignition increases until the concentration exceeds a value at which ignition cannot occur due to insufficient oxidizing agent. This value is called the upper explosion limit (IGW).
From a practical point of view, the NGV is more important and significant than the IGV, because it establishes, in percentage terms, the minimum amount of fuel required to form an explosive mixture. This information is important in the classification of hazardous areas.
According to GOST, the following classification according to the autoignition temperature applies:
- Т1 – hydrogen, water gas, lighting gas, hydrogen 75% + nitrogen 25%”;
- T2 - acetylene, methyldichlorosilane;
- Т3 – trichlorosilane;
- T4 - not applicable;
- T5 - carbon disulfide;
- T6 - not applicable.
- T1 - ammonia, ..., acetone, ..., benzene, 1,2-dichloropropane, dichloroethane, diethylamine, ..., blast furnace gas, isobutane, ..., methane (industrial, with a hydrogen content 75 times higher than in mine methane), propane , ..., solvents, petroleum solvent, diacetone alcohol, ..., chlorobenzene, ..., ethane;
- T2 - alkylbenzene, amyl acetate, ..., gasoline B95 \ 130, butane, ... solvents ..., alcohols, ..., ethylbenzene, cyclohexanol;
- T3 - gasoline A-66, A-72, A-76, "galosh", B-70, extraction. Butyl methacrylate, hexane, heptane, ..., kerosene, petroleum, petroleum ether, polyester, pentane, turpentine, alcohols, fuel T-1 and TS-1, white spirit, cyclohexane, ethyl mercaptan;
- T4 - acetaldehyde, isobutyric aldehyde, butyric aldehyde, propionic aldehyde, decane, tetramethyldiaminomethane, 1,1,3 - triethoxybutane;
- T5 and T6 - do not apply.
- T1 - coke oven gas, hydrocyanic acid;
- T2 - divinyl, 4,4 - dimethyldioxane, dimethyldichlorosilane, dioxane, ..., nitrocyclohexane, propylene oxide, ethylene oxide, ..., ethylene;
- T3 - acrolein, vinyltrichlorosilane, hydrogen sulfide, tetrahydrofuran, tetraethoxysilane, triethoxysilane, diesel fuel, formalglycol, ethyldichlorosilane, ethyl cellosolve;
- T4 - dibutyl ether, diethyl ether, ethylene glycol diethyl ether;
- T5 and T6 - do not apply. As can be seen from the above data, category IIC is redundant for most cases of using communication equipment in real objects.
Additional Information.
Categories IIA, IIB and IIC are determined by the following parameters: safe experimental maximum clearance (BEMZ - the maximum gap between the flanges of the shell, through which the explosion does not transfer from the shell to the environment) and the MTE value (the ratio of the minimum ignition current of an explosive gas mixture and the minimum ignition current methane).
temperature class.
The temperature class of electrical equipment is determined by the maximum temperature in degrees Celsius that the surfaces of explosion-proof equipment can have during operation.
The temperature class of equipment is set based on the minimum temperature of the corresponding temperature range (its left border): equipment that can be used in an environment of gases with an autoignition temperature of class T4 must have a maximum temperature of surface elements below 135 degrees; T5 is below 100, and T6 is below 85.
Marking of equipment for category I in Russia:
Marking example: РВ1В
ExdIIBT4
Ex - sign of explosion-proof equipment according to the CENELEC standard; d – type of explosion protection (flameproof enclosure); IIB - category of explosion hazard of the gas mixture II option B (see above); T4 - mixture group according to ignition temperature (temperature not higher than 135 C °)
FM marking according to NEC, CEC:
Explosion-proof designations according to the American FM standard.
Factory Mutual (FM) are essentially identical to the European and Russian standards, but differ from them in the form of recording. The American standard also indicates the conditions for the use of equipment: the explosive class of the environment (Class), operating conditions (Division) and mixture groups according to their autoignition temperature (Group).
Class can have the values I, II, III: Class I - explosive mixtures of gases and vapors, Class II - combustible dust, Class III - combustible fibers.
Division can have the values 1 and 2: Division 1 is a complete analog of zone B1 (B2) - an explosive mixture is present under normal operating conditions; Division 2 is an analogue of the B1A (B2A) zone, in which an explosive mixture can appear only as a result of an accident or process disturbances.
Working in the Div.1 zone requires especially explosion-proof equipment (intrinsically safe in terms of the standard), and working in the Div.2 zone requires non-incendive class explosion-proof equipment.
Explosive air mixtures, gases, vapors form 7 subgroups that have direct analogies in Russian and European standards:
- Group A - mixtures containing acetylene (IIC T3, T2);
- Group B - mixtures containing butadiene, acrolein, hydrogen and ethylene oxide (IIC T2, T1);
- Group C - mixtures containing cyclopropane, ethylene or ethyl ether (IIB T4, T3, T2);
- Group D - mixtures containing alcohols, ammonia, benzene, butane, gasoline, hexane, varnishes, solvent vapors, kerosene, natural gas or propane (IIA T1, T2, T3, T4);
- Group E - air suspension of combustible metal dust particles, regardless of its electrical conductivity, or dust with similar hazard characteristics, having a specific volume conductivity of less than 100 KΩ - see.
- Group F - mixtures containing combustible dust of soot, charcoal or coke with a combustible content of more than 8% by volume, or suspensions having a conductivity of 100 to 100,000 ohm-cm;
- Group G - combustible dust suspensions having a resistance of more than 100,000 ohm-cm.
ATEX is the new European standard for explosion-proof equipment.
In accordance with the EU directive 94/9/EC from July 01, 2003, a new ATEX standard is introduced. The new classification will replace the old CENELEC and will be implemented in European countries.
ATEX is short for ATmospheres Explosibles (explosive mixtures of gases). ATEX requirements apply to mechanical, electrical equipment and protective equipment intended to be used in a potentially explosive atmosphere, both underground and above ground.
The ATEX standard tightens the requirements of the EN50020/EN50014 standards regarding IS (Intrinsically Safe) equipment. These tightenings include:
- limiting the capacitive parameters of the circuit;
- use of other protection classes;
- new requirements for electrostatics;
- using a protective leather case.
Consider the classification marking of explosion-proof equipment according to ATEX using the following example:
Ecology Side
Explosive limits for mixtures of hydrogen and air
Some gases and vapors in a certain mixture with air are explosive. Mixtures of air with acetylene, ethylene, benzene, methane, carbon monoxide, ammonia, hydrogen are characterized by increased explosiveness. An explosion of a mixture can occur only at certain ratios of combustible gases with air or oxygen, characterized by lower and upper explosive limits. The lower explosive limit is the minimum amount of gas or vapor in air that, if ignited, can lead to an explosion. The top-niche explosive limit is the maximum content of gas or vapor in the air at which, in the event of ignition, an explosion can still occur. The hazardous explosive zone lies between the lower and upper limits. The concentration of gases or vapors in the air of industrial premises below the lower and above the upper explosive limit is non-explosive, since it does not cause active combustion and explosion - in the first case due to excess air, and in the second due to its lack.
Hydrogen, when mixed with air, forms an explosive mixture - the so-called detonating gas. This gas is most explosive when the volume ratio of hydrogen and oxygen is 2:1, or hydrogen and air is approximately 2:5, since air contains approximately 21% oxygen.
It is believed that explosive concentrations of hydrogen with oxygen occur from 4% to 96% by volume. When mixed with air from 4% to 75 (74)% by volume. Such figures now appear in most reference books, and they can be used for indicative estimates. However, it should be borne in mind that later studies (around the end of the 80s) revealed that hydrogen in large volumes can be explosive even at a lower concentration. The larger the volume, the lower the concentration of hydrogen is dangerous.
The source of this widely publicized error is that explosiveness was studied in laboratories on small volumes. Since the reaction of hydrogen with oxygen is a chain chemical reaction that proceeds according to the free radical mechanism, the “death” of free radicals on the walls (or, say, the surface of dust particles) is critical for the continuation of the chain. In cases where it is possible to create "boundary" concentrations in large volumes (premises, hangars, workshops), it should be borne in mind that the actual explosive concentration may differ from 4% both upwards and downwards.
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Ecology Side Explosive limits for mixtures of hydrogen and air Some gases and vapors in certain mixtures with air are explosive. Air mixtures have been characterized by increased explosiveness since June 3, 2011
| – | Lower explosive limit | Upper explosion limit |
| Gasoline B-70 | 0,8 | 5,1 |
| Tractor kerosene | 1,4 | 7,5 |
| Propane | 2,1 | 9,5 |
| n-butane | 1,5 | 8,5 |
| Methane | 5 | 15 |
| Ammonia | 15 | 28 |
| hydrogen sulfide | 4,3 | 45,5 |
| Carbon monoxide | 12,5 | 75 |
| Hydrogen | 4 | 75 |
| Acetylene | 2 | 82 |
An explosion is an instantaneous chemical transformation, accompanied by the release of energy and the formation of compressed gases.
During explosions of gas-air mixtures, a large amount of heat is released and a large amount of gases is formed.
Due to the released heat, the gases are heated to a high temperature, increase sharply in volume and, expanding, press with great force on the building envelope or the walls of the apparatus in which the explosion occurs.
The pressure at the moment of explosion of gas mixtures reaches 10 kgf/cm 2 , the temperature fluctuates between 1500-2000°C, and the speed of propagation of the explosive wave reaches several hundred meters per second. Explosions tend to cause great destruction and fires.
The fire hazard properties of combustible substances are characterized by a number of indicators: flash point, ignition, self-ignition, etc.
Other properties of combustible substances include explosion pressure, the minimum explosive oxygen content, below which ignition and combustion of the mixture become impossible at any concentration of combustible substance in the mixture, the nature of interaction with fire extinguishing agents, etc.
"Occupational health and safety in the gas industry",
A.N. Yanovich, A.Ts. Astvatsaturov, A.A. Busurin
Indicators Methane Propane n-Butane Aviation gasoline Tractor kerosene Industrial oil Vapor flash point, °С —188 — —77 —34 27 200 Autoignition temperature, °С 537 600—588 490—569 300 250 380 .3-15 2.2-9.5 1.9-8.5 0.8-5.2 1.4-7.5 1-4 —(77/52) —(34/4) 27—69 146—191 Speed…
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