2.1 Natural gas - the product produced from the subsoil of the Earth consists of methane (96 - 99%), hydrocarbons (ethane, butane, propane, etc.), nitrogen, oxygen, carbon dioxide, water vapor, helium. On ITSTEC-3 natural gas enters as fuel on a gas pipeline from Tyumen.

The specific weight of the natural gas is 0.76 kg / m 3, the specific heat of the combustion is 8000 - 10,000 kcal / m 3 (32 - 41 mJ / m 3), the combustion temperature is 2080 ° C, the ignition temperature is 750 ° C.

The combustible natural gas for toxicological characteristics refers to substances 4 of the hazard class ("low hazard") in accordance with GOST 12.1.044-84.

2.2 The maximum allowable concentration (MPC) of natural gas hydrocarbons in the air of the working area is 300 mg / m 3 in terms of carbon, hydrogen sulfide PDK in the air of the working area is 10 mg / m 3, hydrogen sulfide in a mixture with hydrocarbons with 1 - C 5 - 3 mg / m 3.

2.3 Safety Instructions for Gas Economic Safety Conducts the following dangerous properties of gaseous fuel:

a / absence odor and colors

b / gas ability to form fire-hazardous mixtures with air

c / choking gas ability.

2.4 Permissible gas concentration in the air of the working area, in the gas pipeline when performing gas hazardous work - no more than 20% of the lower concentration limit of flame distribution (NKPR):

3 Gas sampling rules for analysis

3.1 Smoking and the use of open fire in gas-hazardous places, when checking the gas supply of industrial premises is categorically prohibited.

3.2 Footwear for workers producing measurements of gas supplies and are in gas hazardous places should not have metal horseshoes and nails.

3.3 When performing gas hazardous work, you should use portable lamps in the explosion-proof version of 12 volts

3.4 Before analyzing the analysis, it is necessary to inspect the gas analyzer. Not allowed to use a measurement tool that overdue the period of calibration or there are damage.

3.5 Before entering the PRP premises, it is necessary: \u200b\u200bmake sure that the emergency signal lamp "is ridden" at the entrance to the PPP room does not burn. The signal lamp turns on when the concentration of methane is reached in the air of the PPP premises equal to or above 20% of the lower concentration limit of flame propagation, i.e. equal or higher about. one%.

3.6 Selection of gas samples in the premises (in hydraulic) is made by the portable gas analyzer from the upper zone of the premises mostly badly ventilated zones, because Natural gas is easier than air.

Actions in case of gas supply are listed in clause 6.

3.7 When selecting air sampling from the well, it is necessary to approach it from a windward side, making sure that there is no smell of gas near. One side of the well cover should be raised by a special hook by 5 - 8 cm, a wooden laying is put under the cover at the sampling time. Sampling is made using a hose, lowered to a depth of 20 - 30 cm and connected to a portable gas analyzer, or to a gas pipette.

When the gas is detected in the well, it is carried out for 15 minutes. And repeat the analysis.

3.8 It is not allowed for sampling to descend into wells and other underground structures.

3.9 In the air of the working area, the natural gas content should be no more than 20% of the lower concentration limit of the flame distribution (1% of methane); The oxygen concentration should be not lower than 20% by volume.

The range of values \u200b\u200bof the Chart of the CPRP in the "Fuel Gas - Oxidizer" system, corresponding to the ability of the mixture to ignitance forms the ignition area.

The following factors influence the values \u200b\u200bof the NKPP and VKPRP:

• Properties of reacting substances;
• Pressure (usually the increase in pressure does not affect the NKPR, but the VKPRP can grow strongly);
• Temperature (temperature increase expands the CPRP due to an increase in activation energy);
• Non-combustible supplements - phlegmatizers;

The dimension of the CPRP may be expressed in volumetric percentages or in g / m³.

The introduction into the mixture of the phlegmatizer lowers the value of the VKPRP is virtually proportional to its concentration up to the point of phlegmatization, where the upper and lower limits coincide. The NKPP is raised slightly at the same time. To assess the ability to ignite the system "Fuel + oxidizing agent + phlegmatizer" are built by the so-called. The fire triangle is a diagram where each vertex of the triangle corresponds to the 100% content of one of the substances, decreasing to the opposite side. Inside the triangle allocate the inflammation area of \u200b\u200bthe system. In the fire triangle, the line of minimum oxygen concentration (ICC) corresponding to this value of the oxidant content in the system below which the mixture is not ignited. The assessment and control of the ICC is important for systems operating under vacuum where the sublicas is possible through the looseness of the technological equipment of atmospheric air.

In relation to liquid media, the temperature limits of the flame propagation (TPRP) are also applicable - such fluid temperatures and its vapors in the oxidant medium, in which its saturated pairs form concentrations corresponding to the CPRP.

The CPRP is determined by the estimated way or found experimentally.

It is used in the categorization of premises and buildings on the explosion and fire hazard, to analyze the risk of accident and the assessment of possible damage, when developing measures to prevent fires and explosions in technological equipment.

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lower concentration flame spread limit - NKPR Concentration of combustible gas or steam in the air, below which the explosive gas medium is not formed. [GOST R IEC 60050 426 2006] Themes of explosion protection synonyms NKPR EN Lellower Explosive Limit ...

lower concentration flame spread limit - 3.1.6 Bottom concentration limit of flame distribution (ignition) (Lower Explosive Limit, Lel); NKPR,%: The volume fraction of combustible gas or steam in the air, below which the explosive gas medium is not formed. A source …

lower concentration limit of flame distribution (ignition) (NKPR) - 2.10.1 Bottom concentration limit of flame proliferation (ignition) (NKPR): minimal combustible gas content or steam in air, in which the flame is possible on the mixture at any distance from the source. Source: GOST ... ... Dictionary directory terms of regulatory and technical documentation

bottom concentration limit of flame distribution (NKPR) - 2.1.6 Bottom concentration limit of flame distribution (NKPR): according to GOST 12.1.044. A source … Dictionary directory terms of regulatory and technical documentation

lower concentration limit of flame distribution, NKPR - 3.12 Lower concentration limit of flame proliferation, NKPR (LOWER EXPLOSIVE LIMIT, LEL): The concentration of combustible gas or steam in the air, below which the explosive gas medium is not formed, is expressed as a percentage (see IEC 60079 20 1) ... Dictionary directory terms of regulatory and technical documentation

lower concentration limit of the spread of the NKPR flame Electrotechnical Dictionary

NKPR (lower concentration limit of flame distribution) - 3.37 NKPR (lower concentration limit of flame proliferation): according to GOST 12.1.044. A source … Dictionary directory terms of regulatory and technical documentation

NKPR Lower Concentration Flame Spread Limit - LOWER EXPLOSIVE LIMIT, LEL The fuel gas concentration or steam in the air is below which the explosive gas environment is not formed ... Electrotechnical Dictionary

nizhny (upper) concentration flame spread limit - minimal (maximum) fuel content in a homogeneous mixture with an oxidative medium, in which the flame is possible along the mixture to any distance from the ignition source. [GOST 12.1.044 89] Themes Fire safety ... Technical translator directory

bottom Concentration Limit of Dissemination (NKPR) of Flame (ignition) - 3.5 lower concentration limit of the spread (NKPR) of the flame (ignition): the minimum combustion substance content in a homogeneous mixture with an oxidative medium (NKPR,% OPDA), in which the flame is possible on the mixture to any ... ... Dictionary directory terms of regulatory and technical documentation

Calculation of the concentration limits of flame distribution 1. The calculation of the concentration limits of the flame propagation by the approximation method is carried out by the formula: 100 / (AB + B), (5.6) where j is the lower or upper concentration limit of flame distribution, vol.%; b is a stoichiometric oxygen coefficient equal to the number of oxygen moles per 1 mol of combustible substance in its full combustion; a, V - Universal Constants: for the lower limit a \u003d 8,684; B \u003d 4,679; for upper limit at b ј 7.5 a \u003d 1,559; B \u003d 0,560 at b\u003e 7.5 A \u003d 0.768; B \u003d 6,554. The value B is determined by the reaction equation or by the formula: b \u003d M C + M S + 0.25 (M H - M x) + 0.5 m O + 2.5 m p, (5.7) where m c, m s, m h, m x, m o, m p is the number of atoms, respectively, carbon, sulfur, hydrogen, halogen, oxygen and phosphorus in a combustible molecule. The calculation error in the approximation method is: when calculating the lower limit of 12%, when calculating the upper limit of 12% at B ј 7.5 and 40% at b\u003e 7.5. When carrying out a combustible process in environmental parameters other than standard conditions (t \u003d 25 ° C, p \u003d 760 mm Hg), the lower (upper) limits are calculated by formulas: j n t \u003d j n 25, (5.8) j in t \u003d j at 25. (5.9) The increase in pressure (P) with respect to the atmospheric affects mainly at the magnitude of the upper concentration limit, which is calculated by the formula: j in p \u003d (100 j in atm c p) / (100 - j in atm + j in atm c r), (5.10) where j in p and j in atm - the upper concentration limits at pressure P and normal atmospheric, respectively, atm. 2. Calculation of the concentration limits of flame distribution by GOST 12.1.044-89. 2.1. Calculation of the lower limit for the spread of the flame of individual substances in volume percent at 25 ° C: h \u003d 1100 / h S m s, (5.11) where H S is the group S coefficient affecting the lower limit of the flame propagation, the values \u200b\u200bof which are ... Substances and materials capable of explode and burn when interacting with water, air oxygen or each other in such a quantity that the calculated excessive explosion pressure in the room exceeds 5 kPa
B-explosion-dangerous	Dust and fibers, LVZ with a flash point of more than 28 o C, combustible fluids (GZH) in such a quantity that can form explosive steady or dusty mixtures, when weighing the excessive pressure of the explosion in a room exceeding 5 kPa
fire hazing	Combustible and hard-burning liquids, solid combustible and hard-burning substances and materials (including dust and fiber), substances materials capable of interacting with water, air oxygen and each other only burn, provided that the premises in which they are in presence or appeals are not related to categories a or b
non-explosion-flaying	Non-combustible substances and materials in hot, red or molten state, the processing process of which is accompanied by the release of radiant heat, sparks and flames; combustible gases, liquids and solids that are burned or disposed of fuel
unfortunately dangerous	Non-combustible substances and materials in cold condition

Fire is easier to warn you to stew it. In this principle, fire prevention is based, where measures are planned in advance directed:

to eliminate ignition sources, oxidizing agent, etc.;

preventing the possibility of a fire focus (replacement of flammable substances for non-combustible, decrease in the degree of flammability of substances, work with safe concentrations, temperatures, etc.);

preventing the spread of a fire when it occurs inside the equipment and on pipelines, according to constructive elements of buildings, between buildings, etc. (fireprocerers, cutting valves, backup containers, fire walls, zones, embankments, etc.);

safe evacuation of people in the fire;

primary and stationary means of extinguishing fire.

Tasks and procedure for performing work

Task number 1.The definition of the lower (H) and the upper (c) concentration limits of the flame propagation.

Determine the degree of explosiveness of the mixture of combustible gases (on the task of the teacher) on the experimental setting of the lower (H) and / or the upper (c) limits of the flame propagation limits. The results obtained to compare with the calculated and find the error of the definition. Determine safe concentrations. Set to which class according to PUE there is a zone around the experimental installation, where a cylinder is installed with a given mixture of gases, and to which category of explosion hazard is a room in which this mixture is used: 1) as raw materials; 2) as fuel.

Procedure for performing work

• 1. To get acquainted with the experimental installation and procedure for performing work on it (see the description of the installation).
• 2. To conduct preliminary calculations of the lower (upper) concentration limits of the flame propagation, first for individual substances [see. equations (5.6) or (5.115.13)], and then for a mixture of gases [see Equation (5.15)] indicated in the task of the composition.
• 3. Calculate the volume of the gas mixture necessary to create a concentration corresponding to the lower (top) limit by formula (5.16).
• 4. Prepare a gas-air mixture by mixing air with the calculated volume of the gas mixture in the mixing system of the installation.
• 5. To select the part of the cooked mixture in the explosive cylinder and set fire to its spark discharge.
• 6. If there is an explosion when determining the lower limit (H), reduce the volume, and when determining the upper (B), on the contrary, increase the volume of the separated gas per 1 ml.
• 7. Remove the combustion products from the mixing system and explosive cylinder of the installation and repeat the experiment with a smaller (large) volume of the selected gas. Experiment should be carried out until the next decrease in (increase) the volume of the explosion gas will not be.
• 8. Calculate the experimental value of the lower (upper) limits of the spread of the flame and find the error between the calculated and experimental value. Explain the differences in experimental and calculated value.
• 9. When assessing the degree of danger of gas mixture with air, it is taken into account that all gas-air mixtures having an inflammation area bounded by lower and upper concentration limits, explosive, but mixtures with H 10 vol.% - Specialized, and with H 10 vol.% - Explosive .
• 10. Set the class of the PUE zone around the cylinder with the gas mixture of the specified composition.
• 11. Enough the room category in which this gas mixture is used as: a) raw materials; b) fuel.
• 12. Experimental results can be represented as Table 5.11:

Table 5.11.

Task number 2. Determination of the outbreak temperature and ignition.

Estimate the degree of explosiveness of fluid (on the task of the teacher) on the outbreak temperatures and ignition. Experimentally installed temperatures compare with calculated and reference values, identify errors and in case of discrepancies to explain the differences.

Install the PUE zone class and room category on the NPB105-95, where the fluid has been used. Suggest fire safety methods.

Procedure for performing work

• 1. Get acquainted with the installation of a closed (open) type to determine the flash temperature (T VS.) And ignition (t).
• 2. Calculate and / or find in the reference to the flash temperature for the fluid under study.
• 3. Fill the crucible in the installation on 2/3 of the fluid under study, set the thermometer of the required range and turn on the heating device.
• 4. Welcome and adjust the wicked fittings using the clamp on the gas hose from the gas cylinder.
• 5. For 1015 ° C to the calculated value of T VSP. (or taken from the directory) every 12 degrees to bring the wick to the surface of the liquid and fix the temperature at which the pairs of the liquid will be flashed over the liquid. This will be the experimental flare point - T VSP E.
• 6. Continue the heating of the fluid and bringing the wick wick every 12 degrees of heating to the surface of the fluid. Fix the temperature in which the pairs caught fire and the burning continued at least 1530 s. This will be an experimental ignition temperature - T Ae.
• 7. Close the container with a burning liquid with a lid if the measurements are performed on the open type setting, or close the valve on the closed-type instrument so that the combustion stops.
• 8. Experimental indicators Compare with calculated (reference) and explain discrepancies in temperature values.
• 9. At a found temperature, establish the degree of hazard of the liquid. The most dangerous are the LVZ, which include fluids with T VSP. 61 ° C (on a closed-type device) and 66 ° C (on an open-type device). All housing is explosive. If T VSP. 61 (66) O C is a fire hazard combustible liquid (GJ).
• 10. In terms of the difference between T pro - T VSP \u003d T, establish the risk of fluid during operation in a possible presence of ignition source. The less t, the more dangerous liquid.
• 11. Install the PUE zone class around the equipment in which the fluid has been used.
• 12. Install the room category on the NPB105-95, which uses equipment with liquid.
• 13. Suggest methods for ensuring fire safety when using the fluid under study.

Experimental results can be represented as Table 5.12.

Table 5.12

Task number 3. Determination of the temperature of self-ignition by the method of droplets.

Estimate the degree of explosiveness of the fluid (according to the task of the teacher) at the temperature of self-ignition (T st.). The results obtained are compared with the calculated and reference data. Find the error and explain possible discrepancies in the values \u200b\u200bof T st.

Install a group of explosive mixture and the temperature class of explosion-proof electrical equipment. Find a safe heating temperature of the fluid under study. Suggest fire safety activities when working with fluid test.

Procedure for performing work

• 1. To familiarize yourself with the installation by determining the temperature of self-ignition by the droplet method.
• 2. Calculate the volume of the fluid under study corresponding to the stoichiometric composition of the mixture by formula (5.21).
• 3. Calculate and / or take the temperature of the fluid under study from the directory.
• 4. Turn on the muffle furnace, adjust the potentiometer showing the temperature of the vessel heating and check the presence of a mirror over the vessel.
• 5. Heat the vessel to a temperature of 3040 ° C above the calculated (reference) temperature of the self-ignition of the fluid under study and disconnect the furnace.
• 6. For 1015 ° C to the calculated (reference) T st. After every 23 degrees of the temperature drop in the vessel, the calculated volume of the liquid and through the mirror fix the lighting of the vapor of the liquid.
• 7. With the help of the stopwatch, fix the time from the moment the fluid is added to the vessel before the fluid vapor ignition. This time is increased by the vessel.
• 8. After each experience, combustion products remove from a vessel with a special device.
• 9. The experiments repeat until the pair of liquid will not be ignited within 35 minutes.
• 10. For the experimental temperature of the self-ignition of the fluid under study, the temperature is taken at which the last time the vapor inflammation is recorded into the fluid installation.
• 11. Compare the resulting T st. e with the calculated (T st. P) and reference (T SV), explain the observed discrepancies and establish the error of the definition.
• 12. The degree of danger of fluid is set by finding T st. Group of explosive mixture. The most dangerous fluid belonging to the T6 group, and the least dangerous to the group T1. Group of explosive mixtures and temperature classes of explosion-proof electrical equipment are shown in the literature and in section 5.1 (Table 5.1 and 5.2).
• 13. Find a safe heating temperature of the fluid, determined by formula (5.2).
• 15. Experimental results can be presented in the form of Table. 5.13.

Table 5.13.

Task number 4. Determination of a safe experimental maximum gap (BEMZ).

Assess the degree of explosion hazard of the pair-air mixture (on the task of the teacher) by the BEMZ value defined on the model installation. The results obtained are compared with the calculated and / or reference and explain the observed discrepancies. Calculate the error of determining relative to the calculated value. Suggest fire safety measures when using the fluid under study.

Procedure for performing work

• 1. To familiarize yourself with the model installation by definition of BEMZ.
• 2. Calculate the volume of fluid necessary to create a steam-air mixture of stoichiometric composition according to formula (5.20).
• 3. Calculate the BEMZ value according to formula (5.16) and install this clearance on the installation using the scale. The accuracy of the clearance installation is 0.05 mm.
• 4. Enable the installation and open the protective cover.
• 5. Make into the left and right chambers the calculated volume of the fluid under study and close the hole through which the liquid was introduced (tracing).
• 6. Close the casing and wait the time required for evaporation of the injected liquid and the formation of a steam-air mixture of stoichiometric composition (the time depends on the volatility of the liquid and is indicated by the teacher).
• 7. By pressing the buttons on the front panel of the installation, set fire up the pair-air mixture using an electrical spark at first in the left chamber and then in the right.
• 8. When fixing explosions in both chambers, notice the absence of an explosion transmission from one camera to another.
• 9. After that, set the gap by 0.05 mm more than the previous one.
• 10. Remove combustion products using a ventilation system mounted in the installation by pressing the pedal on the front panel of the installation. The completeness of the removal is fixed by the lack of smell of the fluid under study from the holes through which the contaminated air is removed.
• 11. Experiments to repeat, changing the gap, until the explosion will be recorded when serving a spark in one of the cameras, and when the spark is served to another explosion chamber. This indicates that the gap between the cameras is greater than BEMZ and when the mixture explodes in one chamber through this gap occurs simultaneously an explosion in another chamber, therefore, an explosion transmission is observed. For the experimental value of BEMZ, take the value of the gap, at which the last time was recorded the absence of an explosion from one camera to another.
• 12. Compare the resulting BEMZ value with the estimated and reference. Calculate the error of determining relative to the estimated (reference) value. Explain possible discrepancies in the indicators.
• 13. Evaluation of the degree of explosion hazardous fluid largest BEMZ is carried out by finding the category of explosive mixture in PUE. The most dangerous will be a mixture relating to category IIS and the least dangerous - to category IIA (see Table 5.3).
• 14. Suggest fire safety measures when working with the fluid under study.
• 15. Experimental results can be presented in the form of Table. 5.14.

Table 5.14.

CONTROL QUESTIONS

• 1. General information about fire and burning. Mechanisms of burning process.
• 2. Basic indicators of the explosion hazardous substances and materials (Flash temperature-T VSP, ignition temperature-T pro., Self-ignition temperature-T sv., Nizhny (H) and upper (c) concentration limits of flame distribution, safe experimental maximum gap - BEMZ and etc.).
• 3. Evaluation of the degree of explosion hazardous substances and materials based on T VSP. , t. , T st. , N, B, BEMZ and other indicators.
• 4. Evaluation of the degree of explosion hazardous zones around the equipment where combustible substances are used.
• 5. Evaluation of the degree of explosion hazardous premises for NPB 105-95.
• 6. The procedure for the appointments of the explosion hazardous categories of premises (categories a and b).
• 7. The procedure for the appointment of fire hazardous category (B1-B4) and assessment of the degree of fire danger of premises.
• 8. Activities to prevent the emergence of the fire (decrease in the degree of flammability of substances, eliminating the oxidizing agent and the ignition source).
• 9. Activities to prevent the spread of the fire from its occurrence within the process equipment (fireprocerers, valves, membranes, etc.).
• 10. Activities to prevent the dissemination of a fire on constructive elements of the building and against the destruction of the building during an explosion (fire walls, overlaps, embankments, light-grade structures, etc.).
• 11. Events to ensure the safety of the evacuation of people in the fire.
• 12. Events aimed at extinguishing fires: specialized services, fire alarm means of fire, stationary and primary fire extinguishing agents.

For all harmful substances, currently known, the maximum concentration is established, at which there is no harmful effect on the human body (GOST 12.1.005-88), such a concentration is called maximum permissible concentration (MPC).

PDK - this is a concentration that, with a daily (except weekend) work for 8 hours or with a different duration, but not more than 40 hours per week, during the whole work experience cannot cause diseases or deviations in a state of health detected by modern research methods in The process of work or in the long-term deadlines of the present and subsequent generations.

MPC is of great importance for preventing poisoning and diseases. The smaller the MPC, the more serious requirements should be made to measures to protect the working.

Depending on the values \u200b\u200bof MPC and a number of other indicators, the degree of impact of harmful substances on the human body is determined.

Flawing gases and lvz pairs are able to form explosive mixtures in a mixture with air oxygen.

The smallest concentration of combustible vapors and gases at which an explosion is already possible, called the lower concentration limit of the spread of the NKRP flame (NKPR is the minimum fuel content in a mixture "Fuel substance - oxidative medium", in which the flame is possible on the mixture at any distance from the ignition source).

The greatest concentration of combustible vapors and gases at which an explosion is still possible, called the upper concentration limit of the flame spread of the WPPR (VKPR is the maximum content of fuel in a mixture "Fuel substance - oxidative medium", in which the flame is possible along the mixture to any distance from the ignition source).

The concentration from the NKPR to the WPP is called the explosability range. At a concentration below, the NKRR or above the BVPR explosion does not occur, in the first case, due to the low content of vapors or gases, in the second - due to insufficient oxygen content.

Each substance has its own values \u200b\u200bof the NCR and VKPR, that is, the explosability range for each substance is its own.

Oil is a complex (multicomponent) substance, with the composition of various oils differ from each other, so the range of explosability in different oils is different, as evidenced by the data of the table 3, in which the NKPR is indicated for various oils. Therefore, in order not to make confusion in this matter, for all oils adopted a single (average) explosability range (see Table 4).

In order to ensure the explosion and permissible explosion-proof concentration of the PDV, it is 5% of the values \u200b\u200bof the lower concentration limit of the flame. The PDVC is of great importance when assessing the degree of risk in carrying out various types of work related to the release of combustible vapors and gases.

For analysis of mixtures of various gases In order to determine their qualitative and quantitative composition, enjoy the following the main units of measure:
- "mg / m 3";
- "ppm" or "ppm";
- "% about. d. ";
- "% NKPR".

The mass concentration of toxic substances and the maximum permissible concentration (MPC) combustible gases is measured in MG / M 3.
The unit of measurement "mg / m 3" (eng. "Mass Concentration") is used in the designation of the concentration of the measured substance in the air of the working area, the atmosphere, as well as in the exhaust gases, expressed in milligrams on the cubic meter.
When performing gas analysis, as a rule, end users often translate gase concentration values \u200b\u200bfrom PPM in MG / M 3 and vice versa. This can be done using our calculator values \u200b\u200bof the units of gases.

The million-like proportion of gases and various substances is relative and designated in PPM or PM.
"PPM" (English "Parts Per Million" - "parts per million") - a unit of measuring the concentration of gases and other relative values, similar to the meaning of ppm and percentage.
The PPM unit (PM) is conveniently used to assess low concentrations. One millionth share is one part per 100,00000 parts and has a value of 1 × 10 -6 from the base indicator.

The most common unit of measuring the concentrations of combustible substances in the air of the working area, as well as oxygen and carbon dioxide is the volume fraction, which is denoted by the reduction of "% about. d. " .
"% About. d. " - is the value equal to the ratio of the volume of any substance in the gas mixture to the volume of the entire gas sample. The volume fraction of gas is customary to express in percent (%).

"% NKPR" (LEL - English Low Explosion Level) - lower concentration limit of flame distribution, the minimum concentration of the fuel explosive substance in a homogeneous mixture with an oxidative medium at which an explosion is possible.