The concept of NKPR, VKPR and PDVK, their numerical values ​​for oil vapors. Lower concentration limit of flame spread Limits of flame spread table

2.1 Natural gas - a product extracted from the bowels of the earth, consists of methane (96 - 99%), hydrocarbons (ethane, butane, propane, etc.), nitrogen, oxygen, carbon dioxide, water vapor, helium. IvTETS-3 receives natural gas as fuel through a gas pipeline from Tyumen.

The specific gravity of natural gas is 0.76 kg / m 3, the specific heat of combustion is 8000 - 10000 kcal / m 3 (32 - 41 MJ / m 3), the combustion temperature is 2080 ° C, the ignition temperature is 750 ° C.

Combustible natural gas, according to the toxicological characteristics, belongs to substances of the 4th hazard class ("low-hazardous") in accordance with GOST 12.1.044-84.

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

2.3 The safety regulations for the operation of gas facilities determine the following hazardous properties of gaseous fuel:

a/ lack of smell and color

b/ the ability of gas to form flammable and explosive mixtures with air

c/ asphyxiating ability of the gas.

2.4 Permissible concentration of gas 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 propagation (LCPR):

3 Rules for sampling gas for analysis

3.1 Smoking and the use of open flames in gas-hazardous places, when checking the gas contamination of industrial premises, is strictly prohibited.

3.2 The shoes of workers who measure gas contamination and are in gas hazardous places should not have metal horseshoes and nails.

3.3 When performing gas hazardous work, use explosion-proof portable lamps with a voltage of 12 volts

3.4 Before performing the analysis, it is necessary to inspect the gas analyzer. Measuring instruments with an expired verification period or damage are not allowed to be used.

3.5 Before entering the hydraulic fracturing room, it is necessary: ​​to make sure that the emergency signal lamp "GASED" at the entrance to the hydraulic fracturing room is not lit. The signal lamp turns on when the concentration of methane in the air of the hydraulic fracturing rooms reaches 20% or more of the lower concentration limit of flame propagation, i.e. equal or higher vol. one%.

3.6 Gas sampling in the premises (in the GRP) is carried out by a portable gas analyzer from the upper zone of the premises in the most poorly ventilated areas, because natural gas is lighter than air.

Actions in case of gas contamination are specified in point 6.

3.7 When taking air samples from the well, approach it from the windward side, making sure that there is no smell of gas nearby. One side of the well cover should be lifted with a special hook by 5 - 8 cm, a wooden gasket should be placed under the cover for the time of sampling. Sampling is carried out using a hose lowered to a depth of 20 - 30 cm and connected to a portable gas analyzer, or into a gas pipette.

If gas is detected in the well, it is ventilated for 15 minutes. and repeat the analysis.

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

3.9 In the air of the working area, the content of natural gas should not exceed 20% of the lower concentration limit of flame propagation (1% for methane); The oxygen concentration must be at least 20% by volume.

A fire is easier to prevent than to extinguish. Fire prevention is based on this principle, where measures are provided in advance aimed at:

to eliminate sources of ignition, oxidizer, etc.;

prevention of the possibility of a fire source (replacement of combustible substances with non-combustible ones, lowering the degree of flammability of substances, working with safe concentrations, temperatures, etc.);

prevention of the spread of fire when it occurs inside the equipment and through pipelines, along the structural elements of buildings, between buildings, etc. (fire arresters, shut-off valves, reserve tanks, fire walls, zones, embankments, etc.);

safe evacuation of people in case of fire;

primary and stationary means of extinguishing a fire.

Tasks and work order

Task number 1. Determination of the lower (n) and upper (c) concentration limits of flame propagation.

Determine the degree of explosion and fire hazard of a mixture of combustible gases (on the instructions of the teacher) at the experimental installation by the value of the lower (n) and / or upper (v) limits of flame propagation. The obtained results are compared with the calculated ones and the determination error is found. Determine safe concentrations. Establish which class according to the PUE the area around the experimental facility, where a cylinder with a given mixture of gases is installed, belongs to, and which explosion category the room in which this mixture is used belongs to: 1) as a raw material; 2) as fuel.

Work order

• 1. Get acquainted with the experimental setup and the procedure for performing work on it (see the description for the setup).
• 2. Carry out preliminary calculations of the lower (upper) concentration limits of 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)] specified in the composition specification.
• 3. Calculate the volume of the gas mixture required to create a concentration corresponding to the lower (upper) limit using formula (5.16).
• 4. Prepare the gas-air mixture by mixing air with the calculated volume of the gas mixture in the mixing system of the unit.
• 5. Take part of the prepared mixture into the explosive cylinder and set it on fire with a spark discharge.
• 6. In the presence of an explosion, when determining the lower limit (n), reduce the volume, and when determining the upper limit (c), on the contrary, increase the volume of the sampled gas by 1 ml.
• 7. Remove combustion products from the mixing system and the explosive cylinder of the installation and repeat the experiment with a smaller (larger) volume of the sampled gas. The experiment is carried out until there is no explosion at the next decrease (increase) in the gas volume.
• 8. Calculate the experimental value of the lower (upper) limits of flame propagation and find the error between the calculated and experimental values. Explain the differences between the experimental and calculated values.
• 9. When assessing the degree of danger of a mixture of gases with air, it is taken into account that all gas-air mixtures that have an ignition area limited by the lower and upper concentration limits are explosive, but mixtures with n 10 vol.% are especially explosive, and with n 10 vol.% - explosive .
• 10. Set the zone class according to the PUE around a cylinder with a gas mixture of a given composition.
• 11. Justify the category of the premises in which this gas mixture is used as: a) raw material; b) fuel.
• 12. Experimental results can be presented in the form of Table 5.11:

Table 5.11.

Task number 2. Determination of the flash point and ignition.

Assess the degree of explosion and fire hazard of the liquid (on the instructions of the teacher) according to the flash and ignition temperatures. Compare the experimentally established temperatures with the calculated and reference values, determine the errors and, in case of discrepancy, explain the differences.

Set the class of the zone according to the PUE and the category of the room according to NPB105-95, where the test liquid is used. Suggest methods for ensuring fire safety.

Work order

• 1. Familiarize yourself with the installation of a closed (open) type to determine the flash point (t flash) and ignition (t flash).
• 2. Calculate and / or find in the reference book the flash point for the test liquid.
• 3. Fill the crucible in the installation to 2/3 with the test liquid, install the thermometer of the required range and turn on the heating device.
• 4. Light and adjust the ignition wick using the clamp on the gas hose from the gas cylinder.
• 5. For 1015 o C before the calculated value of t aux. (or taken from the reference book) every 12 degrees, bring the ignition wick to the surface of the liquid and fix the temperature at which the vapor above the liquid flares up for the first time. This will be the experimental flash point - tsp e.
• 6. Continue heating the liquid and bringing the ignition wick every 12 degrees of heating to the surface of the liquid. Record the temperature at which the vapors ignited and combustion continued for at least 1530 s. This will be the experimental ignition temperature - t ref e.
• 7. Close the container with the burning liquid with a lid if measurements are carried out on an open-type installation, or close the valve on a closed-type device so that the combustion stops.
• 8. Compare the experimental indicators with the calculated (reference) ones and explain the discrepancies in the temperature values.
• 9. Based on the found temperature, determine the degree of danger of the liquid. The most dangerous are flammable liquids, which include liquids with t aux. 61 ° C (on a closed type device) and 66 ° C (on an open type device). All flammable liquids are explosive and fire hazardous. If t rev. 61(66) o C is a flammable combustible liquid (GZh).
• 10. By the difference between t resp - t resp \u003d t, establish the danger of the liquid during operation in the conditions of the possible presence of an ignition source. The smaller t, the more dangerous the liquid.
• 11. Establish the class of the zone according to the PUE around the equipment in which the test liquid is used.
• 12. Set the category of the room according to NPB105-95, in which equipment with liquid is used.
• 13. Suggest methods for ensuring fire safety when using the test liquid.

The experimental results can be presented in the form of Table 5.12.

Table 5.12

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

Assess the degree of explosion and fire hazard of the liquid (on the instructions of the teacher) according to the autoignition temperature (t St.). The obtained results are compared with the calculated and reference data. Find the error and explain possible discrepancies in the values ​​of t St.

Set the explosive mixture group and temperature class of explosion-proof electrical equipment. Find a safe temperature for heating the liquid under study. Suggest measures to ensure fire safety when working with the test liquid.

Work order

• 1. Familiarize yourself with the installation for determining the self-ignition temperature by the drop method.
• 2. Calculate the volume of the investigated liquid corresponding to the stoichiometric composition of the mixture according to the formula (5.21).
• 3. Calculate and/or take from the handbook the temperature of the test liquid.
• 4. Turn on the muffle furnace, adjust the potentiometer showing the heating temperature of the vessel and check the presence of a mirror above the vessel.
• 5. Heat the vessel to a temperature of 3040 o C higher than the calculated (reference) self-ignition temperature of the test liquid and turn off the furnace.
• 6. For 1015 o C before the calculated (reference) t St. every 23 degrees of temperature drop, introduce the calculated volume of liquid into the vessel and record the ignition of liquid vapor through a mirror.
• 7. Using a stopwatch, record the time from the moment the liquid is introduced into the vessel until the liquid vapor ignites. This time increases as the vessel cools.
• 8. After each experiment, the products of combustion are removed from the vessel using a special device.
• 9. Repeat the experiments until the vapors of the added liquid ignite within 35 minutes.
• 10. The experimental self-ignition temperature of the liquid under study is taken to be the temperature at which the ignition of the vapors of the liquid introduced into the installation was last recorded.
• 11. Compare the resulting t St. e with the calculated (t St. p) and reference (t St. cn), explain the observed discrepancies and establish the error of determination.
• 12. The degree of danger of a liquid is determined by finding t St. explosive mixture groups. The most dangerous will be a liquid belonging to the T6 group, and the least dangerous to the T1 group. Groups of explosive mixtures and temperature classes of explosion-proof electrical equipment are given in the literature and in Section 5.1 (Tables 5.1 and 5.2).
• 13. Find a safe liquid heating temperature, determined by formula (5.2).
• 15. Experimental results can be presented in the form of a table. 5.13.

Table 5.13.

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

Assess the degree of explosion and fire hazard of the steam-air mixture (on the instructions of the teacher) according to the BEMZ value determined on the model installation. Compare the obtained results with the calculated and/or reference ones and explain the observed discrepancies. Calculate the error of determination relative to the calculated value. Suggest fire safety measures when using the test liquid.

Work order

• 1. Familiarize yourself with the model installation for the definition of BEMZ.
• 2. Calculate the volume of liquid required to create a vapor-air mixture of stoichiometric composition according to formula (5.20).
• 3. Calculate the BEMZ value using formula (5.16) and set this gap on the installation using the scale. Gap setting accuracy 0.05 mm.
• 4. Turn on the unit and open the protective cover.
• 5. Introduce the calculated volume of the test liquid into the left and right chambers and close the hole through which the liquid was introduced (tracing paper).
• 6. Close the casing and wait for the time necessary for the evaporation of the introduced liquid and the formation of a vapor-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 unit, ignite the vapor-air mixture with an electric spark, first in the left chamber, and then in the right.
• 8. When recording explosions in both chambers, note the absence of an explosion transfer from one chamber to another.
• 9. After that, set the gap to 0.05 mm more than the previous one.
• 10. Remove the products of combustion using the ventilation system built into the unit by pressing the pedal on the front panel of the unit. The completeness of the removal is fixed by the absence of the smell of the test liquid from the holes through which the polluted air is removed.
• 11. Repeat the experiments, changing the gap, until an explosion is recorded when a spark is applied to one of the chambers, and there is no explosion when a spark is applied to the other chamber. This indicates that the gap between the chambers is larger than the BEMZ, and when the mixture explodes in one chamber, an explosion occurs simultaneously through this gap in the other chamber, therefore, explosion transmission is observed. For the experimental value of BEMZ, take the value of the gap at which the last time the absence of an explosion transfer from one chamber to another was recorded.
• 12. Compare the obtained value of BEMZ with the calculated and reference. Calculate the error of determination in relation to the calculated (reference) value. Explain possible discrepancies in indicators.
• 13. The assessment of the degree of explosion and fire hazard of a liquid by the value of BEMZ is carried out by finding the category of an explosive mixture according to the PUE. The most dangerous will be a mixture belonging to category IIC and the least dangerous - to category IIA (see Table 5.3).
• 14. Suggest measures to ensure fire safety when working with the test liquid.
• 15. Experimental results can be presented in the form of a table. 5.14.

Table 5.14.

TEST QUESTIONS

• 1. General information about fire and combustion. Mechanisms of the combustion process.
• 2. The main indicators of the explosion and fire hazard of substances and materials (flash point-t flash, ignition temperature-t flash, self-ignition temperature-t St., lower (n) and upper (c) concentration limits of flame propagation, safe experimental maximum clearance - BEMZ and etc.).
• 3. Assessment of the degree of explosion and fire hazard of substances and materials based on t aux. , t resp. , t St. , n, v, BEMZ and other indicators.
• 4. Assessment of the degree of explosion and fire hazard of areas around equipment where combustible substances are used.
• 5. Assessment of the degree of explosion and fire hazard of premises according to NPB 105-95.
• 6. The procedure for assigning explosive and fire hazardous categories of premises (categories A and B).
• 7. The procedure for assigning a fire hazardous category (B1-B4) and assessing the degree of fire hazard of the premises.
• 8. Measures to prevent the occurrence of a fire (reducing the degree of flammability of substances, eliminating the oxidizer and source of ignition).
• 9. Measures to prevent the spread of a fire when it occurs inside the process equipment (flame arresters, valves, membranes, etc.).
• 10. Measures to prevent the spread of fire through the structural elements of the building and against the destruction of the building during an explosion (fire walls, ceilings, embankments, easily dropped structures, etc.).
• 11. Measures to ensure the safety of evacuation of people in case of fire.
• 12. Measures aimed at extinguishing a fire: specialized services, fire alarm means, stationary and primary fire extinguishing means.

BASIC TERMS AND CONCEPTS.

MPC (maximum permissible concentration) of harmful substances in the air of the working area are concentrations that, during daily work within 8 hours during the entire working time, cannot cause diseases or health abnormalities in the worker, detected by modern research methods directly in the process of work or more remote periods. And also the MPC of harmful substances should not adversely affect the health status of subsequent generations. Measured in mg/cu.m.

MPC of some substances (in mg/m3):

Petroleum hydrocarbons, kerosene, diesel fuel - 300

Gasoline - 100

Methane - 300

Ethyl alcohol - 1000

Methyl alcohol - 5

Carbon monoxide - 20

Ammonia (ammonia) - 20

Pure hydrogen sulfide - 10

Hydrogen sulfide mixed with oil hydrocarbons - 3

Mercury - 0.01

Benzene - 5

NKPR is the lower concentration limit of flame propagation. This is the lowest concentration of combustible gases and vapors at which an explosion is already possible when exposed to an ignition pulse. Measured in %V.

LEL of some substances (in % V):

Methane - 5.28

Oil hydrocarbons - 1.2

Gasoline - 0.7

Kerosene - 1.4

Hydrogen sulfide - 4.3

Carbon monoxide - 12.5

Mercury - 2.5

Ammonia - 15.5

Methyl alcohol - 6.7

VCPR – upper concentration limit of flame propagation. This is the highest concentration of combustible gases and vapors at which an explosion is still possible when exposed to an ignition pulse. Measured in %V.

VKPR of some substances (in % V):

Methane - 15.4

Oil hydrocarbons - 15.4

Gasoline - 5.16

Kerosene - 7.5

Hydrogen sulfide - 45.5

Carbon monoxide - 74

Mercury - 80

Ammonia - 28

Methyl alcohol - 34.7

DVK - pre-explosive concentration, is defined as 20% of LEL. (no explosion possible at this point)

PDVK - limiting explosive concentration, is defined as 5% of LEL. (no explosion possible at this point)

Relative density in air (d) shows how many times the vapors of a given substance are heavier or lighter than air vapors under normal conditions. The value is relative - there are no units of measurement.

Relative density in air of some substances:

Methane - 0.554

Oil hydrocarbons - 2.5

Gasoline - 3.27

Kerosene - 4.2

Hydrogen sulfide - 1.19

Carbon monoxide - 0.97

Ammonia - 0.59

Methyl alcohol - 1.11

Gas dangerous places - such places in the air of which there are or may suddenly appear toxic and vapors in concentrations exceeding the MPC.

Gas hazardous places are divided into three main groups.

IGroup – places where the oxygen content is below 18% V, and the content of toxic gases and vapors is more than 2% V. In this case, work is carried out only by gas rescuers, in insulating apparatus, or under their supervision according to special documents.

IIGroup– places where the oxygen content is less than 18-20%V, and pre-explosive concentrations of gases and vapors can be detected. In this case, work is carried out according to work permits, with the exception of the formation of sparks, in appropriate protective equipment, under the supervision of gas rescue and fire supervision. Before carrying out work, an analysis of the gas-air environment (GVS) is carried out.

IIIGroup- places where the oxygen content is from 19% V, and the concentration of harmful vapors and gases may exceed the MPC. In this case, work is carried out in gas masks, or without them, but gas masks must be in good condition at the workplace. In the places of this group, it is necessary to analyze the hot water supply according to the schedule and the selection map.

Gas-hazardous work - all those jobs that are carried out in a gassed environment, or work during which gas can escape from gas pipelines, fittings, units and other equipment. Also, gas-hazardous work includes work that is performed in a confined space with an oxygen content in the air of less than 20% V. When performing gas hazardous work, the use of open flame is prohibited, it is also necessary to exclude sparking.

Examples of gas hazardous work:

Works related to inspection, cleaning, repair, depressurization of technological equipment, communications;

At removal of blockages, installation and removal of plugs on existing gas pipelines, as well as disconnection of units, equipment and individual units from gas pipelines;

Repair and inspection of wells, pumping out water and condensate from gas pipelines and condensate collectors;

Preparation for the technical examination of LPG tanks and cylinders and its implementation;

Excavation of soil in places of gas leaks until they are eliminated.

Hot work - production operations associated with the use of open fire, sparking and heating to temperatures that can cause ignition of materials and structures.

Hot work examples:

Electric welding, gas welding;

Electric cutting, gas cutting;

Application of explosive technologies;

Soldering work;

Educational cleaning;

Machining of metal with the release of sparks;

Heating of bitumen, pitches.

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), this concentration is called maximum permissible concentration (MAC).

MPC- this is the concentration that, during daily (except weekends) work for 8 hours or for another duration, but not more than 40 hours per week, during the entire working experience cannot cause diseases or deviations in the state of health detected by modern research methods in in the process of work or in the remote periods of life of the present and subsequent generations.

MPC is of great importance for the prevention of poisoning and diseases. The lower the MPC, the more serious requirements should be imposed on measures to protect workers.

Depending on the MPC values ​​and a number of other indicators, the degree of exposure to harmful substances on the human body is determined.

Combustible gases and vapors of flammable liquids are capable of forming explosive mixtures in a mixture with atmospheric oxygen.

The lowest concentration of combustible vapors and gases at which an explosion is already possible is called lower concentration limit of flame propagation NKPR(LEC is the minimum fuel content in the mixture "combustible substance - oxidizing environment", at which flame propagation through the mixture is possible at any distance from the ignition source).

The highest concentration of combustible vapors and gases at which an explosion is still possible is called upper concentration limit of flame propagation VKPR(VKPR is the maximum content of fuel in the mixture "combustible substance - oxidizing environment", at which flame propagation through the mixture is possible at any distance from the ignition source).

The concentration from LEL to VKPR is called the explosive range. At a concentration below the LEL or above the LEL, an 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 LEL and VKPR values, i.e., each substance has its own explosive range.

Oil is a complex (multicomponent) substance, and the composition of various oils differs from each other, therefore, the range of explosiveness for different oils is different, as evidenced by the data in Table 3, which indicates the LEL for various oils. Therefore, in order not to introduce confusion in this matter, a single (averaged) explosive range has been adopted for all oils (see Table 4).

In order to ensure explosion and fire safety, the maximum permissible explosion-proof concentration of PDVK is established for all substances, it is 5% of the value of the lower concentration limit of flame propagation. PDVK is of great importance in assessing the degree of risk in carrying out various types of work associated with the release of combustible vapors and gases.

At analysis of mixtures of various gases in order to determine their qualitative and quantitative composition, use the following basic units of measurement:
- "mg / m 3";
- "ppm" or "million -1";
- "% about. d.”;
- "% NKPR".

The mass concentration of toxic substances and the maximum permissible concentration (MPC) of combustible gases is measured in "mg / m 3".
The unit of measurement "mg / m 3" (English "mass concentration") is used to indicate 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 per cubic meter.
When performing gas analysis, it is common for end users to convert gas concentrations from "ppm" to "mg/m3" and vice versa. This can be done using our Gas Units Calculator.

The million fraction of gases and various substances is a relative value and is indicated in ppm or ppm.
"ppm" (eng. "parts per million" - "parts per million") - a unit for measuring the concentration of gases and other relative values, similar in meaning to ppm and percent.
The unit "ppm" (ppm) is convenient to use for assessing low concentrations. One ppm is one part per 1,000,000 parts and has a value of 1×10 -6 of the baseline.

The most common unit for measuring the concentration 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 abbreviation “% vol. etc." .
"% about. etc." - is a 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 usually expressed as a percentage (%).

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