Gas, tasteless, colorless, odorless. Air density 0.554. It burns well, with an almost colorless flame. Self-ignition temperature 537°C. Explosive limit 4.4 - 17%. MPC in the air working area 7000 mg/m3. It has no poisonous properties. Headache is a symptom of suffocation at 80% methane and 20% oxygen. The danger of methane is that with a strong increase in the content of methane, the oxygen content decreases. The danger of poisoning is reduced by the fact that methane is lighter than air, and when an unconscious person falls, he enters an atmosphere richer in oxygen. Methane is a suffocating gas, so after bringing the victim to consciousness (if the victim has lost consciousness), it is necessary to inhale 100% oxygen. Give the victim 15-20 drops of valerian, rub the body of the victim. Filtering gas masks from methane do not exist.

Ticket number 2

1. Define the term "Lower explosive limit (LEL) (lower concentration limit of flame propagation - LEL)". The minimum concentration of combustible gas in air at which an explosion of a mixture of combustible gas and air occurs. When the gas concentration is below the LEL, no reaction occurs.

2. Control of the air environment at gas transportation facilities.

4.1. Before the commissioning of the pipeline for transport natural gas it is necessary to displace air from the pipeline with gas at a pressure of not more than 0.1 MPa (1 kgf / cm 2) at the place of its supply, in compliance with safety measures. The displacement of air by gas can be considered complete when the oxygen content in the gas leaving the gas pipeline is no more than 1% according to the gas analyzer readings.

The analysis of residual oxygen in the pipe when purging the repaired section should be carried out with a specialized device that simultaneously analyzes the content of oxygen (low concentrations) and combustible gas (from 0 to 100% of the volume fraction).

The use of individual gas analyzers designed to ensure the safety of personnel in these cases is unacceptable, as it leads to failure of the sensors.

The equipment used must:

Have an explosion-proof design;

Have a sampling probe for sampling from the pipe;

Have a built-in expense booster;

Have a lower operating temperature limit of minus 30 ° С;

Have automatic calibration (adjustment) of zero;

Have a display for simultaneous display of measured concentrations;

Ensure registration of measurement results.

4.2. The tightness of equipment, pipelines, welded, detachable joints and seals is controlled using leak detectors in explosion-proof design, with the function of protecting the sensor from overloads.

The use of individual gas analyzers for these purposes is unacceptable, since these gas analyzers do not display leaks with a concentration of less than 0.1% LEL.

4.3. Control of gas contamination in wells, including water supply and sewerage, underground premises and closed channels located at industrial sites, is carried out according to the schedule at least once a quarter, and in the first year of their operation - at least once a month, as well as every times immediately before the commencement of work in the indicated places. Gas control should be carried out using remote sampling by portable (individual) gas analyzers with a connected manual or built-in motorized sampling pump.

4.4. The control of leaks and gas contamination along underground gas pipelines is carried out using leak detectors similar to those used in the control of equipment tightness.

4.5. Along with the control of the air environment for gas contamination with stationary devices, it is necessary to continuously monitor (while in the danger zone) the air environment portable gas analyzers:

In rooms where gases and liquids containing harmful substances are pumped;

In rooms where exposure and accumulation is possible harmful substances, and on outdoor installations in places of their possible release and accumulation;

In rooms where there are no sources of emission, but it is possible for harmful substances to enter from the outside;

In places where service personnel are permanently located, where there is no need to install stationary gas detectors;

During emergency work in a gassed area - continuously.

After the liquidation of the emergency, it is necessary to additionally analyze the air in places where harmful substances can accumulate.

4.7. In places of gas leakage and in areas of gas contamination of the atmosphere, a sign “Caution! Gas".

Yellow

black color

4.8. Start-up and operation of equipment and installations of gas transportation facilities with a switched off or faulty monitoring and alarm system for the content of combustible gases in the air is not allowed.

4.9. System health automatic alarm and automatic start emergency ventilation is controlled by operational (duty) personnel when accepting a shift.

Information about the operation of the automatic gas detection system, about the failure of sensors and related measuring channels and automatic signaling channels, about equipment shutdowns carried out by the automatic gas detection system, is received by the operational (duty) personnel, who reports this to the head of the facility (service, section) with entry in the operating log.

The operation of automatic indoor air gas detection systems shall be tested in accordance with the manufacturer's instructions.

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

Mass concentration toxic substances and the maximum allowable concentration (MAC) of combustible gases is measured in "mg / m 3".
The unit of measurement "mg / m 3" (eng. "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" (English "parts per million" - "parts per million") - a unit of measurement for 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.

BASIC TERMS AND CONCEPTS.

MPC (maximum permissible concentration) of harmful substances in the air of the working area are concentrations that, when daily work within 8 hours during the entire working time, they cannot cause diseases or deviations in the state of health of a worker, detected by modern research methods directly in the process of work or at a later date. 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):

Oil 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 vapor given substance heavier or lighter than air vapor 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, the 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 to gas hazardous work include 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, it is prohibited to use open fire, it is also necessary to exclude sparking.

Examples of gas hazardous work:

Works related to inspection, cleaning, repair, depressurization 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.

A fire is easier to prevent than to extinguish. Based on this principle fire prevention where activities are planned 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 and fire hazard category belongs to the room in which this mixture is used: 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. Spend preliminary calculations 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 and fire hazardous, 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. experimental set temperatures compare 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 bottle.
• 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 at the installation open type, or close the valve on the device closed type to stop burning.
• 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 required for the evaporation of the injected 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 combustion products with 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 burning. 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 fire hazard 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.

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 by increasing the activation energy);
• Non-flammable additives - phlegmatizers;

The unit of CPRP 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 ability to ignite the "Fuel + Oxidizer + Phlegmatizer" systems, they build the 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 leakage through the leakage of process equipment of atmospheric air is possible.

In a relationship 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.

It is used when categorizing rooms and buildings according to explosion and fire hazard, for analyzing the risk of an accident and assessing possible damage, when developing measures to prevent fires and explosions in process equipment.

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See what "" is in other dictionaries:

lower concentration limit of flame propagation- LEL The concentration of combustible gas or vapor in air below which an explosive gaseous environment is not formed. [GOST R IEC 60050 426 2006] Topics explosion protection Synonyms NKPR EN LELlower explosive limit ...

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