The lower (upper) concentration limit of flame propagation is the minimum (maximum) fuel concentration in the oxidizing agent, capable of ignoring from the high-energy source, followed by the spread of burning to the entire mixture.

Estimated formulas

The lower concentration limit of the propagation of the flame φ n is determined by the limiting heat of the combustion. It was established that 1 m 3 of various gas-air mixtures on the NKPR highlights with a burning permanent average of heat - 1830 kJ, called the limiting heat of burning. Hence,

if we adopt the average value of q Ave. equal to 1830 kJ / m 3, then φ H 6 goes

(2.1.2)

where Q. n. - lower heat combustion of a combustible substance, KJ / m 3.

The lower and upper CRC of the flame can be determined by the approximation formula

(2.1.3)

where n. - stoichiometric coefficient with oxygen in the equation of chemical reaction; A and B empirical constants whose value is shown in Table. 2.1.1

Table 2.1.1.

The concentration limits of the spread of the flame of the vapor of liquid and solids can be calculated if the temperature limits are known

(2.1.4)

where r not) - pressure of a saturated pair of substance at a temperature corresponding to

lower (top) flame spread limit, pa;

p. about - Environment, PA.

The saturated pair pressure can be determined by the Antoine equation or Table. 13 applications

(2.1.5)

where A, B, with - Constants of Antoine (Table 7 applications);

t. - Temperature, 0 C, (Temperature limits)

To calculate the concentration limits of the spread of flames with mixtures of combustible gases, use the rule of the lestelier

(2.1.6)

where
lower (upper) CRC flame gas mixture,% vol.;

- lower (top) limit of flame spread I-RO combustible gas%, about;

- The molar fraction of the I-RO of combustible gas in the mixture.

It should be kept in mind that σμ i \u003d 1, i.e. The concentration of combustible components of the gas mixture is accepted for 100%.

If the concentration limits of the flame propagation are known at temperatures T 1, then at temperatures T 2. they are calculated by formulas

, (2.1.7)

, (2.1.8)

where
,
- lower concentration limit of flame propagation, respectively at temperatures

T. 2 . and T. 1 ;
and
- upper concentration limit of flame propagation, respectively at temperatures T. 1 and T. 2 ;

T. G. - The temperature of burning the mixture.

Approximately when determining the NKPR flame T. g. Take 1550 K, when determining the WPPR Flame -1100K.

When diluting the gas-air mixture with inert gases (N 2, CO 2 H 2 On a pair, etc.) The ignition area is narrowed: the upper limit is reduced, and the lower - increases. The concentration of inert gas (phlegmatizer), in which the lower and upper limits of the spread of the flame are closed, is called a minimal phlegmatization concentration φ f. . Oxygen content such a system is called the minimum explosive oxygen content of MBSK. Some oxygen content below MVSK is called Safe
.

The calculation of these parameters is carried out by formulas

(2.1.9)

(2.1.10)

(2.1.11)

where
- Standard heat of fuel formation, J / mol;

, ,- Constants depending on the type of chemical element in the fuel molecule and the type of phlegmatizer, Table. 14 applications;

- The number of atoms of the i-th element (structural group) in the fuel molecule.

Example 1. According to the limiting heat of combustion, the lower concentration limit of ignition of butane in the air is determined.

Decision. To calculate the formula (2.1.1) in Table. 15 applications We find the low heat of the combustion of the substance 2882.3 kJ / mol. This magnitude must be translated into other dimension - KJ / m 3:

KJ / m 3

By formula (2.1.1), we define the lower concentration limit of flame distribution (NKPR)

Table. 13 applications find that experimental meaning
- 1.9%. The relative error of the calculation, therefore, was

.

Example 2. Determine the concentration limits of the spread of ethylene flame in the air.

The calculation of the CRC of the flame is carried out according to the approximation formula. Determine the value of the stoichiometric coefficient during oxygen

C 3 H 4 + 3O 2 \u003d 2 o 2 + 2N 2

In this way, n. \u003d 3, then

Determine the relative error of the calculation. Table. 13 applications Experimental values \u200b\u200bof limits are 3.0-32.0:

Consequently, when calculating the NKPR, ethylene is overestimated by 8%, and when calculating the NKRR - underestimated by 40%.

Example 3. Determine the concentration limits of the spread of the flame of saturated methanol vapors in the air, if it is known that its temperature limits are 280 to 312 K. The atmospheric pressure is normal.

To calculate the formula (2.1.4), it is necessary to determine the pressure of saturated vapors corresponding to the lower (7 ° C) and the top (39 ° C) of the flame propagation.

According to the Antoine equation (2.1.5), we find the pressure of a saturated pair using the data of the application tab. 7.

Rn \u003d 45.7 mm.rt.st \u003d 45.7 · 133,2 \u003d 6092.8

R \u003d 250 mm.rt.st \u003d 250 · 133,2 \u003d 33300 pa

By formula (2.1.3), we define the NKPR

Example 4. Determine the concentration limits of the spread of the flame of the gas mixture, consisting of 40% propane, 50% of butane and 10% propylene.

To calculate the CRC of the flame of a mixture of gases, but the rules of the lessel (2.1.6) it is necessary to determine the CRC of the flame of individual combustible substances, the methods of calculating which are considered above.

C 3 H 8 -2.1 ÷ 9.5%; C 3 H 6 -2.2 ÷ 10.3%; C 4 H 10 -1.9 ÷ 9.1%

Example 5. What is the minimum amount of diethyl ether, kg, capable of evaporation in the capacity of 350 m 3 3 to suck an explosive ending.

Concentration will be explosive if φ n. =φ pG where ( φ pG - Concentration of fuel vapor). The calculation (see examples 1-3 of this section) of PLIs along Table. 5 applications find the NKPR diethyl ether flame. It is 1.7%.

We define the volume of dyethyl ether vapors required to create in the amount of 350 m 3 of this concentration

m 3.

Thus, to create an NKPR diethyl ether about the volume of 350 m 3, it is necessary to introduce 5.95 m 3 of its vapors. Taking into account that 1 kmol (74 kg) of the steam given to normal conditions occupies a volume equal to 22.4 m 1, we find the amount of diethyl ether

kg

Example 6. Determine whether the formation of an explosive concentration in a volume of 50 m 3 is possible during evaporation of 1 kg of hexane if the ambient temperature is 300 K.

Obviously, the steam mixture will be explosive if φ n. ≤φ pG ≤φ in - at 300 to the volume of hexane vapors, which formed as a result of evaporation of 5 kg of substance, we find, taking into account that when evaporating 1 km (86 kg) of hexane at 273 to the volume of the steam phase will be equal to 22.4 m 3

m 3.

Hexane vapor concentration in the room with the volume of 50m 3, therefore, will be equal to

Determining the concentration limits of the propagation of the flame of hexane in the air (1.2-7.5%), on tables or by calculation, we establish that the resulting mixture is explosive.

Example 7. Determine whether the explosive concentration of saturated vapor is formed above the surface of the reservoir containing 60% diethyl ether (DE) and 40% ethyl alcohol (ES) at a temperature of 245 k?

The concentration of vapors will be explosive if φ cm n. ≤φ cm nP. ≤φ cm in (φ cm nP. - concentration of saturated vapor of the mixture of liquids).

It is obvious that as a result of various volatility, the composition of the gas phase will differ from the composition of the condensed phase. The content of components in the gas phase in a known composition is determined by the Raoul's law for ideal solutions of liquids.

1. Determine the molar composition of the liquid phase

,

where
- the molar share of substances;

- the weight share of the i-th substance;

- molecular weight of the i-th substance; ( M. DE. =74, M. ES. =46)

2. By equation (2.1.5) using the values \u200b\u200bof Table 12 of the application. We find the pressure of saturated ether and ethyl alcohol at a temperature of 19 ° C (245 K)

R DE. \u003d 70.39 mm.rt.st \u003d 382.6

R ES. \u003d 2.87 mm.rt.st \u003d 382.6

3. According to the Raoul's law, the partial pressure of saturated vapor of the i-th fluid over the mixture is equal to the product of a saturated steam pressure over a clean liquid on its molar stake in the liquid phase, i.e.

R DE (Par) \u003d 9384,4 · 0.479 \u003d 4495.1 Pa;

R ES (pairs) \u003d 382.6 · 0.521 \u003d 199.3 PA.

4. By receiving the amount of partial pressures of saturated dyethyl ether and ethyl alcohol equal to 100%, we define

a) the concentration of vapors in the air

b) molt composition of the gas phase (the law of Raul-Dutier)

5. Having determined the calculation or by reference data (Table 16 of the Annex) of the CRC of the Flame of individual substances (diethyl ether 1.7 ÷ 59%, ethyl alcohol 3.6 ÷ 19%). According to the rule of Le - Stepgere Calculate the CRC of the Steam Phase Flame

6. Comparing the obtained in clause 4, and the concentration of the steam-air mixture with the concentration limits of the flame propagation (1.7-46.1%), we conclude that at 245 k above this liquid phase, an explosive concentration of saturated vapor in the air is formed.

According to Table. 15 applications we find the heat of the formation of acetone 248.1 · 10 3 J / mol. From the chemical formula of acetone (C3H 6 O) it follows that t. from = 3, t. n. = 6, t. about = 1. The values \u200b\u200bof the remaining parameters required to calculate the formula (2.8) are selected from the table. 11 for carbon dioxide

Therefore, with a decrease in oxygen concentration in a four-component system, consisting of acetone vapor, carbon dioxide, nitrogen and oxygen, up to 8.6%, the mixture becomes explosion-proof. When the content of oxygen is equal 10,7% this mixture will be limiting on explosability. According to reference data (reference book "Fire risk of substances and materials used in the chemical industry." - M, chemistry, 1979), the M & IWC of acetone-grade mixture when diluted with its carbon dioxide is 14.9%. Determine the relative error of the calculation

Thus, the results of the calculation of the IVCK are reduced by 28%.

Self-job

The theory of delaction combustion does not impose restrictions on the possibility of reducing the speed of combustion. However, experience shows that the magnitude of the combustion rate cannot be less than a certain critical value. The spread of the flame in the mixtures of fuel and oxidant is possible only in a certain range of their concentrations. When igniting the mixture, the composition of which comes out of these limits, the persistent burning does not occur.

For combustible mixtures, the lower and upper concentration limits of the flame spread are distinguished.

Lower concentration limit The spread of the flame (NKPRP) is the smallest concentration of the combustible substance in the mixture with air, with which already possible persistent, the unlucky spread of burning.

Upper concentration limit The spread of the flame (VKPRP) is the largest concentration of combustible substance in the mixture with air, with which there is still a possible resistant, unlucky spread of burning.

The concentration limits of the spread of the flame (CPRP) is one of the most important characteristics of the explosion of combustible gases and vapors. The concentration area of \u200b\u200ba combustible substance that lies between the lower and the upper CPRP, is characterized by the possibility of sunbathing and stable combustion of the mixture and is called an area of \u200b\u200bexplosive concentrations. If the concentration of a combustible substance goes beyond the concentration limits, the combustible mixture becomes explosion-proof. So, if a fuel concentration is smaller than the lower CPRP, then the burning is not possible at all. If a fuel concentration is larger than VKPRP, then diffusion combustion of such a gas mixture is possible upon exiting it into the surrounding space and the availability of the ignition source.

The maximum reaction rate and the propagation of the flame front is observed in the stoichiometric ratio of the components (the concentration of the fuel equal to the stoichiometric φ gv \u003d φ of the SMC). With a deviation from stoichiometric ratio, the combustion rate, and, consequently, the heat release rate will decrease. So, with φ gv< φстм скорость тепловыделения уменьшается в результате нехватки горючего, и нагревании излишка окислителя, что приводит к дополнительным тепловым потерям. При φ гв > φ SMC Decreased heat dissipation occurs as a result of the lack of an oxidizing agent, and costs for heating an excess fuel that does not participate in a chemical reaction. Thus, for the vapor-gas mixtures, it is possible to distinguish both the minimum (lower) φ n and the maximum (upper) φ n and the concentration of fuel at which the critical conditions for the spread of the flame front occur.

Considering that the concentration limits of the flame propagation may vary with the change in external conditions, not only the concentration limits, but also safe concentrations φ of NB and φ WB, are determined when working with combustible substances, but also the safe concentrations φ and φ WB, lower or higher than which the mixture is guaranteed. Safe concentrations can be calculated by formulas:

Φnb.< 0,9(φн – 0,21), %

φBB ≥ 1.1 (Φv + 0.42),%

where φ n, φ in the NKPRP and VKPRP,%;

The location of the areas of possible concentrations of combustible is displayed in the figure.

Concentration limits of flame proliferation can be strongly changed when external conditions change. CHANGE CHANGES is explained from the point of view of the balance of heat dissipation and heat transfer in the system. All factors whose change will lead to an increase in heat dissipation will expand the CRCR (reduce the lower CRCR and increase the upper CRCR). The factors increasing heat transfer will narrow the CPRP (increase the lower CRCR and reduce the upper CRCR). The greatest impact on the CPRP is provided:

· Oxidizer concentration in the oxidative medium (oxygen content in the air);

· Concentration of inert gases (phlegmatizers);

· Temperature and pressure of the mixture;

· Power source of ignition;

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 fluid. 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.

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.

Basic terms and concepts.

MPC (maximum permissible concentration) of harmful substances in the air of the working area are concentrations that during daily operation within 8 hours during the entire working time cannot cause working diseases or deviations of the health status detected by modern research methods directly during the work or in more Details. And the MPC of harmful substances should not adversely affect the state of health from subsequent generations. Measured in mg / cubic meters

MPC of some substances (mg / cubic meters):

Oil hydrocarbons, kerosene, diesel fuel - 300

Gasoline - 100.

Methane - 300.

Ethyl alcohol - 1000

Methyl alcohol - 5

Carbon monoxide - 20

Ammonia (ammonia alcohol) - 20

Hydrogen sulfide in pure form - 10

Hydrogen sulfide in the mixture with hydrocarbons of oil - 3

Mercury - 0,01

Benzole - 5.

NKPR - Lower concentration flame spread limit. This is the smallest concentration of combustible gases and vapors, in which an explosion is already possible when inflows inflammable. It is measured in% v.

NKPR 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

SPP – upper concentration limit of flame spread. This is the largest concentration of combustible gases and vapors, in which an explosion is still possible when exposed to an inflammation pulse. It is measured in% v.

SVPR of some substances (in% v):

Methane - 15,4.

Oil hydrocarbons - 15.4

Gasoline - 5,16

Kerosene - 7.5

Hydrogen sulfide - 45.5

Carbon Oxide - 74

Mercury - 80.

Ammonia - 28.

Methyl alcohol - 34.7

DVK is a preferential concentration, defined as 20% of the NKRP. (At this point, the explosion is not possible)

PDVK is an extruded-freezed concentration, is defined as 5% of the NKPR. (At this point, the explosion is not possible)

The relative air density (D) shows how many times the pair of this substance is harder or lighter than air vapor in normal conditions. The size of the relative - no units of measurement.

Relative density by 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 hazardous places - Such places in the air there are or can suddenly appear toxic and pairs in concentrations exceeding the MPC.

Gas hazard places are divided into three main groups.

I. Group – places in which the oxygen content is below 18% V, and the content of toxic gases and vapor more than 2% V. In this case, the work is carried out only by gas carriers, in insulating devices, or under their observation on special documents.

II. Group - Places where oxygen content less than 18-20%V, and can be detected at the prerequisites concentrations of gases and vapors. In this case, the work is carried out according to outfits-tolerances, with the exception of the education of sparks, in the respective protective equipment, under the supervision of gas carrier and fire supervision. Before carrying out work, an analysis of the gas-aircraft (DHW) is carried out.

III Group- Places where oxygen content from 19% V, and the concentration of harmful vapors and gases can exceed the PDC. In this case, the work is carried out in gas masks, or without them, but gas masks should be in working places in good condition. In places of this group, it is necessary to analyze the DHW according to the schedule and the selection card.

Gas hazardous work - all those works that performed in the rolled medium, or work, during which gas is possible from gas pipelines, reinforcements, aggregates and other equipment. Also, the gas-hazardous works include works that are performed in a closed space when the oxygen content in the air is less than 20% v. When performing gas hazardous work, the use of open fire is prohibited, it is also necessary to exclude sparking.

Examples of gas hazardous work:

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

W. sending blockages, installation and removal of plugs on active gas pipelines, as well as disconnecting from gas pipelines of aggregates, equipment and individual nodes;

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

Preparation for the technical inspection of reservoirs and cylinders of the Sug and its conduct;

Opening the soil in the gas leaks to their elimination.

Fire work - production operations related to the use of open fire, sparking and heating to temperatures that can cause inflammation of materials and structures.

Examples of fireworks:

Electric welding, gas welding;

Electrorescape, gas cutter;

The use of explosive technologies;

Soldering work;

Recruitment;

Mechanical processing of metal with the selection of sparks;

Heat bitumen, resin.