Methods for normalizing the air composition of the working area. Category of premises with dust Determination of dust content by mass method

A well-studied and long-used method for assessing air dust content industrial enterprises is a weight method, the essence of which is to determine the weight gain when passing a certain volume of test air through a filter. Cotton (absorbent) or glass wool are usually used as filters. 0.5 g of hygroscopic or 2 g of glass wool is placed in a glass tube, called a dust tube, or allonge, with ground stoppers so that the thickness of the filter layer is 3-4 cm. The density of the filter should be such that when passing through the tube 15-20 ml of air per minute the filter resistance was approximately 100 mm of water. Art.

The equipped and tested dust tube is brought to a constant weight by drying. A sample is taken at the breathing level of the worker, recording the volume of air passed through. To obtain a more accurate result, at least two samples are taken at each measurement point.

After completing the measurements, the dust tube is brought back to a constant weight by drying. The difference in the weight of the tube before and after passing dusty air characterizes the dust content in the volume of air passed through the tube. An idea of the dust content of the air under study is given by subsequent recalculation per unit volume (cubic meter of air) and comparison with the established sanitary standard.

In some cases, it is necessary, along with the dust concentration, to also know the particle size (dispersity) of the dust, and sometimes the number of dust particles contained in a unit volume of air. For this purpose, the method of direct observation and counting using a microscope can be used.

In production conditions, when using the gravimetric method, commercially available aerosol analytical filters of the AFA type made of perchlorovinyl fiber are usually used. Recently, radioisotope, optical, electron probe and other methods have become widespread in the study of dusty flows.

Now the industry has mastered the production of various instruments and installations for the analysis of aerosols: radioisotope dust meter “Priz-2” (determination of dust concentrations in the air of the working area in the range of 1–500 mg/m3); control and measuring complex "Post-1" (automatic measurement and recording of dust and soot content in the atmospheric air), integrated laboratory "Post-2", automatic single-channel sampler APP-6-1 (selection of aerosol from the air for

determination of concentrations by direct method), individual dust dosimeter DP-1 (aerosol sampling to determine concentrations by direct method when air dust content is more than 15 mg/m3), sampling device PU-ER-220, sampling device PU-ER-12 (air sampling with subsequent determination of concentration, dispersed, mineral, chemical, microbiological composition and study of aerosol properties with the parallel use of gravimetric, optical, granulometric, electron probe and microbiological analysis of deposited aerosol particles)

Goal of the work

Determine the dust content in the air of industrial enterprises in a laboratory environment.

Job Objectives

Determine the conditions under which dustiness occurs in the air of industrial premises. Determine the research method most suitable for the given conditions. Determine the actual value of the concentration of harmful substances in the air of industrial premises (in laboratory conditions). Determine the compliance of the actual dust concentration determined experimentally with the normative one in accordance with approved state standards.

Supporting means

Instruments and materials for research - electric aspirators -
tors, blowers, dust meters, various samplers, conimeters,
AFA brand filters of various modifications. Weight determination of the amount of dust in the air is carried out using an installation consisting of six main parts:

1. Aspirator (model 822) - a stimulator of air movement.

2. Dust chamber to create artificial dusty air conditions.

3. Devices for spraying a sample of dust in the dust chamber.

4. Allonge (filter holder) and connecting hose.

5. Filters.

6. Analytical balances.

Note: The department has a stationary installation in which all these units are combined.

Exercise

1. Research structure: divide research into industry and for scientific purposes. In industry, air dust levels in the breathing zone of workers at workplaces are studied for a special assessment of working conditions or when drawing up a map of working conditions, as well as when dusty air is released into the atmosphere, using a unified methodology. For scientific purposes, studies of dust levels in the air are carried out depending on the goal, using appropriate methods developed separately for each type of study. Research methods: weight, counting, indirect.

2. Methods for studying air dust levels

When assessing working conditions, air quality, and the degree of dust content in the breathing zone at workplaces, three methods are used: weight, counting and indirect.

Weight method. It allows you to determine the number of milligrams of dust in one cubic meter of air, for which it is necessary to deposit dust from a certain volume of air on a filter and determine its weight. In Russia and a number of other countries, the weight method is standard. When using the gravimetric method, at least one day is required.

Calculation of the weight concentration of dust in mg/m 3 is carried out according to the formula

Where t 1 And t 2- weight of the filter before sampling and after sampling, mg;

v- sampling rate of the device, l/min;

t- duration of sampling, min;

1000 - air volume conversion factor, s l. per m 3.

The gravimetric method has several varieties depending on the absorber material. The simplest, most convenient and more advanced of them is the method using analytical aerosol filters (AFA), in which the Petryanov filter - FP - is used as a filter element. It consists of a uniform layer of ultra-thin polymer fibers with or without a gauze backing. To study air dust levels, AFA-VP-18 filters are usually used (sometimes the letter P is omitted, for example, AFA-V-18. “B” means “weight”, the numbers “18” or “GO” indicate the filtering surface of the filters, cm 2) . In practice, other brands of AFA filters are used, for example, AFA-BA-20, AFA-XM-20, etc., which are used for bacterial, dispersion and chemical analyzes of the air environment.

Conimetry of dusty air.

During air sampling, large particles sometimes fall onto the filter.
particles that are not dangerous to the body. When weighing, they distort the true result. At the same time, smaller particles representing
great danger to the body, are often not caught by the filter. By
to this end, along with the use of the weight method, they use the counting (conimetric) method, which provides data on the size and quantity
dust particles contained in the air. It is known that through the respiratory tract
Dust particles up to 10 microns in size are introduced into the human body. At the core
The method involves counting the number of dust particles contained in 1 cm 3 of the air being tested. The method serves as an additional characteristic to the standard weight method.

Indirect methods. In addition to the weight and counting methods, there are indirect methods, when dustiness is judged by a number of indicators physical properties dusty air or dust (optical properties, electrical charge, light reflection, radioactivity, etc.). Monitoring is carried out with such devices as, for example, the F-1 photodust meter, the IZV-1 radiometric device, the DPV-1 dust meter, etc. The advantage of the method is the speed of analysis, i.e. immediate assessment of air dust content in mg/m 3, ease of maintenance, availability of measurements at any point in the room. The disadvantage is a rather significant error (for some devices up to 30%), depending on the properties of the dust or gas, and a narrow scope of application for a certain type or type of dust.

3. Research methodology

1. Study the methodology and instruments for determining air dust levels.

2. Experimentally determine the amount of dust present in
one cubic meter of air; Record the data in the protocol, table 1.1.

3. Compare the results obtained with the requirements of GN 2.2.5.1313-03 and give a hygienic assessment of the state of the air environment in
breathing zone.

4. Using the data obtained, determine the scope of their application.

The initial data for the calculation are:

Mineralogical composition of dust;

The main properties of dust are density (bulk and true), coagulation, wettability, stickiness, abrasiveness, electrical resistivity;

Properties of the gas flow - temperature, density, kinematic or dynamic viscosity;

The initial concentration of dust at the place of its formation;

Disperse composition of dust, i.e. the content of fractions by “partial residues” or by “full passages”.

Calculation sequence:

1. According to GOST 12.2.043-80, there are five main classification groups of aerosols:

I - very coarse dust;

II - coarse dust (for example, sand for mortars according to GOST 8736-77); ,

III - medium-fine dust (for example, cement);

IV - fine dust (for example, ground quartz according to GOST 9077-82);

V - very fine dust.

The classification group of dust is determined by the nomogram (Fig. 4.1). To use the nomogram, you must have the results of a dust sieve analysis. The dispersed composition is determined by “full passes”. Points corresponding to the content of the first five fractions are plotted on the nomogram, and by connecting them, we obtain a line indicating the classification group.

Table 4.1

Classification group of dust based on adhesiveness	Characteristics of the classification group	Characteristic dust
I	Non-stick ≤ 60 Pa	Slag dust; quartz sand
II	Low sticking 60-300 Pa	Coke dust; apatite dry dust; fly ash from the layer combustion of all types of coal and from the combustion of shale; magnesite dust; blast furnace dust (after primary precipitators); slag dust
III	Medium sticky 300-600 Pa	Fly ash from pulverized combustion of coal without underburning; peat ash; wet magnesite dust; metal dust; pyrites; oxides of lead, zinc and tin; dry cement; soot; powdered milk; flour dust; sawdust
IV	Highly sticky > 600 Pa	Gypsum and alabaster dust; nitrophoska; double superphosphate; cement dust isolated from humid air; fibrous dust (asbestos, cotton, wool, etc.); all dust with particle size< 10 мкм

Table 4.2

Example. Determine the classification group of dust if, according to experimental data, it has the following disperse composition:

Particle size, microns.....< 5 5-10 10-20 20-40 40-60 60

Solution: We calculate the dispersed composition of dust using “full passes”:

Particle size, microns...............<5 <10 <20 <40 <60

We plot the points corresponding to the content of the first five fractions in “full passes” on the nomogram (Fig. 4.1) and, connecting them, we obtain a line located in zone III. Therefore, this dust belongs to classification group III. Particle dispersion distribution beyond interval 5 60 microns. When assessing dust dispersion, this area is not taken into account.

In cases where the graph of the fractional composition of the aerosol, plotted on the classification nomogram, crosses the boundaries of the zones, the dust is assigned to the classification group of the highest of the zones.

2. All dusts of dispersion groups IV and V are practically classified as highly agglomerating dusts, and dusts of group III are classified as moderately agglomerating. In table 4.1 gives the characteristics of dust in terms of adhesion.

3. Particles finer than 10 microns, especially finer than 5 microns, tend to become non-wettable (hydrophobic) regardless of their composition.

4. In ventilation practice, explosive dust is considered to be aerosols whose lower concentration limit of flame propagation is less than 65 g/m3. Dusts with a lower limit of more than 65 g/m 3 are considered flammable.

5. Using the technological map of the production, workshop, site, a diagram of the aspiration system is drawn up (Fig. 4.2), page 243. The procedure for calculating air ducts for aspiration systems is given in the work.

6. The type of dust fan is selected. Fan characteristics are shown in Fig. 4.3 and in the Directory and . To do this, the required air flow Q and pressure loss in the network P are determined.

6.1. The volume of air should be determined using the formulas in table. 11, 10 and the tables given in the work, as the sum that is the sum of the volume of air brought into the shelter by the incoming material (Q e) and the volume (Q n) sucked through the leaks of the shelter to prevent dust from entering the room:

Q = Q e + Q n, m 3 / h

Concentration of aerosols in exhaust air emissions at an air flow rate of more than 15,000 m 3 /h:

Сх = 100 R, mg/m 3, (4.1)

R is the coefficient taken depending on the maximum permissible concentration (MPC) of aerosols in the air of the working area of industrial premises, according to GOST 12.1.005 - 88, mg/m 3:

MPC........................ Up to 2 2-4 4-6 6-10

R ........................... 0.3 0.6 0.8 1.0

The concentration of aerosols in emissions with a volume of less than 15 thousand m3, taking into account the smaller impact on air pollution, can be taken slightly higher according to the formula

C x =(160 - 4 Q) R, mg/m 3, (4.2)

Q - volume of emission, thousand m3.

The concentration calculated using these formulas is checked against the condition that, as a result of the dispersion of the emission in the atmosphere, the concentration of aerosols, taking into account background atmospheric pollution, does not exceed:

a) in the ground layer of the atmosphere of populated areas - concentrations specified in SN 245-71, but not more than the maximum permissible concentration for populated areas;

b) in the air entering production and auxiliary buildings and structures through the intake openings of supply ventilation systems and through openings - 30% of the maximum permissible concentration of the same aerosols, in the working area of the premises - according to GOST 12.1.005-88. The gross emission of each source must not exceed the maximum permissible limit established for it.

If the amount of dust generated is known (M, mg/h), then the required fan performance can be determined as:

Q = M / (C pr - C uh) ,

Cpr - dust concentration in the supply air, mg/m3;

Cx is the concentration of dust in the exhaust air.

6.2. Network pressure losses are determined by the formula:

P = P tr L + P m, Pa,

P tr - specific pressure loss due to friction per 1 linear meter of air duct, Pa;

L - length of the air duct section, m;

Р m - pressure loss due to local resistance, Pa.

The calculation table for the network of air ducts for aspiration systems is given in the work.

The specific pressure loss due to friction for round air ducts is determined by the formula:

R tr = (λ/d)·(V 2 ·ρ/2)

λ - friction resistance coefficient;

d - diameter of the air duct, m;

V - air speed in the duct, m/sec;

ρ - air density, kg/m3;

V 2 ·ρ/2 - velocity (dynamic) air pressure, Pa.

The values of λ/d should be taken according to the table. 22.56.

For rectangular air ducts, the value d is taken to be the equivalent diameter d., of such round air ducts, which at the same speed have the same friction pressure loss as rectangular air ducts:

d e = 2ab/(a + b), m,

a and b - dimensions of the walls of a rectangular air duct, m.

Pressure loss due to local resistance is determined by the formula:

P m = eζ (V 2 ρ/2), Pa,

ζ is the sum of local resistance coefficients.

Local resistance coefficients are given in the tables of Chapter. 22.

An example of calculating pressure losses in an air duct network is given in Table. 22.58.

6.3. To determine the cross-sectional area of the air ducts, you should use the recommended air speeds, which are given in table. 22.57.

The cross-section of the air ducts must ensure an air speed not lower than permissible for this type of dust:

V = 1.3·(ρ m) 1/3,

ρ m - volumetric mass of the material, kg/m 3

When lifting mechanical impurities to a height, formulas (22.16), (22.17) should be taken into account.

7. Based on air flow and pressure loss, we select the type and number of the required fan (Fig. 4.3), using the characteristics of dust fans, which are also given in the appendices of the Directory.

8. Selection and calculation of dust collectors.

Dust collectors used to clean the air from aerosol particles are divided into 5 classes (Table 4.2).

Class 1 dust collectors are characterized by high energy consumption (high-pressure Venturi dust collectors), complexity and high cost of operation (multiple-field electrostatic precipitators, bag filters, etc.)

In table 4.2 indicates the efficiency limits of dust collectors of each class based on the classification of aerosols according to Fig. 4.1. The first of the efficiency values refers to the lower boundary of the corresponding zone, the second - to the upper. The efficiency is calculated based on the conditions of separation from the air of only practically completely (effectively) captured particles, the size of which is indicated in the table. 4.2. The actual efficiency of dust collectors is greater due to the partial capture of particles smaller in size than those indicated in the table. 4.2.

9. The pressure loss in the dust collector is calculated. They are found as a component of the velocity pressure, i.e.:

Р n = ζ n ·(ρ g ·V 2/2),

ζ n - coefficient of local resistance of the dust collector;

To roughly estimate the resistance value (pressure loss) of various dust collectors, you can use the data given in Table. 4.3.

A detailed selection of the type of dust collector is given in Chapter. 4 .

When determining pressure loss in a cyclone ζ n = ζ c, the value of ζ c is determined by the formula:

ζ c = k 1 k 2 ζ o + Δζ o

k 1 - coefficient depending on the diameter of the cyclone (Table 4.4);

k 2 - coefficient for air dustiness (Table 4.5);

ζ o - coefficient of local resistance of the cyclone D=500 mm (Table 4.6);

Δζ o - coefficient depending on the adopted layout of the cyclone group (Table 4.7); for single cyclones Δζ o = 0.

10. The main dimensions of the selected dust collector are calculated. They are determined depending on the performance of the selected fan - (Q, m 3 / h) and the optimal speeds for this type of dust collector:

So, for cyclones, the optimal diameter is determined by the formula:

D = 0.94·(Q 2 - ρ g ζ c /P c) 1/2,

ζ - coefficient of local resistance of the cyclone;

P c - pressure loss in the cyclone;

ρ g - gas flow density.

The diameter of the cyclone can also be found from the cross-sectional area of the cyclone (F), which is defined as:

F = Q/V o, m 3

V o - air speed (Table 4.6), m/s.

Knowing the diameter of the cyclone D, the main dimensions of the dust collector are determined:

Dout = D·0.59,

D out - diameter of the exhaust pipe.

Inlet dimensions:

a x b = D 0.26 x D 1.11

Overall height H = D 4.26

11. The coefficient of air purification from dust is determined:

h = ΔM/M 1 = M 1 - M 2 /M 1 = 1 - M 2 /M 1,

M 1 and M 2 - respectively, the amount of dust entering and exiting the dust separator;

ΔM is the amount of dust collected.

Table 4.3

Type	View	Dust collector class	Suitable application area
Classification group of aerosols by dispersity	Resistance, Pa
I	II	III	IV	V

Gravitational	Dust settling chambers (of arbitrary design)		+	+	-	-	-	100-200
Inertial, cyclones	High capacity cyclones:
single cyclones TsN-15, TsN-24		+	+	-	-	-	600-750
group - cyclones TsN-15		+	+	-	-	-	600-750
High efficiency cyclones:
single cyclones SKTSN-34		-	+	+	-	-	1000-1200
wet film cyclones TsVP		-	+	+	-	-	600-800
Scrubbers	VTI-PSP high-speed washers SIOT		-	+	+	-	-	900-1100
Jet, wet: front driving position		-	-	+	+	-	1200-1950
PVMC, PVMS, PVMB		-	-	+	+	-	2000-3000
drip, Venturi type KMP		-	-	+	+	-	3000-4000
Fabric	Bag dust collectors SMTs-101, SMTs-166B, FVK (GC-1BFM), FRKI		-	-	+	+	-	1200-1250
Nylon mesh, metal mesh for collecting fibrous dust, Venturi, electric precipitators		+	-	-	-	-	150-300
Fibrous	Mist eliminators for acids and alkalis FVG-T		-	-	-	+	-	800-1000
Oil aerosol traps (rotary)		-	-	-	+	-	800-1000
Electrical	Mist eliminators for oils and oily liquids UUP		-	-	-	+	+	50-100

Table 4.4

Correction factor k 1

Table 4.5

Correction factor k 2

Table 4.6

Local resistance coefficients of cyclones with a diameter of 500 mm and optimal air speeds

Cyclone brand	air, m/sec	Values t, cyclones
with release into the atmosphere	with a snail on the exhaust pipe	for group installation ζ o
v o	vin	ζ o	ζ in	ζ o	ζ in
TsN-11	3,5	-		6,1		5,2
TsN-15	3,5	-		7,8		6,7
TsN-G5u	3,5	-		8,2		7,5
TsN-24	4,5	-		10,9		12,5	-
SDK-TsN-33		-		20,3		31,3	-
SK-TsN-34m		-		-	-	30,3	-
SK-TsN-34	1,7	-		24,9	-	30,3	-
CIOT	-	12-15	-		-	4,2	-
LIOT	-	12-15	-	4,2	-	3,7	-
VTsNIIOT	-	12-15	-	10,5		10,4	-

Table 4.7

Coefficient Δζ o

LITERATURE

1. Designer's Handbook. Part 3. Ventilation and air conditioning. Book 1. M.: Stroyizdat, 1992.

2. Designer's Handbook. Part 3. Ventilation and air conditioning. Book 2. M.: Stroyizdat, 1992.

3. Designer's Handbook. Ventilation and air conditioning. Under the general editorship of I. G. Staroverov. M.: Stroyizdat, 1969.

4. GOST 12.2.43-80.

5. GOST 12.01.005-88. General sanitary and hygienic requirements for the air in the working area.

6. Sanitary standards for the design of industrial enterprises. (SN 245-71), M.: Stroyizdat, 1971.

7. Titov V.P. and others. Course and diploma design on ventilation of civil and industrial buildings. M.: Stroyizdat, 1985.

Dear readers, in this article we will talk about how the category of a room with dust is determined.

Despite the fact that the mathematical apparatus of SP 12.13130.2009, which is intended to determine the fire hazard category of a room with dust, is quite simple, determining a number of parameters causes certain difficulties.

Let's look at everything in order. To begin with, it should be noted that rooms with dust can be classified as category B for explosion and fire hazard or explosion and fire hazard.

Before proceeding to the calculation of whether a room belongs to one of categories B for fire hazard, it is necessary to justify by calculation whether the room where the formation of an air suspension is possible belongs to category B for fire and explosion hazard.

The basic calculation formulas are contained in section A.3 of Appendix A of SP 12.13130.2009.

In accordance with formula A.17 of the set of rules, the estimated mass of dust suspended in the room as a result of an emergency situation should be taken as the minimum of two values:

— the sum of the masses of swirling dust and dust released from the apparatus as a result of the accident;

— a mass of dust contained in a dust-air cloud, capable of burning when an ignition source appears.

It should be noted here that not all dust is capable of burning, i.e. the coefficient of participation of combustible dust in the explosion is ≤0.5, which is confirmed by formula A.16 of the set of rules.

The coefficient of participation of suspended dust in combustion depends on the fractional composition of the dust, namely a parameter called the critical particle size.

For most organic dusts (wood dust, plastics, flour, etc.), the critical size value is about 200-250 microns.

Dust consisting of larger particles will not participate in combustion, except when it is burned in special hearths (furnaces). When the category of a room with dust is determined, as a rule, we are dealing with either completely fine dust, the particle size of which is less than critical (for example, powdered sugar), or with dust, which includes particles of various sizes, both larger and smaller than critical. Such dust includes wood dust, grain dust, etc.

The fractional composition of dust is determined experimentally by sifting through a system of special sieves called “fractionator”. It is hardly possible to find such data, although for a number of industrial dusts (powders), data on the fractional composition can be requested from the manufacturer.

In the absence of data, it is assumed that all dust particles have a size less than critical, i.e. capable of spreading fire. The mass of dust that can come out of the device as a result of an emergency is determined by the characteristics of the technological process.

The mass of swirling dust is that part of the deposited dust that can become suspended as a result of an emergency.

In the absence of experimental data, it is assumed that 90% of the mass of deposited (accumulated) dust can become an air suspension. Dust, which is released in small quantities in the production area during normal operation, settles on the enclosing structures (walls, floor, ceiling), on the surface of the equipment (cases of technological devices, transport lines, etc.), on the floor under the equipment.

At the designed production facility, the frequency of dust collections is determined: routine and general. According to SP 12, it is accepted that all the dust that settles in hard-to-reach places for cleaning accumulates there during the period between general dust collections. Dust that settles in places accessible for cleaning accumulates there during the period between current dust collections. Estimation of the proportion of dust settling on a particular surface (accessible or difficult to access) is possible only experimentally or by modeling methods.

Assessing the dust collection efficiency of designed production facilities, as a rule, is also impossible, therefore it is conventionally accepted that all the dust released from the equipment into the room settles inside the room.

The amount of dust settling on different surface areas located in the room also varies. Dust, which is released normally, floats in the air and, due to gravity, gradually settles on various surfaces.

However, it is expected that the greatest amount of dust will settle at lower levels of the room, provided that the source of the dust (equipment) is also located at the lower level. It is obvious that horizontal surfaces can accumulate dust in almost unlimited quantities; a limited amount of dust settles on vertical surfaces, depending on the type of surface.

For, the amount of dust that settles on the walls is as follows: painted metal partitions - 7-10 g/m2, brick walls - 40 g/m2, concrete walls - 30 g/m2. Most likely, the data presented can be used for other industries.

Now let's turn to the formula for calculating the amount of dust depending on the volume of the dust-air cloud. It should be noted that there are no analytical expressions by which the volume of a dust-air cloud can be calculated in the domestic literature.

It has not yet been possible to find such data in foreign fire-technical literature, probably because such an approach is not used in the USA and Europe (meaning the calculation of categories). Therefore, in practice, the volume of the dust cloud has to be estimated in some way.

For example, we can conditionally take as the characteristic shape of a cloud a cone with a height from the floor to the dust source and a base with a radius several times greater than this height. Although, I’m not sure how true this assumption is, since there are no experimental data available.

In addition to the critical size, the stoichiometric dust concentration is also a determining parameter.

Stoichiometric dust concentration is the concentration of dust at which its complete combustion occurs, taking into account the amount of oxygen contained in a unit volume of air.

The stoichiometric dust concentration can be determined by calculation only for substances and materials for which the chemical composition is known. These include most polymer materials (polyethylene, polypropylene, polystyrene, etc.), various medications, metal and alloy powders.

For other materials, for example, for plant (wood and grain dust, tea, etc.) and food materials (flour, milk powder, cocoa, etc.), the stoichiometric concentration must be determined either experimentally, or by looking for the chemical composition of the corresponding material from which it is composed. dust.

Determining the stoichiometric concentration comes down to solving the following sequential problems:

1. The chemical composition of the dust is determined.

2. The chemical equation for the reaction of complete combustion of dust is written.

3. The mass of oxygen required for complete combustion of 1 kg of dust is determined.

4. The mass of oxygen contained in 1 m 3 of air is determined, taking into account the design temperature.

5. The mass of dust that can completely burn in the mass of oxygen contained in 1 m 3 of air is determined. The resulting value is the stoichiometric concentration of dust in the dust-air cloud.

Determining the category of a room with dust does not take into account such an indicator of fire danger as the lower concentration limit of flame propagation (LCFL). As a rule, the concentration of dust in a dust-air cloud during emergency situations exceeds the LEL.

And finally, a couple of very interesting videos about dust explosions in industries. Even without knowledge of English, everything is shown clearly and interestingly. I recommend watching!

I look forward to seeing you again on fire safety!

The air is drawn for 1 minute at 20 l/min. The filter weight before sampling was 707.40 mg. , after sampling - 708.3 mg. Air temperature in the room is 22°C, atmospheric pressure is 680 mmHg.

1. Let us bring the volume of air drawn through the filter to normal conditions:

2. Dust concentration in the air:

After calculating the dust concentration in the air, make a hygienic assessment of the dust content of the air by comparing it with the requirements of SN-245-71 on maximum permissible dust concentrations in the air.

Goal of the work.

Applicable instruments and equipment.

3. Measurement protocol (see Table 4), calculation of dust concentration using the given formulas, determination of dust dispersion (see Table 4).
4. Conclusions: hygienic assessment of air dust content and recommendations for improving the condition of the air environment.