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 category fire danger rooms with dust is quite simple, but 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 main 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 devices 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. participation rate combustible dust in an explosion, ≤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 that is released in small quantities into production premises in normal operation, it settles on enclosing structures (walls, floors, ceilings), on the surface of 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 areas 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 the various areas surfaces located indoors. Dust, which is released in normal mode, floats in the air and, due to gravity, gradually settles on various surfaces.

At the same time, it is expected that greatest number dust settles at lower levels of the room, provided that the source of dust (equipment) is also located at the lower level. It is obvious that horizontal surfaces can accumulate dust in almost unlimited quantities, vertical surfaces A limited amount of dust settles, 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 any analytical expressions by which the volume of a dust-air cloud can be calculated Russian literature are missing.

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 it is known chemical composition. These include the majority polymer materials(polyethylene, polypropylene, polystyrene, etc.), various medicines, powders of metals and alloys.

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 flame propagation (FLP). As a rule, the concentration of dust in a dust-air cloud at emergency situations exceeds the NLPR.

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

I look forward to seeing you again on fire safety!

Industrial dusts are those suspended in the air. working area solid particles ranging in size from several tens to fractions of microns. Dust is also commonly called an aerosol, meaning that air is a dispersed medium, and solid particles are a dispersed phase. Industrial dust is classified according to the method of formation, origin and particle size. .

In accordance with the method of formation, a distinction is made between aerosols, disintegration and quaidence. First; are a consequence

vii production operations associated with the destruction or grinding of solid materials and transportation of bulk substances. The second way of dust formation is the appearance of solid particles in the air due to cooling or condensation of metal or non-metal vapors released during high-temperature processes.

Based on their origin, dust can be divided into organic, inorganic and mixed. The nature and severity of the harmful effects depend, first of all, on the chemical composition of the dust, which is mainly determined by its origin. Inhalation of dust can cause damage to the organs of the duck - bronchitis, pneumoconiosis or the development of general reactions (intoxication, allergies). Some dusts have carcinogenic properties. The effect of Dust is manifested in diseases of the upper respiratory tract, mucous membranes of the eyes, skin. Inhalation of dust can contribute to the occurrence of pneumonia, tuberculosis, and lung cancer. Pneumoconiosis is one of the most common occupational diseases. The classification of dust according to the size of dust particles (dispersity) is of exceptionally high importance: visible dust (size over 10 microns) quickly settles from the air; when inhaled, it lingers in the upper respiratory tract and is removed when coughing, sneezing, with sputum; microscopic dust (0.25 -10 microns) is more stable in the air, when inhaled it enters the alveoli of the lungs and affects the lung tissue; ultramicroscopic dust (less than 0.25 microns), up to 60-70% of it is retained in the lungs, but its role in the development of dust injuries is not decisive, since its total mass is small.

The harmful effects of dust are also determined by its other properties: solubility, particle shape, their hardness, structure, adsorption properties, and electrical charge. For example, the electrical charge of dust affects the stability of the aerosol; particles carrying an electrical charge are retained in the respiratory tract 2-3 times more. "

The main way to combat dust is to prevent it; formation and release into the air, where the most effective are technological and organizational measures: the introduction of continuous technology, mechanization of work;

equipment sealing, pneumatic transportation, remote control; replacement of dust-producing materials with wet, paste-like materials, granulation; aspiration, etc.

The use of artificial ventilation systems is of great importance, complementing the main technological measures to combat dust. To combat secondary dust formation, i.e. by the entry of already settled dust into the air, wet cleaning methods, air ionization, etc. are used.

In cases where it is not possible to reduce the dust content of the air in the work area by more radical measures of a technological and other nature, personal protective equipment is used various types: respirators, special helmets and spacesuits with clean air supplied to them. ,

The need for strict compliance with maximum permissible concentrations requires systematic monitoring of the actual dust content in the air of the working area of ​​the production premises.

Automatic devices for determining dust concentration include the commercially produced IZV-1, IZV-3 (air dust meter), PRIZ-1 (portable radioisotope dust meter), IKP-1 (dust concentration meter), etc.

Ventilation of industrial premises

Ventilation is a complex of interrelated processes designed to create organized air exchange, i.e. removal of contaminated or overheated (cooled) air from the production premises and supply instead; it contains clean and cooled (heated) air, which allows you to create favorable air conditions in the working area.

Industrial ventilation systems are divided into mechanical (see Fig. 6.5) and natural. It is possible to combine these two types of ventilation (mixed ventilation) in various options. " " " V

In the first case, air exchange is carried out with the help of special movement stimulants - fans, in the second -

due to the difference specific gravity air outside and inside the production premises, as well as due to wind pressure (pressure from wind loads). Based on the location of action, a distinction is made between a general ventilation system, which carries out air exchange on the scale of the entire production premises, and a local one, in which air exchange is organized on the scale of only the working area. A specific characteristic of general exchange ventilation systems is the air exchange rate:

k=u/u pom,

where V is the volume of ventilation air, m 3 /hour; V n 0 M is the volume of the room, m 3.

General exchange systems can be supply (only supply is organized, and exhaust occurs naturally due to an increase in pressure in the room), exhaust (only exhaust is organized, and supply occurs by sucking air from outside due to its rarefaction in the room) and supply and exhaust (organized as inflow and exhaust). Supply and exhaust natural ventilation is called aeration. Local systems can be exhaust or supply.

Basic requirements for ventilation systems:

correspondence of the amount of supply air to the amount of air removed. It should be borne in mind that if two areas are located nearby, one of which contains harmful emissions, a slight vacuum is created in this area, for which more air is removed than supplied, and in an area where there are no harmful emissions, vice versa . Increasing the pressure in the “clean” area relative to the adjacent one prevents the penetration of harmful vapors, gases and dust into it;

inlet and exhaust systems ventilation must be properly placed. Air is removed from the area with the most pollution, and air is supplied to areas with the least pollution. The height of the air intake and air distribution devices is determined by the ratio of the air density in the room and the density of the substance polluting it. In case of heavy pollution, air is removed from the lower part of the room, in case of light pollution - from the upper part.

Ventilation systems must ensure the required air purity and microclimate in the work area, be electrical, fire and explosion-proof, simple in design, reliable in operation and efficient, and also should not be a source of noise and vibration. .

Rice. 6.5. Mechanical ventilation: a - supply; b - exhaust; c - supply and exhaust with recirculation

Installations of supply systems! # ventilation (Fig. 6.5a) consist of an air intake device (1), air ducts (2), filters

for cleaning the intake air from impurities, heater

Centrifugal fan (5) and supply devices (6) (openings in air ducts, supply nozzles, etc.).

Installations of the exhaust ventilation system (Fig. 6.56) consist of exhaust devices (7) (holes in the air ducts, exhaust nozzles), a fan (5X air ducts (2), a device for cleaning the air from dust and gases (8) and devices for air release ( 9).

Supply and exhaust ventilation system installations (Fig. 6.5c) are closed air exchange systems. The air sucked from the room (10) by exhaust ventilation is partially or completely re-supplied to this room through the supply system connected to the exhaust system by an air duct (11). When the qualitative composition of the air in a closed system changes, it is supplied or exhausted using

valves (12).

In the production workshops of industrial enterprises, the most common are general exchange ventilation systems designed to remove

removal of harmful vapors, gases, dust, excess humidity or the concentrations specified harmful substances to pre-; strictly acceptable standards. . ,

Several harmful substances can enter production premises at the same time. In this case, air exchange; calculated for each of them. If the released substances act on the human body unidirectionally, then the calculated volumes of air are summed up. .

" G The calculated volume of air should be supplied heated to the working area of ​​the room, and contaminated air should be removed from the places where harmful substances are released from the upper zone of the room.

The volume of air (m 3 / h) required to remove carbon dioxide from the room is determined by the formula:

L=G/(x 2 -x,)y

Where G- the amount of carbon dioxide released in the room, g/h or l/h; Xi- concentration of carbon dioxide in the outside air; X 2 - concentration of carbon dioxide in the air of the working area, g/m3 or l/m3. The volume of air (m^h) required to remove harmful vapors, gases and dust from the room is determined by the formula; :

■ ^1=с/(с^-с^; : ■- 1 " ■" ■ ;

Where G- the amount of gases, vapors and dust released in the room, m 3 / h; With 2 - maximum permissible concentration of gas, vapor or dust in the air of the working area, mg/m 3 ; c t - concentration of these harmful substances in the outside (supply) air, mg/m3. ;

< Объем воздуха (м 3 /ч), который требуется для удаления из? но- Мещения вдагодабытков^ определяют по формуле: : ;

* 1 = S/r.(

Where G- the amount of moisture evaporating in the room, g/h; p - air density in the room, kg/m3; d 2 - moisture content of air removed from the room, g/kg of dry air; d t - moisture content of supply air g/kg dry air.

The volume of air (m 3 /h) required to remove excess heat from the room is determined by the formula:

L ~ Oizb IСp(t ebt m~t n pum) > "

Where Qms - amount of excess heat entering the room, W; WITH - specific heat capacity of air, J/(kgK); r- air density in the room, kg/m3; team - air temperature in the exhaust system, °C;tnpum- supply air temperature, *C. ■■■■ -■ . - ■ ■ ■

We will illustrate the practical application of the calculations given in accordance with SNiP 2-04.05-86 using specific examples.

Example!. N - 50 people gathered in a room for short-term stay of people. The volume of the room is V = 1000 m. Determine how long after the start of the meeting it is necessary to turn on the supply and exhaust ventilation if the amount of CO 2 emitted by one person q = 23 l/h in the outside air X = 0.6 l/m3.

, Y(x 2 -X,)

■■■■- ■■G’ ■ ^

. . .% ....

Where G the amount of CO 2 released by people

G=JVd = 50-23 = 1150l/h,1000 ( 2- 0, 6)

“ T=-- --- = 1.21h=73l<ин

1150 ... . ...... ... . ;.

Example 2. Determine the required air exchange from*

heating units in the assembly shop for the warm period of the year. The total power of equipment in the workshop N 0 b 0р = 120 kW. Number of employees - 40 people. The volume of the room is 2000 m3. Supply air temperature npHT = +22.3 °C, humidity j = 84%. The heat from solar radiation is 9 kW. (Q cp). Specific heat capacity of dry air "C = 0.237 W/kgK; density of supply air p = 1.13 kg/m 3 ; exhaust air temperature t BKT = 25.3" C. Take the amount of heat generated by one person as 0.11<Г кВТ; от оборудования 0,2 на 1 кВт мощности

^ QuafiJ^P^out- ^ad)

, ,. r„ «<&л^ +&**":+fi^v^(u.-w

Amount of heat from people, kW,

^^“=0.116x40 = 4.64

Amount of heat from equipment, kW,

Qu36 ° 6 ° P= 120x 0.2= 24

Required air exchange, m 3 / h,

£= (4.63+ 24+9)-100 _ 44280

0,237-1,13(25,3-22,3)

Air conditioning

With the help of air conditioning in enclosed spaces and structures, it is possible to maintain the required temperature, humidity, gas and ionic composition, the presence of odors in the air, as well as the speed of air movement. Typically, in public and industrial buildings it is necessary to maintain only part of the specified air parameters. The air conditioning system includes a set of technical means that carry out the required air processing (filtration, heating, cooling, drying and humidification), its transportation and distribution in the serviced premises, devices for muffling the noise caused by the operation of the equipment, sources of heat and cold supply , means of automatic regulation, control and management, as well as auxiliary equipment. The device in which the required heat and humidity treatment of air and its purification is carried out is called an air conditioning unit, or air conditioning.

Air conditioning provides the necessary microclimate in the room for the normal flow of the technological process or the creation of comfortable conditions. ■

Heating

Heating involves maintaining in all industrial buildings and structures (including crane operator cabins, control panels and other isolated rooms, permanent workplaces and work areas during main and repair and auxiliary work) a temperature that meets established standards.

The heating system must compensate for heat loss through building fences, as well as provide heating for the cold air penetrating into the room during the import and export of raw materials, materials and workpieces, as well as these materials themselves.

Heating is arranged in cases where heat loss exceeds heat release in the room. Depending on the coolant, heating systems are divided into water, steam, air and combined.

Water heating systems are the most acceptable from a sanitary and hygienic point of view and are divided into systems with water heating up to 100°C and above iOO°C (superheated water).

Water is supplied to the heating system either from the enterprise’s own boiler house, or from a district or city boiler house or thermal power plant.

A steam heating system is suitable for enterprises where steam is used for the technological process. Steam heating devices have a high temperature, which causes food to burn. Radiators, finned pipes and registers made of smooth pipes are used as heating devices.

In industrial premises with significant heat generation, devices with good surfaces are installed that allow them to be easily cleaned. Finned radiators are not used in such rooms, since the settled dust due to heating will burn* giving off a burning smell. Dust at high temperatures can be dangerous due to the possibility of ignition. The temperature of the coolant when heating the local area and heating devices should not exceed: for hot water - 150 ° C, water steam - 130 0 C. *: » ; . :

An air heating system is characterized by the fact that the air supplied to the room is preheated in heaters (water, steam or electric heaters).

Depending on the location and design, air heating systems can be central or local. In central systems, which are often combined with supply ventilation systems, heated air is supplied through a duct system.

A local air heating system is a device in which an air heater and a fan are combined in one unit installed in a heated room.

The coolant can be obtained from a central water or steam heating system. It is possible to use electric autonomous heating. .

In administrative premises, panel heating is often used, which works as a result of heat transfer from building structures in which pipes with coolant circulating in them are laid.

Federal Agency for Maritime and River Transport

Federal State Budgetary Educational Institution

Higher professional education

"STATE MARINE UNIVERSITY NAMED AFTER ADMIRAL F.F. USHAKOV"

Department of Life Safety

Practical work No. 3

on the topic:

“Determination of the class of working conditions by factor

“ASSESSMENT OF THE HARMFUL IMPACT OF DUSTS”

Cadet group 1922

Somkhishvili Irma

Checked by: senior teacher

Pisarenko G.P.

Option 22

I. PURPOSE OF THE WORK

Study the general properties of industrial dust and the requirements of sanitary standards; familiarization with the structure and operation of the aspirator; determine the dust content in the air by weight method and give a sanitary assessment of dust content.

II. GENERAL INFORMATION ABOUT INDUSTRIAL DUST

Industrial dust refers to solid particles suspended in the air, i.e. These are dispersed systems, namely aerosols, where the dispersed phase is particles ranging in size from 10 -2 to 100 microns, and the dispersed medium is air.

The formation of industrial dust occurs during reloading and transportation of bulk cargo, mechanical grinding of solids.

Industrial dust also includes soot formed as a result of incomplete combustion of fuel in marine diesel engines and steam generators.

Industrial dust can be quantitatively characterized by the average particle size, size distribution curve, specific surface area, i.e. the ratio of the total surface of dust particles to their mass or volume. The most important characteristic is the concentration of dust in the air.

Dust enters the human body through the respiratory system, gastrointestinal tract, eyes and skin. For humans, the greatest danger is posed by dust particles smaller than 10 microns, as can be seen from the data given in Table 1

Table 1

A particular danger to the human body is dust consisting of particles of a toxic substance, or dust with sorbed toxic substances on the surface. For example, toxic dust includes coal sand, calcium carbide, lime, lead, etc. A special feature is the presence of adsorbed carcinogenic substances on the surface of the particles, namely 3,4-benzpyrene - this is a condensed aromatic hydrocarbon with carcinogenic properties, i.e. May cause cancer when applied to the skin or when applied under the skin of animals.

The harmful effect of dust on the human body is determined by its content in the air of working premises, that is, the concentration of dust, which can usually vary from 10 -8 to 10 5 mg/m 3. Elevated dust concentrations cause intense harmful effects on the human body.

Based on the degree of impact on the human body, harmful substances (including aerosols) are divided into 4 hazard classes:

1st – extremely dangerous substances;

2nd – highly hazardous substances;

3rd – moderately hazardous substances;

4th – low-hazard substances.

The hazard class of harmful substances is established depending on standards and indicators.

A harmful substance is assigned to a hazard class based on the indicator whose value corresponds to the highest hazard class. It is also necessary to keep in mind that some industrial dusts are explosive.

One of the dangerous dusts for the human body in maritime transport is grain dust, which consists of organic components

(bacteria, spores, etc.) and inorganic (particles of sand, clay, soil). The silicon dioxide content in grain dust reaches 10%.

Prolonged contact with grain dust can lead to the development of pneumoconiosis. Short-term exposure to the mucous membrane of the eyes and upper respiratory tract causes irritation and the development of inflammatory processes. With mechanical impact on the skin, blistering rashes (“grain scabies”) occur, possibly also bacteriological damage with severe headache, chills, palpitations, dizziness and nausea (“grain fever”).

To prevent harmful effects of industrial dusts

A set of measures is applied to the human body:

Maximum permissible concentrations (MAC) of various dusts in the air of the working area are being developed and established;

Ventilation units and aspiration systems are designed and installed;

Personal protective equipment is developed and applied;

III. BASIC OPERATIONS AND CALCULATIONS FOR ANALYSIS OF DUST CONTAINMENT IN WORKING PREMISES

a) Dust study protocol

b) Assessment of dust content in the workplace/room

1. To quantify a dusty work area, it is necessary to know the mass of dust per unit volume. Dust concentration can be determined by various methods, the simplest and most reliable is weight. The essence of the method is to weigh a special filter before and after drawing a known volume of dust-laden air through it.

where: C – dust concentration in the air, mg/m3;

P 1 – filter mass before dust collection, mg;

P 2 – filter mass after dust collection, mg;

V 0 – volume of air at the sample site, o C.

V o =

where: V is the volume of air drawn through the filter under experimental conditions (at t (o C) and pressure B (hPa);

There are many industry documents describing indoor dust conditions. These are SNIPs, GOSTs, and they consider it from their own professional points of view. But nowhere in them are there numbers limiting the dust content in domestic and office premises. This is primarily due to the fact that a variety of materials are used in the decoration of premises in these categories. Namely, from the finishing materials used, the materials used in the equipment of the premises and the design of the premises (ventilation and air conditioning). And by setting dust standards for domestic and office premises, designers risk not meeting them.

In 2004, the broadest document defining standards for dust content in the air was put into effect. This is the "Interstate standard GOST ISO 14644 -1-2002, Clean rooms and associated controlled environments, Part 1, Classification of air purity."

This is such a long and uncomplicated name. For us, in this case, the table is interesting. 1. from section 3.

Previously, there was GOST R 50776-95, which is characterized by normalization of the content of microorganisms (see Table 1, column highlighted in pink), and the values ​​of the amount of dust are not rounded.

Considering that we need guidelines for dust concentration, the data from these two GOSTs are summarized in one table.

Table 1 cleanliness classes for airborne particles for clean rooms and clean areas

ISO Class N (N - classification number)	Maximum permissible concentration of particles, particles/m 3, with sizes equal to or greater than the following values, µm						MK
	0,1	0,2	0,3	0,5	1,0	5,0
ISO Class 1	10	2	nd	nd	nd	nd	nd
ISO Class 2	100	24	10	4	nd	nd	nd
ISO Class 3	1000	237	102	35	8	nd	nd
ISO Class 4	10000	2370	1020	352	83	nd	nd
ISO Class 5	100000	23700	10200	3520	832	29	5
ISO Class 6	1000000	237000	102000	35200	8320	293	50
ISO Class 7	NK	NK	NK	352000	83200	2930	100
ISO Class 8	NK	NK	NK	3520000	832000	29300	500
ISO Class 9	NK	NK	NK	35200000	8320000	293000	NK
Due to the uncertainties involved in particle counting, concentration values ​​of no more than three significant figures should be used for classification.

nc - countable concentration of particles of a given size for a given class is not controlled,

nd - particles of this size and larger should not be in the air,

MK - maximum permissible number of microorganisms, pcs/m 3

I have not yet found data related to the category of air cleanliness in domestic and office premises. Although I came across standards for clean rooms in medical institutions.

And knowing about the strict regulation of dust content in the air of clean industrial premises having a category, we can conclude that classes (categories) 7, 8, 9 are closest to office (7, 8) and household (9) premises.

Conclusion

Although GOST defines the category “for clean rooms and clean areas,” we are interested in ISO class 9, as (in my opinion) the closest to domestic premises, and ISO classes 7 and 8 for office premises equipped with air conditioning and air filtration, respectively.

The given figures can only be used as guidelines when carrying out assessment calculations for air filters of electronic and computer equipment and its operating regulations.

For accurate calculations, you should use the values ​​of dust levels specified in the passports of the premises where the equipment is located.

FYI The amount of dust in the atmospheric air can vary greatly. In areas with continuous green areas, above lakes and rivers, the amount of dust in the air is less than 1 mg/m3, in industrial cities - 3-10 mg/m3, in cities with poorly equipped streets - up to 20 mg/m3. Particle sizes range from 0.02 to 100 microns. Sanitary standards of the USSR-(SN 245-71) limit the average daily maximum permissible concentration of non-toxic dust in the atmospheric air of populated areas 0.15 mg/m3, however, in reality the concentration of dust is often higher, so it is better to proceed from experimental data on the degree of air pollution in a particular area. The concentration of suspended substances in the atmospheric air of Novosibirsk exceeds the Maximum Permissible Concentrations. If the maximum permissible concentration is 0.15 mg/m³, then in 2004 it was 0.26 mg/m³, in 2005 – 0.21 mg/m³, and in 2006 – 0.24 mg/m³. In the center of the capital of Estonia, Tallinn, a fine dust concentration of up to 0.07 mg/m 3 was recorded. In England, the air in cities where residential areas with fireplace heating are combined with large industrial enterprises is characterized by a dust content of up to 0.5 mg/m3, In the USA, the concentration of dust in the air reached 1.044 mg/m3, In Germany, the highest concentration of dust was observed in the cities of the Ruhr - up to 0.7 mg/m 3. The main danger to the human body is precisely particles ranging in size from tenths of a micrometer to 10 and especially up to 5 microns. The structure of dust in domestic premises and offices differs from atmospheric dust and dust in industrial premises and significantly depends on their decoration and the equipment and furniture placed in the room.

Prepared by A. Sorokin,

performed by aspiration weight (gravimetric) method using an electric aspirator (Fig. 2).

Rice. 2. Electric aspirator for collecting single dust samples

Dust is a dispersed system, where the crushed substance (dispersed phase) is in a continuous dispersed medium, i.e. These are suspended in the air, slowly settling solid particles ranging in size from 0.001 to 100 microns or an aerosol.

The principle of operation of the electric aspirator is to draw a certain volume of air through the aspirator.

torus with the deposition of dust particles on a paper filter. The method is based on collecting dust from air sucked through a filter at a standard aspiration rate of 10-20 l/min. followed by conversion to 1 m 3 of air (1 m 3 = 1000 l). Air analysis can be carried out both in samples taken once (duration of sampling 15-20 minutes), and repeatedly at least 10 times a day at regular intervals with averaging of the data obtained (the frequency of sampling during the day determines the boron to assess the type of MPC - average daily or maximum one-time). Air sampling is carried out in the breathing zone. To take a sample, the filter is fixed in the allonge (cartridge) of the electric aspirator, and air is passed through it at a speed of 20 l/min. ( V ) for 10 minutes. ( T ). The volume of the selected air sample is calculated using the formula:

υ=Т V,

Where T – sampling time, min., V – sampling rate, l/min. A non-hygroscopic aerosol filter, which consists of ultra-thin polymer fibers fixed in a paper ring, is weighed on an analytical balance with an accuracy of 0.1 mg to ( A 1 ) and after ( A 2 ) air sampling. Dust content X 3 air in 1 m is calculated using the formula:

X = [(A 2 − A 1) 1000]/ υ,

Where X – dust content in the air, mg/m3; A 1 And A 2 − filter weight before and after sampling, mg; υ − air volume, l.

For the hygienic assessment of air pollution by dust, the established dust content is compared with the maximum or average daily maximum permissible concentration of non-toxic dust in the atmospheric air; characterize the dispersed and chemical composition, morphological structure, electrical state, nature (organic, inorganic, mixed) and mechanism of formation (aerosol disintegration or condensation).

Hygienic dust standards for atmospheric air

− maximum one-time MPC mr 2 = 0.5 mg/m 3,

− average daily maximum permissible concentration s/s 3 = 0.15 mg/m 3 .

In health care facilities, requirements for dust content in the air are determined by the classification of premises by cleanliness and are limited to particle sizes of 0.5 microns and 5.0 microns.

In industrial premises: MPC of non-toxic dust = 10 mg/m 3 , MPC of dust containing free silicon dioxide = 1-2 mg/m 3 .

3. Determination of microbial air pollution osu-

It is carried out by the aspiration method in Kro-tov’s modification. The Krotov apparatus is an aspirator with a removable lid. The air being tested is sucked in at a speed of 20-25 l/min. through a wedge-shaped slot in the cover of the device. When transferring the Krotov apparatus from one room to another, its surface is treated with a disinfectant solution. An air sample is taken for 10 minutes. ( T ) at a speed of 20 l/min ( V ). The volume of the selected air sample is calculated using the formula.