Name the types of artificial grounding.
Remote and contour + horizontal and vertical (conditional)
20. How can the resistance of the ground electrode be reduced?
The total ground resistance depends, as mentioned above, on the resistance of the soil layers adjacent to the ground electrode. Therefore, it is possible to achieve a decrease in ground resistance by lowering the soil resistivity only in a small area around the ground electrode.
An artificial decrease in soil resistivity is achieved either chemically with the help of electrolytes, or by laying ground electrodes in pits with bulk coal, coke, clay.
dustiness
1, What is called dust?
Dust is called crushed particles of solid matter, capable of being suspended in the air for some time.
2. What is the hygienic hazard of dust?
Dust is a hygienic hazard, as it adversely affects the human body. Under the influence of dust, diseases such as pneumoconiosis, eczema, dermatitis, conjunctivitis, etc. can occur. The finer the dust, the more dangerous it is for humans. Particles ranging in size from 0.2 to 7 microns are considered the most dangerous for humans, which, getting into the lungs during breathing, are retained in them and, accumulating, can cause disease.
There are three ways dust can enter the human body: through the respiratory system, the gastrointestinal tract and the skin.
3, what is the MPC of a harmful substance?
The maximum permissible concentration (MAC) is a sanitary and hygienic standard approved by law. MPC is understood as such a concentration of chemical elements and their compounds in the environment, which, under daily influence for a long time on the human body, does not cause pathological changes or diseases established by modern research methods at any time in the life of the present and subsequent generations.
The essence of the weight method for determining the concentration of dust.
The essence of the method lies in the fact that a certain volume of dusty air is passed through a highly efficient filter and the mass concentration of dust is calculated from the increase in mass and volume of the filtered air:
5. How is dust count measured?
Its essence lies in the preliminary separation of dust from the air and its deposition on glass slides, followed by counting the number of particles using a microscope. By dividing the number of particles determined by the calculation by the volume of air from which they are deposited, the counting concentration of dust (particles / l) is obtained:
6. How is the volume of air sucked through the filter measured by the gravimetric method of measuring dust concentration?
V0 is the volume of filtered air reduced to normal conditions (temperature 0 °C and barometric pressure B0 = 760 mm Hg), m3.
where P0, P – barometric pressure, Pa, respectively, under normal and operating conditions (P0 = 101325 Pa, P = B × 133.322 Pa); T is the air temperature at the place of dust sampling, °C; V is the volume of air passed through the filter at temperature T and pressure B, m3,
where w– volumetric rate of air suction through the filter, l/min;
t– duration of sampling, min.
7. What sanitary and technical measures allow to reduce the concentration of dust at workplaces to the MPC level?
7.4. To reduce dust and create acceptable microclimate parameters in the cabs of machines, it is necessary to seal doors and windows and use installations for cleaning, heating or cooling air.
7.5. The use in sections of machines with internal combustion engines without effective means of neutralization and purification of exhaust gases is not allowed. Neutralizers and cleaning agents must ensure the content of harmful substances in the air of the working area at levels not exceeding the MPC. The use of leaded gasoline is prohibited.
7.6. The schedule of movement of vehicles should not allow their accumulation with running engines on work sites, ledges, sections of the road. The minimum distance between heavy dump trucks (10 tons and above) must be at least 30 m. When organizing loading operations, preference should be given to a loop scheme for the entrance of vehicles to the loading site.
7.7. The rock mass loaded into the body of a dump truck, wagon or onto a conveyor belt in the warm season should be irrigated. The irrigation flare must cover the loading area.
7.8. To improve air exchange in the sections, guides and protective aerodynamic devices that regulate natural air flows should be provided.
7.9. During long inversions and calms in case of accumulation of harmful gases at workplaces in stagnant zones of cuts with a depth of more than 100 m, artificial ventilation using special devices should be provided.
7.10. When designing, manufacturing or importing mining, transport and other machines, one should take into account their possible use in various climatic and geographical regions and mountain and geological zones of the country (presence of: polar day and night, permafrost, specifics of rocks, strong winds, calm, temperature inversions, a wide temperature range of outdoor air from + 40 °С to - 60 °С, prolonged fogs), as well as the content of toxic substances in exhaust gases, which must comply with domestic standards.
Objective
Determine the dust content of the air of industrial enterprises in a laboratory.
Work tasks
Determine the conditions under which there is dust in the air of industrial premises. Determine the most suitable research method 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 the approved state standards.
Supporting funds
Instruments and materials for research - electric aspirators -
tori, 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) - air movement stimulator.
2. Dust chamber to create artificial conditions for dusty air.
3. Devices for spraying a sample of dust in a 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: subdivide research in industry and for scientific purposes. In industry, the dust content of air in the breathing zone of workers at workplaces is examined for a special assessment of working conditions or when compiling a map of working conditions, as well as when emitting dusty air into the atmosphere, according to a unified methodology. For scientific purposes, the study of air dust content is carried out depending on the goal set according to the appropriate methods developed separately for each type of study. Research methods: weight, counting, indirect.
2. Methods for studying the dust content of air
When assessing working conditions, air quality, the degree of its 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 the filter and determine its weight. In Russia and a number of other states, the weight method is standard. When using the weight method, at least one day is required.
The calculation of the weight concentration of dust in mg / m 3 is carried out according to the formula
where t 1 and t 2- filter weight before sampling and after sampling, mg;
v- speed of sampling on the device, l/min;
t- duration of sampling, min;
1000 - air volume conversion factor, l. on m 3.
The weight method has several varieties depending on the material of the absorber. The simplest, most convenient and more advanced of them is the method using analytical aerosol filters (APA), in which the Petryanov filter - FP is used as a filter element. It consists of a uniform layer of ultra-fine polymer fibers on or without a gauze backing. To study the dust content of air, AFA-VP-18 filters are usually used (sometimes the letter P is omitted, for example, AFA-V-18. “V” means “weight”, the numbers “18” or “GO” indicate the filtering surface of the filters, cm 2) . In practice, other brands of AFA filters are also used, for example, AFA-BA-20, AFA-XM-20, etc., which are used for bacterial, dispersion and chemical analyzes of the air.
Conimetry of dusty air.
During air sampling, the filter sometimes gets large
particles that are not harmful to the body. They distort the true result when weighing. At the same time, smaller particles representing
a great danger to the body, often not captured by the filter. By
To this, along with the use of the weight method, a counting (conimetric) method is used, which gives data on the magnitude and quantity
dust particles 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
method is to count the number of dust particles contained in 1 cm 3 of the air under study. The method serves as an additional characteristic to the standard weight method.
indirect methods. In addition to weighting and counting methods, there are indirect ones, when dust content is judged by a number of indicators of the physical properties of dusty air or dust (optical properties, electric charge, light reflection, radioactivity, etc.). The control is carried out by such devices as, for example, photodust meter F-1, radiometric device IZV-1, dust meter DPV-1, 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 measurement at any point in the room. The disadvantage is a rather significant error (up to 30% for some devices), depending on the properties of dust or gas, and a narrow scope for a certain type or type of dust.
3. Research methodology
1. To study the methodology and instruments for determining the dust content of air.
2. Experimentally determine the amount of dust in
one cubic meter of air; write down the data in the protocol, table 1.1.
3. Compare the obtained results 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.
Federal Agency for Sea and River Transport
Federal State Budgetary Educational Institution
Higher professional education
"STATE MARITIME 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 the factor
DUST EXPOSURE ASSESSMENT
Cadet group 1922
Somkhishvili Irma
Checked by: senior lecturer
Pisarenko G.P.
Option 22
I. PURPOSE OF THE WORK
To study the general properties of industrial dust and the requirements of sanitary standards; familiarization with the device and operation of the aspirator; determine the dust content in the air by weight and give a sanitary assessment of dust content.
II. GENERAL INFORMATION ABOUT INDUSTRIAL DUST
Industrial dust is called 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, which is 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, 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, dust particles smaller than 10 microns are the most dangerous, as can be seen from the data given in Table 1.
Table 1
Of particular danger to the human body is dust consisting of particles of a toxic substance, or dust having sorbed toxic substances on the surface. For example, toxic dust includes coal sand, calcium carbide, lime, lead, etc. A feature is the presence of adsorbed carcinogenic substances on the surface of the particles, namely 3,4-benzpyrene, which 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, i.e. the concentration of dust, which can usually vary from 10 -8 to 10 5 mg/m 3 . Elevated concentrations of dust cause intense harmful effects on the human body.
According to the degree of impact on the human body, harmful substances (including aerosols) are divided into 4 hazard classes:
1st - substances are extremely dangerous;
2nd - highly hazardous substances;
3rd - moderately dangerous substances;
4th - substances of low danger.
The hazard class of harmful substances is established depending on the norms and indicators.
The assignment of a harmful substance to a hazard class is carried out according to the indicator, the value of which corresponds to the highest hazard class. It must also be borne 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 content of silicon dioxide in grain dust reaches 10%.
Prolonged contact with grain dust can lead to the development of pneumoconiosis. With short-term exposure to the mucous membrane of the eyes, upper respiratory tract, irritation and the development of inflammatory processes are caused. With a mechanical effect on the skin, bubble rashes occur ("grain scabies"), possibly also a bacteriological lesion with severe headache, chills, palpitations, dizziness and nausea ("grain fever").
To prevent the harmful effects of industrial dusts
a set of measures is used on the human body:
Maximum allowable concentrations (MACs) of various dusts in the air of the working area are developed and established;
Ventilation installations and aspiration systems are designed and installed;
Develop and apply personal protective equipment;
III. BASIC OPERATIONS AND CALCULATIONS ON THE ANALYSIS OF DUST IN THE WORKROOM
a) Dust protocol
b) Evaluation of the dust content of the workplace / room
1. To quantify a dusty working environment, it is necessary to know the mass of dust per unit volume. It is possible to determine the concentration of dust by various methods, the simplest and most reliable is by weight. The essence of the method consists in weighing a special filter before and after pulling a known volume of dusty air through it.
where: С – concentration of dust in the air, mg/m 3 ;
Р 1 – filter mass before dust extraction, mg;
Р 2 – filter mass after dust sampling, mg;
V 0 - the volume of air at the sample site, o C.
Vo = 
where: V is the volume of air drawn through the filter under the experimental conditions (at t (o C) and pressure B (hPa);
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 designed to determine the fire hazard category of a room with dust, is quite simple, the determination of 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 or fire hazard.
Before proceeding to the calculation of whether the room belongs to one of the C categories in terms of fire hazard, it is necessary to justify by calculation whether the room, where the formation of air suspension is possible, belongs to category B in terms of explosion and fire hazard.
The main calculation formulas are contained in section A.3 of Appendix A to SP 12.13130.2009.
In accordance with formula A.17 of the code of practice, the calculated mass of dust suspended in the room as a result of an emergency should be taken as the minimum of two values:
- the sum of the masses of swirling dust and dust that came out of the vehicles as a result of the accident;
- masses of dust contained in a dusty cloud, capable of burning out when an ignition source appears.
It should be noted here that not all dust is capable of burning; coefficient of participation of combustible dust in the 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 is about 200-250 microns.
Dust, consisting of particles of a larger size, 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 either with 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, which are 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 the critical one, i.e. capable of spreading fire. The mass of dust that can exit the apparatus as a result of an emergency is determined by the features 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 pass into the air suspension. Dust, which is released in small quantities in the production room in normal operation, settles on the enclosing structures (walls, floor, ceiling), on the surface of the equipment (cases of technological apparatuses, transport lines, etc.), on the floor under the equipment.
At the designed production, the frequency of dust collection is determined: current and general. According to SP 12, it is assumed 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 between current dust collections. Estimation of the proportion of dust deposited on a particular surface (accessible or hard-to-reach) is possible only experimentally or by modeling methods.
As a rule, it is also impossible to assess the efficiency of dust collection in the designed production facilities, therefore, it is conditionally assumed that all the dust emitted from the equipment into the room settles inside the room.
The amount of dust deposited on different parts of the surface located in the room is also different. Dust, which is released in normal mode, soars in the air and gradually settles on various surfaces due to gravity.
However, it is expected that the greatest amount of dust settles at the lower levels of the room, provided that the dust source (equipment) is also located at the lower level. It is obvious that horizontal surfaces can accumulate dust in practically unlimited quantities, while 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 / m 2, brick walls - 40 g / m 2, concrete walls - 30 g / m 2. Most likely, the given data 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 dusty cloud. It should be noted that there are no analytical expressions that can be used to calculate the volume of a dusty cloud in the domestic literature.
So far, such data have not been found in foreign fire-technical literature either, probably because such an approach is not used in the USA and Europe (meaning the calculation of categories). Therefore, in practice, it is necessary to estimate the volume of the dust cloud in some way.
For example, one can conditionally take a cone with a height from the floor to the dust source and a base with a radius several times greater than this height as a characteristic cloud shape. Although, I'm not sure how true this assumption is, since experimental data are not available.
In addition to the critical size, the stoichiometric dust concentration is also a determining parameter.
The stoichiometric concentration of dust is the concentration of dust at which it is completely burned, taking into account the amount of oxygen present in a unit volume of air.
The stoichiometric concentration of dust can be calculated by calculation only for substances and materials for which the chemical composition is known. These include most polymeric materials (polyethylene, polypropylene, polystyrene, etc.), various drugs, 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 the chemical composition of the corresponding material of which the dust.
The determination of the stoichiometric concentration is reduced to solving the following sequential tasks:
1. The chemical composition of the dust is found.
2. The chemical equation for the reaction of complete combustion of dust is written.
3. The mass of oxygen required for the 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 calculated temperature.
5. The mass of dust is determined, which can completely burn out in the mass of oxygen contained in 1 m 3 of air. The obtained value is the stoichiometric dust concentration in the dust cloud.
The definition of the category of a room with dust does not take into account such a fire hazard indicator as the lower concentration limit of flame propagation (LEL). As a rule, the concentration of dust in a dusty cloud in emergency situations exceeds the LEL.
And finally, a couple of very interesting videos about explosions in factories with dust. Even without knowledge of English, and so everything is intelligibly and interestingly shown. I recommend viewing!
Looking forward to seeing you again on fire safety!
Study of air dust content
Industrial premises
Guidelines for performing laboratory work
in the discipline "Life safety"
for students of all specialties
Novokuznetsk
UDC 658.382.3(07)
Reviewer:
Doctor of Technical Sciences, Professor
Department of technology and automation of forging and stamping production of SibSIU
Peretyatko V.N.
P24 Study of dust content in the air of industrial premises: Method. Dec./Comp.: I.G. Shilingovsky: SibGIU, Novokuznetsk 2007. - 19 p.
Methods for determining the dust content of air are considered, schemes for the construction of aspirators, a sampler, radiation devices and the rules for using them are given.
Designed for students of all specialties.
Laboratory work
Study of dust content in the air of industrial premises
Objective: to familiarize students with the basic methods and instruments for measuring the concentration of dust in the production room, as well as teach them how to measure and evaluate the value of dust concentration.
During the laboratory work, students should:
– get acquainted with the basic information about industrial dust, its sources and concentration measurement methods;
- to study the device for measuring the concentration of dust;
- to make an experiment .
Basic information about industrial dust
industrial dust are called solid particles suspended in the air of the working area ranging in size from several tens to fractions of a micron. Dust is also called 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, dust (aerosols) of disintegration and condensation are distinguished. The former are the result of production operations associated with the destruction or grinding of solid materials and the transportation of bulk materials. The second way of dust formation is the occurrence of solid particles in the air due to cooling or condensation of vapors of metals or non-metals released during high-temperature processes.
By origin, organic, inorganic and mixed dusts are distinguished. The nature and severity of harmful effects depend primarily on the chemical composition of the dust, which is mainly determined by its origin. Inhalation of dust can cause damage to the respiratory system - bronchitis, pneumoconiosis or the development of general reactions (intoxication, allergies). Some dusts are carcinogenic. The effect of dust is manifested in diseases of the upper respiratory tract, mucous membranes of the eyes, and 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 (dispersion) is of exceptionally high importance: visible dust (size over 10 microns) quickly settles out of 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), in the lungs it is retained up to 60 - 70%, but its role in the development of dust lesions is not decisive, since its total mass is small.
The harmful effect of dust is also determined by its other properties: solubility, shape of particles, their hardness, structure, adsorption properties, electrical charge. For example, the electrical charge of dust affects the stability of the aerosol; particles carrying an electric charge are 2 to 3 times more retained in the respiratory tract.
The main way to combat dust is to prevent its 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 conveying, remote control; replacement of dusty materials with wet, pasty ones, granulation; aspiration, etc.
Of great importance is the use of artificial ventilation systems, which complements the main technological measures to combat dust. To combat secondary dust formation, i.e. already settled dust enters the air, use wet methods of cleaning, air ionization, etc.
In cases where it is not possible to reduce the dust content of the air in the working area by more radical technological and other measures, individual protective equipment of various types is used: respirators, special helmets and spacesuits with clean air supplied to them.
Automatic devices for determining the concentration of dust include commercially available IZV-1, IZV-3 (air dust meter), PRIZ-1 (portable radioisotope dust meter), IKP-1 (dust concentration meter), etc.
The need for strict compliance with MPC requires systematic monitoring of the actual dust content in the air of the working area of the production facility.
Maximum permissible concentrations of dust
Table 1 - Maximum permissible concentrations of dust
Maximum Permissible Concentration (MPC) of a harmful substance is a concentration that, during daily work for 8 hours or another duration, but not more than 40 hours per week, during the entire working experience, cannot cause diseases or deviations in the state of health. To determine the dust content of air means to measure the dust content per unit volume of air, that is, to measure the concentration of dust. To determine the dust content in the air, sampling should be carried out in the breathing zone and the working zone under typical production conditions, taking into account all influencing factors.
Dust Meter
The device used is a radioisotope portable dust concentration meter “Priz-01”, designed for express analysis of dust concentration directly at workplaces and industrial sites.
The concentrator operates in semi-automatic mode: after cocking the sensor mechanism of the dust sampling operation and measuring the sample, it returns to its original position automatically.
The measured value of dust concentration is displayed in a digital field on the instrument panel.
Method for measuring dust concentration
Dust concentration measurement methods are divided into two groups: methods based on preliminary deposition (weight, radioisotope, optical, piezoelectric, etc.) and methods without preliminary dust deposition (optical, electrical, acoustic).
The main advantage of the methods of the first group is the ability to measure the mass concentration of nyla.
In laboratory work, weight and radioisotope methods for measuring dust concentration are used.
weight method It is based on pulling dusty air through a filter that traps dust particles. Knowing the mass of the filter before and after sampling, as well as the amount of drawn air, it is possible to determine the dust content per unit volume of air. Dust concentration is calculated by the formula:
where Δm is the mass of dust on the filter, mg;
V is the volumetric rate of air suction through the filter, l/min;
t – sampling time, min.
The place for sampling dusty air is a model of a production facility with sources of dust (aerosol) of various compositions placed in it.
The filters used are AFA filters made of FPP fabric (based on perchlorovinyl fabric). They are resistant to chemically aggressive environments, have a high percentage of particle retention.
The air movement stimulator is an electric aspirator model 882, which has a device for measuring the volumetric air movement velocity (rheometers). The optimal sampling rate is equal to the rate of human breathing (pulmonary ventilation) - 10 - 15 l / min.
Radioisotope method is based on the use of the property of radioactive radiation to be absorbed by dust particles. The dusty air is pre-filtered, then the mass of settled dust is determined by the attenuation of radioactive radiation when it passes through the dust sediment.
experimental part
Exercise. Measure the concentration of dust in the layout of the production facility and select respiratory protection equipment.
1. Familiarize yourself with the installation device.
2. Turn on the installation and the necessary devices.
3. Take three dust samples (the composition is set by the teacher).
4. Switch off the unit and devices.
.jpg)
