Diseases caused by exposure to the heating microclimate of foundry (hot) shops and their prevention. Air spraying of workplaces Air shower, its purpose and fields of application

The intensity of human thermal radiation is regulated based on the person's subjective sensation of the radiation energy. According to the requirements of regulatory documents, the intensity of thermal radiation working from the heated surfaces of technological equipment, lighting devices should not exceed:

- 35 W / m 2 with irradiation of more than 50% of the body surface;

- 70 W / m 2 with irradiation from 25 to 50% of the body surface;

- 100 W / m 2 with irradiation of no more than 25% of the body surface.

From open sources (heated metal and glass, open flame), the intensity of thermal irradiation should not exceed 140 W / m2 when irradiating no more than 25% of the body surface and the mandatory use of personal protective equipment, including face and eye protection.

Sanitary standards also limit the temperature of heated surfaces of equipment in the working area, which should not exceed 45 ° C, and for equipment inside which the temperature is close to 100 ° C, the temperature on its surface should not exceed 35 ° C.

In a production environment, it is not always possible to meet regulatory requirements. In this case, measures should be taken to protect workers from possible overheating:

- remote control of the technological process;

- air or water-air spraying of workplaces;

- arrangement of specially equipped rooms, cabins or work places for short-term rest with the supply of conditioned air;

- use of protective screens, water and air curtains;

- the use of personal protective equipment, overalls, special footwear, etc.

Shielding of radiating surfaces is one of the most common methods of dealing with heat radiation. There are three types of screens:

1. Opaque - such screens include, for example, metal (including aluminum), alpha-foil (aluminum foil), lined (foam concrete, foam glass, expanded clay, pumice), asbestos, etc. In opaque screens, the energy of electromagnetic waves interacts with screen material and is converted into heat energy. By absorbing radiation, the screen heats up and, like any heated body, becomes a source of thermal radiation. In this case, the radiation by the screen surface opposite to the shielded source is conventionally considered as transmitted radiation from the source.

2. Transparent - these are screens made of various glasses: silicate, quartz, organic, metallized, as well as film water curtains (free and flowing down the glass), water-dispersed curtains. In transparent screens, radiation, interacting with the substance of the screen, bypasses the stage of conversion into thermal energy and propagates inside the screen according to the laws of geometric optics, which ensures visibility through the screen.

3. Semi-transparent - these include metal nets, chain curtains, screens made of glass reinforced with a metal mesh. Semi-transparent screens combine the properties of transparent and opaque screens.

By the principle of operation, the screens are divided into:

- heat-reflecting;

- heat-absorbing;

- heat sinks.

However, this division is rather arbitrary, since each screen has the ability to simultaneously reflect, absorb and remove heat. The assignment of the screen to one or another group is made depending on which of its abilities is more pronounced.

Heat-reflecting screens have a low degree of surface blackness, as a result of which they reflect a significant part of the radiant energy incident on them in the opposite direction. Alfol, sheet aluminum, galvanized steel, and aluminum paint are widely used as heat-reflecting materials in the construction of screens.

Shields made of materials with high thermal resistance (low thermal conductivity) are called heat-absorbing screens. Refractory and heat-insulating bricks, asbestos, slag wool are used as heat-absorbing materials.

The most widely used heat-dissipating screens are water curtains that freely fall in the form of a film, irrigate another shielding surface (for example, metal), or enclosed in a special casing made of glass (aquarium screens), metal (coils), etc.

The effectiveness of protection against thermal radiation using screens is estimated by the formula:

where Q bz -the intensity of thermal radiation without the use of protection, W / m 2, Q s -the intensity of thermal radiation with the use of protection, W / m 2.

The multiplicity of attenuation of the heat flux, t, by the protective screen is determined by the formula:

where Q bz - flux intensity of the emitter (without using a protective screen), W / m 2, Q s - the intensity of the thermal radiation flow from the screen, W / m 2.

The heat flux screen transmittance, τ, is equal to:

τ \u003d 1 / m. (2.8)

Local forced ventilation is widely used to create the required microclimate parameters in a limited amount, in particular, directly at the workplace. This is achieved by creating air oases, air curtains and air showers.

The air flow directed directly to the worker allows to increase the heat transfer from his body to the environment. The choice of the air flow rate depends on the severity of the work to be done, as well as on the intensity of the radiation, but it should, as a rule, not exceed 5 m / s, since in this case the worker experiences unpleasant sensations (for example, tinnitus). The effectiveness of air showers increases when the air directed to the workplace is cooled or when finely atomized water is added to it (water-air shower).

An air oasis is created in separate areas of high-temperature working rooms. For this, a small working area is covered with light portable partitions 2 m high and cool air is fed into the fenced space at a speed of 0.2 - 0.4 m / s.

Air curtains are created to prevent the penetration of cold outside air into the room by supplying warmer air at a high speed (10 - 15 m / s) at a certain angle towards the cold flow.

Air showers are used in hot workshops at workplaces under the influence of a high-intensity radiant heat flux (more than 350 W / m 2).

The effectiveness of air showers increases when the air directed to the workplace is cooled or when finely atomized water is added to it (water-air shower).

Appointment of air showers. An air shower is the flow of air directed to a confined workplace or directly to a worker. The use of air showers is especially effective when the worker is exposed to heat. In such cases, an air shower is arranged at the place of the longest stay of a person, and if short breaks for rest are provided in the work, then at the place of rest. The upper parts of the body, as the most sensitive to the effects of heat radiation, should be blown with air.

The speed and temperature of the air at the workplace when using air showers is prescribed depending on the intensity of thermal radiation of a person, the duration of his continuous stay under radiation and the temperature of the surrounding air.

Air spraying should be provided at permanent workplaces with an irradiation intensity of 350 W / m2 or more. At the same time, an air flow can be directed to a person at a speed of o \u003d 0.5 ... 3.5 m / s and a temperature of 18-24 ° C, depending on the period of 1 year and the intensity of physical activity.

Constructive execution of air showers. The air coming out of the choke tube should wash the head and body of a person at a uniform speed and have the same temperature.

The axis of the air flow can be directed to the human chest horizontally or from above at an angle of 45 ° while ensuring the specified temperatures and air velocities at the workplace, as well as to the face (breathing zone) horizontally or from above at an angle of 45 ° while ensuring the permissible concentrations of harmful secretions.

The distance from the spray nozzle to the workplace should be at least 1 m with a minimum diameter of the nozzle of 0.3 m. The width of the working platform is assumed to be 1 m.

According to their design, spraying installations are divided into stationary and mobile.

Fan type BA-1... The unit consists of a cast iron frame on which an axial fan No. 5 of the MC type with an electric motor is mounted, a shell with a collector and a mesh, a confuser with guide vanes and a fairing, a pneumatic nozzle of the FP-1 or FP-2 type and pipelines with fittings and flexible hoses for supply water and compressed air. The unit is manufactured with a fan rotation around the frame axis up to 60 ° and a vertical lift of the trunk by 200-600 mm.

In addition to the fan type VA units, the PAM-24 rotating unit in the form of an axial fan 800 mm in diameter with an electric motor on one shaft is used. The capacity of the unit is 24,000 m3 / h with a jet range of 20 m. The unit is equipped with a pneumatic nozzle for spraying water in an air stream.

Stationary shower units both untreated and treated (heated, cooled and humidified) outside air are supplied to the spray nozzles. Mobile units supply room air to the workplace. Water can be sprayed into the air stream supplied by them. In this case, water droplets, falling on clothing and exposed parts of the human body, evaporate and cause additional cooling.

Spraying of fixed workplaces can be carried out by spraying nozzles of various types. The branch pipes have a compressed outlet section, a swivel joint for changing the direction of the air flow in the vertical plane and a rotary device for changing the direction of the flow in the horizontal plane within 360 °. Regulation of the direction of the air flow in the branch pipes is carried out in the vertical plane by turning the guide vanes, and in the horizontal plane using a rotary device. The PD branch pipes can be used both with nozzles for pneumatic water spraying, and without them. The branch pipes should be installed at a height of 1.8-1.9 m from the floor (to the bottom edge).

Calculation of air showers. When combating thermal radiation for air spraying systems operating in the outside air, the design parameters of the outdoor air of category B are taken, and in other cases, the design parameters of the outdoor air of category A for the warm season and category B for the cold season.

Calculation of the sprinkler installation (according to the method of Doctor of Technical Sciences P.V. Uchastkin) is reduced to determining the cross-sectional area of \u200b\u200bthe sprinkler pipe Fo from the condition of ensuring the normalized air parameters at the workplace. The calculation is carried out in the following order.

An air shower is the flow of air directed to a confined workplace or directly to a worker.

The use of air showers is especially effective when the worker is exposed to heat. In such cases, an air shower is arranged at the place of the longest stay of a person, and if short breaks for rest are provided in the work, then at the place of rest.

The upper parts of the body, as the most sensitive to the effects of heat radiation, should be blown with air.

Fan type BA-1

1 - electric motor;
2 - shell;
3 - grid;
4 - axial fan;
5 - confuser;
6 - fairing;
7 - pneumatic nozzle;
8 - guide vanes

Constructive execution of air showers.

The air coming out of the choke tube should wash the head and body of a person at a uniform speed and have the same temperature.

The distance from the spray nozzle to the workplace should be at least 1 m with a minimum diameter of the nozzle of 0.3 m. The width of the working platform is assumed to be 1 m.

Unit design VA-1

According to their design, spraying installations are divided into stationary and mobile.

A fan-shaped unit of type VA-1 consists of a cast-iron frame on which an axial fan No. 5 of type MC with an electric motor is mounted, a shell with a collector and a mesh, a confuser with guide vanes and a fairing, a pneumatic nozzle of the FP-1 or FP-2 type and pipelines with fittings and flexible hoses for water and compressed air supply. The unit is manufactured with the fan turning around the axis of the bed up to 60 ° and lifting the barrel vertically by 200-600 mm.

In addition to the fan type VA units, the PAM-24 rotating unit in the form of an axial fan 800 mm in diameter with an electric motor on one shaft is used. The capacity of the unit is 24,000 m 3 / h with a jet range of 20 m. The unit is equipped with a pneumatic nozzle for spraying water in an air stream.

Stationary spray units supply both untreated and treated (heated, cooled and humidified) outside air to the spray nozzles. Mobile units supply room air to the workplace. Water can be sprayed into the air stream supplied by them. In this case, water droplets, falling on clothing and exposed parts of the human body, evaporate and cause additional cooling.

Spraying of fixed workplaces can be carried out by spraying nozzles of various types. GIPD branch pipes have a compressed outlet section, a swivel joint for changing the direction of the air flow in the vertical plane and a rotary device for changing the direction of the flow in the horizontal plane within 360 °.

The direction of the air flow in the PD nozzles is controlled in the vertical plane by turning the guide vanes, and in the horizontal plane using a rotary device. PD branch pipes can be used both with nozzles for pneumatic water spraying, and without them. The branch pipes should be installed at a height of 1.8-1.9 m from the floor (to the bottom edge).

Air spraying is used to create the required meteorological conditions at permanent workplaces under heat irradiation and in open production processes, if the technological equipment emitting harmful substances does not have shelters or local exhaust ventilation. When spraying, either outside air can be supplied with its processing in the supply chambers (cleaning, cooling and heating in the cold season, if necessary), or internal air. When designing air spraying, measures must be taken to prevent the blowing of industrial hazardous emissions to nearby permanent workplaces. The air jet should be directed so that, if possible

it excluded the suction of hot or gas-polluted air. Systems supplying air to air showers are designed separately from systems

other purpose. Air distributors are usually installed at a height of at least 1.8 m from the floor (to their lower edge). The distance from the place of air release to the workplace should be taken at least 1 m, and the air flow should be directed: -to the person's chest horizontally or from above at an angle of up to 45 ° to ensure the normalized temperatures and air velocity at the workplace; -in the face (breathing zone) horizontally or from above at an angle of up to 45 ° to ensure the permissible concentration of gas and dust at the workplace in this case, the normalized temperature and speed of air movement must be ensured. Depending on the air supplied and treatment, air shower systems are divided into: 1. supplying external air with treatment, 2. supplying external air without treatment, 3. supplying internal air with cooling, 4. supplying internal air without treatment. Falling air flow is a type of air spraying. It is carried out by feeding from a close distance to fixed workplaces or to places of rest of workers. The drop-down flow allows to provide at a workplace where conditions do not meet sanitary standards, favorable environmental conditions with low consumption of cold, heat and electricity. Air oases- a certain volume of the room in which meteorological conditions are maintained that differ from the entire volume of the room. Arranged in rooms with excess heat and high heights. A small area of \u200b\u200bthe workshop, which is the place of permanent residence of the service personnel, is fenced off from the entire workshop with partitions 2-2.2 m high and flooded with cold air.

14. Measures to combat mechanical and aerodynamic noise generated by ventilation units.

If a complex sound does not contain clearly expressed frequency components

put, they call him noise. To assess the noise, spectroscopic

trograms in which the sound energy of a complex sound is distributed over frequencies or frequency bands.

Vibration isolation of ventilation units with spring dampers,

Application of soundproofing walls in the ventilation chamber,

The device of false ceilings.

Arrangement of floating floors and reduction of air velocity.

To reduce the level of mechanical noise, it is necessary to connect the air ducts to the fan through flexible connectors.

To reduce the level of aerodynamic noise on the main sections of the air ducts, sound attenuators (plate and tubular) should be provided

Noise reduction measures in ventilation and air conditioning systems are based on two types of operations, applied simultaneously or sequentially:

Measures related to the source of the noise itself;

Measures related to noise transmission channels.

Sound waves appear as a result of non-stationary processes

owls, always accompanying the steady-state fan operation.

Velocity pulsations and pressure fluctuations in the air flow,

flowing through the fan cause aerodynamic noise (vortex noise, noise from local flow irregularities, rotation noise)

vibrations of the ventilation elements

installations cause mechanical noise. Excitation of mechanical noise in fans is usually of shock nature - in ball bearings, drive, knocking in the gaps.

The noise generated by the ventilation unit is transmitted as follows

in the following ways:

a) by the air inside the air ducts into the room through

supply and exhaust grilles or into the atmosphere through the intake grilles of supply systems or through the shafts of the exhaust systems; b) through the walls of transit air ducts into the room through which they are laid;

c) by the air surrounding the ventilation unit, to

the enclosing structures of the chamber and through them into adjacent rooms

schenia. Each of the listed noise transmission paths determines the appropriate measures that must be provided to reduce noise in rooms with a standardized sound level.

NORMALIZATION OF NOISES

Noises are normalized based on their permissible impact on the body

humanism, that is, an effect in which noise either does not affect a person's well-being at all or this effect is insignificant. (63-8000 Hz)

ACOUSTIC CALCULATION OF THE VENTILATION SYSTEM The task of acoustic calculation of ventilation systems is to determine the level of sound pressure created at the design point by the operating ventilation unit.

REDUCTION ACTIONS

SOUND PRESSURE Reduction of sound pressure levels at constant

workplaces or at the calculated points of the premises can be carried out

using a set of the following measures: 1) installation of fans, the most advanced in terms of acoustic characteristics; 2) the choice of optimal operating modes of the fans: a) at the maximum efficiency; b) with the minimum possible pressure developed by the fan 3) reducing the speed of air movement in the outlets, elbows, tees and other elements of the ventilation network: a) up to 5-6 m / s in the main air ducts and up to 2-4 m / s in the branches for public buildings and auxiliary buildings of industrial enterprises; b) up to 10-12 m / s in main air ducts and up to 4-8 m / s in branches for industrial buildings. 4) a change in the acoustic qualities of a room, a decrease in the sound power level of noise sources along the path of sound propagation by installing mufflers or lining the inner surfaces of air ducts with sound-absorbing materials.

SILENCER CONSTRUCTIONS

To muffle noise in ventilation units, use

silencers of dissipative action, i.e. those in which there is

scattering of sound energy.

By design, mufflers are divided into tubular, honeycomb

high, lamellar and chamber

VIBRATION INSULATION OF VENTILATION UNITS

Vibrations arising during the operation of the ventilation unit,

are transmitted to the ductwork and the base on which the unit is mounted Vibrations cause structural sound *. When the fan is installed on a foundation, ground vibrations are transmitted to the foundations, walls and floors of the building. When the fan is installed on the floor, the structural sound is directly transmitted to the underlying room. Structural sound transmission to the base can be reduced by installing fans on vibration dampers.

An air shower is a localized stream of air directed at a person. In the area of \u200b\u200bthe air shower, conditions are created that differ from those in the entire volume of the room. With the help of an air shower, the following air parameters can be changed at the location of a person: mobility, temperature, humidity and the concentration of one or another hazard. Typically, the area of \u200b\u200baction of an air shower are: fixed workplaces, places of the longest stay of workers and places of rest. In fig. 3.19 schematically depicts an air shower used to create the necessary conditions in the workplace.

The most common use of air showers is in hot workshops in workplaces exposed to heat radiation.

Fig. 3.18. Onboard suction: a - simple; b - overturned; c - in advance

Fig. 3.19. Air shower: a - vertical; b - inclined; c - group

3.0 m / s, the temperature can vary from 16 to 24 ° C. If an air shower is used to combat dust, the air speed should not be higher than 0.5-1.5 m / s in order to prevent the dust that has settled on the floor from rising.

The design of the air outlet (supply nozzle) has a great influence on the efficiency of the air shower. It is advisable to have this device rotatable and at the same time provide for the possibility of changing the angle of inclination of the flow axis by introducing rotary blades. In fig. 3.20 shows the supply nozzles designed by V.V. Baturin, made taking into account these two requirements.

Classification of ventilation and air conditioning systems

Fig. 3.20. Supply nozzles designed by V.V.Baturin: a - at the top supply; b - with bottom air supply

For the air shower, outside air or air taken from the room can be used. The latter, as a rule, undergoes appropriate processing (most often cooling). Outside air can also be processed to give it the required parameters.

Dusters can be stationary or mobile.

In mobile units, air from the room is used, which is often treated by spraying water in the outgoing air stream.

The adiabatically evaporating water allows the air temperature to be reduced. In fig. 3.21 and 3.22 show water-air showers of this type of construction of the Moscow and Sverdlovsk institutes of labor protection.

In air curtains, as well as in air showers, the main property of the supply torch is used - its relative range. Air curtains are arranged in order to prevent the flow of air through technological openings or gates from one part of the building to another or outside air into production facilities. In fig. 3.23 shows diagrams of air curtains designed to prevent or drastically reduce the penetration of cold outside air through the gate into the workshop. The air supplied to the curtain can be preheated, and then the curtains are called air-heat curtains.

Air curtains designed to prevent the penetration of cold air should be provided at gates that open more often than five times or for at least 40 minutes per shift, as well as at technological openings of heated buildings, located located in areas with a design outside air temperature for designing a heating system- 15 ° С and below, when the possibility of device gateways is excluded. If the decrease in indoor air temperature(by technological or sanitary- hygiene reasons) is not allowed, curtains can be designed for any duration of opening and any design outdoor temperature. This requires technical- economic justification for this decision.

Fig. 3.21. Small model MIOT type water-air shower:

Fig. 3.22. Mobile fan-shaped unit SIOT-3:

Fig. 3.23. Air curtains: and - operating principle; b - different ways of air supply:

I - bottom air supply; II - side air discharge from one side; III - the same on both sides

1 - pipeline for water supply

from the water supply; 2 - casing; 3 - electric motor; 4 - axial fan; 5 - drain pipe; 6 - stand 1 - axial fan; 2 - electric motor; 3 - nozzles; 4 - metal fairing; 5 - stand on wheels; 6 - pipeline for supplying water from the water supply

In the case of a short-term (up to 10 minutes) opening of the gate, as a rule, it is allowed to reduce the air temperature at workplaces protected from the blowing of air rushing through the gate, screens or partitions. The degree of reduction depends on the nature of the work performed: with light physical work - up to 14 ° С, medium-heavy work - up to 12 °, hard work - up to 8 °. If there are no permanent jobs in the area of \u200b\u200bthe gate, the temperature in the working area of \u200b\u200bthis area can be reduced to + 5 °.

The so-called air buffers created by supplying warm air to the vestibules of public buildings (shops, clubs, theaters, etc.) are very close to air-thermal curtains in their purpose.

At present, the necessary air conditions at the workplace are quite often created using the device of special ventilated cabins. In such cabins, conditions are maintained that are different from those in the entire volume of the production room. This is achieved most often by supplying specially prepared air to the cabins: in hot shops - cooled, in cold, unheated rooms - heated. Ventilated cabins can be classified as local ventilation systems. Naturally, their use is possible when the workplace is strictly fixed, for example, at the control panel. In fig. 3.24 shows a ventilated cabin for a crane control station, developed by the Leningrad Institute for Labor Protection.

General ventilation systems can be supply and exhaust (Fig. 3.5, 3.6, 3.9). When using general exchange systems, the task is to create the necessary conditions for the air environment in the entire volume of the room or in the volume of the working area. In contrast to local systems, in this case, all harmful emissions emitted in the room are distributed throughout the entire volume. Consequently, the main task that must be solved in the design of the systems under consideration is that the content of this or that harmfulness in the room air does not exceed the maximum permissible concentration, and the values \u200b\u200bof meteorological parameters meet the relevant requirements.

Often, the room is equipped with supply and exhaust general ventilation systems (Fig. 3.10).

The general exchange method for creating specified air conditions is also widespread in combination with air conditioning systems.

Fig. 3.24. Ventilated cab

In this course, a lot of attention is paid to this method, since it is the main one for MO objects.