Filtering units (FVU)

Filter-ventilation units (FVU) provide purification of the air supplied to the shelter from radioactive, poisonous substances and biological aerosols; creating excess pressure in it and maintaining the required air composition.

The air entering the room must provide the air exchange necessary to maintain normal conditions, habitability (in terms of temperature, humidity and gas composition of the air environment) and create a backwater that prevents the penetration of contaminated air through leaks and cracks. Excess air is vented from the room to the atmosphere or neighboring rooms through slots and special overflow valves. Control over the amount of air supplied to the room and the overpressure of air in the room is carried out using instrumentation. Control over the working out of the filter-absorber for toxic substances is carried out by taking into account the total time of the filter, or with the help of a breakthrough warning.

FVU can work in two modes:

— Mode 1 “Clean ventilation mode”;

— Mode 2 “Filter ventilation mode”. [nine]

In the clean ventilation mode, the outside air is cleaned of dust, and in the filter ventilation mode, from RW, RH and BS.

Filtering units may include:

— anti-explosive devices;

— pre-filters;

– universal filters absorbers (FP-100U, FPU-200, FP-300),

— carbon monoxide filters;

– manual or electric fan;

– overpressure valves;

– air ducts;

– control and measuring devices.

Anti-explosive devices are designed to prevent blast waves from flowing into shelters.

Pre -filters are designed to clean the air from dust and coarse smoke.

According to their design, pre-filters are a set of straight and corrugated galvanized metal meshes enclosed in a metal case and impregnated with a viscous wetting agent consisting of a mixture of paraffin and rosin. Nets impregnated with a viscous wetting agent are capable of retaining coarse aerosols (including radioactive ones) on their surface due to their adhesion to a viscous wetting agent.

The filter absorber (AF) is designed to purify the air supplied to the shelter from toxic, radioactive substances and biological aerosols.

The principle of operation of the filter-absorber is that the air containing toxic, radioactive substances and biological agents is sucked in by a fan through the air ducts into the upper or lower end opening of the filter. First, it passes through an anti-aerosol filter, where it is cleaned of solid particles and fog, then through a charge, in which it is cleaned of substances in the air in vapor or gaseous states, and exits through a side opening in the filter housing. Purified air is supplied through air ducts to gas-protected premises.

If it is necessary to increase the productivity for parallel operation, no more than three filters are included in the column.

The filter absorber is a sealed metal cylinder with a lid and bottom, which is equipped with filter material and catalyst carbon (Fig. 6.2).

Rice. 6.2. Universal filter absorber:

1 – body; 2 – charge; 3 – nipple ring; 4 – plug with a handle;

5 – side hole; 6 – smoke filter; 7 – top cover; 8 – filter frame; 9 – bottom.

The filter-absorber has three openings in the body (two end and one side) and consists of a casing assembly, two perforated (perforated) cylinders covered with nets, a central pipe with holes, a bottom, a cover. To increase the strength of the casing, there are two transverse ridges in its upper and lower parts. For ease of carrying, two handles are fixed on the casing. Between the perforated cylinders is placed a coal-catalyst (charge), designed to absorb vapors of toxic and radioactive substances. Between the small perforated cylinder and the central pipe there is an anti-aerosol filter designed to capture radioactive dust, biological aerosols, toxic fumes and mists from the incoming air. The anti-aerosol filter is made up of a long strip of filter cardboard and has the shape of a ribbed barrel with a large number of longitudinal folds. Absorber filters can be equipped with overshoot warning devices (Fig. 6.3).

Rice. 6.3. Suction device for overshoot warning.

In civil defense shelters, filters of the type FP-100U, FPU-200, FP-300 are used (Fig. 62 and Tables 23, 24).

FP-100U FP-300
Rice. 6.4. Filter absorbers are universal.

Table 6.2.

Estimated protective power of absorber filters according to AHOV [47]

Name AHOV Filter absorbers
FP-100u FP-200-59 FPU-200 FP-300
Ammonia 16.6 g 23 g 23 g 11.3 g
Chlorine 760 g 1050 g 1050 g 516 g

Filter absorbers can be mounted in columns, two or three in each (Fig. 6.5). Mounting a column with more than three filters is not recommended, since this significantly increases the resistance of the filter collector.

In shelters of small and medium capacity, filter-ventilation units FVA are often used (Fig. 6.6). The FVA kit includes: an electric manual fan, one filter absorber or a column of filter absorbers, a hermetic valve, a flow meter, connecting and fasteners.

Rice. 6.5. Scheme of mounting a column of two FPs. Rice. 6.6. Filtering unit with one FP.
1 – filters-absorbers; 2 – tee; 3 – angular branch pipe; 4 – a glass with a nipple; 5 – coupling coupling; 6 – tie-down clamps. Means of regeneration

In the area of massive fires, the low content of oxygen and the increased content of carbon dioxide in the air atmosphere does not allow the use of this air for air supply according to the filter ventilation mode. In this case, it becomes necessary to transfer the shelter to mode 3 “Total isolation mode” with the regeneration of the internal air.

The shelter is also transferred to the “full isolation mode” when the composition of the air is unknown, in the presence of low-boiling and poorly sorbed organic substances (methane, ethane, etc.) in the outside air, and at high concentrations of hazardous chemicals.

Under the “full isolation mode”, the sheltered premises must have increased tightness in order to completely block the access of outside air to the shelter.

The set of means of regeneration may include: regeneration units, regenerative cartridges and oxygen cylinders.

A regenerative cartridge (RP) is used to absorb carbon dioxide CO 2 emitted by people when they breathe.

The principle of operation of the regenerative cartridge is that the air passing through the cartridge is cleaned of carbon dioxide, which reacts with a chemical absorber, for example, containing calcium hydroxide. The reaction proceeds with the release of water vapor and heat. Regenerative cartridges only absorb carbon dioxide, so the lack of oxygen when using regenerative cartridges is replenished with oxygen stored in oxygen tanks. Oxygen from cylinders is supplied to the ventilation network through a reducer. Regenerative cartridges can be mounted in columns of 2 and 3 cartridges [47].

Regeneration units (RU) are designed to absorb carbon dioxide CO 2 and saturate the air with oxygen. Regeneration is accompanied by an increase in air temperature up to 130…150 0 C, which requires mandatory cooling. The action of RR is based on the use of sodium or potassium superperoxide compounds, which ensure the simultaneous absorption of carbon dioxide and the release of oxygen.

The most modern domestic air regeneration system is the S-2.455 system (Fig. 6.5). It is designed to regenerate air for oxygen and carbon dioxide in sealed closed objects.

The S-2.455 system automatically maintains in the atmosphere of the object: oxygen concentration within 19-21% by volume and carbon dioxide concentration not more than 0.5% by volume when operating in the main mode (with forced ventilation); oxygen concentration within 19-23% by volume, carbon dioxide concentration not more than 1.3% by volume when operating in emergency mode (without electricity) [49].

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