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Basics of disinfecting hazardous substances
General concepts and definitions
Disinfection is the reduction to the maximum permissible norms of contamination of objects with hazardous substances (radioactive substances (RV), hazardous chemicals (OHC), bacterial agents (BS) by degassing, decontamination, disinfection, as well as sanitary treatment of personnel of the ASF and civil defense units and the public .
Decontamination is the disinfection (neutralization) of objects infected with RVs.
Degassing is the decontamination (decontamination) of objects contaminated with chemical agents (HVAC).
Disinfection is the process of destroying or removing the causative agent of an infectious disease of a person or animal.
Disinsection is the extermination of insects and ticks, BS carriers.
Deratization is the extermination of rodents, BS transporters.
Sanitary treatment is the mechanical cleaning and washing of the skin and mucous membranes of people exposed to contamination and contamination of PB, OM, OHV, BS, and also disinfection of their clothes and shoes when leaving the emergency area.
It is known that the phase state of contamination can be solid, liquid and gaseous. Solid particles on the surface are fixed weak adhesive forces (Coulomb, capillary, etc.). Liquid and gaseous contaminants are fixed on the surface due to molecular processes of adsorption (chemisorption) and first create a surface or slightly fixed type of pollution. Subsequently, as a result of wetting, dissolution, diffusion, and contamination, they penetrate into absorbent materials, thus forming even a voluminous type of contamination.
Thus, in practice one has to deal with adhesive, surface, deep and volumetric contamination of materials and, depending on this, methods and methods of disinfection are determined.
Disinfection methods: removal, detoxification, binding and isolation of pollution.
Removal is the removal of dirt from an infected surface or the removal of an infected object itself from a person.
Detoxification is the chemical, thermochemical, or biochemical conversion of pollution to low-toxic compounds.
Binding is a reduction in the mobility of pollution, a decrease in the rate of evaporation and the prevention of its transfer to surrounding objects (i.e., a reduction in the risk of secondary contamination and entry into the human body).
Insulation is the isolation of the source of contamination from the environment, as well as the covering of contaminated surfaces with films and other materials.
Methods of disinfection: physical, chemical, combined (physico-chemical) and thermal (thermochemical). In addition, there are liquid and liquid-free methods of disinfection. The choice of method depends on the pollutant and its state of aggregation. The implementation of these methods is carried out using various working media (formulations, i.e. substances or mixtures of substances active with respect to OHV, OM, PB, BS) and technical means of special treatment.
Solid adhesion contamination can be either physically removed (by sweeping, blowing, flushing - mainly RV), or chemically disinfected (OM, OHV, BS).
Removal of surface liquid and gaseous contamination is possible only after overcoming the adsorption forces by solvation with solvent molecules (dissolution) or by increasing the surface temperature.
Removal of deep contamination is carried out by washing (using extractants - special solvents) and drying with hot air.
Filtration, sorption and ion exchange processes are used to remove bulk contamination from water or air.
Thermochemical method of detoxification is based on supplying high-intensity energy fluxes to the infected surface in the form of radiation from the light, IR and UV ranges, or treatment with high-temperature plasma. At the same time, thermal decomposition processes of pollutants (OM, OHV, BS) are sharply activated with the formation of low-toxic products.
The chemical method is based on the use of liquid chemically-active formulations.
The entire set of OHVs can be conventionally reduced to two pairs:
the first is of an acidic nature, giving an acidic environment in water (chlorine, nitrogen oxides, sulfur oxides, etc.), and an alkaline character, giving an alkaline environment in water (ammonia, amines, etc.);
the second is oxidizing and reducing agents (combustible substances, heptylide, etc.).
In each pair of substances are antagonists and, therefore, with equivalent interaction neutralize each other. Thus, the selection of a neutralizing substance is quite simple:
alkaline substances are used to neutralize substances of an acidic nature and, on the contrary, acid is used to neutralize alkalis;
a reducing agent is used to neutralize the oxidizing agent and vice versa.
Disinfection of various surfaces of objects is mainly carried out using two types of formulations:
surface active or detergent;
chemically active or degassing (neutralizing).
Washing formulations contribute to the separation and retention of contamination in the solution.
The degassing (neutralizing) formulations destroy, bind (absorb), decompose and dilute the liquid phases of OHV.
Destruction is based on the reaction between OHV and a reagent that is chemically active towards it.
Binding (absorption) is achieved by the use of adsorption materials (soil, sand, slag, etc.).
Decomposition occurs as a result of exposure to high temperatures.
Dilution is made with water or solutions of neutral substances.
Substances and solutions used to neutralize OHV (OS).
For decontamination (neutralization) of hazardous substances in the decontamination of the territory, equipment, vehicles, shoes and clothing you can use:
- caustic soda (NaOH - caustic soda) - white solid, well soluble in water. Stored in iron drums. It is used to neutralize chlorine, hydrocyanic acid, as well as nitric, hydrochloric and other acids;
- soda ash (PA 2 CO 3 ) - white, fine-crystalline powder well soluble in water. It is used to neutralize acids, acrylonitrile;
- sodium thiosulfate (PA 2 SO 2 ) x 5 H 2 O - colorless crystals. Fire and explosion hazard. It is well dissolved in hot water, in cold - worse. It is used to neutralize the straits of chlorine;
- ferric chloride (FeCl 3 ) - dark brown crystals with a greenish tint. Well dissolved in water. It is used for disinfection of hydrocyanic acid after treatment with ammonia water. Ammonia water dilutes the acid, and iron chloride forms a neutral salt with it;
- milk of lime (Ca (OH) 2 ) - a mixture of hydrated lime and water. Slightly soluble in water. It is used to neutralize acids, as well as to precipitate vapors of a cloud infected with phosgene.
The consumption of neutralizing substances during decontamination of OHV is determined by the type of OHV, the nature of infection (drip-liquid, vapor, aerosol), the object of infection (terrain, transport, clothing, etc.), the method of neutralization (spraying, spraying, wiping with a brush or rag, boiling and others), the type of neutralizing substances and a number of other factors.
The amount of neutralizing substances is calculated by the equations of chemical reactions.
Assume that it is necessary to neutralize 1 t of phosgene (CoCl 2 ). We determine how much neutralizing substance is needed, for example, caustic soda (NaOH).
We make the equation of a chemical reaction:
СОСl 2 + 4NаОН → NA 2 CO 3 + 2 NaCl + 2H 2 O
From the periodic system D.I. Mendeleev find the atomic weights of all the elements involved in the reaction and make up the proportion:
Thus, to neutralize 1 t of phosgene, it is necessary: 1.6 tons of sodium hydroxide or 0.7 tons of ammonia.
And, for example, to neutralize 1t of chlorine requires 12t of a 10% alkali solution, or 100 tons of water. The use of water due to high consumption is impractical. It is also not recommended to neutralize chlorine using aqueous solutions of ammonia, due to the formation of nitrogen chloride, which is explosive upon contact with a solid medium.
Small ammonia spills can be neutralized with water. The use of water to neutralize large quantities of ammonia is unacceptable due to a sharp increase in the gaseous phase due to the heat of reaction and an increase in the depth of distribution of damaging concentrations.
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