From Big Medical Encyclopedia

HUMIDITY — contents in various objects of water in a liquid or vaporous state. An amount of water, the causing B. bodies, changeably also depends by nature substance and relative V. of the environment, and in solids, besides — on degree of their izmelchennost. Century of gaseous bodies (contents in them vaporous water) depends on the partial pressure of water vapors at data temperature and pressure and decides on the help of special devices (see. Hygrometer , Psychrometer ).

Century of construction materials, fuel, foodstuff, soils, industrial raw materials, chemical drugs and other substances usually express content of water in them percentage of the weight or volume.

Establishment of degree of V. of bodies has important economic value (e.g., grain, cement and other substances can be stored only at a certain degree of V.). On creation of certain conditions of V. various ways of fight are based on disease-producing microbes and wreckers of page - x. and industrial output, and also ways of extension of shelf-lifes of food stuffs and other materials.

The universal method of definition of V. does not exist. Various physical. and chemical methods of definition of V. most often allow to define the general water content in a specimen. The following methods of definition of V. are most widely applied: drying of substances to constant weight in drying ovens at a certain temperature; the otgonka of water by means of various hydrocarbons and some of their derivatives, and water in distillate is allocated in the form of a separate phase and is determined by volume; absorption of water dehumidifiers, napr, the concentrated chamois to - that, silica gel, alumina or calcium, alkali in sticks, anhydrous Calcium chloratum, phosphoric anhydride, anhydrous magnesium perchlorate (anhydrone) or its crystalline hydrate (degidrid), calcium sulfate (dreyerite), etc. Other ways are based on measurement of conductivity, index of refraction, hydration heat, viscosity and so forth; for gaseous bodies — on definition of a dew point, warmth of dissolution, etc. Centrifuging, and also the connections which are actively interacting with water are applied (e.g., calcium carbide, Grignard reagent, magnesium nitride, sodium amide and so forth). The method of definition of water based on direct titration of a specimen by Fisher reagent was widely adopted (see Aquametry). For the drugs containing except moisture, crystal water, also their drying in the closed space, napr, in the exsiccator in the presence of solutions a chamois to - you or salts of various concentration which elasticity of vapors corresponds to elasticity of vapors of the examinee of crystalline hydrate is applied. In all cases when V. is defined by means of drying, the weight loss of a wet body gives an amount of water, the causing V. (as a percentage the initial weight of a wet body).

Hygienic value of humidity

Hygienic value of humidity is connected generally with its influence on heat exchange of a human body with the environment as this or that value B. of air defines a possibility of overheating or overcooling of an organism (see. Cooling of an organism , Overheating of an organism ). It is connected with change physical. properties of air depending on moisture content and, on the other hand — V.'s influence on intensity sweating (see).

Century of a ground layer of the atmosphere is one of the most important elements of the characteristic of climate of the land surface, defines quantity of an atmospheric precipitation. Being condensed in fog, air moisture causes opacification of the atmosphere owing to what there is a delay solar radiation because of its absorption and dispersion. In particular it belongs to a short-wave part of a solar range (ultraviolet rays).

In industrial regions fog can absorb various industrial gases, including and toxic which, reacting with water, form various harmful connections which are besieged on buildings, sidewalks, clothes of people etc. People have a feeling of metal smack in a mouth, burning in a nasopharynx, dacryagogue.

For the account a gigabyte. values B. absolute V. (partial pressure of water vapors in air) how many relative V. (percentage of absolute V. to maximum, i.e. to pressure of saturated water vapors is taken into account not so much at this temperature). At the same time air from relative V. to 55% is considered dry, within 56 — 70% — moderately dry, from 71 to 85% — moderately wet and St. 85% — strongly wet. The difference between the maximum and absolute V. carries the name deficit of saturation. The more deficit of saturation, the more moisture can absorb air.

Century in combination with a thermal factor exerts a great influence on an organism. So, e.g., low level of relative V. at high temperature of air causes dryness of mucous membranes and emergence of microcracks. High temperature of air is transferred much easier at low indicators relative Century. At high levels of V. in combination with high temperature (climate of tropics) of people feels worse since heat output due to evaporation is at a loss. In these conditions overall health can worsen, working capacity goes down. High V.'s combination of air to low temperature causes opposite effect — bystry overcooling of an organism due to increase in heat output since at low temperatures the humid air becomes rather good conductor of heat and causes a feeling of a chill. Long and frequent stay of people in the conditions of the raised V. and low air temperature burdens the course of such diseases as nephrite, a polyneuritis, quinsy, rheumatism, pneumonia, Qatar of upper respiratory tracts and flu.

Relative V. of air of opportunities howls influence and on survival of viruses. So, conditions for long survival of an influenza virus in air are more optimum Are created at low relative V. (less than 20%) and small temperature variations (17 — 22 °). At increase relative V. Vozdukh (St. 40%) the influenza virus is quickly enough inactivated; his death (in an aerosol) occurs at relative V. within 50 — 70% and above. In this regard during the period epid, the outbreaks of flu in rooms with the conditioned air it is recommended to Maintain relative humidity within 50 — 70% that promotes reduction of danger of infection and spread of an infection (V. V. Vlodavets and R. A. Dmitriyeva, 1966). Long influence of a humid air and crude clothes in combination with low temperatures promotes strong cooling of a body surface and development of freezing injuries even at the above-zero temperature of air.

V.'s increase of air (from 25 to 65%) with the temperature range of 24 — 30 ° is followed by tension thermal controls (see) even in a condition of relative rest. At physical. to moderately severe work under the same conditions value of various levels B. on a functional condition of an organism comes to light more clearly.

The role of humidity against the background of high temperature is shown in works of A. A. Smirnova (1961), N. Strydom et al. (1966). At air temperature 40 ° and relative humidity of 15 — 20% of people there can be quite long time; functional indicators at the same time change, but in fiziol, acceptance limits. At relative humidity of 70 — 75% and the same temperature after 4-hour stay body temperature increases to 37,2 — 37,3 °, pulse rate — to 100 — 110 blows, a respiration rate — to 19 — 22 in 1 min.

Gigabyte. relative V.'s standard of air in premises makes 30 — 60%, at air temperature ° and very weak movement of air B. shall be 16 — 20 within 40 — 60%. During execution of physical. works at air temperature apprx. 20 ° relative B. air shall make 30 — 40%, at a temperature over 25 ° — to decrease to 20%.

According to Sanitary standards of design of the industrial enterprises (CH-245-71), at the air temperature of production rooms to 24 ° relative V. shall not exceed 75%; at a temperature of 26 ° — no more than 65%, at air temperature 28 °, being marginal for the warm period of year, relative V. shall be not higher than 55%. These recommendations belong to the warm period of year (temperature of fresh air +10 ° above), they are established for the rooms which are characterized by insignificant excess of explicit heat (20 kcal/m 3 in an hour and less), at easy and moderately severe works (see. Microclimate ).

Measures of fight against high V. in rooms consist in observance established a gigabyte. norms of air volume on one person, the device of rational ventilation (see), isolation of walls of the building from a subsoil water. Kitchens and bathing rooms provide exceeding of norm of ventilation. In production rooms the events directed to reduction of receipt in air of water vapors, ensuring their timely removal (special ventilation) and also on prevention of condensation of water vapors on walls, ceilings and so forth

See also shall be held Atmosphere , Air .

Bibliography: Minkh A. A. Reference book on sanitary and hygienic researches, M., 1973; Smirnov A. A. Influence of high temperatures and air humidity on the speed of overheating of a human body, the Gigabyte. and dignity., No. 10, page 16, 1961; Fedotova N. A. Hygienic justification of humidity at the air temperature of production rooms, in the same place, No. 8, page 13, 1969.

Yu. V. Novikov, P. K. Agasyan.