The natural environment in which labor activity is carried out is characterized by a number of parameters, the main of which are physical parameters, in particular meteorological ones.

The main meteorological parameters include air temperature, relative humidity, wind speed, and barometric pressure. The first three parameters determine the process of thermoregulation of the body, i.e. maintaining the body temperature in the range of 36-37 ⁰C. Thermoregulation is a physiological process controlled by the central nervous system.

It provides a balance between the amount of heat continuously generated in the body during metabolism and the excess heat continuously released to the environment, i.e. it supports the thermal balance of the human body.

There is a distinction between chemical and physical thermoregulation.

The main value is physical thermoregulation, through which the body releases heat to the environment. This process can proceed in three ways:

1. In the form of infrared rays emitted by the surface of the body to an environment with a lower temperature. In this way, about 45% of all thermal energy produced by the body is lost.
2. By heating the air washing the surface of the body. At the same time, about 30% of the heat is lost.
3. Evaporation of sweat loses about 13 % and about 5% of the heat is spent on heating the food taken and inhaled air.

Heat transfer by radiation and convection occurs when the ambient temperature is lower than the body temperature. Moreover, the evaporation rate depends on the relative humidity of the air. If the relative humidity of the air exceeds 80 %, heat transfer by evaporation of sweat is difficult and the body may overheat, called thermal hyperthermia and convulsive illness, which can later lead to heat stroke, which occurs with loss of consciousness and an increase in body temperature to 40-41 ⁰C.

The physical parameters of air must be taken into account when organizing all types of activities, especially military service, which usually takes place in difficult climatic conditions in various regions of the country. Of particular importance are the parameters of the indoor microclimate, i.e. temperature, relative humidity and air mobility.

Optimal microclimate parameters are shown in Table 1.

Table 1

Optimal microclimate parameters

When meteorological parameters deviate from the optimal ones, various processes aimed at regulating heat production and heat transfer begin to occur in the human body in order to maintain a constant body temperature. As the air temperature rises, heat transfer processes increase. Moreover, when the temperature rises to values exceeding 25 ⁰C, evaporation becomes the predominant heat transfer process (tab. 2).

Table 2

The amount of moisture released from the surface of the human skin and lungs (g / min)

When 1 g of water evaporates, the body loses about 2.5 kJ of heat. It is established that at a temperature of about 30 ⁰C, with heavy physical work per day, the body can lose 15-20 liters of fluid. With intense sweating, if the sweat does not have time to evaporate, it is released in the form of drops. At the same time, moisture on the skin not only does not contribute to the return of heat, but, on the contrary, prevents this. Such sweating leads only to the loss of water and salts, but does not perform the main function-increasing heat output. [3]

A significant deviation of the microclimate of the working area from the optimal state can cause a number of physiological disorders in the body of workers, lead to a sharp decrease in working capacity and even to occupational diseases.

When studyingthe impact of hydrometeorological conditions on a person, it is necessary to take into account the simultaneous influence of numerous time-varying factors on a person (solar radiation, temperature, humidity and air pressure, wind, etc.). Weather changes affect the depth and frequency of respiration, the speed of blood circulation, the supply of oxygen to cells and tissues of the body, the carbohydrate content, salt and water metabolism, muscle tone, etc.

A certain state of the environment corresponds to a certain level of biochemical processes occurring in the body’s cells. This ensures the production of heat in the body and its release to the environment to maintain the temperature of the internal parts of the body at an isothermal level, while creating a different voltage of the thermoregulatory system of the body.

All these indicators depend not only on the weather, but also on the level of physical activity of a person, which in the case of recreational activities is equated to moderate work in the open air. In addition, the thermal insulation qualities of clothing are taken into account.

Certain climate and recreation criteria have been developed [1], according to which the heat balance is determined by the average weighted surface temperature of the body. Depending on this temperature, different weather categories are distinguished. Based on all these data, a classification of weather types by degree of favorability was developed.

In order to distinguish certain weather conditions by their thermal impact on humans, an assessment scale was constructed based on urgent observations (fig. 1), which can be used to determine the impact of daily geophysical and meteorological conditions on humans.

Figure 1. Estimated scale of recreational weather types (where Q is total radiation, kW /^m2; n is cloud cover, points; T is air temperature,⁰C0)

It should also be remembered that during certain geophysical events (strong winds of more than 6 m/s, precipitation of more than 3 mm during daylight hours, severe thunderstorms and fogs, hurricanes, tornadoes, mudslides, etc.), human activity may be limited or completely excluded.

All weather patterns that occur throughout the year in different parts of the country are divided into the following types:

2. Comfortable days (weather type H) are the most favorable days when there is minimal stress on the body’s thermoregulatory systems and any summer types of recreation that create a certain load on these systems are possible.
3. Cool sub-comfortable days (weather type 1-Х) — the load is higher than a certain thermal level.
4. Hot sub-comfortable days (weather type 1-T) — days when there is a weak tension in the temperature systems, when recreational activities are possible, but with some restrictions.

In conditions of cool subcomfort, the working time can be increased by using natural shelters that reduce the body’s heat transfer. Also with increased work intensity, at which the body’s heat production increases.

In a hot subcomfort, natural factors and artificial objects are used to mitigate the heat: radiation and wind effects of seas, lakes, rivers, reservoirs, as well as the protective effect of forested and green areas, barriers and awnings that create shade.

These types of weather (1, 2, 3) add up to an extremely important indicator of the territory’s climatic resources for recreation — the distribution of favorable days over it.

4. Uncomfortable days -are days when there is such a strong tension in the body’s thermoregulatory systems that it can lead to pathological reactions and even threaten a person’s life, or when recreational activities are dangerous or impossible. This includes hot weather types: 2-T, 3-T, 4-T too cold weather types: 1-X,2-X, 3-X,4-X; Type 4 is an array of unfavorable days.[4]

Using the presented assessment scale and actual meteorological parameters of the environment, it is possible to actually determine the recreational type of weather and the physiological state of a person.

Thus, a physiological and genetic classification of weather conditions has been developed, which is based on the following indicators: теплоощущенияhuman heat sensation, average weighted skin temperature, sweating, and temperature load. According to them, there are nine types of weather, for the characteristics of which only the main meteorological values that determine the thermal state of a person and their well-being are selected. In the warm season, these include air temperature, solar radiation, wind speed, and cloud cover.

In the cold season, heat sensations depend primarily on the air temperature and wind speed. The arrival of solar radiation is not taken into account due to the short day, low sun exposure, and winter clothing. The classification is focused on a person who performs light work outdoors in clothing with certain thermal insulation properties and can be used to evaluate various types of economic, observation, and engineering research activities.

Industrial processes performed at low temperatures, high mobility and humidity can cause cooling and even hypothermia of the body (hypothermia).

To estimate the combined cooling effect of low temperatures and wind speed on a person during the cold period of the year, an equivalent temperature can be used (tab. 3).

Table 3

Equivalent temperature values

For optimal use of human labor resources, ensuring the safety of life under various hydrometeorological conditions plays an important role. [2]

In hydrometeorologicalsupport and life safety, the main task is to take into account and analyze hydrometeorological conditions that have a significant impact on human activity, as well as their subsequent assessment and development of recommendations.

An objective assessment of a person’s thermal state requires a method that takes into account the main hydrometeorological parameters (air temperature, humidity (in temperate zones, humidity usually plays a secondary role), wind speed, and solar radiation (at least at high altitude of the sun)).