The chemical composition of air and its hygienic

The primary components of atmospheric air are oxygen (21%), nitrogen (78%), carbon dioxide (0,03-0,04%), water vapour and inert gases, ozone, hydrogen peroxide (about 1%).
Oxygen is the most integral part of air. With his direct participation proceed all the oxidative processes in humans and animals. Alone person consumes in a minute about 350 ml of oxygen, and the heavy physical work, the amount of oxygen consumed increases several times.
Breathe in the air contains 20,7-20.9% oxygen and exhale is about 15-16%. Thus, the tissues of the body absorb about 1/4 of oxygen available in the inhaled air.
In the atmosphere the oxygen content does not change significantly. Plants absorb carbon dioxide and, splitting it, absorb carbon, and the released oxygen is released to the atmosphere. A source of formation of oxygen is also photochemical decomposition of water vapor in the upper atmosphere under the influence of ultraviolet radiation of the sun. In providing a constant composition of atmospheric air is the value of the mixing of air flows in the lower atmosphere. The exception is hermetically closed areas, where due to long time people the oxygen content can be significantly reduced (submarines, asylum, pressurized cabins of planes and other).
For the body is important partial pressure * oxygen, not its absolute content in the air we breathe. This is because the transition of alveolar oxygen from the air into the blood and from the blood into tissue fluid is under the influence of the difference in partial pressure. The oxygen partial pressure decreases with increasing altitude above sea level (table. 1).

Table 1. The oxygen partial pressure at different altitudes
Height above sea level (m) Barometric pressure (mm RT. Art.) The partial pressure of oxygen (mm RT. Art.)

Great importance is the use of oxygen for the treatment of diseases involving anoxia (oxygen tents, inhalers).
The carbon dioxide. Carbon dioxide content in the atmosphere fairly constant. This permanence is explained by its cycle in nature. Although the processes of rot, the life of the organism is accompanied by release of carbon dioxide, a significant increase in its content in the atmosphere, as carbon dioxide is absorbed by plants. When the carbon is to build organic substances and oxygen enters the atmosphere. In the exhaled air contains up to 4.4% carbon dioxide.
Carbon dioxide - physiological pathogen respiratory centre, so when artificial breathing it in small amounts add to the air. In large quantities it can have a narcotic effect and may cause death.
Carbon dioxide is and hygienic value. Its content is judged on the purity of air in residential and public premises (i.e. areas where the people). When people are crowded together in a poorly ventilated areas parallel to the accumulation of carbon dioxide in the air increases the content of other products of human activity, increased temperatures and increased humidity.
It is established that if carbon dioxide content in the air of premises exceed 0,07-0,1%, the air unpleasant smell and may violate the functional state of the organism.
Parallelism change any of the properties of air in residential and increasing concentrations of carbon dioxide, as well as the ease of defining its content is possible to use this indicator for the hygienic assessment of air quality and ventilation efficiency of public premises.
Nitrogen and other gases. Nitrogen is the main part of the atmospheric air. In the body it is dissolved in the blood and tissue fluids, but is not involved in chemical reactions.
Currently experimentally established that in conditions of high pressure nitrogen from the air causes the animals disorder neuromuscular coordination, further stimulation and drug status. Similar phenomena researchers observed among divers. Application for divers breathing helium-oxygen mixture allows increasing the depth of 200 m without symptoms of intoxication.
When electric lightning discharges and under the influence of ultraviolet rays of the sun in the air produces negligible amounts of other gases. Hygiene is relatively small.

* Partial pressure of a gas in a mixture of gases is called the pressure that would produce this gas, if he took up the whole volume of the mixture.