A building may have a roof ventilator to allow the rising warm air to escape. Convection currents are caused by the sinking of colder and therefore heavier air, which displaces the warmer air. The pressure difference promotes circulation into the building on the windward side and out of it on the lee side. Winds raise air pressure slightly on the windward side of a building and lower it slightly on the lee side. Natural ventilation depends on winds outside and convection currents inside a building. Lack of air currents and the increase in relative humidity and temperature (especially noticeable in crowded, poorly ventilated places) prevent normal evaporation of perspiration and loss of heat from the surface of the skin. ![]() There is evidence to show, however, that the deleterious effects result largely from interference with the heat-regulating mechanism of the body. ![]() It was formerly believed that the discomfort, headache, and lethargy commonly associated with poor ventilation were caused entirely by the increase in the amount of carbon dioxide and the decrease in the oxygen content of the air. Proper ventilation requires also that there be a movement or circulation of the air within the space and that the temperature and humidity be maintained within a range that allows adequate evaporation of perspiration from the skin. Ventilation, process of supplying fresh air to an enclosed space and removing from it air contaminated by odors, gases, or smoke.
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