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PRINCIPLES OF NATURAL VENTILATION

A basic knowledge of the principles of natural ventilation can help you understand how to use general ventilation as a way of controlling exposure to contaminants produced in the workplace.

 

Natural ventilation is produced by the effects of temperature and changes in air pressure ie wind. Temperature and air pressure differences in a building create an upward movement of air or stack’ effect. Occasionally, there can be downward air movement if the air is cold.

 

Wind forces are affected by wind speed, wind direction and the shape of the building. Cross-ventilation occurs when wind blows air through a room or building which has openings, for example windows on opposite sides. Single-sided ventilation occurs when there are one or more openings (such as a window and a door] on one side only.

 

Stack ventilation may be effective enough to carry vapours generated by small-scale hot industrial processes upwards. They can then be removed through the roof via roof ventilators or extraction fans. If cooler air comes in at a low level, it will displace the warm rising contaminated air, ie displacement ventilation.