CHAPTER XXVIII 

 VENTILATION 



398. Object of Ventilation. Ventilation is the process of 

 removing from an enclosed space foul air, laden with im- 

 purities, and replacing it with fresh air. An exact displace- 

 ment, however, does not always take place. The incoming 

 fresh air may merely dilute the foul air to a point suitable for 

 healthful breathing. The standard of pure air is taken as 

 that existing in the open country; it contains about four 

 parts of carbon dioxide (CO 2 ) per ten thousand of air and 

 is free from dust. An increase of two parts of carbon dioxide 

 is accepted as the standard of pure air. Any excess above 

 this is considered impure air. Badly ventilated rooms often 

 contain as many as 80 parts of carbon dioxide per ten thou- 

 sand of air. 



399. Methods of Ventilation. There are three ways of 

 removing dust and impurities from air in a building: (1) the 

 natural method ; (2) forced ventilation by means of fans, and 

 (3) the exhaust method. 



Natural ventilation is produced through doors and windows. 

 The air in a room is changed by this method about three 

 times an hour. If there is a fireplace in addition, the total 

 number of changes per hour will be about four. A furnace 

 will produce five changes of air per hour. Every room should 

 be large enough to allow proper ventilation without too much 

 draught. Authorities agree that not less than 300 cu. ft. of 

 air space should be allowed for each person. 



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