4.2　Natural Ventilation

4.2.1　For production buildings and auxiliary buildings emitting heat，natural ventilation may be calculated only per the effect of thermal pressure.

4.2.2　For the buildings designed with natural ventilation，the doors and windows of buildings shall be served as air intakes and exhaust outlets as far as possible，and if they cannot meet to satisfy ventilation requirements，closable holes，clerestory windows，funnel cap and scuttles may be used.

4.2.3　Airflow distribution of natural ventilation shall prevent contaminated airflow from being blown into non-contaminated areas，and shall not interfere with the controlled airflow for local exhaust.

4.2.4　The production buildings that make use of scuttles for exhaust，shall be provided with sheltered scuttles for any of the following cases:

a）In the hot summer-cold winter or hot summer-warm winter regions（the mean temperature for the hottest months in years is higher or equal to 28℃）with the in door heat gain greater than 23 W/m3.

b）In other regions with the indoor heat gain greater than 35 W/m3.

c）Where air backflow is not allowed.

4.2.5　Natural ventilation shall not be used for production buildings where extremely toxic substances are emitted.Additionally，natural ventilation shall not be used for production buildings with surrounding air severely contaminated by dust or other harmful substances.