Analysis of natural condition dependability of natural smoke control and exhaust

Starting from the natural condition ie. the relationship between symmetry of the thermal buoyancy and the wind pressure and the equal probability of the random events, based on the probability theory, analyses and calculates the possibility of impacts of thermal buoyancy and wind pressure as random events on natural smoke control and exhaust while fire occurs. Works out the regularity and determines the natural condition dependability of natural smoke control and exhaust is 50 percent. Considers that the total dependability including nature, substance and man, that the dependability of natural condition is merely one of the three factors and that the total dependability is lower than the natural condition dependability. Analyses it and elicits some conclusions.