 assessments of inhalation exposure to environmental agents necessitate quantitative estimates of pulmonary ventilation rates . estimating a range of exposures in a given population 
 requires an understanding of the variability of ventilation rates in the population . 
 distributions of ventilation rates ( ve ) were described based on the results of a large study where ve were measured while subjects performed a variety of physical tasks . 
 three distinct ventilation levels were identified using cluster analyses of the mean ve and then various activities were assigned to the three levels using a k - means procedure . 
 separate distributions were identified for the three ve levels for adult males , adult females , and children . 
 the variability of ve was consistent with a lognormal distribution for all groups . 
 an aggregate daily inhalation rate can be estimated based on the distributions of ve.imagesfigure 1.figure 1.figure 1 . 
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