Re: Inhalation pathway question

["Otto G. Raabe" <ograabe@ucdavis.edu>]

October 28, 1998
Davis, CA

The ICRP Lung Model uses estimates of actual deposition of inhaled
particles as a function of aerodynamic and diffusive size in the various
parts of the respiratory tract during inhalation. Hence, the so-called
"respirable fraction" is fully accounted by this calculation. The newest
models even account for "inhalability" which considers the inhalation
sampling efficiency of the human head for particles as large as 100
micrometer. 

The "respirable fraction" is defined as the fraction of inhaled particle
that are AVAILABLE for deposition in the lower respiratory tract during
inhalation. This is a useful concept in industrial hygiene practice for
gross dust samples. But the ICRP goes a step further and actually estimates
the deposition probability, not just the fraction available for deposition.
However, the ICRP approach is dependent on the chosen particle size
distribution. It is NOT appropriate to apply a "respirable" fraction to the
ICRP model results and found in FGR 11.

Otto 
		*****************************************************
		Prof. Otto G. Raabe, Ph.D., CHP
              Institute of Toxicology & Environmental Health (ITEH)
		     (Street address: Old Davis Road)
		University of California, Davis, CA 95616
		Phone: 530-752-7754  FAX: 530-758-6140
		E-mail ograabe@ucdavis.edu
              *****************************************************
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