For most typical radiological contamination situations involving the inhalation of radioactive material, organ dose commitments are calculated using published inhalation dose conversion factors. Inhalation dose conversion factors are available for activity on particles of less than 10um in diameter; however, inhalation dose conversion factors for large particles are not available in the published literature. Accordingly, for the purpose of this dose calculation a set of large-particle inhalation dose conversion factors is developed. For particles greater than 10ywm diameter, essentially all of the inhaled material is initially deposited in the nasal or nasopharyngeal region of the respiratory tract (Reference 17). This material is removed by chemical (absorption) and mechanical processes, and goes either to the blood, with subsequent transfer to other body organs, or to the gastrointestinal (GI) tract, with subsequent transfer to the blood and further transfer to other body organs or bodily elimination by excretion. The "pulmonary clearance classification" of the inhaled material (roughly analogous to the solubility of the material) determines the amount of the material that is initially transferred to the blood or the GI tract; for example, 99 percent of an "insoluble" material will go to the the GI tract with only | percent going to the blood, whereas a "very soluble" material will be divided evenly between the GI tract and the blood (Reference 16). As ingestion plays a major role in the fate of an inhaled large particle, the largeparticle inhalation dose conversion factors used for the present dose calculation are Obtained by modifying ingestion dose conversion factors. This modification is necessary to properly account for that portion of the inhaled materia! that is initially transferred to the blood, rather than to the GI tract. construct large-particle’ inhalation ORNL/NUREG/TM-190 radionuclides. dose (Reference 16) for The TM-190 dose conversion The metabolic data needed to conversion the most factors are radiologically given in significant factors, based on the most current dosimetry information, are used in conjunction with these. For those radionuclides not addressed in TM-190, unmodified ingestion dose conversion factors are taken from NUREG-0172 (Reference 18). 21