On 15 October 1965, a fire in a plutonium fabrication plant resulted in a large-scale spread of plutonium oxide. The Rocky Flats body counter was used to measure the plutonium in the lungs of all employees working in the area. Of approximately 400 employees counted, 25 were found to have enough plutonium in their lungs to deliver a dose of 15 rem/yr or greater. Data from each employee were obtained with two scintillation detectors in contact with the subject's chest. The 60-keV photon peak of 241Am was used in the measurements. The 241Am content of the plutonium released in the fire was determined and the plutonium quantity was then determined from calibrations done on a chest phantom with similar 241Am:239Pu ratios. The plutonium consisted of “high-fired” PuO2. Particle size measurements of air samples collected after the fire indicated a 0.32-μ mass median diameter (MMD) with a geometric deviation (rg) of 1.83. Lung data so far show very slow clearance. This confirms the high degree of insolubility and the small particle size. On the average, 30 per cent of material initially deposited was cleared in 2–3 months. The remaining material is clearing very slowly with little or no measurable absorption into the bloodstream.
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