Syracuse University Test Report On Uptake Factor Resulting From A Dropped Storage Container

Gao, Z. ; Zhang, J. S.

Oak Ridge Y-12 Plant

关键词: 42 Engineering;    61 Radiation Protection And Dosimetry;   

DOI  :  10.2172/1027099
RP-ID  :  SU-BEESL/RP-802068-0001 000 00
RP-ID  :  DE-AC05-00OR22800
RP-ID  :  1027099

美国|英语

来源: UNT Digital Library

【 摘 要 】

Under certain circumstances, powder from an accidently dropped container can become airborne and inhaled by people nearby such as those who are moving the containers. The inhaled fine particles can deposit on respiratory tracts and lungs, causing asthma, lung cancer, and other acute respiratory illnesses and chronic symptoms. The objective of this study was to develop a standard procedure to measure the airborne concentrations of different size particles within the vicinity of a dropped container where a significant portion of the contained powder is ejected. Tungsten oxide (WO{sub 3}) was selected in this study to represent relatively heavy powders (7.16 g/cm3 specific gravity for WO{sub 3}). A typical can with the outer dimensions of 4.25” diameter and 4.875” tall was used as the container. The powder was dropped in two different configurations: 1) contained within a can covered by a lid that has a 0.25” diameter hole, and 2) contained within a can without a lid. The packing volume of the powder was 51.4 in{sup 3} (842.7 cm{sup 3}) and the target mass was 1936 g. The tests were carried out in a full-scale stainless steel environmental chamber with an interior volume of 852 ft{sup 3} (24.1 m{sup 3}). The chamber system includes an internal recirculation loop with a rectangular air diffuser and 10 variable frequency drive fans to provide a typical room air recirculation flow pattern. Two air filters were installed in the chamber air supply duct and return duct to achieve the required low background particle concentration. The initial chamber air conditions were set at 70°F (± 5°F) and 50% (± 10%) RH. A supporting frame and releasing device were designed and built to trigger consistently the dropping of the can at a height of 8 feet from the bottom of the can to the impacting surface. The particle sampling inlet was placed 5 ft above the floor and 6 inches laterally away from the can’s falling path. Concentrations of particles between 0.5 μm and 20 μm were recorded in units of mass and number of particles per unit volume. The data acquisition rate was once every 2 seconds during the first 2 hours and every 20 seconds thereafter. A test procedure was developed and a total of nine drop tests were performed. In most cases (seven tests), the can tipped over after dropping. The can in Test 1 stayed upright. The can in Test 7 showed a special behavior: after the rebound, it turned upside down and stayed upright. Major findings are summarized below:  The amount of spilled powder varied from 0.12 g to 252.35 g and the non-recovered powder varied from 0.11 g to 1.18 g. The corresponding percentage of the spilled powder ranged from 0.01% to 13%.  The peak value of particle number concentration after the dropping of the can occurred at approximately 0.9 μm particle size per measured data of individual channels. The peak value of particle mass concentration occurred in the range of 4.3 - 10 μm particle size per grouped data calculated from the measured data with the exception of Test 4 where a different batch powder with unexpectedly different bulk density and particle size distribution.  After the dropping of the can, the total airborne mass concentrations ranged from 0.03 to 0.35 mg/m{sup 3}, while the total airborne number concentrations ranged from 2 to 125 #/cm{sup 3} except for Test 4. The number concentration in Test 4 was 1 or 2 orders of magnitude less than those of other tests because the powder was from a different batch. However, its mass concentration was comparable to that in Test 7 because relatively more big airborne particles were detected in Test 4. In general, tests with lid (Test 5, 6, 7 and 8) had smaller concentrations than tests without lid (Test 0, 1, 2, and 3). The influence of lid was not as prominent as the powder (Test 4). However, this needs more tests for verification.  The ratio of airborne mass to non-recovered mass ranged from 0.1% to 2%. This means that it is challenging to use this method to check the mass balance, while the uptake factor and associated inhalation exposure can be readily assessed.  The calculated cumulative uptake mass within first 10 minutes after the dropping of the can for each test was within the range of 0.002 mg to 0.035 mg. Assuming a breathing rate of 1.2 m{sup 3}/h, the uptake factor during the first 10 minutes was calculated to be between 10{sup -9} and 2×10{sup -8} in reference to the amount loaded; or between 10{sup -8} and 6×10{sup -5} in reference to the amount spilled. The experimental results of this study will be useful for standardizing the test method and provide data for estimating the exposure and associated risk to building occupants in the case of an accidental dropping of heavy powder containers.