TAB M - Characterizing DU Aerosols
The actual level of aerosols generated during the various impact tests has varied widely. One of the first hard impact tests conducted on DU ammunition was reported in Characterization of Airborne Uranium from Test Firings of XM-744(sic) Ammunition, 1979. This report concluded that as much as 70% of the 105mm penetrator would turn into aerosol upon impact. Although this 70% has been frequently cited, it is flawed and misleadingmainly because it was "back-calculated" from cloud data and represented a worst-case scenario (i.e., an impact against a hard target, which was not penetrated). The 1982 report from the Ballistic Research Laboratory entitled Aerosolization Characteristics of Hard Impact Testing of Depleted Uranium Penetrators contradicted the results of the 1979 test. In this test, about 3% was aerosolized 2-3 minutes after impact. Allowing for error, it is highly unlikely that more than 10% of the penetrator was aerosolized in the 1982 test. The 1982 test found that 70% of the aerosolized particles were less than 7 micronsi.e., respirable particles.
Hard impact testing in 1990 of the M829A1 120mm cartridge and the XM900E1 105-mm cartridge produced somewhat contradictory numbers. This study characterized particulate levels after hard impact with both complete and partial penetration of the armor. The tests were performed with both the M829A1 and XM900E1 rounds, as well as two non-DU rounds, the M865 and DM13. (The purpose of the non-DU round firings was to evaluate DU resuspension during hard impact tests.) The sample results were questioned when only about 0.2% to 0.5% of the DU was aerosolized for the M829A1 and 0.02% to 0.04% for the XM900E1. (These values were approximately two orders of magnitude below expected values.) After comparing Real-Time Aerosol Monitor (RAM) data with RAM data from a previous test, researchers eventually estimated that the percent aerosolized was closer to 18%substantially less than the 70% previously cited by Battelle in the 1979 test. The respirable aerosol fraction [less than 10 m m AED (Aerodynamic Equivalent Diameter)] was 91% to 96% for the M829A1 and 61% to 89% for the XM900E1. Evaluation of the respirable dust fraction indicated that 57% to 76% was class "Y" material and 24% to 43% was class "D" material, in keeping with other studies which indicated that a high percentage of the respirable dust from hard impact testing was soluble in the lungs. (Note: Class "D" materials have dissolution half-times less that 10 days, class "W" materials have dissolution half-times of 10 to 100 days and class "Y" materials have dissolution half-times greater than 100 days.) The resuspension tests indicated that most of the resuspended dust was non-respirable, which is consistent with the theory that most of the respirable dust was removed by the filtering system in the enclosure. The aforementioned tests are but a few of the tests performed on DU munitions in an attempt to characterize aerosol formation and assess potential exposures. As a result of recommendations made in the 1995 Health and Environmental Consequences of Depleted Uranium Use in the US Army: Technical Report, Battelles Pacific Northwest Laboratory conducted an evaluation of existing test data for predicting aerosol exposures. Their report (entitled Evaluation of DU Aerosol Data: Its Adequacy for Inhalation Modeling) identified some of the technical problems with estimating exposure under various combat scenarios. The following is a brief discussion of DU aerosol generation scenarios present in the report:
Two recent tests conducted after the Battelle Summary report raise some questions concerning the nature and extent of respirable particulates generated during fires and hard impact testing. In June 1995, the Army fired 120 mm and 25 mm DU munitions against Soviet armored equipment. Although technical and procedural difficulties seriously affected the data and limited the conclusions that could be drawn from the test, several key findings were cited in the Draft report. They were:
The second test was the 1994 burn test of a Bradley Fighting Vehicle (BFV) equipped with TOW anti-tank missiles and 1,125 M919 25mm cartridges. This was the first time that a vehicle with a full combat load of DU munitions was actually used in a burn test. Most of the previous data for fires were generated from stack testing wooden or metal shipping crates. The BFV was completely engulfed by the fire and burned vigorously for about an hour. The fire subsided after an hour, but continued to emit a plume over the next five hours with smoldering hot spots into the next day. Of the 1,125 DU penetrators, 625 were accounted for, including nine live rounds found within a few meters of the test pad. Although 500 rounds were unaccounted for, the report indicated that a large percentage was trapped within the melted remains and a significant amount of the DU oxide was mixed within the ash and settled inside and around the hull of the vehicle. Six piles of DU oxide were detected on the vehicle surface after the fire. Analysis of the DU oxide indicated that approximately 33% of the oxide particulates were respirable. However, only trace amounts of DU oxide were detected on the air monitoring filters at various distances during the 29 hours of air sampling. Although the higher percentage of respirable particulates (33%) measured in the piles of DU oxide after the fire is an important consideration for assessing resuspension potential during recovery, further research is needed to determine whether the higher values of respirable particulates were unique to this test or if results are truly valid for vehicle fires involving DU munitions.
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