No abstract

One of the first steps in establishing safe handling procedures for explosives is small‐scale safety and thermal (SSST) testing. To better understand the response of homemade or improvised explosives (HMEs) to SSST testing, 16 HME materials were compared to three standard military explosives in a proficiency‐type round robin study among five laboratories, two U.S. Department of Defense and three U.S. Department of Energy, sponsored by the Department of Homeland Security, Science & Technology Directorate, Explosives Division. The testing included impact, friction, electrostatic discharge (ESD) and thermal. The testing matrix was designed to address problems encountered with improvised materials: powder mixtures, liquid suspensions, partially wetted solids, immiscible liquids, and reactive materials. All testing materials and/or precursors came from the same batch distributed to each of the participants and were handled, pretreated, and mixed by standardized procedures. For this proficiency test, the participants had similar equipment, usually differing by vintage. This allowed for a direct comparison of the results from each participant to the average of the results from all the participants. Some general trends observed for each series of tests were: (1) Drop hammer – LLNL usually found the materials less sensitive than the average with materials that have high sensitivity to impact and LANL usually found the materials less sensitive than the average with materials that have high sensitivity to impact; (2) friction – LLNL found the materials less sensitive than the average; (3) and ESD – IHD usually found the materials less sensitive than the average. In this report, the proficiency test data from all the participants is compared and contrasted for impact, selected friction, and ESD testing. Other friction and thermal data will be addressed elsewhere as well as the statistical analysis of several repeated measurements on the proficiency test standards.

The Integrated Data Collection Analysis (IDCA) program has conducted a proficiency test for small‐scale safety and thermal (SSST) testing of homemade explosives (HMEs). Described here are statistical analyses of the results from this test for impact, friction, electrostatic discharge, and differential scanning calorimetry analysis of the RDX Class 5 Type II standard. The material was tested as a well‐characterized standard several times during the proficiency test to assess differences among participants and the range of results that may arise for well‐behaved explosive materials. The analyses show there are detectable differences among the results from IDCA participants. While these differences are statistically significant, most of them can be justified for comparison purposes to assess potential variability when laboratories attempt to measure identical samples using methods assumed to be nominally the same. The results presented in this report include the average sensitivity results from the IDCA participants and the ranges of values obtained. The ranges represent variation about the mean values of the tests of between 26 % and 42 %. The magnitude of this variation is attributed to differences in operator, method, and environment as well as the use of different instruments that are also of varying age. The results appear to be a good representation of results generated by the broader safety testing community based on the range of methods, instruments, and environments included in the IDCA proficiency test.

LX-04 is a widely used HMX-based plastic bonded explosive, which contains 85 weight % HMX and 15 weight % Viton binder. The sensitivity of LX-04 to a single stimulus such as heat, impact, and shock has been previously studied. However, hazard scenarios can involve multiple stimuli, such as heating to temperatures close to thermal explosion conditions followed by fragment impact, producing a shock in the hot explosive. The sensitivity of HMX at elevated temperatures is further complicated by the beta to delta solid-state phase transition, which occurs at approximately 165˚C. This paper presents the results of shock initiation experiments conducted with LX-04 preheated to 190˚C, as well as density measurements and small scale safety test results of the δ phase HMX at room temperature. This work shows that LX-04 at 190˚C is more shock sensitive than LX-04 at 150˚C or 170˚C due to the volume increase during the β to δ solid phase transition, which creates more hot spots, and the faster growth of reaction during shock compression.

We have applied thermal insults on LX-04 at 185 o C and found that the material expanded significantly, resulting in a bulk density reduction of 13%. Subsequent detonation experiments (3 cylinder tests) were conducted on the thermally-damaged LX-04 samples and pristine low-density LX-04 samples and the results showed that the fractions reacted were closed to 1.0. The thermally damaged LX-04 and pristine low-density LX-04 showed detonation velocities of 7.7 to 7.8 mm/µs, significantly lower than that (8.5 mm/µs) of pristine high-density LX-04. Detonation energy densities for the damaged LX-04, low-density pristine LX-04, and hot cylinder shot of LX-04 were 64.8 kJ/cm 3 , 66.2 kJ/cm 3 , and 65.8 kJ/cm 3 , respectively, lower than the detonation energy density of 81.1 kJ/cm 3 for the high density pristine LX-04. The break-out curves for the detonation fronts showed that the damaged LX-04 had longer edge lags than the high density pristine LX-04, indicating that the damaged explosive is less ideal.