Testing confinement sensitivity

Larger Scale Testing. The standard card gap test (2) is test No. 1 of a series of larger scale tests designed to determine the sensitivity of liquid propellants to hydrodynamic shock. In this test, relative sensitivities of various propellants are determined in terms of the number of 0.01-inch thick cellulose acetate cards required to attenuate a standard shock sufficiently just to prevent initiation in the test sample. When performed according to the exacting conditions of apparatus and procedure, the results are very reproducible from one laboratory to another. However, small variations in the apparatus or procedure can cause major variations in the resulting data, and therefore the test can be considered only relative. A major drawback of the standard test is that it cannot accommodate materials that are volatile under the test condition. At TCC-RMD some special equipment has been developed that allows tests to be made on confined samples at elevated temperature and pressure. 

The insensitivity of nitromethane to detonation by shock under normal conditions of handling has been demonstrated by a number of fljH-scale tests. Sensitivity to shock increases with temperature at 60° C, nitromethane can be detonated by a No. 8 blasting cap. Nitroethane can be initiated only when heated near its boiling point under heavy confinement neither it or the nitropropanes can be detonated in unconfined conditions. 

It was found that under confined conditions, LA mixts contg up to 28% w are more sensitive than dry LA mixts, while in unconfined tests, the reverse is evident (Refs 39, 40 41). This study, as a corollary to the Lidestone test work, is indicative of the uncertainties inherent in expl initiation when w is present... 

The power of Parazol, as detd by Cope (Ref 1), is about 86% of TNT (Bal Mort Test, consisting of detg the quantity of Parazol required to cause deflection equal to the deflection from lOg of TNT). It is less sensitive to detonation than TNT and, when confined, requires a very powerful detonator... 

The explosive decomposition of the solid has been studied in detail [6], The effect of moisture upon ignitibility and explosive behaviour under confinement was studied. A moisture content of 3% allowed slow burning only, and at 5% ignition did not occur [7], Thermal instability was studied using a pressure vessel test, ignition delay time, TGA and DSC, and decomposition products were identified [8], The presence of acyl chlorides renders dibenzoyl peroxide impact-sensitive [9], There is a further report of a violent explosion during purification of the peroxide by Soxhlet extraction with hot chloroform [10], Residual traces of the peroxide in a polythene feed pipe exploded when it was cut with a handsaw [11]. The heat of decomposition has been determined as 1.39 kJ/g. The recently calculated value of 69° C for critical ignition temperature coincides with that previously recorded. 

The determination of the mechanical shock sensitivity or impact sensitivity is applicable to both solids and liquids. The principle involved is that a drop weight falls from a specified height onto the confined test sample. The load can be varied by changing the height of the drop and by changing the drop weight. 

When large quantities of a substance are handled, sensitivity of the material to heating under confinement may need to be considered to demonstrate the effect on the stored/handled, and probably confined, substance in the event of an external heat load. Tests such as the steel sleeve test or Koenen test [24, 137], the Dutch pressure vessel test (DPVT) [143], and the United States pressure vessel test (US-PVT) [143] may be applicable. These tests are used mostly for transportation considerations. The tests generally subject the sample substances to very high energy inputs under confined conditions, and thus are more severe than the deflagration and autoclave tests previously discussed in Section 2.3.3.2. As an example, the Koenen test, used mainly in Europe, is illustrated in Figure 2.32. 

Segment 11 teratogenicity study. This concentrates on the most sensitive part of gestation, from the time of implantation imtil major organogenesis is complete. This is the period during which a test substance is most likely to cause malformation of the embryo. Exposure of the mother to the test substance is usually confined to this period. Conventionally, the study is conducted in rats and rabbits. Rabbits are intolerant to antibiotics and the mouse is an acceptable alternative in most cases. 

C) Dunkle s Syllabus (1960-1961), p 13a (Stein found the rifle-bullet sensitivity of expls to increase with increasing thickness of confinement. For equivalent thickness, the expls were more bullet-sensitive in steel than in A1 bombs. As a quantitative test of deton of the expl, measurements by means of piezoelectric shock-velocity gages showed promise. When there was no firm indication... 

Fia 6 Effect of A on shock sensitivity of various explosives. NQ-f is low-bulk-density nitroguanidine with hollow-needle crystals of about 5 n diam X 60-65 it long. NQ-h is the high-bulk-density material made up of solid particles of about GO-65 n diam. DATB, TNT, and Tetryl are, respectively, dia-minotrinitrobenzene, trinitrotoluene and trinitro-phenylmethylnitramine. RDX is cyclotrimethyl-enetrinitramine which contains 2.5% lubricant. Measurements were carried out with a standardized test (Ref 16) in which a 3.65-cm-diam test explosive confined in 0.55-cm-thick steel is the acceptor and polymethyl methacrylate is the gap material MGl = NCro filt ro uasiM i ... 

The shock sensitivity of materials are also frequently evaluated in a drop weight test. A variety of drop weight testers have been developed, but the standard device used to evaluate the sensitivity of liquid propellants is test No. 4 of the Joint Army-Navy-Air Force Panel on Liquid Propellants (2). A sample of material (usually less than 0.1 gram) is confined in an enclosed volume, and a calibrated weight is allowed to... 

The explosive was exhaustively characterized for thermal behavior, impact sensitivity and electrostatic discharge sensitivity etc. Based on this data, CP has been described as much less sensitive to accidental initiation than primary explosives such as LA but at the same time, initiation grows rapidly to detonation when properly confined. Its performance evaluation in a test detonator or hardware indicates that CP can replace primary explosives in many hot wire detonator applications especially if safety considerations are of prime importance [239]. 

Explosion temperature no ignition up to 340° Impact sensitivity - less sensitive than TNT Power by Trauzl test, 86% of TNT Sensitivity to initiation, requires a powerful detonator when confined... 

Black Powder is much more sensitive when tested under confinement... 

Moist BkPdr (up to 7% moisture) is more sensitive than dry,BkPdr when tested under partial confinement... 

Sensitivity. 1) B.D. Pollock R.F. Gentner, Impact Sensitivity of Wetted Primary Explosives as Determined by the Ball Drop Test , PATR 4311 (1972) [Table 8 lists the impact sensy data found by these workers on unconfined dry and w-wet Pb Azide. Addnly, they found that w completely desensitized Pb Styphnate and Tetracene and that all fully-wetted unconfined primary expls were less sensitive to impact than when dry, but that partially wet (w-soaked but no excess of w present) confined initiating expls are more sensitive to impact than when fully dried... 

The rate of detonation of ammonium chlorate of density 0.9 g/cm3 is 3300 m/sec, and its expansion in the lead block test is about 250 cm3. Ammonium chlorate is sensitive to impact it explodes if a 2-kg weight is dropped on it from a height of 15-20 cm. It takes fire from the flame produced by a safety fuse, and if confined the flame causes it to explode. 

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