Impact shock

Explosives are commonly categorized as primary, secondary, or high explosives. Primary or initiator explosives are the most sensitive to heat, friction, impact, shock, and electrostatic energy. These have been studied in considerable detail because of the almost unique capabiUty, even when present in small quantities, to rapidly transform a low energy stimulus into a high intensity shock wave. 

Centrifuging of Test material for impact/shock sensitivity and unstable material, thermal hazards shock sensitive, alternate (low energy) separation process for material could shock sensitive/unstable material result in decomposition. CCPS G-13... 

The objective in these gauges is to measure the time-resolved material (particle) velocity in a specimen subjected to shock loading. In many cases, especially at lower impact pressures, the impact shock is unstable and breaks up into two or more shocks, or partially or wholly degrades into a longer risetime stress wave as opposed to a single shock wave. Time-resolved particle velocity gauges are one means by which the actual profile of the propagating wave front can be accurately measured. 

Figure 6.7. Lagrangian time-distance diagram of a symmetric impact shock.

This polyazide (82.3% N) explodes on impact, shock or rapid heating to 170-180°C [1]. When preparing 2,4-diazido-6-dimethylamino-l,3,5-triazine from the 2,4-dichloro compound and sodium azide, there is the possibility of forming the triazido derivative, which detonates violently when touched. Reactions involving organic chlorides and excess sodium azide are extremely dangerous [2]. 

The monomeric azide and several precursors are explosives of moderate to considerable sensitivity to initiation by impact, shock, friction or heat. 

Elliot, M. A. et al., Kept. Invest. No. 4169, Washington, US Bin. Mines, 1948 Tests of sensitivity to initiation by heat, impact, shock or ignition sources were made on mixtures of a variety of absorbent materials containing a stoicheiometric amount of 40-70% perchloric acid. Wood meal with 70% acid ignited at 155°C and a mixture of coal and 60% acid which did not ignite below 200° C ignited at 90° C when metallic iron was added. Many of the mixtures were more sensitive and dangerous than common explosives. 

Overpressure The pressure on an object as a result of an impacting shock wave. 

Case histories regarding reactive chemicals teach the importance of understanding the reactive properties of chemicals before working with them. The best source of data is the open literature. If data are not available, experimental testing is necessary. Data of special interest include decomposition temperatures, rate of reaction or activation energy, impact shock sensitivity, and flash point. 

Lerom, M. W. et al., J. Chem. Eng. Data, 1974, 19, 389-392 Several difluoroaminopolynitro derivatives of stilbene, biphenyl, terphenyl and their precursors are explosives, sensitive to initiation by impact, shock, friction or rapid heating. 

Several fluorodinitro compounds of methane (1,1,1-) and ethane (1,2,2-) are described as explosive, sensitive to initiation by impact, shock, friction or other means [1]. Procedures for safe handling of fluorine and explosive fluoronitro compounds are detailed [2],... 

Chyba, C. F. and Sagan, C. (1992). Endogenous production, exogenous delivery and impact-shock synthesis of organic molelcules an inventory for the origin of life. Nature, 355, 125-32. 

Hj) Height of Burst (Sonic) Test. The purpose of this test is to det the height of burst of a fuze using sonic techniques. This technique requires the measurement of the time of arrival of sound at directional microphones precisely placed in a plane. A brief description of this test is given on p IIIB-20 Ref 39 Addnl info can be obtd from "Instrumentation Section, Technical Services Laboratory, Ammunition Development Division, Ammunition Engineering Directorate, Picatinny Arsenal, Dover, NJ 07801 H2) Hydraulic Ram and Vibrator Test. This test could be used to simulate impact shock on bombs or rockets assembled with fuzes that are launched from aircraft. It also could check the transportability of fuzes that experience this environment. This test is listed, but not described in Ref 39, p IIB-37... 

Initiation by Projectile Impact is a complicated process which depends on a combination of shock initiation, impact initiation and hot fragment initiation effects. For fast projectile impact, shock initiation effects are predominant. With slow projectiles the initiation resembles Impact Initiation. Further complications are introduced if the impacting projectiles are hot a special case where the explosive is part of the projectile is the so-called Susan Test—see Barrier Tests Their Comparison with Shooting Tests in Vo 4, pp D145-147 and Detonation (and Explosion) Experimental Procedures in Vol 4, pp 333-335... 

Okada s conclusions are supported by Streng Kirshenbaum (Ref 20) who found that a stoichiometric mixture (33 mole% CH4) of liq methane and liq oxygen had a higher brisance (in this case they really measured brisance) and a higher detonation rate than other mixts containing from 6 to 80 mole % CH4. They also determined the expl limits and detonation rates of these mixts and examined the sensitivity of the stoichiometric mixt to impact, shock waves, and flame sparks. Their results are summarized below ... 

Various means have been employed to measure shock and free surface velocities. We quote from Ref 7 The earliest work employed a pin technique. Pointed metal pins were spaced at graded distances from the free surface. When the surface was impelled forward by the impacting shock front, it made contact with each of the pins in turn. The pins were wired to separate pulseforming circuits, and the pulses produced on contact were displayed on a high-speed oscilloscope sweep. In this way the free surface velocity... 

The reader is urged to read Initiation of Explosives by Impact in Vol 7,135-R ff of this Encycl, Whereas that article dealt principally with the testing of expls, we shall want to include propints in the discussion. There is probably no subject in hazards analysis which is so actively studied as the role of impact, shock and thermal effects on the safety of expls and proplnts and which is as poorly understood. We have alluded to this incomplete state of theoretical development in the section of this article on Application of Computer Programming... 

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