Detonations direct initiation

This chapter is organized as follows. First, an overview of experimental research is presented. Experimental research has focused on identifying deflagration-enhancing mechanisms in vapor cloud explosions and on uncovering the conditions for a direct initiation of a vapor cloud detonation. 

Because the major causes of blast generation in vapor cloud explosions are reasonably well understood today, we can approach the overview of experimental research more systematically by treating and interpreting the experiments in groups of roughly similar arrangements. Furthermore, some attention is given to experimental research into the conditions necessary for direct initiation of a detonation of a vapor cloud and the conditions necessary to sustain such a detonation. 

A detailed study performed by McKay et al. (1989) revealed some of the conditions necessary for a turbulent jet to initiate a detonation directly. These experiments are covered in more detail in Section 4.1.5. 

V.P. Karpov A.S. Sokolik, "On the Mechanism of Generation of Shock Waves, Their Amplification on Interaction with the Flame, and Transition to Detonation , Ibid, Paper 85, p 149 (Abstracts only) 89h) J.H. Lee et al, "Direct Initiation of Spherical Detonations in Gaseous Explosives , Ibid, Paper 86, p 150 (Abstracts only) 90)... 

G.G. Bach et al, "Direct Initiation of Spherical Detonations in Gaseous Explosions , Ibid, 853-64... 

In some cases, simple burning or deflagration goes over to detonation, after more or less delay. As an example, may be cited MF in which detonation is preceded by a very short period of burning, which started on the surface of the grains and proceeded inward. LA, on the contrary, seemed to detonate directly and it was suggested that it is normally initiated within interior of the grains (See Note)... 

Functioning. The fuze becomes armed after the locking segment moves into the armed position (this occurs at a rotational speed of 6000 to 8500 rpm) and the delay arming shutter moves into the aimed position (this occurs at a rotational speed of 7000 to 8500 rpm). Upon either direct or graze impact, the steel ball moves the striker assembly forward until the striker needle hits the detonator and initiates it. The impulse will be transmitted thru the lead to booster and then to the main charge... 

Civil explosives are also known as commercial or blasting explosives and are typically used for mining, quarrying, construction and tunnel building. They are chemical compositions, which detonate when initiated by high explosive primers or boosters or directly by detonators. They are relatively insensitive to shock, friction or impact... 

Lasers have been used to initiate deton in RDX. Three types of initiation mechanisms have been described (Ref 102) (1) instantaneous deton caused by a shock wave in a thin metallic film (deposited on the expl) with the shock wave generated by a Q-switched laser pulse (2) instantaneous deton by direct interaction of a Q switched laser pulse and the test expl and (3) DDT produced by free-running laser pulses. Coarse RDX cannot be initiated, but milled RDX (particle size less than 40 microns) is readily initiated at various packing densities. The threshold fluences for the initiation of 1.18g/cc l,52g/cc milled RDX via mechanism (1) are 45,3J/cm2 and 127.9J/cm2, respectively. Detons are either essentially instantaneous or the sample bums without deton. For direct initiation [mechanism (2)], the threshold laser energy for 1.18g/cc RDX was 0.8J, or the same as in thin film initiation. However, deton was no longer instantaneous but required about 2 microsec for build-up. The 1.52g/cc RDX was initiated directly without delay (laser energy not given)... 

A detonation can be produced by direct initiation or by a deflagration-to-detonation transition (DDT). The direct initiation of a detonation requires deposition of a large amount of energy into the explosive medium in a very short time (on the order of microseconds). Existing low-pressure data indicate that the transition of a deflagration to a detonation is possible if any of the following occur ... 

Detonation of a gas-air mixture may occur by direct initiation of detonation by a powerful ignition source or by transition from deflagration. This transition occurs in pipelines but is most unlikely in vessels. Two useful rules are ... 

E. K. Dabora, The Relationship between Energy and Power for Direct Initiation of Hydrogen-Air Detonations, in Proceedings of the Second International Conference on the Impact of Hydrogen on Water Reactor Safety, Sandia National Laboratories, Albuquerque, N.M. (1982), 931-952. 

The EBW detonator functions differently from the hot-wire initiators we have seen, in which the ignition material is brought to a critical temperature and then starts to bum. Instead, the EBW produces a shock wave by means of actually exploding the bridgewire and, in turn, initiating detonation directly by the impulse of the shock. 

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