Spread of detonation

Spread of Detonation. See under Detonation (and Explosion), Initiation (Birth), and Propagation (Growth or Spread) in Explosive Substances in Vol 4, D402 ff... 

In the past it was difficult to prevent the spread of explosions through vent systems, as flame arrestors were effective only when located at the ends of pipes. Effective inline detonation arrestors are now availabe. Like all flame arrestors they will, of course, need regular cleaning, something that is often neglected. In other cases, when tanks have been over-... 

Nitroglycerine can detonate in pipes of diameter down to approximately 5 mm. In nitroglycerine manufacture there is, therefore, an inherent danger of transmission of detonation from one manufacturing house to another in the series. Even a pipe which has been emptied of nitroglycerine can have on it a skin of the product sufficient to enable transmission of detonation from one end of the pipe to the other. To prevent the spread of an accident it is now usual to transfer nitroglycerine as a non-explosive emulsion in an excess of water. Such emulsion transfer is particularly convenient with the NAB process, as the emulsion transfer lines can also carry out the necessary process of washing and purification. 

A recent alternative to shaped charges is known as the squashhead projectile. As the name implies, this contains a plastic explosive which spreads on impact so as to make contact with the largest possible area of the tank before detonating. When the explosive detonates, reflection of the shock wave causes a scab of metal to be displaced from the inside surface of the armour plate (see p. 135). The effect inside the tank can therefore be greater than is the case with a shaped charge which may do little more than penetrate the armour. The amount of scabbing is approximately proportional to the area of contact of the explosive at the moment of detonation. 

Decomposition of a 70% nitric acid-ammonium nitrate slurry explosive led to overflow, contact with wood and a fire. This spread to detonators, which initiated detonation of the slurry. 

Studies were made of the detonation with hemispherical, ellipsoidal, and conical liners and a theory was developed which appeared to give a plausible explanation of the optimum shapes of liners. It was discovered during these studies, that highspeed rotation decreased very markedly the cavity effect, and that consequently, spin-stabilized projectiles were ill-adapted to cavity charges. Towards the end of 1943, the spreading of the jet, due to rotation, was confirmed photographically by the Kerr-cell camera... 

For more detailed description of particle-velocity measurements, see "Detonation, Particle Velocity in and Its Determination Andreev Belyaev (Ref 44, pp 247-49) describe a method of experimental determination of pressure of detonation, using the arrangement shown in Fig B, Here 1 is charge of an explosive enclosed in a metallic container, and 2 is a metallic (usually aluminum) plate, 1-2mm thick, firmly inserted as a cover at the end of cartridge opposite detonator, 3. On initiation of charge, a shock wave will spread to plate 2 and, when the wave reaches the outer surface of the plate, it will start to move with initial velocity VH (here H is nachaT-naya, which means initial). After determining this velocity experimentally, the... 

In the case of a freely spreading detonation wave (in a cartridge not closed with plate 2), pM is not equal to pD, which is the pressure of detonation at the Chapman-Jouguet Point (ie in the plane of completion of chemical reaction), but can be calculated. If detonation velocity, D, and its density, are known, pD may be calcd... 

Abel assumed that molecules of each.expl vibrate during deton and thus incite vibrations of the surrounding medium at a frequency characteristic for each. expl. The particles of the medium spread in all directions and, if another charge of the same expl is in the neighborhood, its particles start to vibrate in resonance and thus might initiate deton. This was an explanation of the phenomenon known now as "detonation by influence or "sympathetic detonation . The propagation of deton in condensed expls was assumed to be caused by. spread of vibrations in resonance with particles inside the expl. This theory was abandoned in 1883 in favor of the Berthelot Theory of Detonation, which is briefly described in Vol 2 of this Encycl, p B106-L. Berthelot s Theory was further developed by. P. Vieille... 

Explosion, Effects of the Physicol Structure and the State of Aggregation on the Detonating Capacity of Explosives. Liquid TNT detonates only if the diam of the specimen is above 32mm. TNT powder compressed to the sp gr of the liquid TNTj detonates at diams of 2.1mm or greater. Pieces of solid TNT are similar to liquid TNT- Maximum diams for liquid TNT and TNT powder are 2.3 and less than 2mm, respectively. Gas space between expl particles facilitates deton, presumably because hot gases spread the deton Ref A.Ya. Apin V.K. Bobolev, ZhFizKhim 20, 1367—70(1946) Engl abstract in CA 41, 3297(1947)... 

Taking all 80 data sets, the average absolute difference between P0ai0 [Eq. (1)] and JP pti is 5.41% the 90% confidence interval is d=4.38% (72 of 80 data sets excluding results marked with ). The results break down as follows 22 calculated detonation pressures differ from measured values by 0-3% 36, by 3-6% 10, by 6-9% 9, by 9-12% and one each, by + 14%, +18%, and —28%. In view of the spread of the experimental results and the inherent inaccuracies mentioned above, we consider such agreement to be about as good as might be expected of any calculational method. 

The PETN crystals are transferred to a large sheet of waxed paper, spread out and allowed to dry. When the solvents have evaporated from them, the PETN can be processed into plastic. My favorite PETN plastic is made by mixing PETN with nitroglycerin. I like it because it is extremely powerful (more powerful than C-4), easily detonated, and made from readily available materials. Its lone drawback is that the ease of detonation also means that rough handling could set it off. It must be treated with respect. 

To study the detonation of liquid explosives and its spreading/transportation, nitromethane, nitroglycerine, diethyleneglycol dinitrate, and methyl nitrite are designed as the objectives of liquid explosives to study the chemical dynamics and the complex unsteady process of shock waves combustion. These phenomena determine the structure of detonation wave fronts and spreading limit of detonation waves. They help to clear the flow dynamics of wave fronts, and refer suggestions for the formula of liquid explosives, study and application of equipment features. They help to improve and perfect the detonation theory. 

In the past, it is believed that the detonation of an explosive only has overcompressed detonation, and normal detonation, or DTT detonation from self-sustaining spread combustion/buming to detonation. Although there are detonation phenomena, which are not normally explained, only CJ detonation and its features gained the attention. Other kind of detonation is seldom being referred. If proper ignition method is used, most detonation can be transited into under-compressed detonation. Under compressed detonation is corresponding to the over compressed detonation state . Earlier it was also named weak detonation [4, 5]. 

The classic detonation theory has proved that the stable/steady detonation waves of explosives propagate with CJ rate and there are sonic flows in the boundaries of detonation reactions. If the detonation waves propagate faster than CJ rate, there are subsonic flows in the boundaries of reactions. The classic detonation theory predicted that there were sustaining stable/steady detonation waves and possible special unsustaining detonation waves. The spread rates of ultrasonic waves in the boundaries of reactions are eigenvalue detonation rates. 

When a detonation occurs, a blast wave is produced which spreads out from the point of detonation like the ripples produced by dropping a stone into a pond. The blast wave travels faster than the speed of sound in air, compressing the air in front of it and producing an almost instantaneous rise in pressure lasting a fraction of a millisecond before falling away to a negative pressure (see Fig. 3.3). Atmospheric pressure is then restored as the blast wave passes. The blast wave is responsible for primary blast injuries (pages 95-96). 

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