Explosives blasting mechanics

Equipment (usually a motor vehicle with or without a mechanical delivery device) that transports explosives, blasting agents or ingre-... 

Explosion blasting includes all mechanical impacts of explosion for the surrounding materials. The blasting of explosives are related to the packed mass, properties of explosives, the geometric figuration, and the surrounding media property (within a distance). 

The present statistical study has been motivated by a desire to better understand and interpret dynamic fragmentation in mechanical systems. Applications include the blasting of rock with explosives or the fragmentation caused by the impact of a high-velocity projectile. For the reasons noted earlier it is difficult to verify the present statistical theory with experiments. Recently, however, support for the theories have emerged from rather diverse sources. 

Generally, at any moment of time the concentration of components within a vapor cloud is highly nonhomogeneous and fluctuates considerably. The degree of homogeneity of a fuel-air mixture largely determines whether the fuel-air mixture is able to maintain a detonative combustion process. This factor is a primary determinant of possible blast effects produced by a vapor cloud explosion upon ignition. It is, therefore, important to understand the basic mechanism of turbulent dispersion. 

If the combustion process within a gas explosion is relatively slow, then expansion is slow, and the blast consists of a low-amplitude pressure wave that is characterized by a gradual increase in gas-dynamic-state variables (Figure 3.7a). If, on the other hand, combustion is rapid, the blast is characterized by a sudden increase in the gas-dynamic-state variables a shock (Figure 3.7b). The shape of a blast wave changes during propagation because the propagation mechanism is nonlinear. Initial pressure waves tend to steepen to shock waves in the far field, and wave durations tend to increase. 

At first glance, the science of vapor cloud explosions as reported in the literature seems rather confusing. In the past, ostensibly similar incidents produced extremely different blast effects. The reasons for these disparities were not understood at the time. Consequently, experimental research on vapor cloud explosions was directed toward learning the conditions and mechanisms by which slow, laminar, premixed combustion develops into a fast, explosive, and blast-generating process. Treating experimental research chronologically is, therefore, a far from systematic approach and would tend to confuse rather than clarify. 

The combustion-flow interactions should be central in the computation of combustion-generated flow fields. This interaction is fundamentally multidimensional, and can only be computed by the most sophisticated numerical methods. A simpler approach is only possible if the concept of a gas explosion is drastically simplified. The consequence is that the fundamental mechanism of blast generation, the combustion-flow interaction, cannot be modeled with the simplified approach. In this case flame propagation must be formalized as a heat-addition zone that propagates at some prescribed speed. 

Acoustic and similarity methods provide useful information in relation to the mechanism of blast generation by gas explosions. These methods of solution, however, require drastic simplifications such as, for instance, symmetry and constant flame speed. Consequently, they describe only hypothetical problems. In point of fact, because of a complex of flame-flow interactions, freely propagating flames do not have constant flame speeds. Furthermore, these methods do not cover decay characteristics. 

Oppenheim, A. K. 1973. Elementary blast wave theory and computations. Proc. of the Conf. on Mechanisms of Explosions and Blast Waves. Yorktown, Virginia. 

Woolfolk, R. W., and C. M. Ablow. 1973. Blast waves for non-ideal explosions. Conference on the Mechanism of Explosions and Blast Waves, Naval Weapons Station. York-town, VA. 

Explosives may be detonated electrically or nonelectrically. A nonelectric firing system will consist of a blasting cap, a length of time (safety) fuse or a firing device attached to the cap, and a means of activating the system match, fuse lighter, delay mechanism, or trip wire. The electric system requires an electric cap which has two wires attached, perhaps additional wire, and a battery or batteries to provide the current which activates the cap. 

The blast wave resulting from a chemical explosion is generated by the rapid expansion of gases at the explosion site. This expansion can be caused by two mechanisms (1) thermal heating of the reaction products and (2) the change in the total number of moles by reaction. 

Various methods are available to limit the damage from the effects of an explosion. The best options are to provide some pre-installed or engineered features into the design of the facility or equipment that allow for the dissipation or diversion of the effects of a blast to nonconsequential areas. Wherever these mechanisms are used the overpressure levels utilized should be consistent with the risk analysis estimates of the WCCE incident. 

Detonation (and Explosion), Mechanical Effects of. These include blast effects, which are described in Vol 2 of Encycl, pp B180 ff and shattering effect, described in Vol 2, pp B265 ff, under BRISANCE. The latter effect causes fragmentation of bombs, shells, grenades, rockets, mines, torpedoes,etc... 

The word detonics in the title is chosen in preference to the word detonation to indicate the physics of detonating high explosives and their mechanical effects. The major emphasis is on commercial high explosives for rock blasting, with the exclusion of Permitted Explosives and the many complicated problems connected with these... 

The compressed pellets are finally dried at 50°C to increase their resistance to mechanical shock. On drying, the moisture content falls below 1%. Blackpowder in the form of cylindrical pellets is the most suitable type of explosive for blasting. Cannon blackpowder was also once produced in the form of prisms (this will be discussed later, in the chapter on cannon blackpowder). 

Delay. A mechanical, electronic, or explosive train component which introduces a controlled time delay in some phase of the arming or functioning of a blasting cap or fuze Ref Glossary of Ord (1959h 91-L... 

Figure 96. Manufacture of Detonators. (Courtesy Hercules Powder Company.) The safe mixing of the primary explosive charge for blasting caps is accomplished mechanically behind a concrete barricade by lifting slowly and then lowering first one corner of the triangular rubber tray, then the next corner, then (lie next, and so on. In the background, the rubber bowl or box in which the mixed explosive is carried to the building where it is loaded into caps.

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