Field blasting

Near-field blast effects were found to be highly directional for the spheroid burst and the cylindrical detonation. 

Basics of Free-Field Blast Waves. The most severe types of energy releases which can occur in toxic chemical and explosives facilities are explosions of high explosive materials. When such materials are initiated by some stimulus, they may burn, deflagrate or detonate. Detonation is by far the most severe of these three chemical reactions, so it is usually assumed to occur in accident situations, unless one can prove otherwise quite conclusively. 

The ideal side-on parameters almost never represent the actual pressure loading applied to structures or targets following an explosion. So a number of other properties are defined to either more closely approximate real blast loads or to provide upper limits for such loads. (The processes of reflection and diffraction will be discussed later.) Properties of free-field blast waves other than side-on pressure which can be important in structural loading ares... 

Directional Venting. Most vented explosion safety structures are designed with blowout wall panels, entire walls, entire roofs, or even the entire roof and one wall. Other walls and roofs in the structure are designed to withstand a worst-case explosion without catastrophic failure. The explosion-proof parts of the structure provide some close-in blast protection, and hopefully complete protection from fragments and thermal radiation. But blast in the venting directions is not always attenuated compared to free-field blast and can even be enhanced in certain directions. 

When the free field blast wave from an explosion strikes a surface, it is reflected. The effect of this blast wave reflection is that the surface will experience a pressure much more than the incident side-on value. The magnitude of the reflected pressure is usually determined as an amplifying ratio of the incident pressure ... 

The following loads are computed from free field blast wave parameters. Refer to Chapter 3 for load determination procedure. 

The near field blast loading due to main tunnel excavations, could generate displacements in the rock mass, only when the peak particle velocity exceeded the critical vibration levels (V ). After repeated exposures of vibrations due to blast rounds at MAT, CVT and TRT, plastic displacements observed even at lower levels of vibrations than the V. The extra damage due to repeated... 

A free-field blast wave emanates from an explosion until it reaches an object and interacts with it. Sources of explosions that have very high energy and power densities produce ideal blast waves that have predictable properties. A blast wave decays with distance from the source. For high explosive materials, the distance for a blast wave is related to the cube root of the charge weight. In some cases, one can estimate the forces involved in an explosion from the fragment distribution pattern. 

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