Explosion pressure wave

Vessel mptures can also occur when a higher-temperature liquid or solid is combined with a cooler low boiling liquid, transferring sufficient heat from the hotter material to the colder material such that the colder material rapidly vaporizes. No chemical reactions are involved instead, the explosion occurs because the cooler liquid expands as it is converted to vapor, creating high pressures. These are called physical explosions. A common example is a steam explosion, which occurs when liquid water is accidentally introduced into a process vessel operating at an elevated temperature. If the hotter material is above the superheat limit temperature of the evaporating liquid, initial confinement by a vessel is not required to create an explosion pressure wave. 

Explosion-hazard areas should be designed for rapid pressure relief one or more walls or ceilings should be easily pushed out by an explosion pressure wave score window panels for easy rupture. 

When the explosion pressure waves reach the free interface of soils and air, they transport down from the free interface (Fig. 2.35b). Because of expansion waves and the pressure of product gases, the top soils above the explosives lift up (Fig. 2.35c). The tensile waves and shear waves are produced. These second stage producing waves transport radially to all directions have the maximum amplitudes, and induce the waves with maximum oscillations on the earth surface. 

This chapter considers the external impact of crashing aircraft, sabotage and the effect of explosive pressure wave. The external impact is considered with reference to engineering defence measures aircraft impact, otherwise, can be prevented, with variable degrees of effectiveness, by provisions such as by modifying flight corridors or by protecting the nuclear power plant with special forces, etc. 

External hazards must not constitute a large part of the residual risk so specific design measures were taken to consider a more appropriate approach on earthquakes, explosion pressure waves and military aeroplane crashes. This requirement had a significant impact on layout requirements. ... 

The procedure used for determining the load from an explosion pressure wave is demonstrated here in the example of a liquefied propane vessel. In a spherical vessel of 21,000 mm diameter, propane gas is stored under a pressure of 18 bar (Figure 7,44). Because of a manufacturing defect, the vessel is ripped below the liquid level. 

If the inherent capacity of the structure does not suffice, an additional barrier or distance separation should be provided. An increase in the concrete thickness of the exposed structure may also be considered if this enhances the structural capacity to resist other postulated loads. Additionally, heat resistant cladding or tumescent coatings could be used to provide further protection for structural elements. However, it should be verified that such improvements are not endangered by secondary effects potentially associated with the fire scenario (e.g. explosion pressure waves and generated missiles). 

FIG. II-6. Standard load-time function for explosion pressure wave (adapted from Ref [II-5]). 

A laser beam is capable of putting so much energy into a substance in a very short space of time that the substance rapidly expands and volatilizes. The resulting explosive shock wave travels through the sample, subjecting it to high temperatures and pressures for short times. This process is also known as ablation. 

An explosion model is used to predict the overpressure resulting from the explosion of a given mass of material. The overpressure is the pressure wave emanating from a explosion. The pressure wave creates most of the damage. The overpressure is calculated using a TNT equivalency technique. The result is dependent on the mass of material and the distance away from the explosion. Suitable correlations are available (2). A detailed discussion of source and consequence models may be found in References 2, 8, and 9. 

The hot gases expand and produce pressure waves, which travel ahead of the flame. Any dust lying on surfaces in the path of the pressure waves will be thrown into the air and could cause a secondary explosion more violent and extensive than the first. 

Explosions are either deflagrations or detonations. The difference depends on the speed of the shock wave emanating from the explosion. If the pressure wave moves at a speed less than or equal to the speed of sound in the unreacted medium, it is a deflagration if it moves faster than the speed of sound, the explosion is a detonation. 

Uneonfined vapour eloud explosion a large flammable gas or vapour-air eloud burns in free spaee with suffleient rapidity to generate pressure waves, whieh propagate through the eloud and into the suiTounding atmosphere. Sueh events are extremely rare. 

Explosive hazards are reduced by using similar techniques and by structures for explosions through the use of blow-out doors to direct the pressure wave in harmless directions,... 

Shock wave A pressure wave resulting from the rapid closure of a valve or damper in a pipeline or ductwork system, or from an explosion. 

For the two explosive loading systems used, the initial pressure wave into the powder is relatively low, varying from perhaps 1.5-4 GPa. In such cases the most relevant compression characteristic of the powder compact is its crush strength , i.e., the pressure required to compress the porous compact to solid density. In the simulations, this strength can be varied over a wide range with the P-a model. The wavespeed of the initial waves was modeled on the basis of shock-compression data on rutile at densities from 44% to 61% of solid density [74T02]. 

Shock Wave A transient change in the gas density, pressure, and velocity of the air surrounding an explosion point. The initial change can be either discontinnons or gradual. A discontinnons change is referred to as a shock wave, and a gradual change is known as a pressure wave. 

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. 

As described in Section 6.2.1., British Gas performed full-scale tests with LPG BLEVEs similar to those conducted by BASF. The experimenters measured very low overpressures firom the evaporating liquid, followed by a shock that was probably the so-called second shock, and by the pressure wave from the vapor cloud explosion (see Figure 6.6). The pressure wave firom the vapor cloud explosion probably resulted from experimental procedures involving ignition of the release. The liquid was below the superheat limit temperature at time of burst. 

An explosion is defined by StrelUow and Baker " as an event in wliich energy is released over a sufficiently small period of time and in a sufficiently small volmne to generate a pressure wave of finite amplitude traveling away from tlie source. Tliis energy may have been originally stored in tlie system as chemical, nuclear, electrical, or pressure energy. However, tlie release is not considered to be explosive unless it is rapid and concentrated enough to produce a pressure wave tliat can be heard. 

The factors tliat affect miconfined I apor cloud explosions me not well understood. In a model developed by William, it is assmned tliat ignition occurs at a point source, tliat tlie flame front travels out from tlie core at a flame speed S, and tliat the pressure waves produced by the flame generate a weak shock wave tliat travels ahead of tlie flame with a time-dependent velocity. Tlie equation for the flame speed for spherical systems is... 

The maximum explosion pressure is a function of and is directly proportioiuil to die initial pressure. Blast waves are pressure waves of finite amplitude tliat are generated in air by a rapid release in energy and an instantaneous rise in pressure. The most conunon plant explosion types eiicomitered in iiidustiy are chemical, nuclear, expanding vapors, and pressurized gas. 

For pipelines, bursting disks have been proven practical, especially when equipped tvith a sensor to pick up the explosion and a detonator to rupture the disks in advance of the pressure wave. The installation of a moveable... 

In the 1950s, the more descriptive schlieren records of the interactions between pressure waves and deflagration fronts were obtained [16-18], and Oppenheim [9] introduced the hypothesis of the "explosion in the explosion" (of the detonating mixture) occurring in the regime of accelerating flame to explain the sudden change in the velocity of the combustion wave observed in the experiments. 

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