Mechanical overpressure explosions

Chapter 3 Explosives Dehnition of Explosion Categories of Explosions Phases of Explosions Mechanical Overpressure Explosions Mechanical/Chemical Explosions Chemical Explosions Dust Explosions Nuclear Explosions Components of an Explosion Types of Explosives... 

The term explosion is best defined as a process that involves a sudden release of energy resulting in a rapid and significant buildup of overpressure. Explosions can be categorized into physical/mechanical and chemical explosions. For example, an explosion caused by a sudden release of compressed gas is a physical explosion. A chemical explosion is caused by a chemical reaction(s), which could be combustion, exothermic decomposition or exothermic reaction. Chemical explosions can occur in gas, liquid or solid phase. Chemical explosions that occur in liquid and solid phases are sometimes called condensed phase explosions. Explosive explosions fall in this category. 

Overpressure, overtemperature, hydrogen explosion, steam explosion, and core melt through are mechanisms that may fail the containment of nuclear and chemical reactors,... 

Turbulence may arise by two mechanisms. First, it may result either from a violent release of fuel from under high pressure in a jet or from explosive dispersion from a ruptured vessel. The maximum overpressures observed experimentally in jet combustion and explosively dispersed clouds have been relatively low (lower than 1(X) mbar). Second, turbulence can be generated by the gas flow caused by the combustion process itself an interacting with the boundary conditions. 

Release mechanisms are classified into wide and limited aperture releases. In the wide aperture case a large hole develops in the process unit, releasing a substantial amount of material in a short time. An excellent example is the overpressuring and explosion of a storage tank. For the limited aperture case material is released at a slow enough rate that upstream conditions are not immediately affected the assumption of constant upstream pressure is frequently valid. 

The final method uses thermodynamic availability to estimate the energy of explosion. Thermodynamic availability represents the maximum mechanical energy extractable from a material as it comes into equilibrium with the environment. The resulting overpressure from an explosion is a form of mechanical energy. Thus thermodynamic availability predicts a maximum upper bound to the mechanical energy available to produce an overpressure. 

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. 

Finally, there must be a flame acceleration mechanism, such as congested areas, within the flammable portion of the vapor cloud. The overpressures produced by a vapor cloud explosion are determined by the speed of flame propagation through the cloud. Objects in the flame pathway (such as congested areas of piping, process equipment, etc.) enhance vapor and flame turbulence. This turbulence results in a much faster flame speed which, in turn, can produce significant overpressures. Confinement that limits flame expansion, such as solid decks in tnulti-lcvc process structures, also increases flame speed. Without flame acceleration, a large fireball or flash fire can result, but not an explosion. 

The prediction of the overpressure-time history associated with the combustion of an explosive mixture under specified conditions is the central problem of research in the loss prevention field. In the past decade, significant progress has been made in the understanding of the fundamental mechanisms involved in the complex combustion processes. Prompted by the urgency in resolving safety issues in LNG transport, offshore oil production platforms, and nuclear reactors, extensive research programs on gas... 

Important mechanisms for harm to humans as well as damage to the environment and property, which may arise from process plants, are explosions. An explosion results from a spontaneous release of energy. This causes a pressure wave. If the pressure is measured at right angles to the pressure wave we speak of side-on overpressure, which is occasionally also called free field overpressure. If the pressure measuring device is placed in the middle of a wall onto which the pressure wave travels we measure the reflected overpressime. The dynamic pressure is defined as 1/2 pu, where p is the density of the gas involved and u its travelling velocity. 

Therefore, there are three main types accidents of tank area can trigger a domino effect fire, explosion, and fire—explosion occurred in both cases simultaneously cross. The first accident has devastating effects of thermal radiation, and other physical effects like overpressure effects may work on equipment close to the first unit, resulting in the close tank rupture, fire, explosion, that is the secondary accident. Under certain conditions, the secondary accident may lead to higher levels of three or more accident, causing extremely serious consequences of the accident. In simple terms is that two or more times of accidents caused by the initial Tank accident (mainly fire and explosion), and became a serious consequences phenomenon is called Tank domino effect. Figure 1 shows the mechanism of Domino effect in LPG tank area accidents. 

Design deficiencies that render the incineration system unable to overcome the difficulties caused by thermal, mechanical, chemical or radiological failures Introduction of materials into the waste feed that lead to excessive temperatures, overpressurization and/or explosive conditions within the incineration... 

Serious and damaging consequences may result from accidents caused by fires and explosions. Therefore, the incineration system and its off-gas treatment system should be designed to withstand the effects of the overpressure caused by an explosion, and provided with a suitably located pressure relief mechanism. Furthermore, the following measures shall be instituted to minimize the potential for explosions or fires ... 

Special care should be taken particularly in the case of gas cloud explosions as the TNT method overpredicts near field effects and underpredicts far field effects. In some States the application of TNT equivalency is limited to overpressure values of 0.5 bar and other approaches are used for higher values, such as multienergy methods in which the separate effects from pressure and drag wind coming from different explosion cells are accounted for. However, the use of different TNT equivalencies in the near and far fields can overcome such a modelling deficiency. In general, TNT methods are considered suitable for greater distances from the source, for which the source mechanism is less important and such a simplified approach is more realistic and widely valid. 

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