BLEVE explosion

This section first presents literature review on pressure vessel bursts and BLEVEs. Evaluation of energy from BLEVE explosions and pressure vessel bursts is emphasized because this value is the most important parameter in determining blast strength. Next, practical methods for estimating blast strength and duration are presented, followed by a discussion of the accuracy of each method. Example calculations are given in Chapter 9. 

Planas-Cuchi, E., Salla, J., and Casal, J. (2004) Calculating overpressure from BLEVE explosions. Journal of Loss Prevention in the Process Industries 17, 431-436. 

When these two conditions are met, a practically instantaneous evaporation of the contents takes place, with the formation of a large number of boiling nuclei in all the liquid mass (homogeneous nucleation). In these conditions, the velocity at which the volume increases is extraordinary and the explosion is therefore very violent. Strictly speaking, this is the phenomenon associated with the BLEVE explosion. 

Instead, if during the heating process the liquid temperature reaches, for example, 89°C (point R in Fig. 22.2), during the depressurization the tangent line will be reached (point S in Fig. 22.2). In this case the conditions required (superheating) by the aforementioned spontaneous homogeneous nucleation would exist and a BLEVE explosion would occur. 

When a BLEVE explosion involves a flammable substance, it is usually followed by a fireball and intense therm radiation will be released. The thermal energy is released in a short time, usually less than 40 seconds (although this time is a function of the mass in the tank). The phenomenon is characterized from the first moments by strong radiation this eliminates the possibility of escaping for the persons nearby (who also will have suffered the effects of the blast). 

When a vessel bursts in a BLEVE explosion, the mechanical energy contained inside is released (note that toe units of pressure are energy per unit volume). The substance contained in the vessel instantaneously increases in volume due to toe expansion of toe vapor already existing in the vessel at toe moment of toe explosion and the superheated liquid, which undergoes a partial vaporization practically instantaneously (flash). 

The energy released in a BLEVE explosion is distributed among toe following ... 

In fact, most vessels or tanks are constructed with materials that are ductile at the operating conditions. A fragile failure is found only in very special conditions, when the stress reached by the material is much higher than its plastic limit. This only happens with tempered steel and glass. Therefore, BLEVE explosions usually consist of ductile breaking. 

Furthermore, if the vessel contained superheated liquid—as in the case of a BLEVE explosion—the released energy can be estimated approximately by using the same method. In this case, it must be taken into account that the mass of liquid will partly vaporize suddenly when reaching atmospheric pressure. The volume of this vapor at the pressure in the vessel just before the explosion must then be calculated adding this fictitious volume to the real one, the equivalent mass of TNT will be ... 

The pressure wave generated by the explosion can be estimated from the equivalent TNT mass. This method implies a certain inaccuracy because in the BLEVE explosion of a vessel the energy is released at a lower velocity than in a TNT explosion and also because the volume of the vessel is much larger than that which would have the equivalent amount of a conventional explosive. Nevertheless, the method is simple and allows useful estimations. 

Because of their random behavior, projectiles from BLEVEs are one of the most difficult hazards to quantify (Birk, 1996). The fragments thrown by the explosion have a restricted and directional action, but with a larger radius of destructive effects than the pressure wave and the thermal effects of the fireball. These fragments can cause a domino effect if they destroy other tanks or equipment. The velocity required by a fragment to penetrate another similar tank ranges from 4 to 12 m s , and the maximum velocity that can be reached by the fragments in a BLEVE explosion—a function of the conditions at which the explosion occurs, the volume of vapor initially contained in the vessel, and the shape of the vessel— ranges from 150 to 200 m s. ... 

Evaluating the Characteristics of Vapor Cloud Explosions, Elash Eires, and BLEVEs Technical Management of Chemical Process Safety (Corporate)... 

Frank T. Bodurtha/ Sc D / E. I. du Pont de Nemours and Co., Inc., (retired) Consultant, Frank T. Bodui tha, Inc. (Gas Explosions Unconfined Vapor Cloud Explosions [UVCE.s] and Boiling Liquid Expanding Vapor Explosions [BLEVE.s])... 

UNCONFINED VAPOR CLOUD EXPLOSIONS (UVCEs) AND BOILING LIQUID EXPANDING VAPOR EXPLOSIONS (BLEVEs)... 

BLEVE Boiling Liquid Expanding Vapor Explosion... 

BLEVE, BOILING LIQUID EXPANDING VAPOUR EXPLOSION Instantaneous release and ignition of flammable vapour upon rupture of a vessel eontaining flammable liquid above its atmospherie boiling point. 

Explosion a confined vapour cloud explosion (CVCE) can result from ignition of vapour within a building or equipment a boiling liquid expanding vapour explosion (BLEVE) can result when unvented containers of flammable chemicals burst with explosive violence as a result of the build-up of internal pressure unconfmed vapour cloud explosion (UVCE) can result from ignition of a very large vapour or gas/air cloud. 

Instantaneous and continuous releases including spills, leaks, fires, explosions, and BLEVEs. 

Avoid direct sunshine on containment surfaces in hot climates. Direct spills of flammable materials away from pressurized storage vessels to reduce the risk of a boiling liquid expanding vapor explosion (BLEVE). 

Undesired reactions catalyzed by materials of construction or by ancillary materials such as pipe dope and lubricants Boiling liquid, expanding vapor explosions (BLEVEs)... 

At first it was thought that the spheres burst because their relief valves were too small. But later it was realized that the metal in the upper portions of tlie spheres was softened by the heat and lost its strength. Below the liquid level, the boiling liquid kept the metal cool. Incidents such as this one in which a vessel bursts because the metal gets too hot are known as Boiling Liquid Expanding Vapor Explosions or BLEVEs. 

This text is intended to provide an overview of methods for estimating the characteristics of vapor cloud explosions, flash flies, and boiling-liquid-expanding-vapor explosions (BLEVEs) for practicing engineers. The volume summarizes and evaluates all the current information, identifies areas where information is lacking, and describes current and planned research in the field. 

Chapters 7, 8, and 9 demonstrate the consequence modeling techniques for vapor cloud explosions, BLEVEs, and flash fires, respectively, by presenting sample problems. These problems contain sufficient detail to allow an engineer to use the methods presented to evaluate specific hazards. 

Accidents involving fire have occurred ever since man began to use flammable liquids or gases as fuels. Summaries of such accidents are given by Davenport (1977), Strehlow and Baker (1976), Lees (1980), and Lenoir and Davenport (1993). The presence of flammable gases or liquids can result in a BLEVE or flash fire or, if sufficient fuel is available, a vapor cloud explosion. 

This chapter describes the main features of vapor cloud explosions, flash fires, and BLEVEs. It identifies the similarities and differences among them. Effects described are supported by several case histories. Chapter 3 will present details of dispersion, deflagration, detonation, ignition, blast, and radiation. 

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