Boiling liquid expanding vapor cloud explosion

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)... 

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. 

Potential explosion phenomena include vapor cloud explosions (VCEs), confined explosions, condensed-phase explosions, exothermic chemical reactions, boiling liquid expanding vapor explosions (BLEVEs), and pressure-volume (PV) ruptures. Potential fire phenomena include flash fires, pool fires, jet fires, and fireballs. Guidelines for evaluating the characteristics of VCEs, BLEVEs, and flash fires are provided in another CCPS publication (Ref. 5). The basic principles from Reference 5 for evaluating characteristics of these phenomena are briefly summarized in this appendix. In addition, the basic principles for evaluating characteristics of the other explosion and fire phenomena listed above are briefly summarized, and references for detailed evaluation of characteristics are provided. 

Boiling-liquid expanding-vapor explosion (BLEVE) A BLEVE occurs if a vessel that contains a liquid at a temperature above its atmospheric pressure boiling point ruptures. The subsequent BLEVE is the explosive vaporization of a large fraction of the vessel contents possibly followed by combustion or explosion of the vaporized cloud if it is combustible. This type of explosion occurs when an external fire heats the contents of a tank of volatile material. As the tank contents heat, the vapor pressure of the liquid within the tank increases and the tank s structural integrity is reduced because of the heating. If the tank ruptures, the hot liquid volatilizes explosively. 

Daniel A. Crowl, Ph.D. Professor of Chemical Engineering, Michigan Technological University Fellow, American Institute of Chemical Engineers (Section Editor, Process Safety Introduction, Combustion and Flammability Hazards, Gas Explosions, Vapor Cloud Explosions, Boiling-Liquid Expanding-Vapor Explosions)... 

Boiling liquid expanding vapor explosion (BLEVE) or boiling liquid compressed bubble explosion (BLCBE), discussed in Section 2.5.3 and in Guidelines for Evaluating the Characteristics of Vapor Cloud Explosions, Flash Fires, and BLEVEs (CCPS, 1994). 

A Latin American chemical plant experienced a catastrophic fire and series of Boiling Liquid Expanding Vapor Explosions (BLEVEs) that resulted in the loss of one life and 5 million in direct damages (1977 dollars). The initial vapor cloud occurred as a maintenance mechanic started to remove a pneumatic actuator from the liquid discharge line below a tank of flashing flammable liquid that had a boiling point of 7° F (—14° C). 

This means "Boiling Liquid Expanding Vapor Explosion" and characterizes the physical explosion of a liquefied gas/supercritical fluid that is brutally decompressed to atmospheric pressure, in case of pressure vessel rupture or opening. Catastrophic BLEVE occurred when liquefied petroleum gases vessels burst (Mexico, Feyzin,...), followed by the "chemical" explosion due to gas cloud inflammation. In fact, this hazard is directly linked to metal weakening in case of fire around the vessel(s). It is the reason why it is recommended to install fire detectors that could order immediate depressurization of the whole plant in case of fire. 

Fire is more likely tlian an explosion where tliere is a loss of contaimnent of a flammable material from a railroad car, barge, ship lank, or from a pipeline. However, both uiiconfiiicd vapor cloud explosions (UVCES) and boiling liquid-expanding vapor e. plosions (BLEVES) can occur as a result of transport accidents, (sec Section 7.5)... 

A boiling liquid-expanding vapor explosion occurs when a pressure vessel containing a liquid is heated to a temperature liigh enough to cause tlie metal to lose strength and rupture. The source of tlie heat is normally another fire near tlie vessel. The effects of a BLEVE depend on whether tlie liquid in die vessel is flanunable. If the liquid is flammable, it may eitlier cause a fire, which radiates heat, or fonii a vapor cloud, which could result in a second explosion. 

Incident Outcome The physical manifestation of the incident for toxic materials, the incident outcome is a toxic release, while for flammable materials, the incident outcome could be a boiling liquid expanding vapor explosion (BLEVE), flash fire, vapor cloud explosion (VCE), etc. For example, the incident ontcome for a leak of chlorine from a railcar is a toxic release. 

Overpressure for explosions (for a confined explosion, boiling liquid expanding vapor explosion [BLEVE], or vapor cloud explosion [VCE])... 

Many types of outcomes are possible for a release. This includes vapor cloud explosions (VCE) (Section 3.1), flash fires (Section 3.2), physical explosions (Section 3.3), boiling liquid expanding vapor explosions (BLEVE) and fireballs (Section 3.4), confined explosions (Section 3.5), and pool fires and jet fires (Section 3.6). Figure 3.1 provides a basis for logically describing accidental explosion and fire scenarios. The output of the bottom of this diagram are various incident outcomes with particular eflfects (e.g., vapor cloud explosion resulting in a shock wave). 

Figure 1. Comparison of major accidents in Middle Eastern case (blue) with world accidents (red) in the oil and gas industry percentages of different scenarios. (LOCA Loss of containment F Fire EX Explosion BLEVE boiling liquid expanding vapor explosion IE internal explosion TOX toxic release VCE vapor cloud explosion VCF vapor cloud fire VEEB vapor escape into, and explosion in, building, B blowout).

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