BLEVE

An important hazard in the process industry is the boiling liquid expanding vapour explosion (BLEVE). This is understood to be the explosively rapid vaporization and corresponding release of energy of a liquid, flammable or otherwise, upon its sudden release from containment under greater-than-atmospheric pressure at a temperature above its atmospheric boiling point [37]. It is a physical explosion which is a consequence of sudden pressure relief. If a flammable material is involved a chemical explosion or a fireball can follow. 

Most BLEVEs occur with storage vessels, rail or road tankers containing a pressure liquefied gas if they are exposed to a fire or mechanical load, for example following crash or derailment. Furthermore a BLEVE may result from a spontaneous vessel failure. 

The physical explosion is treated here. If it is followed by a fireball (vid. Sect. 10.6.2.1) the following may be assumed if 36 % or more of the liquid is vaporized on pressure relief, the total released mass of fuel contributes to the fireball. For hazard assessments it is reasonable to suppose that three times the mass vaporized by depressurization (upper limit 100 %) partakes in the fireball [37]. 

Since a sudden depressurization is at the start of a BLEVE one may assume that the accompanying turbulences cause an intense mixing of the released material with air. That is why often conservatively and simplilying one assumes that the entire liquid fraction released is vaporized by intake of heat from the air and the condensation of moisture from the air. 

Not in every case a BLEVE will follow depressurization. We may rather encounter a strong vaporization. According to [65] the outcome depends on the initial pressure and the degree of superheat. 

---

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. 

The risk with liquefied petroleum gas in eylinders is signifieantly greater than with a highly flammahle liquid in drums heeause of the potential for rapid release of heavy flammahle gas. In a fire around a eylinder there is a potential BLEVE hazard (see p. 178) ignition of a leak from a valve will eause a jet fire. 

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)... 

Useful formulas for BLEVE fireballs (CeSP, 1989) are given by equations 9.1-27 thru 9.1-30, where M = initial mass of flammable liquid (kg). The initial diameter describes the short duration initial ground level hemispherical flaming-volume before buoyancy lifts it to an equilibrium height. 

The heat flux, E, from BLEVEs is in the range 200 to 350 kW/m is much higher than in pool fires because the flame is not smoky. Roberts (1981) and Hymes (1983) estimate the surface heat flux as the radiative fraction of the total heat of combustion according to equation 9.1-32, where E is the surface emitted flux (kW/m ), M is the mass of LPG in the BLEVE (kg) h, is the heat of combustion (kJ/kg), is the maximum fireball diameter (m) f is the radiation fraction, (typically 0.25-0.4). t is the fireball duration (s). The view factor is approximated by equation 9.1-34. where D is the fireball diameter (m), and x is the distance from the sphere center to the target (m). At this point the radiation flux may be calculated (equation 9.1-30). 

Problem Size Duration and Flux from a BLEVE (CCSP, 1989)... 

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. 

A similar incident to that at Feyzin occurred at this refinery in Brazil in 1972. According to press reports, the relief valve failed to open when the pressure in an LPG sphere rose. To try to reduce the pressure, the operators opened the drain valve. Little water came out, and the LPG that followed it caused the valve to freeze, and the flow could not be stopped. There was only one drain valve. The LPG ignited, the vessel BLEVEd, and 37 people were killed. 

BLEVE The Tragedy of San Jiianico, Skandia International Insurance Corporation, Stockholm, Sweden, 1985. 

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. 

---