Unconfined 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 explosion Unconfined explosions occur in the open. This type of explosion is usually the result of a flammable gas spill. The gas is dispersed and mixed with air until it comes in contact with an ignition source. Unconfined explosions are rarer than confined explosions because the explosive material is frequently diluted below the LFL by wind dispersion. These explosions are destructive because large quantities of gas and large areas are frequently involved. 

F. Blast effects from a nearby explosion (unconfined vapor cloud explosion, bursting vessel, etc.), such as blast overpressure, projectiles, structural damage... 

Unconfined Vapor Cloud Explosions Unconfined vapor clouds are open-air concentrations of fuels in vapor form. The cloud can dissipate to a harmless condition (from a flammability viewpoint) in which the concentration is too low to bum. In some cases, a source can ignite a cloud as contents exit a container. If ignited at a somewhat controlled... 

The problem of explosion of a vapor cloud is not only that it is potentially very destructive but also that it may occur some distance from the point of vapor release and may thus threaten a considerable area. If the explosion occurs in an unconfined vapor cloud, the energy in the blast wave is generally only a small fraction of the energy theoretically available from the combustion of all the material that constitutes the cloud. The ratio of the actual energy released to that theoretically available from the heat of combustion is referred to as the explosion efficiency. Explosion efficiencies are typically in the range of 1 to 10 percent. A value of 3 percent is often assumed. 

K. Gugan, Unconfined Vapor Cloud Explosions, Gulf Publishing, Houston, Tex., 1979. 

S has been approximated for flames stabili2ed by a steady uniform flow of unbumed gas from porous metal diaphragms or other flow straighteners. However, in practice, S is usually determined less directly from the speed and area of transient flames in tubes, closed vessels, soap bubbles blown with the mixture, and, most commonly, from the shape of steady Bunsen burner flames. The observed speed of a transient flame usually differs markedly from S. For example, it can be calculated that a flame spreads from a central ignition point in an unconfined explosive mixture such as a soap bubble at a speed of (p /in which the density ratio across the flame is typically 5—10. Usually, the expansion of the burning gas imparts a considerable velocity to the unbumed mixture, and the observed speed will be the sum of this velocity and S. ... 

Unconfined Vapor Cloud Explosions (UVCEs) and Boiling Liquid Evaporating Vapor Explosions (BLEXT s)... 

Storage Facilities The Fhxborough disaster (Lees, 1980) occurred on June I, 1974, and involved a large, unconfined vapor cloud explosion (or explosions—there may have been two) and Fire that killed 28 people and injured 36 at the plant and many more in the surrounding area. The entire chemical plant was demolished and 1821 houses and 167 shops were damaged. 

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

Unconfined Vapor Cloud Explosion (UCVE) Occurs when a sufficient amount of flammable material (gas or liquid having high vapor... 

A basic distinction is made between confined unconfined explosions. Confined ex occur within some sort of containment such as a vessel pipework, or a building. Explosio open air are unconfined explosions. 

If the explosion occurs in an unconfined vapor cloud, the energy in the blast wave is only a small fraction of the energy calculated as the product of the cloud mass and the heat of combustion of the cloud material. On this basis, explosion efficiencies are typically in the range of 1-10%. 

Gas dispersion models provided the toxic effects of chemical releases, fire, or unconfined vapor cloud explosion. 

Any flammable liquid under pressure above its normal boiling point will behave like LFG. Liquefied flammable gases are merely the most common example of a flashing liquid. Most unconfined vapor cloud explosions, including the one at Flixborough (Section 2.4), have been due to leaks of such flashing liquids [2],... 

Davenport [1] has listed more than 60 major leaks of flammable materials, most of which resulted in serious fires or unconfined vapor cloud explosions. Table 9-1, derived from his data, classifies the leak by point of origin and shows that pipe failures accounted for half the failures— more than half if we exclude transport containers. It is therefore important to know why pipe failures occur. Following, a number of typical failures (or near failures) are discussed. These and other failures, summarized in References 2 and 3, show that by far the biggest single cause of pipe failures has been the failure of construction teams to follow instructions or to do well what was left to their discretion. The most effective way of reducing pipe failures is to ... 

Detonation Limits (Vol %) for Confined and Unconfined Explosions and Flammability Limits (Vol %) in Oxygen and Air... 

Gugan, K. 1978. Unconfined vapor cloud explosions. Rugby IChemE. 

Historically, this phenomenon was referred to as unconfined vapor cloud explosion, but, in general, the term unconfined is a misnomer. It is more accurate to call this type of explosion simply a vapor cloud explosion. ... 

As with a high explosive, a fuel-air mixture requires a minimum charge thickness to be able to sustain a detonation wave. Hence, a fully unconfined fuel-air charge should be at least 10 to 13 characteristic-cell sizes thick in order to be detonable. If the charge is bounded by a rigid plane (e.g., the earth s surface) the minimum charge thickness is equal to 5 to 6.5 characteristic-cell sizes (Lee 1983). 

Kjaldman, L., and R. Huhtanen. 1985. Simulation of flame acceleration in unconfined vapor cloud explosions. Research Report No. 357. Technical Research Centre of Finland. 

Kletz, T. A. 1977. Unconfined vapor cloud explosions—an attempt to quantify some of the factors involved. AlChE Loss Prevention Symposium. Houston, TX. 1977. 

Lewis, D. J. 1980. Unconfined vapor cloud explosions—Historical perspective and predictive method based on incident records. Prog. Energy Comb. Sci., 1980. 6 151-165. 

Lind,C. D. 1975. What causes unconfined vapor cloud explosions. A/CfiF Low Prevewtion Symp. Houston, proceedings pp. 101-105. 

Munday, G., and L. Cave. 1975. Evaluation of blast wave damage from very large unconfined vapor cloud explosions. International Atomic Energy Agency, Vienna. 

Pickles, J. H., and S. H. Bittleston. 1983. Unconfined vapor cloud explosions—The asymmetrical blast from an elongated explosion. Combustion and Flame. 51 45-53. 

Prugh, R. W. 1987. Evaluation of unconfined vapor cloud explosion hazards. Int. Conf. on Vapor Cloud Modeling. Cambridge, MA. pp. 713-755, AIChE, New York. 

Zeeuwen, J. P., C. J. M. Van Wingerden, andR. M. Dauwe. 1983. Experimental investigation into the blast effect produced by unconfined vapor cloud explosions. 4ih Int. Symp. Loss Prevention and Safety Promotion in the Process Industries. Harrogate. UK, IChemE Symp. Series 80 D20-D29. 

Hasegawa, K., and K. Sato 1987. Experimental investigation of unconfined vapor cloud explosions and hydrocarbons. Technical Memorandum No. 16, Fire Research Institute, Tokyo. 

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