Unconfined vapor cloud

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. 

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 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... 

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 ... 

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. ... 

The introduction of obstacles within unconfined vapor clouds produced flame acceleration. On a small scale, an array of vertical obstacles mounted on a single plate (60 X 60 cm) resulted in flame accelerations within the array (Van Wingerden and Zeeuwen 1983). Maximum flame speeds of 52 m/s for acetylene-air were found, versus 21 m/s in the absence of obstacles, over 30 cm of flame propagation. 

Local partial confinement or obstruction in a vapor cloud may easily act as an initiator for detonation, which may propagate into the cloud as well. So far, however, only one possible unconfined vapor cloud detonation has been reported in the literature it occurred at Port Hudson, Missouri (National Transportation Safety Board Report 1972 Burgess and Zabetakis 1973). In most cases the nonhomogeneous structure of a cloud freely dispersing in the atmosphere probably prevents a detonation from propagating. 

If environmental and atmospheric conditions are such that vapor cloud dispersion can be expected to be very slow, the possibility of unconfined vapor cloud detonation should be considered if, in addition, a long ignition delay is likely. In that case, the full quantity of fuel mixed within detonable limits should be assumed for a fuel-air charge whose initial strength is maximum 10. 

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. 

Bradley, D. "Unconfined Vapor Cloud Explosions." Fire Prevention Science and Technology 21. Leeds University. 

Mancini, R. A. "Workshop on Unconfined Vapor Cloud Explosions."Plant/Op-erations Progress 11, No. 1. January 1992. 

Unconfined explosions. Explosions that occur in the open air are unconfined explosions. An unconfined vapor cloud explosion is one of the most serious hazards in the... 

The problem of the explosion of an unconfined 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. 

---