Cloud dispersion

S. R. Hanna and P. J. Drivas, Guidelines for Use ofUapor Cloud Dispersion Models American Institute of Chemical Engineers, Center for Chemical Process Safety, New York, 1987. 

Many computer codes, both public and private, are available to model dense cloud dispersion. A detailed review of these codes, and how they perform relative to actual field test data, is available (Hanna, Chang, and Strimaitis, Atmospheric Environment, vol. 27A, no. 15, 1993, pp. 2265-2285). An interesting result of this review is that a simple nomograph method developed by Britter and McQuaid (1988) matches the available data as well as any of the computer codes. This method will be presented here. 

The Britter and McQiiaid model was developed by performing a dimensional analysis and correlating existing data on dense cloud dispersion. The model is best suited for instantaneous or continuous ground-level area or volume source releases of dense gases. Atmospheric stability was found to have little effect on the results and is not a part of the model. Most of the data came from dispersion tests in remote, rural areas, on mostly flat terrain. Thus, the results would not be apphcable to urban areas or highly mountainous areas. 

Steven R. Elanna and Peter j. Privos, Guidelines for Use of Vapor Cloud Dispersion Models, Second Edition, American Institute of Chemical Engineers, New York, NY, 1996. 

Hanna, S. R., and Dtivas, P. J., "Guidelines for Use of Vapor Cloud Dispersion Models."... 

TRACE II Toxic Release Analysis of Chemical Emissions Safer Emergency Systems, Inc. Darlene Davis Dave Dillehay 756 Lakefield Road Westlake Villa, CA 91361 (818) 707-2777 Models toxic gas and flammable vapor cloud dispersion. Intended for risk assessment and planning purposes, rather than realtime emergencies. 

Hanna, S. R. and D. Strimaitis, 1989, Workbook of Test Cases for Vapour Cloud Dispersion Modes, CCPS, New York. 

Spicer, J. W. and J. Havens, 1989, "User s Guide for the DEGADIS 2.1 Dense Cloud Dispersion Model, EPA-4504-89-0I9, November. 

A fuel-air mixture is detonable only if its composition is between the detonabil-ity limits. The detonation limits for fuel-air mixtures are substantially narrower than their range of flammability (Benedick et al. 1970). However, the question of whether a nonhomogeneous mixture can sustain a detonation wave is more relevant to the vapor cloud detonation problem because, as described in Section 3.1, the composition of a vapor cloud dispersing in the atmosphere is, in general, far from homogeneous. 

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. 

The major objective of the experimental program was to obtain data that could be used to assess the accuracy of existing models for vapor cloud dispersion. The combustion experiments were designed to complement this objective by providing answers to the question, What would happen if such a cloud ignited ... 

Maurer, B., K. Hess, H. Giesbrecht, and W. Leuckel. 1977. Modeling vapor cloud dispersion and deflagration after bursting of tanks filled with liquefied gas. Second Int. Symp. on Loss Prevention and Safety Promotion in the Process Irui., pp. 305-321. Heidelberg. 

Guidelines for the Use of Vapor Cloud Dispersion Models, the associated Workbook of Test Cases for Vapor Cloud Source Dispersion Models and research now in progress are directed toward a more complete understanding of the geographic areas affected by a release to the atmosphere. 

Guidelines for Vapor Cloud Dispersion Models, DIERS/ AIChE, 1987. 

Octane and cyclohexane are another liquid pair whose intermolecular interactions are alike. Both have low polarities, so these molecules in the pure liquids are held together by the dispersion forces caused by their polarizable electron clouds. Dispersion forces in solutions of octane and cyclohexane are about the same as in the pure liquids. Again, these two liquids are miscible. 

Guidelines for Safe Storage and Handling of High Toxic Hazard Materials Guidelines for Use of Vapor Cloud Dispersion Models Understanding Atmospheric Dispersion of Accidental Releases Expert Systems in Process Safety... 

Two types of neutrally buoyant vapor cloud dispersion models are commonly used the plume and the puff models. The plume model describes the steady-state concentration of material released from a continuous source. The puff model describes the temporal concentration of material from a single release of a fixed amount of material. The distinction between the two... 

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