Consequence modeling

The use of computers for rapidly and easily estimating the effects from explosion, fire, and smoke events has grown tremendously in the last several years. 

Specialized risk consultants and even insurance risk offices can now offer a variety of software products or services to conduct mathematical consequence modeling of most hydrocarbon adverse events. The primarily advantage of these tools is that some estimate can be provided on the possible effects of an explosion or fire incident where previously these effects were rough guesses or unavailable Although these models are effective in providing estimate they still should be used with caution and consideration of other physical features that may alter the real incident outcome. 

All mathematical models require some assumed data on the source of release for a material. These assumptions form the input data which is then easily placed into a mathematical equation. The assumed data is usually the size or rate of mass released, wind direction, etc. They cannot possibly take into account all the variables that might exist at the time of the incident. Unfortunately most of the mathematical equations are also still based on empirical studies, laboratory results or in some cases TNT explosion equivalents. Therefore they still need considerable verification with tests simulations before they can be fully accepted as valid. 

The best avenue is to use input data that would be considered the WCCE for the incident under evaluation. One should then question if the output data provided is realistic or corresponds to historical records of similar incidents for the industry and location. In other cases where additional analysis is needed, several release scenarios (small, medium and large) can be examined and probabilities can be assigned to each outcome. This would then essentially be an Event Tree exercise normally conducted during a quantitative risk analysis. Certain releases may also be considered so rare an event they may be outside the realm of accepted industry practical protective requirements. 

Some readily available commercial consequence models include the following  

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Once the source modeling is complete, the quantitative result is used in a consequence analysis to determine the impact of the release. This typically includes dispersion modeling to describe the movement of materials through the air, or a fire and explosion model to describe the consequences of a fire or explosion. Other consequence models are available to describe the spread of material through rivers and lakes, groundwater, and other media. 

An explosion model is used to predict the overpressure resulting from the explosion of a given mass of material. The overpressure is the pressure wave emanating from a explosion. The pressure wave creates most of the damage. The overpressure is calculated using a TNT equivalency technique. The result is dependent on the mass of material and the distance away from the explosion. Suitable correlations are available (2). A detailed discussion of source and consequence models may be found in References 2, 8, and 9. 

For any specific incident there will be an infinite number of incident outcome cases that can be considered. There is also a wide degree of consequence models which can be apphed. It is important, therefore, to understand the objective of the study to limit the number of incident outcome cases to those which satisfy that objective. An example of variables which can be considered is as follows. 

The models you use to portray failures that lead to accidents, and the models you use to propagate their effects, are attempts to approximate reality. Models of accident sequences (although mathematically rigorous) cannot be demonstrated to be exact because you can never precisely identify all of the factors that contribute to an accident of interest. Likewise, most consequence models are at best correlations derived from limited experimental evidence. Even if the models are validated through field experiments for some specific situations, you can never validate them for all possibilities, and the question of model appropriateness will always exist. 

Berger, S. A., and R. J. Lantzy (1996). Reducing Inherent Risk Through Consequence Modeling. 1996 Process Plant Safety Symposium, Volume 1, April 1-2, 1996, Houston, TX, ed. H. Cullingford, 15-23. Houston, TX South Texas Section of the American Institute of Chemical Engineers. 

Kaiser, G. D., 1986, Implications of Reduced Source Terms for Ex-Plant Consequence Modeling and Emergency Planning," Nuclear Safety 27,3, pp 369-384, July-September. 

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. 

Pitblado, R. M. 1986. Consequence models for BLEVE incidents. Major Industrial Hazards Project, NSW 2006. University of Sydney. 

Once you have selected the quantities of material, hazard criteria, and representative materials, consequence models can determine the potential hazard zone. Generally, several of the releases will be very similar and it may be possible to reduce the number of modelling runs by grouping similar releases together. The modelling package you choose will provide guidance on how to set up and run the models. 

It is important to understand tiiat for any specific incident tiiere will be an infinite number of incident outcome cases tliat can be considered. Therefore it is necessary to limit die number of possible incident outcome cases so that die proper consequence model can be applied. 

Cause-consequence analysis serves to characterize the physical effects resulting from a specific incident and tlie impact of these physical effects on people, tlie environment, and property (causes are discussed tluoughout Cliapter 16). Some consequence models or equations (see Chapter 17) used to estimate the potential for dniiuige or injury fall into several categories. ... 

Risk screening (Section 4.3) Information used in consequence modeling I Generic frequency data on events of concern from similar plants I Risk tolerance criteria or methodologies ... 

The company had no consistent design and spacing standards that applied to the process units being evaluated. Therefore, the decision was made to perform consequence modeling as a next step in the screening. 

Consequently, modeling of a two-phase flow system is subject to both the constraints of the hydrodynamic equations and the constraint of minimizing N. Such modeling is a nonlinear optimization problem. Numerical solution on a computer of this mathematical system yields the eight parameters ... 

Pula, R., Khan, F., Veitch, B., and Amyotte, P., 2005. Revised fire consequence models for offshore quantitative risk assessment. Journal of Loss Prevention in the Process Industries 18, 443-454. 

DanieI A. Crowl, Consequence Modeling for the EPA Risk Management Plan (RMP), Process Safety Progress (Spring 1997), pp. 1-5. 

Review the details of the RMP (40 CFR 68), and describe the three program categories that are used for consequence modeling. 

All models, including consequence models, have uncertainties. These uncertainties arise because of (1) an incomplete understanding of the geometry of the release (that is, the hole size), (2) unknown or poorly characterized physical properties, (3) a poor understanding of the chemical or release process, and (4) unknown or poorly understood mixture behavior, to name a few. 

Toxic release and dispersion models are an important part of the consequence modeling procedure shown in Figure 4-1. The toxic release model represents the first three steps in the consequence modeling procedure. These steps are... 

The release mitigation procedure is part of the consequence modeling procedure shown in Figure 4-1. After selection of a release incident, a source model is used to determine either the release rate or the total quantity released. This is coupled to a dispersion model and subsequent models for fires or explosions. Finally, an effect model is used to estimate the impact of the release, which is a measure of the consequence. 

Consequence-Based Ranking Systems Release consequence modeling can be used to rank potential chemical hazards. For example, the USEPAs RMP regulations require consequence modeling for a predefined worst-case scenario—release of the entire contents of the largest container of a material in 10 min. EPA provides lookup tables and software (RMPComp) to assist in estimating the hazard distances for materials covered by the RMP regulations. 

Portions or all of the more complex calculation processes, using specific consequence models, have been incorporated into a few com-... 

A heat flux rate is commonly specified during consequent modeling of hydrocarbon fires. Heat flux is considered the more appropriate measure by which to examine the radiation effects from a fire. A radiant heat flux of 4.7 kw/m (1,469 Btu/ft. ) will cause pain on exposed skin, a flux density of 12.6 kw/rrfl (3,938 Btu/ft.2) or more may cause secondary fires and a flux density of 37.8 kw/m (11,813 Btu/ft. ) will cause major damage to a process plant and storage tanks. 

Consequence Modeling - A description of the possible incidents that can occur. 

Conrad-Limpach-Knorr synthesis, of quinolines, 21 189 Conrad recycling process, 21 455 Conradson carbon test method, 11 705, 721 Consensus materials standards, 15 743 Consent decree protocols, in the United States, 11 692-694 Consent decrees, 11 689-690 Consequence analysis, 21 860-861 Consequence modeling, 13 165-166 Conservation applications, high performance fibers in, 13 398 Conservation of energy, 21 290 Conservation of mass, 11 737, 738-739 Conservation, of resources, 24 164-167 Conservation scientists, 11 398-399 Consistent force field, 16 744 Consolidants, in fine art examination/ conservation, 11 410... 

See also Hazard acceptance Hazard assessment Hazard identification entries limitations of, 13 153-154 probability, 13 166-170 purpose of, 13 152 scenario identification, 13 165 source modeling and consequence modeling, 13 165-166 sustainable development and, 24 183-188 techniques for, 13 152-154 Hazard and operability (HAZOP) analysis, 13 154, 157-159 guide words for, 13 158t sample, 13 159... 

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