Explosion effect models

This is why NATO AC/258 (Group of Experts on the Safety Aspects of Transportation and Storage of Military Ammunition and Eixplosives) decided to take advantage of this new knowledge and reinvestigate some of the explosion effect models for future inclusion in their safety manual [12] as well as in a proposed NATO risk analysis manual. 

Explosion effect models predict the impact of blast overpressure and projectiles on people and objects. 

Explosion effect models are easy to use. Projectile effect models are more difficult to apply. 

A principal parameter characterizing an explosion is the overpressure. Explosion effect modeling generally is based on TNT explosions to calculate the overpressure as a function of distance. Although the effect of a TNT explosion differs from that of a physical or a chemical explosion (particularly in the near-field), the TNT model is the most popular because a large data base exists for... 

One of the complicating factors in the use of a TNT-blast model for vapor cloud explosion blast modeling is the effect of distance on the TNT equivalency observed in actual incidents. Properly speaking, TNT blast characteristics do not correspond with gas explosion blast. That is, far-field gas explosion blast effects must be represented by much heavier TNT charges than intermediate distances. 

Blast effects can be represented by a number of blast models. Generally, blast effects from vapor cloud explosions are directional. Such effects, however, cannot be modeled without conducting detailed numerical simulations of phenomena. If simplifying assumptions are made, that is, the idealized, symmetrical representation of blast effects, the computational burden is eased. An idealized gas-explosion blast model was generated by computation results are represented in Figure 4.24. Steady flame-speed gas explosions were numerically simulated with the BLAST-code (Van den Berg 1980), and their blast effects were calculated. 

A more deterministic estimate of a vapor cloud s blast-damage potential is possible only if the actual conditions within the cloud are considered. This is the starting point in the multienergy concept for vapor cloud explosion blast modeling (Van den Berg 1985). Harris and Wickens (1989) make use of this concept by suggesting that blast effects be modeled by applying a 20% TNT equivalency only to that portion of the vapor cloud which is partially confined and/or obstructed. 

Effect models describe the impact of the physical effects of a fire, e.xplosion, or toxic gas release on exposed people, the environment or property, based on the results of tlie source, dispersion, and fire and explosion models. 

Cause-consequence analysis serx es to characterize tlie physical effects resulting from a specific incident and the impact of these physical effects on people, the environment, and property. Some consequence models or equations used to estimate tlie potential for damage or injury are as follows Source Models, Dispersion Models, Fire Explosion Models, and Effect Models. Likelihood estimation (frequency estimation), cliaractcrizcs the probability of occurrence for each potential incident considered in tlie analysis. The major tools used for likelihood estimation are as follows Historical Data, Failure sequence modeling techniques, and Expert Judgment. 

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. 

For this purpose the knowledge on the effects of explosives forms a basis. Many of the available correlations refer to the effect of explosions of TNT (trinitrotoluene). The important difference between the explosion of an explosive and that of a flammable gas is its brisance. It is reflected by a particularly short pressure wave. This is true as well for TNT. Despite this difference the TNT equivalent is the most frequently used model for assessing explosion effects. Values between 4,190 and 4,650 kJ/kg are quoted for the equivalent (cf. [15]). In [2] a value of 4,681 kJ/kg is used. In what follows a value of 4,650 kJ/(kg TNT) is chosen. It serves to convert the energy released in an explosion into an equivalent quantity of TNT. 

ABSTRACT Oil storage tank is flammable, explosive or toxic substances accumulation area. For the fire explosion accident, it s likely to cause secondary or more accidents, which are known as the domino effect . This paper summarizes the deflnition of the domino effect . LPG storage tank is selected as the research object. The study is focused on the domino effect mechanism and the improvement of criteria of escalation consequence severity. Damage threshold and probabihty model are estabhshed. The calculation method of chain effect of tank area is introduced into the safety evaluation. Through a case study, the calculation steps and result of the method is described. The accident severity and the probabihty of domino effect were obtained based on fire and explosion model. The quantitative evaluation of tank explosion damage model is realized according to different escalation vectors. By comparing the result between primary and domino accident, domino effect needs more consideration. 

Confined Explosions. Confined explosions occur when a flammable mixfure in a confined space is ignited. A typical example is the case of a flammable liquids tank. When these tanks are emptied, residu liquid may evaporate and form a flammable mixture in the tank. If ignited, a confined explosion would be produced. The modeling of confined explosion effects is analogous to the modeUng of BLEVEs. Here the explosion energy released is obtained from the enthalpy of combustion. 

In this paper we describe a mathematical model of melt/water physical explosions. This model has been developed to study the escalation and propagation stages of a vapor explosion. After describing the physics of this problem, we give a complete description of the conservation equations and constitutive relations that form the model. We then describe the the solution procedure and present some results from simulations that have been performed to study the effect of the presence of permanent gas in the coarse mixture and to compare our predictions using an approximate equation of state (EOS) with those using a standard steam table package. 

Simulation and optimization are key tools for improving the operations of a chemical process. Unfortunately, the results from these tools are only a good as the accuracy and appropriateness of the process model. This paper presents a model of a polymer batch process that has been modified to include safety constraints. These safety constraints are based upon reactor being able to contain an explosion. Based upon this idea, runaway behavior and cooler limitations are incorporated in the process model since they determine the possibility of an explosion. Neither modeling task was simple to include since they relied upon conditional statements, generation of multiple scenarios, and computational complexity from nonlinear equations such as log mean temperature difference. The optimization of the process model with respect to runaway behavior required the analysis of multiple scenarios or parallel simulations for example. These multiple scenarios would describe the effect of runaway reactions at different times from the basic process profile. In the end, the simulation of the process model ran satisfactory and work on the optimization of the model is in process. 

Most effect models for explosions are based on either the blast overpressure alone, or a combination of blast overpressure, duration, and/or specific impulse. The blast overpressure, impulse and duration are determined using a variety of models, including TNT equivalency, multi-energy and Bakcr-Strehlow methods. See Section 3.1 for details on these models. 

The strength of explosion and projectile effect models is their base of experimental data and general simplicity of approach. A weakness relates to the difference... 

Given quantitative results from explosion overpressure models and projectile analysis, effects can be determined by reference to published data on damage or injury level. No special computational resources arc required. 

All hydrocarbon fire mechanisms and estimates will be affected to some extent by flame stability features such as varying fuel composition as lighter constituents are consumed, available ambient oxygen supplies, ventilation parameters, and wind effects. Studies and experimental tests are ongoing by some research institutes and industries to provide more precise modeling techniques into the release of gas, its dispersion, fire, and explosion effects. 

Many sophisticated models and correlations have been developed for consequence analysis. Millions of dollars have been spent researching the effects of exposure to toxic materials on the health of animals the effects are extrapolated to predict effects on human health. A considerable empirical database exists on the effects of fires and explosions on structures and equipment. And large, sophisticated experiments are sometimes performed to validate computer algorithms for predicting the atmospheric dispersion of toxic materials. All of these resources can be used to help predict the consequences of accidents. But, you should only perform those consequence analysis steps needed to provide the information required for decision making. 

Consequence Phase 3 Develop Detailed Quantitative Estimate of the impacts of the Accident Scenarios. Sometimes an accident scenario is not understood enough to make risk-based decisions without having a more quantitative estimation of the effects. Quantitative consequence analysis will vary according to the hazards of interest (e.g., toxic, flammable, or reactive materials), specific accident scenarios (e.g., releases, runaway reactions, fires, or explosions), and consequence type of interest (e.g., onsite impacts, offsite impacts, environmental releases). The general technique is to model release rates/quantities, dispersion of released materials, fires, and explosions, and then estimate the effects of these events on employees, the public, the facility, neighboring facilities, and the environment. 

---