Gas release modeling

I hong, J., 1980, Hazardous Gas Release Model, Air Resources Branch, EMGRESP Program Documentation, Ontario Ministry of the Environment. 

Toxic Gas Release Modeling. A form of consequence analysis performed by a growing number of operations is the study of the dispersion of released gases into the atmosphere. This is most often used to determine the possible effects of a hypothetical accident. One can calculate a concentration profile at any time, or the concentration at any distance from the source as a function of time, if given the following information ... 

A bumup-dependent fission gas release model has been used to determine the internal gas pressure as a function of irradiation time (Section 4.2.3.1.2 of Reference 6.1). This information has been used to ensure that the plenum volume of the fuel rod has been designed such that the maximum internal pressure of the fuel rod will not exceed the value which would cause fuel damage. Void volume and clearances are provided within the fuel rods to accommodate fission gases released from the fuel, as well as differential thermal expansion between the clad and the fuel, and fuel density changes during irradiation. In addition, the ends of the fuel pellets themselves are dished slightly to allow greater axial expansion at the pellet centreline and to increase the void volume for fission gas release. 

FIG. 26-51 The procedure for using a gas dispersion model to estimate the release impact. 

Models toxic gas releases. Two models available SHELL SPILLS and TRPUF (based on EPA PUFF). Graphical output. Requires 512K memory and 132 column printer. 

Release modeling system. Contains database of chemicals and characteristics which may be modified by user. User selects chemical, weather conditions and type of release for simple or heavy gas modeling. Output is numeric for times and distances with graphic capabilities. 

TOXIC, PUFF, SPILLS, INPUFF, AND INPUFF 2.0 Bowman Environmental Engineering P.O. Bo 29072 Dallas, TX 75229 (214) 241-1895 In ascending order of data complexity, these systems address toxic gas releases using models designed for each type of release, based on emission rate, facility characteristics and weather data. 

The source-term models consist of gas release from a reservoir, a liquid release from a... 

It is user friendly and possesses a graphical user interface for developing the flow paths, ventilation system, and initial conditions. The FIRIN and CFAST modules can be bypassed and temperature, pressure, gas, release energy, mass functions of time specified. FIRAC i.s applicable to any facility (i.e., buildings, tanks, multiple rooms, etc,) with and without ventilation systems. It is applicable to multi species gas mixing or transport problems, as well as aerosol transport problems, FIRAC includes source term models for fires and limitless flow paths, except the FlRlN fire compartment limit of to no more than three... 

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

The released ammonia forms a pool of refrigerated liquid which evaporates by heat transfer from the soil. A constant mass value was assumed for the evaporation rate and a heavier-than-air gas dispersion model was used. 

Ziomas, I. C. et al., 1989, Design of a System for Real Time Modeling of the Dispersion of Hazardous Gas Releases from Industrial Plants, J. Loss Prevention 2 October. 

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. 

If this group has a value greater than or equal to 2.5, then the dense gas release is considered continuous. If the group value is less than or equal to 0.6, then the release is considered instantaneous. If the value lies in-between, then the concentrations are calculated using both continuous and instantaneous models and the maximum concentration result is selected. 

Use the Britter-McQuaid dense gas dispersion model to determine the distance to the 1% concentration for a release of chlorine gas. Assume that the release occurs over a duration of 500 s with a volumetric release rate of 1 m3/s. The wind speed at 10 m height is 10 m/s. The boiling point for the chlorine is —34°C, and the density of the liquid at the boiling point is 1470 kg/m3. Assume ambient conditions of 298 K and 1 atm. 

If gas release is included in the measurements and in the model, these results can be used as boundary conditions for the gas phase combustion, as discussed in the next section. 

The analysis of the potential consequences of an accident is a useful way of understanding the relative inherent safety of process alternatives. These consequences might consider, for example, the distance to a benchmark level of damage resulting from a fire, explosion, or toxic material release. Accident consequence analysis is of particular value in understanding the benefits of minimization, moderation, and limitation of effects. This discussion includes several examples of the use of potential accident consequence analysis as a way of measuring inherent safety, such as the BLEVE and toxic gas plume model results shown in Figures 4, 5, and 6. 

To proceed with a quantitative illustration, it is necessary to adopt some specific model for gas release. It is usually assumed that Fick s law applies, and the problem can be treated as volume diffusion (Section 2.7). As a first approximation, it is often assumed that the sample is composed of uniform spheres of radius a. If it is further assumed that at some initial time / = 0 the gas concentration is uniform, and that the concentration of gas is always nil at the surface of the sphere. Then, after diffusion to time t, the fraction / of the original gas that remains in the sphere is (Carslaw Jaeger, 1959)... 

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