Source models

The next part of the procedure involves risk assessment. This includes a deterrnination of the accident probabiUty and the consequence of the accident and is done for each of the scenarios identified in the previous step. The probabiUty is deterrnined using a number of statistical models generally used to represent failures. The consequence is deterrnined using mostiy fundamentally based models, called source models, to describe how material is ejected from process equipment. These source models are coupled with a suitable dispersion model and/or an explosion model to estimate the area affected and predict the damage. The consequence is thus determined. 

Once the scenario has been identified, a source model is used to determine the quantitative effect of an accident. This includes either the release rate of material, if it is a continuous release, or the total amount of material released, if it is an instantaneous release. Eor instance, if the scenario is the mpture of a 10-cm pipe, the source model would describe the rate of flow of material from the broken pipe. 

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. 

Develop an appropriate source model to calculate the release rate or total quantity released based on the specified scenario (see Discharge Rates from Punctured Lines and Vessels). 

For large downwind distances, the virtual distances will be negligible and the point source models are used directly. 

Air pollution dispersion models derived from the UNAMAP6 stationary source models and other specialized dispersion models. Uses more than 20 models. Requires 512K memory and 132 column printer. 

In reality, heat sources are seldom a point, a line, or a plane vertical surface. The most common approach to account for the real source dimensions is ro use a virtual source from which the airflow rates are calcu-lared " " see Fig. 7.64. The virtual origin is located along the plume axis at a distance on the other side of the real source surface. The adjustment of the point source model to the realistic sources using the virtual stmrce method gives a reasonable estimate of the airflow rate in thermal plumes. The weakness of this method is in estimating the location ol the virtual point source. 

Another design method uses capture efficiency. There are fewer models for capture efficiency available and none that have been validated over a wide range of conditions. Conroy and Ellenbecker - developed a semi-empirical capture efficiency for flanged slot hoods and point and area sources of contaminant. The point source model uses potential flow theory to describe the flow field in front of a flanged elliptical opening and an empirical factor to describe the turbulent diffusion of contaminant around streamlines. 

In the point-source model, it is assumed that a selected fraction (/) of the heat of combustion is emitted as radiation in all directions. The radiation per unit area and per unit time received by a target (q) at a distance (x) from the point source is, therefore, given by... 

The solid-flame model can be used to overcome the inaccuracy of the point-source model. This model assumes that the fire can be represented by a solid body of a simple geometrical shape, and that all thermal radiation is emitted from its surface. To ensure that fire volume is not neglected, the geometries of the fire and target, as well as their relative positions, must be taken into account because a portion of the fire may be obscured as seen from the target. 

Flgura 4.13. Contributing acoustic signals superimposed on distributed-voiume source model for a pancake-shaped vapor cloud explosion. 

Section 3.5 mentions two approaches, the point-source model and the solid-flame model. In the point-source model, it is assumed that a certain fraction of the heat of combustion is radiated in all directions. This fraction is the unknown parameter of the model. Values for fireballs are presented in Section 3.5.1. The point-source model should not be used for calculating radiation on receptors whose plane intercepts the fireball (see Figure 6.9B). 

The solid-flame model, presented in Section 3.5.2, is more realistic than the point-source model. It addresses the fireball s dimensions, its surface-emissive power, atmospheric attenuation, and view factor. The latter factor includes the object s orientation relative to the fireball and its distance from the fireball s center. This section provides information on emissive power for use in calculations beyond that presented in Section 3.5.2. Furthermore, view factors applicable to fireballs are discussed in more detail. 

Hymes (1983) presents a fireball-specific formulation of the point-source model developed from the generalized formulation (presented in Section 3.5.1) and Roberts s (1982) correlation of the duration of the combustion phase of a fireball. According to this approach the peak thermal input at distance L is given by... 

Alternative reproach point-source model. Another method of calculating the radiation received by an object relatively distant from the fireball is to use the point-source model. From this approach, the peak thermal input at distance L from the center of the fireball is... 

TABLE 9.2. Effect on Humans from Two Radiation Source Models... 

Ground Distance (m) Solid Flame Model Point Source Model... 

Provides air quality data analysis, source modeling and assessment, meteorological services, small business tccluiical assistance, a source m magcmcnt system, and quality assurance mid calibration standards for air monitoring... 

CALINE3 (California Line Source Model) is a line source dispersion model tliat can be used to predict carbon monoxide concentrations near liighways and arterial streets given traffic emissions, site geometry, and meteorology. 

Source models describe tlie release rate of material from tlie process equipment into tlie external enviromiient, and tlie rate of release of spilled vapors and volatile liquids into the atmosphere. 

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. 

Communication systems, channel models of discrete memoryless, 194,208 discrete, 192 models, 193 random process, 193 source models, 193 discrete memoryless, 194 Compatibility table for magnetic groups, 742... 

The data analysis procedure for the case of constant heat flux is based on the theory describing the response of an infinite line source model (Ingersoll and Plass, 1948 Mogeson, 1983). Although this model is a simplification of the actual experiment, it can successfully be used to derive the geothermal properties (e.g. Kavenaugh, 1984 Austin,. 1998 Gehlin, 1998). 

It is known that the line-source model employed can be rather sensitive to perturbations caused by outside influences such as the daily atmospheric temperature cycle or passing weather fronts (e.g. Austin, 1998 Gehlin, 1998 ... 

The first hours were run with a constant heat flux, allowing an estimate with the line source model. Results of the line source model are an estimated ground thermal conductivity of 2.05 W/m K and a borehole resistance of 0.12 K/(W/m), taking into account fluid properties, flow conditions and average shank spacing this borehole resistance equates to a conductivity of the borehole material of about 2.0 W/m K. 

Figure 1.9 Reaction cycle for an aspartyl protease illustrating the conformational changes within the active site that attend enzyme turnover. Source Model based on experimental data summarized in Northrop (2001). 

There were 311 major chemical manufacturing or consuming plants covered in this study. Because some major chemical plants were sources of more than one chemical, specific point source modeling was applied for 538 plants. Since there may be more than one source type in a plant, dispersion-dosage modeling was conducted for a total of 1819 individual point sources in this study. 

There were 62 source categories involved in the prototype modeling, each modeled in nine regions. Hence, the prototype point source modeling was conducted for a total of 558 prototype sources. 

Further plate-out studies were conducted using radon progeny and thoron progeny reference sources, models Rn-190 and Th-190, respectively, manufactured by Pylon Electronic Development (Ottawa), hereafter referred to as Pylon sources, for simplicity. These are small cylindrical containers (<40 cm3 volume) provided with a Ra-226 source or Th-228 source. The containers can be opened at their base and some suitable material can be placed in it for exposure purposes (Vandrish et al., 1984). The Ra-226 and Th-228 sources decay, respectively, to Rn-222 and Rn-220 which in turn, decay into their progeny. In this respect, the above sources can be considered miniature RTTFs quite suitable or plate-out studies, in which air flow pattern effects are minimized. 

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