Screening Analyses

The plant internal PSA can be used to identify critical equipment that could be damaged by fire. This form of screening was employed in the fire-risk portions of ZIP. At each location considered, the loss of all the equipment in the zone is postulated regardless of the size or position of the fire in the zone. If this does not show the occurrence of an initiating event (LOCA or transient) or if the safety functions are not damage to required for safe shutdown, the location is eliminated from consideration. If the location is found to be critical, it is considered furilier lot-detailed fire growth and fire suppression analyses. 

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Suspension Polymers. Methacrylate suspension polymers are characterized by thek composition and particle-size distribution. Screen analysis is the most common method for determining particle size. Melt-flow characteristics under various conditions of heat and pressure are important for polymers intended for extmsion or injection molding appHcations. Suspension polymers prepared as ion-exchange resins are characterized by thek ion-exchange capacity, density (apparent and wet), solvent sweUing, moisture holding capacity, porosity, and salt-spHtting characteristics (105). 

The products are an oversize (underflow, heavies, sands) and an undersize (overflow, lights, slimes). An intermediate size can also be produced by varying the effective separating force. Separation size maybe defined either as a specific size in the overflow screen analysis, eg, 5% retained on 65 mesh screen or 45% passing 200 mesh screen, or as a d Q, defined as a cut-off or separation size at which 50% of the particles report to the oversize or undersize. The efficiency of a classifier is represented by a performance or partition curve (2,6), similar to that used for screens, which relates the particle size to the percentage of each size in the feed that reports to the underflow. 

There are no official U.S. specifications for teUurium and producers pubUsh thek own standards. TypicaUy the producer specifies the weight and shape of the pieces, a screen analysis of powders, and a maximum content of certain impurities. 

The data for a plot like Fig. 18-60 are easily obtained from a screen analysis of the total crystal content of a known volume (e.g., a liter) of magma. The analysis is made with a closely spaced set of testing sieves, as discussed in Sec. 19, Table 19-6, the cumulative number of particles smaller than each sieve in the nest being plotted against the aperture dimension of that sieve. The fraction retained on each sieve is weighed, and the mass is converted to the equivalent number of particles by dividing by the calculated mass of a particle whose dimension is the arithmetic mean of the mesh sizes of the sieve on which it is retained and the sieve immediately above it. 

Bentonite has expected sihca content of 0.5 weight percent (F is 0.005). Silica density (A ) is 2.4 gm per cii cm, and bentonite (Ag) is 2.6. The calculation requires knowledge of mineral properties described by the factor (fghd ). Value of the factor can be estabhshed from fundamental data (Gy) or be derived from previous experience. In this example, data from testing a shipment of bentonite of 10 mesh top-size screen analysis determined value of the mineral factor to be 0.28. This value is scaled by the cube of diameter to ys-in screen size of the example shipment. The mineral factor is scaled from 0.28 to 52 by multiplying 0.28 with the ratio of cubed 9.4 mm (ys-in screen top-size of the shipment to be tested) and cubed 1.65 mm (equivalent to 10 mesh). 

Example 3 Calculating Sample Weight for Screen-Size Measurement Weight W of bulk sample for screen analysis is calculated by the Gayle model for percent retained on a specified screen with relative standard error s.e. in percent... 

Figure 16-1 and 16-2 present the decision networks that guide contaminant release screening analysis. Figure 16-1 deals with contaminants in or under the soil and Fig. 16-2 addresses aboveground wastes. Any release mechanisms evident at the site will require a further screening evaluation to determine the likely environmental fate of the contaminants involved. 

Perform a preliminary screening analysis to identify aspects of human performance where failures can have serious consequences. 

The purpose of the Critical Task Identification and Screening analysis is to reduce the amoimt of analysis required by focusing on tasks that have a significant error potential. The screening process essentially asks the following questions ... 

Select Task Steps on the Basis of Screening Analysis... 

The task analysis is performed on tasks 2, 3, and 4. Tasks 1 and 5 were eliminated from the analysis because they did not involve any direct exposure to hazardous substances (from the initial screening analysis described in Section 2.1). The analysis considers operations 2.1 to 2.5, 3.1 to 3.2 and 4.1 to 4.5 in Figure 5.6. 

Sieb, n. sieve screen, riddle, bolter, stra ner (for rays) filter mesh, -analyse, /. screen analysis. 

DRY SIEVING OR SCREEN ANALYSIS WOVEN WIRE SIEVES... 

The simplest and the most common method of separating mixtures exclusively by size alone is to make a screen analysis using testing sieves. A set of standard screens is arranged serially in a stack, with the smallest mesh at the bottom and the largest at the top. The analysis is carried out by placing the sample on the top screen. The stack is agitated manually or mechanically for a definite period. The particles retained on each screen are removed... 

The performance of an ideal screen in terms of the screen analysis of the feed is shown in Figure 2.13 (A). The cut point is the point C in the curve. Fraction A comprises all particles bigger than Dpc, and fraction B comprises all particles smaller than Dpc. The fractions A and B are the overflow and underflow respectively. Screen analyses of the ideal fractions A... 

Figure 2.13 Ideal versus actual screening. (A) Ideal screening (B) screen analysis of products from ideal screening (C) actual screening (D) mass balance across a screen.

The equations derived from consideration of material balances over a screen are found to be useful in calculating the ratios of feed, oversize, and underflow from the screen analysis of the three streams and knowledge of the desired cut diameter. Let F stand for the mass of the feed flow, D for the mass of the overflow flow, B for the mass of the underflow flow, mF for the mass fraction of material, A in feed, mD for the mass fraction of material A in the overflow and mB for the mass fraction of material A in the underflow. The mass fractions of material A are shown in Figure 2.13 (C). The mass fractions of material B in the feed, the overflow, and the underflow are 1 - mF, 1 - mD, and 1 - mn respectively. Since the total material fed to the screen must exit either as underflow or as overflow,... 

Bogusz, M., Franke, J. P., de Zeeuw, R. A., and Erkens, M., An overview of the standardization of chromatographic methods for screening analysis in toxicology by means of retention indices and secondary standards. Part II. High performance liquid chromatography, Fresenius ]. Anal. Chem., 347, 73, 1993. 

For screening purposes, however, the analysis has shown that a building of low blast resistance and high episodic occupancy, and that is potentially impacted by three different process units may present an undue aggregate risk and should be evaluated further. In retrospect, this conclusion should have been obvious without the need to resort to the risk-screening analysis. 

Under contract to the Systems and Strategy Development Division of the OAQPS/EPA, Systems Applications developed and applied modeling methods for the estimation of human exposure and dosage from airborne materials. The model is intended for a screening analysis of the impacts of chemicals under EPA review as potentially hazardous by the definitions of the NESHAPS program. 

The actual solutions that were developed are not shown here because they are not needed for a screening analysis. The major features of the solutions Include the following ... 

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