Evacuating—Example

To evacuate 3000 cubic foot vessel full of air at atmos- 

Step 1. Determine evacuation time in minutes per hundred cubic feet. 

Step 2. Go to the final pressure on left of Evacuation Time chart (5 in. Hg hs). Read across and find evacuation time equal to or less than 5 minutes. See Table 6-15. 

The U-2 will evacuate the tank in 5.33 minutes per hundred cubic feet and the U-3 will complete the evacuation in 3.42 minutes per hundred cubic feet. 

Step 3. Read steam consumption of selected unit off Capacity Factor Chart. See Table 6-16. The unit to select 

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For example, assume that it is desired to evacuate air at 2.94 IbFin" with a steam ejector discharging to 14.7 IbFin" with available steam... 

At very low temperatures with hquid air and similar substances, the tank may have double walls with the interspace evacuated. The weh-known Dewar flask is an example. Large tanks and even pipe hues are now built this way. An alternative is to use double walls without vacuum but with an insulating material in the interspace. Perlite and plastic foams are two insulating materials employed in this way. Sometimes both insulation and vacuum are used. 

The insertion of low-emissivity floating shields within the evacuated space can effectively reduce the heat transport by radiation. The effect of the shields is to greatly reduce the emissivity factor. For example, for N shields or N + 2) surfaces, an emissivity of the outer and inner surface of and an emissivity of the shields of the emissivity factor reduces to... 

Where substances are sufficiently stable, removal of solvent from recrystallised materials presents no problems. The crystals, after filtering at the pump (and perhaps air-drying by suction), are heated in an oven above the boiling point of the solvent (but below this melting point of the crystals), followed by cooling in a desiccator. Where this treatment is inadvisable, it is still often possible to heat to a lower temperature under reduced pressure, for example in an Abderhalden pistol. This device consists of a small chamber which is heated externally by the vapour of a boiling solvent. Inside this chamber, which can be evacuated by a water pump or some other vacuum pump, is... 

Pure uninhibited tetrafluoroethylene can polymerise with violence, even at temperatures initially below that of room temperature. There is little published information concerning details of commercial polymerisation. In one patent example a silver-plated reactor was quarter-filled with a solution consisting of 0.2 parts ammonium persulphate, 1.5 parts borax and 100 parts water, and with a pH of 9.2. The reactor was closed and evacuated, and 30 parts of monomer... 

For example, one section of the contractor s SSAHP for Site F required personnel to evacuate the site during an emergency, while other sections of the plan indicated that personnel may respond to spills, leaks, or fires. Neither contractors SSAHPs at Sites C or G identified the individuals responsible for coordinating emergency response activities. 

External events are accident initiators that do not fit well into the central PSA structure used for "internal events." Some "external events" such as fire due to ignition of electrical wires, or flood from a ruptured service water pipe occur inside the plant. Others, such as earthquakes and tornados, occur outside of the plant. Either may cause failures in a plant like internal events. External initiators may cause multiple failures of independent equipment thereby preventing action of presumably redundant protection systems. For example, severe offsite flooding may fli 1 the pump room and disable cooling systems. An earthquake may impede evacuation of the nearby populace. These multiple effects must be considered in the analysis of the effects of external events. 

For example, given a BWR-1 release (Table 8,2-1), typical weather conditions, no rain and less than one mile from the accident immersion, inhalation, and ground produce about the same magnitude doses for exposure times of several hours or less. The exposure from a cloud ceases once the cloud has passed, but exposure may continue from the ground until the area is decontaminated or evacuated. If the exposure time is long, the ground dose can eventually dominate. Tables 9-6 and 9-7 in NUREG/CR-2300 show examples of the relative importance of these pathways. 

The team suggested mitigations. For example, the consequences of an ammonia release could be markedly reduced by a reliable and quick-acting water spray system. The probability of damage due to ship collisions could be reduced by a f tor of five by a speed limit of eight knots. Evacuation of the potentially affected is practicable and effective. 

To estimate tlie potential iiupaet on tlie publie or tlie environment of aeeidents of different types, the likely emergeney zone must be studied. For example, a liazardous gas leak, fire, or explosion may eause a toxie cloud to spread over a great distance. The minimum atmospheric dispersion model. Vtirious models can be used tlie more difficult models produce more realistic results, but tlie simpler and faster models may provide adequate data for planning purposes. A more tliorough discussion of atmospheric dispersion is presented in Part 111 - Healtli Risk Assessment. 

Example 6-10 Size Selection. Utilities and Evacuation Time for Single Stage Ejector... 

Example 6-14 Evacuation of Vessel Using Steam Jet for Ptunping Gases... 

Example Using Penberthy Model U Ejector for Evacuation Time... 

Principles Details of the process and plant, which consists essentially of a heated A/, vapour source contained within a closed coating chamber capable of evacuation to 13-1.3 kN/mm, for example, have been given elsewhereThe subject has also been reviewed by Fabian... 

Dusts, particle sizes, 225 Dusts, hazard class, 521-523 Explosion characteristics, 524 Efficiency, centrifugal pumps, 200 Ejector control, 380 Ejector systems, 343, 344, 351 Air inleakage, table, 366, 367 Applications, 345 Calculations, 359-366 Chilled water refrigeration, 350 Comparison guide, 357, 375 Evacuation lime, 380, 381 Charts, 382 Example, 381 Features, 345... 

Pressure/vacuum, 435, 466 Vacuum systems, 343 Absolute pressure conversions, 363 Air inleakage, 366 Calculations, 366-375 Dissolved gases release, 368 Estimated air inleakage, table, 366 Evacuation time, 371 Maximum air leakage, chart, 367 Specific air inleakage rates, 368 Temperature approach, 375 Classifications, 343 Diagrams, 380 Pressure drop, 353 Pressure levels, 343, 352 Pressure terminology, 348 Pump down example, 381 Pump down time, 380 Thermal efficiency, 384 Valve codes, 26... 

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