Safety with vacuum

Occasionally the odor of hydrogen cyanide can be detected during the distillation, even when a trap filled with sodium hydroxide pellets precedes the usual trap cooled in dry ice and acetone to protect the pump. For safety, the vacuum pump should be placed in a hood, or provision should be made for the pump exhaust to be vented into a hood or out-of-doors during the distillation. 

Investigators observed a device that appeared to be a combination safety relief valve and a vacuum breaker. The information on this chrome-topped instrument read, Press 26,700 CFM 32.5 psig, and VAC Relief 1,750 1 psig. Despite the nameplate, the trailer was not equipped to deal with vacuum [1],... 

The virtues of the present design are simplicity, portability (static vacuum insulation is used), safety with the use of liquid hydrogen, low liquid hydrogen or helium consumption when these liquids are used, the ability to recover all helium gas if desired and the ability to obtain any temperature in the range between 4 and 300 K without the use of external heat exchangers. The cryostat was designed to withstand forces of up to 5000 lb. These features will be discussed in detail or will become obvious in the succeeding sections. 

For the practical application of safety characteristics, especially for the assessment of explosion hazards at pumping of explosive atmospheres with vacuum pumps, the different conditions for the determination of the safety characteristics and the operating conditions of the vacuum pumps have to be considered. 

Schlenk flask (100 mL), magnetic stirrer, vacuum distillation apparatus, long Vigreux-column with vacuum isolation, safety glasses, laboratory coat, and protective gloves. 

Another option available with rotary vacuum dmm filters is fiiU enclosure. This enables operation under nitrogen or other atmospheres, for reasons such as safety, prevention of vapor loss, etc. Enclosure may also be used to prevent contamination of the material being filtered or to confine the spray from washing nozzles. The rotary dmm filter also can be enclosed in a pressure vessel and operated under pressure. 

Nonmolecular species, including radiant quanta, electrons, holes, and phonons, may interact with the molecular environment. In some cases, the electronic environment (3), in a film for example, may be improved by doping with impurities (4). Contamination by undesirable species must at the same time be limited. In general, depending primarily on temperature, molecular transport occurs in and between phases (5), but it is unlikely that the concentration ratios of molecular species is uniform from one phase to another or that, within one phase, all partial concentrations or their ratios are uniform. Molecular concentrations and species that are anathema in one appHcation may be tolerable or even desirable in another. Toxic and other types of dangerous gases are handled or generated in vacuum systems. Safety procedures have been discussed (6,7). 

Cellulose acetate-propionate (Tenite Propionate-Kodak) is similar to cellulose propionate. With the shorter side chains, cellulose propionate and cellulose acetate propionate tend to be harder, stiffer and of higher tensile strength than CAB. Like CAB they are easy to vacuum form and also tend to be used for similar applications such as steering wheels, tool handles, safety goggles and blister packs. 

Figure 7-8D. Disk of Figure 7-8B with an attached (underside) vacuum support to prevent premature rupture in service with possible less than atmospheric pressure on underside and/or pulsation service. By permission, B.S. B. Safety Systems, Inc. 

The submitters concentrated the reaction mixture by vacuum distillation (100 mm, bath temperature 70°C, vapor temperature 51°C). The weight after concentration was ca. 120 g. The checkers used rotary evaporation with a bath temperature of 65 to 70°C without any problems, and employed an explosion shield as a safety precaution. 

Vacuum operation. The second consideration, illustrated in Figure 24.32, is that at the evaporator temperature, evaporator pressure below atmospheric pressure should be avoided. An evaporator pressure above atmospheric avoids potential problems with the ingress of air into the cycle, which can cause performance and safety problems. However, special designs can use evaporator pressures below atmospheric. The boiling points of some common refrigerants are given in Table 24.3 at atmospheric pressure. 

Two 4 1 cylindrical glass(QVF) vessels with stainless steel end plates, serve as reservoirs(Figure 1) for surfactant solution(B) and water(9). Facility is available to evacuate these vessels as required by means of a rotary vacuum pump with glass cold trap in line to minimise water vapour. Another pipeline permits supply of pure nitrogen, or other gas, at low pressure, to the vessels, to provide a blanket, as desired. Proper operation and safety from over pressure is ensured by a pressure relief valve(10 in Figure 1) and the pressure gauge(P in Figure 1). 

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