Closed-transfer system effectiveness

Studies on the Effectiveness of Closed-Transfer Systems for Mixing and Loading Toxicity Category I and II Products Containing Organophosphates and N-methyl Carbamates... 

The regulations adopted by the California Department of Food and Agriculture requiring the use of closed-transfer systems went into effect in April 1977. At that time, several types of equipment were put into use, and a series of studies were undertaken to evaluate their effectiveness in protecting workers. 

In one study (2), plasma and RBC ChE activities were followed from May to September in two mixer-loaders (ML) who used a Swampmate closed-transfer system (Cherlor Manufacturing Co., Salinas, California), and in three mixer-loader applicators (MLA) who used a Model SS 12-4 closed-transfer system (Soil Serv, Salinas, California). The results shown in Fig. 1 indicate that the activities of plasma and RBC ChE were depressed during the application season, but returned to normal by the middle of September. The MLA showed less plasma and RBC ChE depression. It is interesting to note that the plasma ChE showed the "rebound effect," recording levels way above baseline. 

The results indicate that the closed-transfer system reduced worker exposures below that of previously used methods. Powders are hard to handle, however, and workers must be trained to use the equipment effectively. 

The Department has developed methods for monitoring the exposure of workers exposed to organophosphate and carbamate pesticides. These methods utilize the determination of plasma and red blood cell cholinesterase activities and urinary alkyl phosphates. Studies are reported vrti ich show that these methods have proven useful in evaluating the safety effectiveness of closed-transfer systems and in determining reentry times for field workers. 

An important consequence of quantal charge transfer between ions and ion pairs (dipoles) is the appearance of non-pairwise-additive cooperative or anticooperative contributions that have no counterpart in the classical theory. These nonlinear effects strongly stabilize closed-CT systems in which each site is balanced with respect to charge transfers in and out of the site, and disfavor open-CT systems in which one or more sites serves as an uncompensated donor or acceptor. This CT cooperativity accounts for the surprising stability of cyclic (LiF) clusters, which are strongly favored compared with linear structures. 

An appropriate electron carrier such as PMS (5-N-methyl-phenazonium methylsulfate) can mediate a cyclic electron transfer around photosystem 1. PMS mediates the cyclic electron flow by serving as an electron acceptor on the reducing side of PS 1 with the reduced PMS serving as a donor of electrons directly to photooxidized P700, as illustrated in Fig. 9 (A). Thus a simple system containing just photosystem I embedded in a closed membrane system that also contains the ATP synthase plus the electron carrier PMS should in principle carry out photophosphorylation. Indeed, Hauska, Samoray, Orlich and Nelson prepared such a simple, minimum system using purified individual membrane complexes of chloroplasts, namely, photosystem I and ATP synthase, plus a soybean phospholipid (asolectin) as the membrane matrix to demonstrate its expected effectiveness. 

Transfer system. The principal system used to transfer fuel and other components to and from the reactor vessel is the closed loop ex-vessel machine (CLEM) shown in Fig. A.2. The CLEM loads all components into the reactor vessel and removes all components from the reactor vessel and operates only when the reactor is shutdown. Under most conditions, CLEM moves a core component pot (CCP) that contains the fresh or SNF fuel to and from the reactor vessel. In a fast reactor, the core power density is very high thus, there is significant decay heat in each SNF assembly immediately after reactor shutdown. To prevent fuel failure from overheating, the SNF is kept in sodium at all times to ensure effective cooling. This is accomplished by transferring each fuel assembly in its own pot of sodium—the CCP. CLEM is also used to transfer a variety of other components within the reactor containment. 

A closely related solvent effect can be achieved by use of phase transfer catalysis. These catalysts are salts in which one of the ions has large nonpolar substituent groups which confer good solubility in nonpolar solvents. The most familiar examples are quaternary ammonium and quaternary phosphonium salts with several long-chain alkyl substituents. In a two-phase solvent system consisting of water and a nonpolar organic solvent containing a salt, there will be virtually no ions present... 

Gas-Cycle Systems. In principle, any permanent gas can be used for the closed gas-cycle refrigeration system however, the prevailing gas that is used is air. In the gas-cycle system operating on the Brayton cycle, all of the heat-transfer operations involve only sensible heat of the gas. Efficiencies are low because of the large volume of gas that must be handled for a relatively small refrigera tion effect. The advantage of air is that it is safe and inexpensive. 

Recent developments in rotary atomization include the use of semiconductive composites (qv) for the rotary cup permitting the constmction of a unit that does not produce an ignition spark when brought close to a grounded workpiece yet has the transfer efficiencies associated with a rotary atomizer. In addition, the use of the semiconductive material softens the electrostatic field and results in less edge buildup and better penetration into recess areas. Other systems use electronic means to effectively prevent arcing to grounded surfaces. 

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