Horizontal flow cabinets

Horizontal-flow cabinets are satisfactory for aseptic manipulations such as media preparation where potentially hazardous aerosols are not generated. In these the filtered air enters through the back of the cabinet and leaves through the front. A horizontal-flow cabinet is a miniaseptic room which is much easier and cheaper to maintain than a walk-in aseptic room. In addition, it has the advantage that the worker is not confined within a small room which may become extremely hot and stuffy and, secondly, that the worker s head is separated from the cultures by a perspex screen thus further reducing the chance of contamination. 

Horizontal laminar flow cabinets used for product protection, for example, in the pharmaceutical industry, exhaust directly into the face of the operator. This equipment must never be used as a biological (microbiological) safety cabinet. 

A unit sometimes confused with a Class I biological safety cabinet is a horizontal laminar flow cabinet or work table. This type of unit serves precisely the opposite function of a class I cabinet. Clean air which has been HEPA filtered is blown across the work surface toward the worker so that the research or product materials are protected against contamination, but the worker is not protected at all. Such a unit is unsuited for microbiological work, except for applications which would cause no harm to the users, such as a work involving noninfectious or non-aUergenic materials. 

Horizontal laminar flow clean air benches are not BSCs (Section 10.3.4). They discharge HEPA-filtered air across the work surface and toward the user. These devices only provide product protection. They can be used for certain dean activirie.s, such as the dust-free assembly of sterile equipment or electronic devices. These benches should never be used when handling potentially infectious materials. The worker can be exposed to materials on the clean bench. Horizontal clean air benches should never be used as a substitute for, i biological safety cabinet. 

NOTE—The various recommendations regarding air supplies and pressure differentials may need to be modified where it becomes necessary to contain pathogenic, highly toxic or radioactive materials. In such circumstances microbiological safety cabinets complying with BS 5726 should be used. Cabinets giving horizontal air-flow should NOT be used.)... 

Thermobalances are available in two different designs, i. e. a horizontal construction (Fig. 5-1) and vertical construction. For the vertical construction there are two different versions the top-loading balance, which has the oven above the balance (Fig. 5-2), and the thermobalance with the sample tray hanging on a thin hangdown wire into the oven below the balance (Fig. 2-4). The suppliers claim some advantages for the horizontal arrangement such as complete lack of buoyancy, the avoidance of condensation in the balance cabinet, and the reduction of sensitivity to vibration. However the last two points cannot be confirmed by the author s experience. Despite an efficacious gas flow, a diffusion of condensates was observed opposite to the flow direction of the gas. The sensitivity to vibrations seems to be comparable with the vertical design. Of the vertically constructed balances, the top loader is more convenient to manipulate. 

Figure 1.Reduction Reaction Installation Figuer2.Reduction Swelling Installation 1—gas 2—flow meter 3— flow control cabinet 4—pellet 5—electronic balance 6—quartz tube 7— vertical tube furnace 8—horizontal tube furnace 9—infrared camera 10—computer...

---