Vertical flow cabinets

Laminar flow cabinets serve two purposes to protect the samples and to protect the worker and the environment. For most tissue culture applications sample protection is sufficient, but increasingly often we are becoming aware of hazards associated with biological samples and the cabinet to choose combines both aspects of protection. Such are the vertical laminar flow cabinets available, for example, from Flow Laboratories (Gelaire) or M.D.H. (Appendix 3). 

Vertical Laminar Flow Vertical Flow Biological Clean Bench Safety Cabinet... 

A pre-PCR area, where reaction mixes are prepared. This area can be a positive-pressure vertical laminar flow cabinet equipped with an ultraviolet (UV) lamp that is switched on for 20 min after use to destroy any possible contaminating DNA. 

The capacity per unit area of cabinet dryers is limited by two conditions need for direct radiation on the drying material and small airflow rate. To dry larger quantities of material, the basic area of the dryer has to be increased. To avoid this problem it is preferable to place the material in several independent layers the necessary heat transfer is thus accomplished by convection. The increase in the mass flow rate of air can be achieved by increasing the effects that prodnce natural convection. These effects mnst also be increased if the air is to be circulated through a material laid in several layers one over the other, or through a thick layer, as in the case of the static bed type. To keep up the natural pressure difference without using a ventilator (for instance, in a field), the chimney effect must be exploited. For this purpose the vertical flow of hot air in the dryer must be increased. 

Class II BSC. The Class II BSC (Fig. 9) provides product, personnel, and environmental protection, and is the most common BSC employed in pharmaceutical manufacturing and pharmacy-compounding operations. The Class II BSC has several subclassifications, based upon cabinet ventilation design (Table 1). The Class II BSC (Fig. 8), the most widely used by hospital and home-care pharmacies, features a front access opening with carefully maintained inward airflow for replacement of air exhausted from the cabinet, a HEPA-filtered vertical laminar flow airstream within the entire work area, and HEPA-filtered exhaust air. The vertical laminar flow airstream and front access opening are common to all Class II cabinets, although LAF velocities and patterns, HEPA filter sizes and position, ventilation rates, and cabinet exhaust methods vary considerably in different designs (Fig. 7). 

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. 

Class II Biological Safety Cabinets. A Class II biological safety cabinet also has an open front with a 75 ft/ min face velocity. It has vertical laminar flow air movement. The air moves through HEPA filters and gets recirculated within the cabinet. Some air also... 

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...

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