Vertical laminar flow

Vertical laminar flow clean benches also are not BSCs. They may be useful, for example, in hospital pharmacies when a clean area is needed. Although these units generally have a sash, the air is usually discharged into the room under the sash, resulting in the same potential problems as the horizontal laminar flow clean benches. 

Figure 6.1 Vertical Laminar-flow Class II hood. 

An electrical resistance heater with more turns at the tube ends (to compensate for heat losses) surrounds each tube. There is a vertical laminar flow hood over the loading area to minimize particle contamination of the wafers being loaded. As we can see, there are temperature controls for the furnace tubes, and a power module to provide the electrical power. When operated as a LPCVD system, a unit including both the gas flow and vacuum systems is positioned on the right side. Such a unit is shown in Figure 8. Here we can see the vacuum pumps on the left, and the mass flow controllers on the right. The vacuum pump oil recirculation systems are shown in the slide out drawers. As can be seen in Figure 9, this system, as well as most current similar systems, operate under computer control. 

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, upward flow, laminar flow reactors which have been used to study stabilized cool-flames and two-stage ignitions are a development of the atmospheric pressure, vertical, laminar flow reactors, pioneered at the Naval Research Laboratories in Washington [71]. These types of systems have been used by other research groups [72-74]. The flow tube that was... 

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

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). 

How is laminar, both horizontally and vertically. Laminar flow in this context means flowing gently, smoothly, and withont tnrbnlence. 

Chemical preconcentration of the samples (e.g., extraction into chloroform and dithizone) was used in the past by several authors in order to determine the very low concentration of Pb in ancient Antarctic ice (6, 45, 64). Although this method gave reliable results, it needed a huge amount of sample (500-1000 g) and a long period of sample treatment with organic solvents. Another method is based on the preconcentration onto W wire loops that can be placed directly in a graphite furnace of instrument AAS for the atomisation of adsorbed metals for the analysis (44, 65). To minimise the contamination problems from the air of the laboratory the whole preconcentration procedure was carried out inside a vertical laminar flow clean bench. Detection limits of 0.01, 0.47, 0.22 and 0.24 pg/g were obtained for Cd, Cu, Pb and Zn respectively (44). These extremely low detection limits have recently enabled the concentrations of heavy metals in Antarctic ancient ice and recent snow to be determined (28, 72). 

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. 

Figure 5 illustrates a vertical laminar flow canopy such as might be used for localized protection of a filling machine or the off-loading station from a sterilizer. Fixed ot portable versions of this type of unit are available and have a wide application in aseptic manufacture. 

Fig. 5 Vertical laminar flow canopy (showing smoke patterns for full- and half-length curtains).

The problem is where to measure the velocity The options are close to the filter face, in the working area, or at the extremities of the protected area (air exiting from, say, the curtains of a vertical laminar flow canopy). The resolution of where to measure may not be easy. For instance the filter face of a large vertical flow canopy shrouding a filling machine may be more than 1 m above the filling zone. By and large the pharmaceutical industry has chosen to measure air velocity close to the filter face. 

Thus, for either horizontal or vertical laminar flow... 

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 2.9-3. Vertical laminar flow of a liquid film (a) shell momentum balance for a control volume A jc thick (b) velocity and momentum flux profiles.

Many times odors are associated with chemical contaminants coming from inside or outside the fab manufacturing area. The complexity of the semiconductor manufacturing process coupled with tremendous volumes of air circulation by the vertical laminar flow hoods make the identification of the odor sources very difficult. Also, Ihe use of a wide variety of toxic substances in the process adds to concern by employees in the fab area that unusual odors may indicate a potentially harmful exposure. Often, these odors are transient in nature whichmakes response time a critical element in their identification. 

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