Safety laminar flow

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. 

As indicated earlier, non-Newtonian characteristics have a much stronger influence on flow in the streamline flow region where viscous effects dominate than in turbulent flow where inertial forces are of prime importance. Furthermore, there is substantial evidence to the effect that for shear-thinning fluids, the standard friction chart tends to over-predict pressure drop if the Metzner and Reed Reynolds number Re R is used. Furthermore, laminar flow can persist for slightly higher Reynolds numbers than for Newtonian fluids. Overall, therefore, there is a factor of safety involved in treating the fluid as Newtonian when flow is expected to be turbulent. 

Laminar flow biological safety cabinet, class II. 

Section 4.4 discusses how to determine whether flow will be turbulent or laminar. It is important to do this because a larger relief system is likely to be required for laminar flow. For turbulent flow the choice of method will depend on whether relief is via a safety valve or a bursting disc. Figure 9.4 may be used to select a method for calculating G. 

Laminar flow is known to reduce the capacity of safety valves for single-phase liquid flow and a capacity correction chart is available13,41. The derivation of this chart has recently been reviewed151 and this review gives additional information about the applicability of the correction factor to different sizes of valve. 

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

Laminar Flow Biological Safety Cabinets, A Training Manual for Biomedical Investigators National Cancer Institute Washington, 1972. 

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. 

Table 3.7 provides a summary of the characteristics of the three types of Class II biosafety cabinets. Class II biosafety cabinets are intended for low- to-moderate-risk hazards. As a minimum, they should be required to meet the National Safety Foundation (NSF) Standard 49 for Class II (laminar flow) a biohazard cabinetry. The working enclosures and plenums through which air moves should be constructed of materials that are easy to decontaminate, such as staMess steel or a durable plastic. 

McGarrity G.J. and Coriell, L.L., Modified laminar flow biological safety cabinet. Applied Microbiology, 28(4), 647-650, October 1974. 

Effective Use of the Laminar Flow Biological Safety Cabinet, (slide/cassette) NAC no. 00971 and no. 003087, National Audio Visual Center (GSA), Washington, D.C., 1976. 

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... 

Controlled environments also regard to aseptic handling in pharmacies, where they are achieved using laminar flow cabinets, biological safety cabinets or isolators (see Sect. 28.4). 

The concerns for sterility can he addressed by installation of laminar flow sterile air filters that provide a constant source of clean air to the work area. Mechanically, room air is channeled through a prefilter and then a sterile high-efficiency particulate air (HEPA) filter prior to flowing across the work surface at uniform velocity (Fig. 18.2). Fully equipped laminar flow safety cabinets are very expensive (> 8000) and may not be justified in the winery microbiology laboratory. However, tabletop workstations that incorporate HEPA-filtered air are available at considerably less cost ( 3000) and serve as good alternatives. 

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