Laminar airflow

These features have to be well designed, installed, validated, and maintained. Critical operation has to be performed under the unidirectional airflow (laminar airflow). Air turbulence deteriorates air quality by intake of air from the surrounding less clean areas. 

Where product is exposed at transitions or packing operations use containment devices such as gloveboxes provide airflow control (laminar flow booths) or as a last resort use the room as containment and provide suitable personal protective equipment for the operators... 

The fitting of limiting boundaries such as walls pros ides solutions similar to those of laminar airflow (LAP) units tir cabinets. An increase in the supply and exhaust supply rates provides a solution similar to ventilated booths (.see Section 10,. ). 

Class HA in a Class IIA BSC, an internal blower (Fig. 10.9,St draws sui-ficient room air into the front grill to maintain a minimum calculated measured average velocity of at least 0.37 m s at the opening of the cabinet. The supply air flows through a HEPA filter and provides particulate-free air to the work surface. Laminar airflow reduces turbulence m the work zone and niim-mizes the potential for cross-contamination. 

A development of the simple booth is the laminar flow system, which uses a nominal velocity at the face of 0.5 m/s. As the airflow is laminar, all parts of the booth are subjected to its effect. 

Filtered air may be used to purge a complete room, or it m be confined to a specific area and incorporate the principle of laminar flow, which permits operations to be carried out in a gentle current of sterile air. The direction of the airflow may be horizontal or vertical, depending upon the type of equipment being nsed, the type of operation and the material being handled. It is important that there is no obstruction between the air supply and the exposed product, since this may resnlt in the deflection of microorganisms or particulate matter fiom a non-sterile surface and canse contamination. Airflow gauges are essential to monitor that the correct flow rate is obtained in laminar flow units and in complete suites to ensure that a positive pressure fiom clean to less clean areas is always maintained. 

Recent sterilizer developments have led to the use of dry-heat sterilizing tunnels where heat transfer is achieved by infra-red irradiation or by forced convection in filtered laminar airflow tunnels. Items to be sterilized are placed on a conveyer belt and pass through a high-temperature zone (250 - 300 + °C) over a period of several minutes. 

The greatest risk of contamination of a pharmaceutical product comes from its immediate environment. Additional protection from particulate and microbial contamination is therefore essential in both the filling area of the clean room and in the aseptic unit. This can be provided by a protective work station supplied with a unidirectional flow of filtered sterile air. Such a facility is known as a laminar airflow unit in which the displacement of air is either horizontal (i.e. from back to front) or vertical (i.e. from top to bottom) with a minimum homogenous airflow rate of 0.45 ms" at the working position. Thus, airborne contamination is not added to the work space and any generated by manipulations within that area is swept away by the laminar air currents. 

Workbenches, including laminar airflow units, and equipment, should be disinfected immediately before and after each work period. Equipment used should be of the simplest design possible commensurate with the operation being undertaken. 

Aseptic manipulations should be performed in the sterile air of a laminar airflow unit. Speed, accuracy and simplicity of movement, in accordance with a complete understanding of what is required, are essential features of a good aseptic technique. 

As a precaution against accidental contamination, product testing must be carried out under conditions of strict asepsis using, for example, a laminar airflow cabinet to provide a suitable environment (Chapter 22). 

Diffusion is the dominant mechanism of lung deposition for radon daughter aerosols. It is generally assumed that airflow is laminar in the smaller airways and that deposition in each airway generation can be calculated adequately (Chamberlain and Dyson, 1936 Ingham, 1975). However, there is no such consensus on the treatment of deposition in the upper bronchi. Some authors (Jacobi and Eisfeld, 1980 NCRP, 1984) have considered deposition to be enhanced by secondary flow, on the basis of experimental results (Martin and Jacobi, 1972). It has been shown that this assumption reduces the calculated dose from unattached radon daughters by a factor of two (James, 1985). 

Verify that the laminar airflow units in class 100 areas are operational. Verify that the ventilation and air conditioning systems are operating in balance. 

Determine whether the generated turbulence can carry contaminants from other areas to critical points of the line. If so, adjust the airflow to ensure a minimum of turbulence and rapid cleaning (covers and diffusers can be used over the filling equipment). If turbulence carries contaminants from any area to the critical areas, the system should be re-evaluated and analyzed in terms of the filling, capping, and laminar-flow equipment. 

If the results of the preceding three steps are unsatisfactory, the laminar-airflow system cannot be validated and the rest of the validation tests should not be carried out until a satisfactory operation has been reached. Otherwise, the system is valid and can be certified. 

Laminar Turbulence Smoke Travels away from Critical Work Surface Cascade Airflow ... 

After the cycle, aseptically transfer the spore strip to vessels of culture media. If spore suspensions were used, aseptically transfer the inoculated bottles to a laminar airflow workstation and add culture media to the bottles. Use appropriate positive and negative controls. 

Provide a laminar airflow with an average velocity of 90 ft per min over the entire air exit area. The air velocity should be high enough to maintain the unidirectional flow pattern. 

Laboratory laminar airflow cabinet BH-EN 2004-S. Type II, Categorie 2 (Microbiological Safety Cabinets) for cell manipulations in sterile conditions. 

For laminar airflow in a tube, when 8 approaches the tube radius, Poiseuille flow or a parabolic flow profile is fully developed. This is accomplished by the acceleration of the central portion of the flow. However, when Re exceeds a value lying somewhere between 104 and 106, the laminar boundary layer becomes so thick that it is no longer stable, and a turbulent boundary layer develops. 

Figure 7-6. Schematic illustration of originally nonturbulent air (straight anrows in upwind side on left) flowing over the top of a flat leaf, indicating the laminar sublayer (shorter straight anrows), the turbulent region (curved arrows), and the effective boundary layer thickness, 5bl. The length of an arrow indicates the relative speed, and the curvature indicates the local direction of air movement. A similar airflow pattern occurs on the lower leaf surface.

A laminar boundary layer develops on the upwind side of a cylinder (Fig. 7-8). This layer is analogous to the laminar sublayer for flat plates (Fig. 7-6), and air movements in it can be described analytically. On the downwind side of the cylinder, the airflow becomes turbulent, can be opposite in direction to the wind, and in general is quite difficult to analyze. Nevertheless, an effective boundary layer thickness can be estimated for the whole cylinder (to avoid end effects, the cylinder is assumed to be infinitely long). For turbulence intensities appropriate to field conditions, in mm can be represented as follows for a cylinder ... 

---