Airflow unidirectional flow

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. 

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. 

The unidirectional flow velocity should be such that it does not disrupt the sensitivity of balances in weighing areas. Where necessary the velocity may be reduced to prevent inaccuracies during weighing, provided that sufficient airflow is maintained to provide containment. 

Fig. 15 illustrates a situation where an open bin is placed below a vertical unidirectional flow distributor. The downward airflow should be prevented from entering the bin, and then being forced to rise again, as this would carry dust up towards the operator s face. 

The manufacturer should select either vertical or horizontal unidirectional flow (Fig. 17) and an appropriate airflow pattern to provide the best protection for the particular application. 

The airflow schematics of the two systems (Figs 24 and 25) indicate airhandling units with return air or recirculated air, having a percentage of fresh air added. Fig. 25 is a schematic diagram of an air-handling system serving rooms with horizontal unidirectional flow, vertical unidirectional flow and turbulent flow, for rooms A, B and C, respectively. 

Airflow velocity (To verify unidirectional flow or containment conditions) All classes 12 months Air velocities for containment systems and unidirectional flow protection systems to be measured. In accordance with ISO 14644-3 Annex B4... 

To create unidirectional low-turbulence flow, air is supplied with a low velocity supply diffusers and exhaust openings have large surfaces (e.g., filter mats). Airflow can be either vertical (air supplied from the ceiling and exhausted through the floor or vice versa (Fig. 7.1 la)), or horizontal (air supplied through... 

In vertical unidirectional airflow benches, the area along the vertical wall in front of the operator is usually entirely or partially open. When the other side walls reach down to the working surface in the bench a stagnation flow with stationary vortices is usually created as shown in Fig. 10.53. 

Turbulent flow, or non-unidirectional airflow, is air distribution that is introduced into the controlled space and then mixes with room air by means of induction. unidirectional airflow (UDAF)... 

Unidirectional airflow is a rectified airflow over the entire cross-sectional area of a clean zone with a steady velocity and approximately parallel streamlines (see also turbulent flow). (Modern standards no longer refer to laminar flow, but have adopted the term unidirectional airflow.)... 

Fig. 16 shows that a solid worktop can sometimes cause deflection of the vertical unidirectional airflow resulting in a flow reversal. A possible solution would be to have a 100 mm gap between the back of the table and the wall, with the air being extracted here. 

Air barriers can be created by allowing air to flow in a uniform direction at a uniform velocity. (You may have seen so-called air curtains in use in entries to some large buildings.) If the air velocity is sufficiently high, about 0.5 meters per second (100 linear feet per minute), cross-currents are not likely to penetrate this curtain of air. Since the airflow is unidirectional and has a uniform velocity, the airflow is referred to as being laminar, i.e., it is nonturbulent. 

---