Unidirectional airflow

To create unidirectional airflow field over the rootn area by supply air... 

The purpose of open unidirectional airflow benches is to protect products from particulate contaminants by creating a controlled environment. These benches are used, for example, in electronic, biological, pharmaceutical, and food industries. It should be mentioned that within pharmaceutical production, aseptic sterile processes must be carried out in a Class 100 environment (U.S. Federal Standard 209 E, Airborne Particulate Cleanliness Classes in Cleanrooms and Clean Zones). To avoid particle contamination in the bench, horizontal or vertical airflow with high-efficiency particulate air (HEPA)-filtered air is used. The air velocity is normally 0.4-0.5 ra s". Some examples of typical arrangements of open unidirectional airflow benches are shown in Fig. 10.51. 

FIGURE 10.5 I Examples of typical arrangements of open unidirectional airflow benches. 

The bench should be supplied with HEPA-filtered unidirectional airflow, having a velocity sufficient to sweep particulate matter away from the working area. Normally a velocity of 0.45 m s plus or minus 20% is adequate. It is important to monitor the air velocity at suitable intervals because significant reduction in velocity or uniformity in velocity can increase the risk of contamination. 

It has also been shown, using visual illustrative methods, that accumulation can occur in the wake of people or objects, provided that the contaminants are emitted in the vortex region. Special consideration must be taken with instabilities and vortices generated by the working person. Vortices can also occur in empty open unidirectional airflow benches. 

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. 

FIGURE 10.53 Vortices in a unidirectional airflow bench with covered side walls. 

FIGURE 10.54 An example of observed stagnation region in a bench with vertical unidirectional airflow. 

When open unidirectional airflow benches are being used in production sensitive to contamination, a thorough function check should always he carried out before the start of production. Studies of air movements with visual illustrative methods give both quick and valuable information. 

Shroud constmction is of Plexiglas or vinyl material to enhance the unidirectional airflow to the working surface. The ceiling of the area is constructed of the HEPA filter face with lighting projected below the HEPA filter face. The average illumination at work surfaces is approximately 500 lux. The mechanical drawings that provide specific details are on file. 

The minimum number of sample locations required for verification in a clean zone with unidirectional airflow shall not be less than the lesser of (a) or (b) ... 

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. 

Ordinarily, present within the preparation area are localized areas of ISO 5 unidirectional airflow (Class 100) utilized to protect washed components prior to sterilization and/or depyrogenation. These areas are not aseptic and should not be subjected to the more rigorous microbial expectations of aseptic processing. They are designed to reduce/eliminate the potential for particle contamination of unwrapped washed materials. Operators accessing these protective zones wear gloves at all times when handling materials. 

Air Sampling The relative cleanliness of air in the most critical environment is assessed using passive sampling systems such as settle plates or estimated volumetri-cally using active air samplers. Active air samplers should be designed to be isokinetic in operation to avoid disruptions to unidirectional airflow. Considerable variability has been reported among the several sampling methods employed for... 

Battery-operated unidirectional airflow carts to a remote lyophilizer... 

Unidirectional airflow at 90ft/min. gNon-unidirectional airflow. 

GMP Grade D cleanroom. The cleanliness of the internal nitrogen environment is maintained using non-unidirectional airflow. Manipulations are achieved using a combination of glove and half-suit systems. 

Conventional airflow (also known as turbulent, or non-unidirectional airflow) incorporates HEPA filters, located in-duct, or as room terminal filtration modules (TPMs Fig. 5). Often confused with LAP, conventional airflow does not meet that definition because it allows multiple-pass circulating characteristics or a non-parallel airflow direction, or both. This type of airflow is incapable of producing first air, and is normally used as secondary or buffer filtration in treating a processing or compounding space that contains laminar airflow devices (LAFDs) to maintain primary critical work surface conditions, or in treating other... 

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.)... 

Unidirectional airflow (UDAF) should be used where appropriate to provide product protection by supplying a clean air supply over the product, minimizing the ingress of contaminants from surrounding areas. 

Where appropriate, the unidirectional airflow should also provide protection to the operator from contamination by the product. 

A dispensary or weighing booth should be provided with unidirectional airflow for protection of the product and operator. 

Example In Fig. 12 the dust generated at the weighing station is immediately extracted through the perforated worktop, thus protecting the operator from dust inhalation, but at the same time protecting the product from contamination by the operator by means of the vertical unidirectional airflow stream. 

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. 

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