For many years microbiologists have attempted to devise more efficient techniques for controlling microbial contamination. These efforts have ranged from the use of cotton-plugged tubes to large germ-free isolators. In the meantime, laminar or minimal-turbulence airflow system has been used by the aerospace industry to control particulate contamination such as dust or lint, which could affect the reliability of precision parts. Equipping with needs of controlling contamination and generally accepted practice in the aerospace industry, laminar flow clean benches have been introduced and played an essential role in world's today science.
What is laminar flow?
Laminar flow is a type of fluid (gas or liquid) flow in which the fluid travels smoothly or in regular paths, in contrast to turbulent flow, in which the fluid undergoes irregular fluctuations and mixing. In laminar flow, sometimes called streamline flow, the velocity, pressure and other flow properties at each point in the fluid remain constant. Laminar flow over a horizontal surface may be thought of as consisting of thin layers all parallel to each other.
Because of these characteristics of laminar flow, it has participated in cleannroom and clean bench technology for many decades. In general, the units consist of a bank of HEPA filter (s) enclosed in a cabinet or hood. The air stream, at decent velocity, moves essential in parallel patterns so that the cleanliness of the air is independent of activities occurring down or cross-stream. Undoubtedly, laminar flow is the most important part of Laminar Flow Clean benches to provide an environment free from microorganisms moving inward to the workspace, with excellent and consistent results.
What is a laminar flow clean bench?
The laminar flow clean bench is a workbench or similar enclosure, which provides protection to product that being conducted inside the workspace from outside contaminants. Similar to cleanroom, this clean bench utilizes HEPA filter(s) to generate clean-filtered air supply over entire workspace inside the clean bench.
Today, beside from laboratories, laminar flow clean benches are widely used in variety of application throughout life science, hospital, pharmaceutical, food and drink industry and other research and production environments.
Principle of laminar flow clean bench
The principle of laminar flow clean bench is to achieve particle-free working environment inside and protect the work from cross contamination by any contaminants outside.
Contaminated" air in laboratory (or outside) is drawn through inside the clean bench through the opening area (not passing workspace).
"Contaminated" air is filtered by HEPA filter(s) and becomes "clean-particle-free" air pass through the entire area of workspace.
The "mixed" air passes over the front opening and expose to outside environment.
Clean bench function
The clean bench provides protection to products by ensuring that the entire workspace is solely covered with HEPA-filtered air.
The clean bench is applicable and recommended for work with non-hazardous agents/materials where cross contamination is the most concerned issue, and therefore, particle-free air quality is required.
The clean bench DOES NOT provide protection to personnel and environment at any level.
The clean bench, unlike laboratory chemical fume hood, is not designed to contain aerosols generated by the procedure. The personnel are exposed to these aerosols.
Clean benches are not Biological Safety Cabinets
These two cabinets, although there are not differed in appearance, are totally different and cannot substitute each other.
Clean bench provides only product protection while (some type of) the Biological Safety Cabinet is capable for product, personnel and environment protection.
Unlike biological safety cabinet, laminar flow clean bench is inappropriate for use with any potentially biohazardous materials including infectious agents, infected animal tissue and hazardous chemicals and volatile radioisotopes.
Unlike clean bench, "mixed-contaminated" air, after passing through workspace, is drawn into front air grille of biological safety cabinet. This mechanism ensures none of contaminated air is exposed to personnel outside the cabinet.
Unlike, clean bench, there is a HEPA exhaust filter in the biological safety cabinet. All air exhausted either to the room or outside is always clean and particle-free.
The HEPA Filter
HEPA filter stands for "High Efficient Particulate Air" Filter and it is considered as the heart of all laminar flow clean benches. This filter removes particulates, generally airborne, such as microorganisms, from the air. However, it does not provide filtration to vapors or gases.
Disposable dry-type filter, constructed of borosilicate microfibers cast into a thin sheet, much like a piece of paper.
Particle retention is achieved by multiple mechanisms of HEPA filter working together including sieving, interception, inertial impaction and diffusion.
Rated on their ability to retain particle 0.3 micrometers in diameter. If the filter allows one or less droplets to penetrate with an initial concentration of 10000, the filter is rated 99.99% efficiency.
Variations in filter efficiency, for example from 99.95% to 99.99% are usually due to manufacturing techniques.
Pharmacy and laboratory applications, in general, require a 99.99% filtration efficiency of HEPA filter(s).
Types of Laminar Flow Clean Benches
Laminar Flow Clean Benches are classified to two types based on their direction of HEPA-filtered airflow over the workspace inside the benches.
1. Horizontal Laminar Flow Clean Bench
"HEPA-filtered" air flows across entire workspace from the back of the clean bench toward the front opening in horizontal direction. HEPA filter is aligned perpendicularly to the working plane.
2. Vertical Laminar Flow Clean Bench
"HEPA-filtered" air flows across entire workspace from the top of the clean bench in vertical direction and exit outside through the front opening. HEPA filter is aligned parallel to the working plane.