Cleanroom System Components: How To Select a Pass-Thru Airlock

Selecting the right pass-thru airlock means fewer people enter the cleanroom, which reduces contamination and increases operating efficiency.

By Katie Addis, Clean Air Products

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Modular cleanrooms protect manufacturing operations from the constant threat of air particulate contamination. Pass-thru cabinets (also called pass-thru airlocks) are a component of a cleanroom system and play an important role in reducing contamination. Clean manufacturing environments that are free of dust and bacteria are requirements not only in the production of medical devices and pharmaceuticals, but are also an increasingly common requirement of the modern manufacturing industry as a whole: computers and consumer electronics, food processing, vehicles, air and spacecraft, and many new manufacturing processes in biotechnology and nanotechnology.

Preventing product contamination increases productivity and also enables manufacturers to comply with industry quality standards. For example, cleanroom systems, including pass-thrus used in compounding pharmacies, must comply with USP 797 and USP 800, which stipulate cleaning requirements. As manufacturing evolves in sophistication and advanced manufacturing techniques emerge, the demand for cleanroom systems increases. To meet this increasing demand it is important to understand how cleanrooms function, and how to evaluate and choose the right components that make up an effective cleanroom system. In this article we will focus on pass-thrus: what their role is in relation to cleanrooms, how a pass-thru works, and how to select a pass-thru for a specific application.

THE ROLE OF A PASS-THRU
There are different levels of cleanroom standards, depending on the manufacturing process. Most cleanrooms require basic cleaning, air filtering and a constant positive air pressure. A cleanroom is kept clean by filtered air under positive pressure relative to the lower pressure “dirty air” in the surrounding rooms. This positive pressure controls the amount of air particulates already present in the cleanroom, stabilizes particles created during activity in the cleanroom, and resists the influx of particulates in air brought into the cleanroom.

To prevent contamination of the cleanroom, people and materials must pass through some kind of vestibule that connects the controlled environment of the cleanroom to less-controlled “dirty air” or surrounding space. People walk through air showers, where high-velocity air nozzles remove particulate from clothing while a person stands in the air-locked space for a minute or so. Materials, products and specimens and transferred into the cleanroom through a pass-thru, which are cabinets mounted on the wall or floor of a cleanroom. Pass-thrus prevent cleanroom air from leaking out and depressurizing the cleanroom and also prevent dirty, untreated air from flowing into the cleanroom. Passing items through the pass-thru’s interlocked doors means fewer people have to enter the cleanroom, which reduces cleanroom contamination and increases operating efficiency. Properly designed and constructed, a pass-thru is easy to clean and maintain, which is crucial for maintaining cleanroom standards.

HOW A PASS-THRU WORKS
Pass-thru doors are designed with interlocks, so that only one side door can be opened at a time, preventing depressurization of the cleanroom. Transferring materials into the cleanroom begins when an operator opens the pass-thru door on the “dirty air” side; the interlock mechanism automatically or manually locks the cleanroom-side door shut.

The operator places materials into the pass-thru on the “dirty air” side and closes and latches the door. The pass-thru’s sturdy, latching doors on both sides tightly compress against closed-cell or non-absorbent gaskets to prevent air loss from the cleanroom. If the air pressure in the cleanroom drops, untreated dirty air at lower pressure will flow into the cleanroom.

Next, the interlocking mechanism releases, an operator opens the cleanroom-side door and transfers materials into the cleanroom. After transfer is complete, the cleanroom side door is closed. When both doors are closed, the interlock is released and the pass-thru is ready for another use.

HOW TO SELECT FOR YOUR APPLICATION
The function of every pass-thru is to transfer materials with minimal impact on the cleanroom. Well-designed pass-thrus contribute to this requirement; they are made of rugged, durable stainless steel so they withstand constant use and are easy to clean and maintain, especially in sterile environments. Inter-locks are an essential mechanism; models with double-wall construction hide and protect the interlock.

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