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Pharmaceutical Technology BIOLOGICS AND STERILE DRUG MANUFACTURING 2020 35 or physical (e.g., f luorescent and ultraviolet light, radiation, vibration) and can be introduced in a variety of ways (e.g., as airborne particles, infected cell lines, contaminated water, or during routine maintenance or operating procedures) (1). Some contaminants require a very proactive approach to detection and management, such as regular quar- antine and testing to help avoid the introduction of mycoplasma-infected cell lines. The type, ex- tent, and frequency of contamination determine the severity of the consequences, which drain re- sources, whether time, samples, or reagents. Re- peating work and reinvesting in those resources exacerbate losses, and subsequent experiments typically become more costly as additional pre- cautions are incorporated into their procedures. However, these costs pale when compared with the long-term implications of undetected contamina- tion, where misidentified cell lines and erroneous data can compromise reproducibility and lead to paper retractions (2). Contamination control is complex and chal- lenging, particularly when laboratory environ- ments are constantly changing, with various components being replaced based on seasonal changes in building ventilation requirements. Efforts to protect cell cultures and experiments must, therefore, be multidimensional and thor- ough, and BSC use is no exception. BSCs protect the product, environment, and operator through two primary mechanisms of containment: precise control of airf low and high efficiency filtration, which purifies the air that enters the BSC, main- taining an air barrier between operators and their work. High efficiency particulate air (HEPA) filters remove microscopic particles from the air, which is then recirculated within the BSC and discharged elsewhere, depending on the design—into the room or a building's exhaust system. In Class II Type A2 BSCs, the most common class, approximately 70% of the air is recycled and pushed back into the BSC work area; the remaining 30% is exhausted through the HEPA filter. Integrated approach needed In addition to understanding airf low dynamics, the use of BSCs to prevent contamination involves the thoughtful application of scientific knowledge and an integrated approach. Best practices from the quality control field must be applied to reduce or eliminate variation in output. In practice, this requires examining every movement and process and taking steps to support the consistent execution of those processes. For example, designated spaces might be marked out for specific items in a supply tray, so the operator can quickly confirm that he or she has everything required to perform the task at hand. It is easy to underestimate the benefits of these simple steps, but there are significant benefits to supporting the consistent execution of precise processes. Simplified workf lows help limit opera- tor distractions, which is particularly important to maintaining an aseptic environment. Traditionally, the industry has relied heavily Some contaminants require a very proactive approach to detection and management, such as regular quarantine and testing to help avoid the introduction of mycoplasma- infected cell lines.