Which of the following is NOT a source of exceeding CFU action levels in air sampling?

In the context of air sampling and control of microbial contamination in sterile compounding environments, it's essential to understand the sources that can lead to exceeding colony-forming unit (CFU) action levels. Contaminated surfaces are indeed a significant concern, as they can release particles and microorganisms into the air, potentially leading to increased CFU levels during air sampling. However, the question specifically asks for the option that is NOT a source of exceeding CFU action levels in air sampling.

When analyzing the remaining options, HVAC systems have a critical role in maintaining air quality in compounding areas, and any malfunction or inefficiency can contribute to increased levels of airborne contaminants. Damaged HEPA filters can also allow particles that would normally be trapped to escape, thereby increasing CFU counts in the air. Changes in personnel garbing could create situations where particulate shedding occurs, influencing microbial counts.

Therefore, contaminated surfaces are indeed a direct source responsible for exceeding action levels in air samples, making them a relevant concern while your selected option does not specifically relate to air contamination in this context. Thus, the choice of contaminated surfaces acknowledges its direct link with increasing airborne CFUs during sampling, validating the idea that it is a source of potential contamination.