Non-viable airborne particle testing directly measures what aspect?

Non-viable airborne particle testing is essential in sterile compounding environments because it assesses the effectiveness of engineering controls that are put in place to maintain air cleanliness. This testing directly measures the presence and concentration of airborne particles in controlled areas, such as clean rooms, by determining whether the air quality meets the required standards for sterile compounding.

By quantifying the number and size of non-viable particles, this testing helps to ensure that the air filtration systems, such as HEPA filters, are functioning properly and that the environment is safe for the preparation of sterile products. If particle counts exceed acceptable levels, it indicates potential issues with air cleanliness, aiding in the identification of problems with airflow or filtration that need to be addressed. This type of monitoring is critical for maintaining the integrity of compounded sterile preparations and for ensuring patient safety.

The other options, such as measuring the size of air particles, assessing moisture levels, or checking temperature, do not directly evaluate the overall effectiveness of the engineering controls designed to maintain the sterility of the environment.