USP general chapter - 797 1. Unidirectional airflow 2. Sweeping action over and away from the product under dynamic conditions. 3. It is useful in identifying eddy currents and recirculation of air flow as a means of assessing risk of contamination in critical areas within a clean room. First air should contact critical components or products before contacting anything else. It should be free of eddy currents or deviant air that can act as a channel or reservoir for contaminants. It is important to evaluate air flow patterns to assure that these patterns do not pose a risk of distributing particles from sources such as surrounding environment, personal, operations, materials or equipment. These tests are used to demonstrate that airflow under operational conditions doesn't contribute to contamination risk. Regulatory bodies requires documented air pattern analysis with written conclusions including the effects of the aseptic interventions in critical areas. Smoke s...