Staff Sgts. Aaron Waite and Jon Andrew, 28th Medical Operations Squadron bioenvironmental engineer technicians, uses a balometer to measure air flow in the 28th Medical Group building on Ellsworth Air Force Base, S.D., Nov. 30, 2011. This procedure checks ventilation systems for sufficient airflow to ensure a healthy and safe environment for patients and staff. (U.S. Air Force photo by Airman Alystria Maurer/Released)