An officer trainee walks by a temporarily installed portable air-handling unit in a hallway at Officer Training School, May 7, 2020, Maxwell Air Force Base, Alabama. Permanent units are being affixed to the HVAC systems in the school’s eight buildings. The air-handling technology, along with the current use of HEPA filters, show promise in decreasing airborne spread of bacterial and viral infectious diseases, such as the coronavirus that causes COVID-19. (Courtesy photo)