text: Natural ventilation  is a key factor in reducing the spread of airborne illnesses such as tuberculosis, the common cold, influenza, meningitis or COVID-19. Opening doors and windows are good ways to maximize natural ventilation, which would make the risk of airborne contagion much lower than with costly and maintenance-requiring mechanical systems. Old-fashioned clinical areas with high ceilings and large windows provide the greatest protection. Natural ventilation costs little and is maintenance free, and is particularly suited to limited-resource settings and tropical climates, where the burden of TB and institutional TB transmission is highest. In settings where respiratory isolation is difficult and climate permits, windows and doors should be opened to reduce the risk of airborne contagion. Natural ventilation requires little maintenance and is inexpensive.
  Natural ventilation is not practical in much of the infrastructure because of climate. This means that the facilities need to have effective mechanical ventilation systems and or use Ceiling Level UV or FAR UV ventilation systems.
  Ventilation is measured in terms of Air Changes Per Hour (ACH). As of 2023, the CDC recommends that all spaces have a minimum of 5 ACH. For hospital rooms with airborne contagions the CDC recommends a minimum of 12 ACH. The challenges in facility ventilation are public unawareness, ineffective government oversight, poor building codes that are based on comfort levels, poor system operations, poor maintenance, and lack of transparency. 
  Everyone assumes that everything is okay in terms of facility ventilation but that is not the case. The situation is similar to water pollution where unless someone actually assesses the situation, it is likely that there is a problem. The reality is that Heating,_ventilation,_and_air_conditioning rates have been dropping since the energy crisis in the 1970s and the banning of cigarette smoke in the 1980s and 1990s . Today the ventilation rates are dropping even further with the new challenge to reduce carbon footprints. The tradeoffs are reduced carbon footprint versus increased risk of respiratory infection because of insufficient ventilation to reasonably mitigate airborne infections. The research in this area is new as of 2023.