Ventilation – “CDC recommends a layered strategy to reduce exposures to SARS-CoV-2, the virus that causes COVID-19. This includes using multiple mitigation strategies with several layers of safeguards to reduce the spread of disease and lower the risk of exposure. While it may not be necessary to apply every consideration to be protective, implementing multiple mitigation strategies is recommended, if possible, to improve effectiveness. In addition to ventilation, the layered approach includes efforts to improve social distancing, wearing face masks, and hand hygiene. SARS-CoV-2 viral particles spread between people more readily indoors than outdoors. When outdoors, the concentration of viral particles rapidly reduces with the wind, even a very light wind.  When indoors, ventilation mitigation strategies help to offset the absence of natural wind and reduce the concentration of viral particles in the indoor air. The lower the concentration, the less likely some of those viral particles can be inhaled into your lungs; contact your eyes, nose, and mouth; or fall out of the air to accumulate on surfaces. Protective ventilation practices and interventions can reduce the airborne concentration, which reduces the overall viral dose to occupants. Below is a list of ventilation interventions that can help reduce the concentration of virus particles in the air, such as SARS-CoV-2. They represent a list of “tools in the mitigation toolbox,” each of which can be effective on their own.  Implementing multiple tools at the same time is consistent with CDC mitigation strategies and increases overall effectiveness. These ventilation interventions can reduce the risk of exposure to the virus and reduce the spread of disease, but they will not eliminate risk completely. While the list of tools is intended to be universally applicable across indoor environments, applying them to different building types, occupancies, and activities under environmental and seasonal changes can be challenging. The specific combination of tools chosen for use at any point in time can change. It will be up to the building owner/operator (obtaining expert consultation as needed) to identify which tools are appropriate for each building throughout the year…”