This model is based on a published COVID risk and transmission estimator in the link above and tailored to Smithsonian spaces and terminology. Each variable entered into the model is part of an overall equation that calculates the risk of transmission using the Wells-Riley aerosol disease transmission model.
The preset scenarios were chosen as typical spaces used and in response to some specific questions. Modifying those scenarios to fit your particular space is encouraged. SI Explorer can be used to determine square footage and ceiling height can be estimated or you can measure it yourself.
Air exchanges in any given Smithsonian space change based on the humidity and temperature requirements for the collections and to meet indoor air quality standards. We have used the lowest number of exchanges required to maintain the indoor air quality standards as a conservative estimate of risk. The actual number of air exchanges in a given location during normal use will exceed this minimum number. As more visitors or staff enter into a gallery space, the temperature and relative humidity increase causing the HVAC system to respond by increasing air exchanges to return the environmental conditions to the set ranges. The SI systems are generally not set up in a way that SI can adjust the number of air exchanges for a given space- but they are set to exceed the baseline standards.
The Smithsonian uses MERV 13 or better rated filters in all systems possible. The Castle HVAC system is slated for replacement with the Castle Revitalization project, and there are a few locations at NZP and SCBI (in residential housing only) that have systems that cannot use MERV-13 filters. Otherwise it is accurate to assume a MERV-13 rating for SI HVAC systems. Filter ratings for home HVAC systems are typically printed on the filter or can be found online.
One of the variables that makes a large difference in risk is the number of infected persons. If the number of infected persons is known or assumed, then that number should be used. Otherwise use the online calculator to enter the percent chance (based on current county COVID Case rates) that a person in your estimated group would be infected.
Specific vaccination rates are not available for Smithsonian staff. We encourage you to either use zero for the most conservative estimate or publicly available vaccination rates for your location (county or national). If you are using this for your home or personal events, of course use what you know!