Simplified Model for Aerosol Relative Risk Transmission (SMARRT) Developed by: Sigma Expert Solutions, LLC Analysis Date and Time: 2020-11-22 21:28:45.388287 Requestor: DISCLAIMER: These results are provided for informational purposes only and provide insight on the level of risk that business and social activities may pose due to aerosol spread of the SARS-CoV-2 virus. The information provided in no way implies a guarantee of safety from spread of infection. See information below to understand the assumptions used. For a more detailed assessment, or additional information, contact info@sigmaexpertsolutions.com ASSUMPTIONS: This calculation was performed as a simplified model and does not capture the complexity of most situations. The critical assumptions made of relevance include: --Assumptions about the space-- 1. The air within the defined space volume is evenly mixed. 2. Ventilation air exchange rates are uniform over the space - aka, no dead spots. --Assumptions about infection spread-- 1. Aerosol spread of viroid particles is the only means of tranmission 2. Probability of infection is based on the equation in Reference 1. 3. The same infectious dose is applicable to all people. 3. Every person in the space has the same breathing rate. RESULTS: --How to Read the Results-- The following output shows the relative risk of the scenario when compared to the reference scenario. The inputs for the reference and gathering scenarios is at the bottom of this document. In this simulation, the gathering poses the same amount of risk as the reference at 42 minutes. The table below shows the relative risk at various timesteps during the simulation. For example, a result showing a relative risk of .5 at 30 minutes indicates that at 30 minutes into the scenario, your risk is half of what it would be in the reference scenario conditions. Time Relative Risk (min) (-) 0 0.0 12 0.08 24 0.33 36 0.74 48 1.3 60 2.0 72 2.84 84 3.8 96 4.88 108 6.07 120 7.35 HOW TO REDUCE RISK 1. Decrease the amount of particles expelled in the air. The number of particles exhaled is activity dependent. Reference 2 is used as the basis for this model and provides valuable insight through real-life testing. Much like risk, the values provide a point of comparison where a reference activity with 0.2 particles per ml will result in 30% fewer viroids exhaled per respiration than an activity with 0.3 particles per ml. 2. Increase the air exchanges with fresh air. This has the greatest impact as it dramatically decreases the concentration of viroids resulting in extending the time until an infectious dose is accumulated. 3. Use a larger space. Assuming the air within the space is evenly mixed, either with installed ventilation or temporary fans, the larger volumes dilutes the concentration of viroids. 4. Limit your time in the space. The longer you stay in a space with viroids, the higher your risk for getting an infection becomes. ADDITIONAL NOTES AND GUIDANCE: 1. Air changes within a space can be highly variable and range from .18 per hour for most houses to three per hour in healthcare facilities. For very "tight" houses, the lower end of this scale should be used, but if there are windows open with some sort of exhaust flow, the air changes could greatly exceed the upper end of this scale. REFERENCES: 1. Infection Risk Assessment of COVID-19 through Aerosol Transmission: a Case Study of South China Seafood Market, Xiaole Zhang, et. al, American Chemical Society PMID 32543176, June 16, 2020. 2. International Coalition Performing Arts Aerosol Study, Dr. James Weaver, et.al, https://www.nfhs.org/media/4294910/third-aerosol-report.pdf INPUTS: --REFERENCE SCENARIO-- Number of infected people in the space = 1 Number of particles exhaled on average (particles per ml) =.2 Number of reference volume air changes (air changes per hour) = 0.0 Reference space air volume (cubic feet) = 72.0 The amount of time infectious people are present (minutes) = 15 Probability of infection spread to target (%) = 1 --GATHERING SCENARIO-- Number of infected people in the space = 3 Number of particles exhaled on average (particles per ml) =1 Number of reference volume air changes (air changes per hour) = .18 Reference space air volume (cubic feet) = 8100.0 The amount of time infectious people are present (minutes) = 120 Time you enter the space after infectious people were present (minutes) = 0.0 Time you exit the space after infectious people were present (minutes) = 120 REQUESTOR COMMENTS: comments =