Introduction
A Powerful Calculator for Everyone
Our calculator features great extensbility while maintaining the ease of use. Estimations are made based on solid researches, normal users can easily use default settings to get decent estimations, while advanced users can import their custom rooms and modify assumptions based on the situation in their own regions. We also provide an interactive visualization for convenient comparison between cases.
How to Use
Quick Estimation
To get estimation, please first select the target building and room, then select or input your custom VAV (Variable Air Volume), the ASHRAE Recommended Minimum option stands for minimum VAV recommended by The American Society of Heating, Refrigerating and Air-Conditioning Engineers. If you use air purifier, you can input its cfm, which adds additional airflows to the environment. Input other informations, click "Go" and you can have your estimation.
Visualization
After you input all information and receive the estimation, click "Add to Visualization" will add the case to the visualization, move the cursor to the columns you will see the information of the event. You can remove events from visualization by inputing their cases numbers (e.g: 1, 2 means cases 1 and 2) and click "Remove Inputted Events".
Advanced Modification
To add custom rooms, click "Add Custom Rooms" and upload files containing your custom rooms using the given format (click to download sample files for custom rooms). Please make sure all information inputted are valid, all information should be numbers except names of building and rooms.
To modify assumptions, please first read the "Important Assumptions" to understand the assumptions we made and their reasons, then modify the assumptions accordingly based on your evaluations. (click to download assumptions files) All modifications are recorded immediately after input. Please make sure all inputs are valid.
How it Works
Methods
To calculate the risk of airborne infection in a given room the emission rate of quanta is needed. A quantum is defined as the viral load i.e. the dose of contaminated airborne droplet nuclei required to cause infection in 63% of persons. The emission rate of quanta is calculated with the following formula from Morawska et al. 2020 :
Where Ni is the droplet concentration by diameter. These droplet concentrations were taken from Morawska et al. 2009.
Cv corresponds to the viral load in the sputum (i.e. infectious mucus) of the infected person. The viral load in the sputum of an infected person varies and is dependent on the stage of infection so for this estimator we will choose a large viral load of 1e9 RNA copies per milliliter to simulate the worst case scenario for infection spread [based on Walsh et al. 2020 ].
IR (Inhalation Rate) the product of breathing rate and tidal volume, expressed in cubic meters per hour. IR is dependent on the activity of the infected subject. We chose IR values from Adams 1993 .
To calculate the concentration of quanta over time we are using the following equation based on Gammaitoni and Nucci's 1997 paper:
IVRR (hr−1) represents the infectious virus removal rate in the room. The IVRR is the sum of three parameters: the air change per hour (ACH) via ventilation, the particle deposition on surfaces via gravitational settling which is 0.63 according to Doremalen et al. 2020, and the viral inactivation rate which is 0.24 per hour according to Chatoutsidou and Lazaridis, 2019.
n0 represents the initial number of quanta in the space, we presume there is no initial quanta, which means n0 = 0.
I is the number of infected people.
V is the volume of the indoor environment considered.
After collecting all information above, we can calculate the estimated infection risk R using the formula:
Important Assumptions
These are assumptions we used in calculation. They are selected based on our researches, you can modify them in "Modify Assumptions".
Infection Rate: 0.0075, calculated by number of positive cases / number of tested students and employees, based on Return to Learn in UC SanDiego. If you are not estimating infection risks in UC SanDiego, you should modify this using the data in your own region.
Viral Load in the Sputum (CV): Viral Load in the Sputum, assigned to be 1e9 based on Turu Watanabe.
Conversion Factor (CI): Quanta per RNA copy, assigned to be 0.02 based on Xia Yu.
Inhalation Rate (IR): Inhalation rate of quanta, based on activity, it's 3.3 for heavy exercise, 2.35 for moderate exercise, 1.38 for light exercise, 0.49 for sitting, 0.54 for standing. Based on Air Resources Board Research Division.
Deposition Rate of Infectious Particle: 0.24 based on Sofia Eirini Chatoutsidou.
Inactivation Rate of Infectious Particle: 0.63 based on The New England Journal of Medicine.
Initial Quanta: Initial Quanta in the environment is 0.
Droplet Concetrations: The concetration of droplet emitted by people varies a lot for different activities. Based on L. Morawska, they are: {".8μm": 0.4935,"1.8μm": 0.1035, "3.5μm": 0.073, "5.5μm": 0.035} for speaking, {".8μm": 0.236, "1.8μm": 0.068, "3.5μm": 0.007, "5.5μm": 0.011} for counting, {".8μm": 0.110, "1.8μm": 0.014, "3.5μm": 0.004, "5.5μm": 0.002} for whispering, {".8μm": 0.751, "1.8μm": 0.139, "3.5μm": 0.139, "5.5μm": 0.059} for singing, {".8μm": 0.084, "1.8μm": 0.009, "3.5μm": 0.003, "5.5μm": 0.002}} for breathing,
Tidal Volume: varies by Droplet Size, it's 0.26808257310632905 for 0.8 micrometer droplet, 3.053628059289279 for 1.8 micrometer droplet, 22.44929750377706 for 3.5 micrometer droplet, and 87.11374629016697 for 5.5 micrometer droplet. Based on L. Morawska.
Masks Efficiency: The effectiveness of masks (normal surgical masks) varies based on the size of droplet, it's 20% for 0.8 micrometer droplet, 40% for 1.8 micrometer droplet, 70% for 3.5 micrometer droplet, 80% for 5.5 micrometer droplet. Based on Tara Oberg.
