Table 2.
Parameter descriptions for ventilation-system effect evaluations. *All simulated worlds were square-shaped. †Based on linear modeling described in Appendix S2, these values equate to 1 (SD = 0) and 970 (SD = 390) quanta/hr. ‡Standard deviations are given in parentheses. §Das et al. (2020) estimated the average travel distance of a 100-micrometer droplet expelled from a height of 1.7 m at a velocity of 0.5 m/s to be 0.55 m. They also found that the majority of 100-μm droplets will fall 0.55–2.35 m away from the expelling individual, depending on initial velocity, but droplets may settle up to 3.2 m away very rarely. a random draw of 10,000,000 samples from a log-normal distribution parameterized using 1.7-m and 0.2095-m droplet spread distance mean and standard deviation values, respectively, generated a distribution in line with this finding. The standard deviation we use in simulations for non-coughing expectoration is proportionate to the one used in this random draw. ¶These parameter values were only used when the Forced air parameter value was set to “on.” #These parameter values were only used when the Forced air parameter value was set to “off.” **All patches on the east side of the simulated world acted as supply vents. All patches on the west side acted as return vents. ††Zero-percent mask efficacy is equivalent to no mask use. ‡‡Instead of specifying a fixed number of individuals in simulations, we scaled the simulated population with world size.
| Parameter/Model Input | Value (s) | Reference (s) |
|---|---|---|
| Infectiousness parameters | ||
| Cough frequency (coughs/min) | 0.19 | Lee et al., 2012 |
| Droplet count (droplets/expectoration)† | 1000 (0)‡, 9.7e5 (3.9e5)‡ | Miller et al., 2020,Appendix S2 |
| Droplet spread angle – coughing (º) | 35 | Kwon et al., 2012 |
| Droplet spread angle – not coughing (º) | 63.5 | Kwon et al., 2012 |
| Droplet travel distance – coughing (m) | 5 (0.256)‡ | Bourouiba et al., 2014 |
| Droplet travel distance Рnot coughing (m) | 0.55 (0.068)ठ| Das et al., 2020 |
| Scenario environment and individual behavior inputs | ||
| Area (m2)* | 9, 36, 81 | – |
| Expectoration height (m) | 1.7 | Fryar et al., 2018 |
| Inhalation rate (m3 air/min) | 0.023 | Adams, 1993 |
| Maximum people in a single 1-m2 patch (people) | 2 | Hamner et al., 2020 |
| Number of infectious individuals (people) | 1 | – |
| Proportion of infectious individuals that are symptomatic (%) | 0, 100 | – |
| Scenario virion behavior inputs | ||
| Virion count (virions/mL fluid) | 2.35e9 | Wölfel et al., 2020 |
| Virion decay rate (%/min) | 1.05, 5¶, 10¶, 25¶, 50¶, 75¶, 90¶ | van Doremalen et al., 2020 |
| Virion infection risk (%/inhaled virion) | 6.24 | Appendix S2 |
| Scenario airflow inputs | ||
| Diffusion rate (m3/min) | 1.5e-3 | Castillo and Weibel, 2018 |
| Forced air | on, off | – |
| Forced air direction** | East-to-West | – |
| Air change rate (%/min) | 0#, 1¶, 5¶, 10¶, 25¶, 50¶ | – |
| Re-circulated air filtration (%/min) | 0#,1¶, 5¶, 90¶, 100¶ | – |
| Scenario intervention inputs | ||
| Attempted social distancing (m) | 0 | – |
| Contact duration (min) | 10, 30, 60 | – |
| Mask efficacy (%) | 0†† | – |
| Population density (people/m2)‡‡ | 0.333, 0.667, 1, 1.667 | – |