Predicting SARS-2

Predicting SARS-2 Exposure and Probability of Infection

Location – (Web PDC)

Instructions regarding how to log onto the web PDC and the conference call phone number, as well as handouts, will emailed to the registered participants the week before the PDC.


Paul Hewett Ph.D. CIH

Course Description

There are numerous online tools for predicting the “probability of infection” due to exposure to SARS-CoV-2 virus.  Most (if not all) of these tools are based on the venerable Wells-Riley aerosol infectious disease model.  The Wells-Riley model calculates exposure to respirable infectious particles using the well known industrial hygiene One Box, Well-mixed Room (WMR) model.

The Wells-Riley model will be presented – in industrial hygiene terms – and used to estimate (a) exposure to SARS-CoV-2 infectious particles, (b) inhaled dose, and (c) the probability of infection.

The critical “emission rate” information is at this time sparse and tentative.  Consequently, estimates of the probability of infection have to be viewed with caution.  However, using existing emission rate estimates, the model can be used to evaluate ventilation control strategies, show the value of using face masks or respirators, predict the benefit of social distancing, and examine the benefit of portable air cleaners and the use of UV germicidal irradiation.  (Better estimates of emission rates for both droplets (which increase the near field risk) and aerosols (which increase the far field risk) will no doubt be available in the near future.)

Various online tools for predicting the “probability of infection” will be reviewed and compared.  The Task Exposure Assessment Simulator (TEAS) program (available at this website) has been modified to include the Wells-Riley model.  Using a beta version of TEAS-C19, various scenarios will be modeled and critiqued, and compared to the predictions of online tools.

(NOTE: TEAS and TEAS-C19 are different programs.  TEAS was designed to predict occupational exposures to toxic chemicals.  TEAS-C19 is a modified version of TEAS that combines the Wells-Riley infectious disease model with various well-mixed room models.)

Each PDC is 3.0 hours, with an additional 30 minutes for Q&A.  Each participant will receive a certificate confirming participation in the PDC.

WARNING: This web PDC does not provide a background on COVID-19 disease.  It is primarily designed for those who are asked by risk managers for quantitative assessments of risk, and wish to understand how the various online tools calculate the probability of developing an infection due to single indoor encounters where there is at least one infectious person

To assist the student, EAS Inc. will provide a student version of TEAS-C19.

Learning Objectives

Upon completion, participants will have a working knowledge of …

  • the Wells-Riley infectious disease model ( from an industrial hygiene perspective)
  • procedures for …
    • estimating exposure to SARS-2 (given the available information) (for a simple one room, one meeting, one source scenario).
    • calculating dose and the probability of infection.
  • how to use the various One and Two Box Well-Mixed Room models to estimate exposure.
  • how to incorporate additional controls – e.g., portable air cleaners and UV inactivation – into the Wells-Riley model.
  • ability to evaluate the benefit of respiratory protection and social distancing for a specific scenario.
  • an appreciation for the uncertainty in the current “emission rate” estimates.
  • a familiarity with several online and software tools for estimate the probability of infection.


  • Recommend …
    • taking the “Predicting Exposure I” web PDC.
    • having a basic familiarity with SARS-CoV-2 and COVID-19.
  • Recommended Reading
    • CDC recommendations for minimizing personal risk.
  • Presentation List (tentative)
    • Introduction to the Wells-Riley Infectious Disease Model and Source-Receptor Modeling
    • Predicting Exposure, Dose, and Probability of Infection
    • Software Tools
    • Emission Rates
    • Face Mask and Respirator Filtration Efficiencies
    • Virus Loss Rates (due to inactivation, portable air cleaners, UV inactivation)
    • Summary and Recommendations
    • Q&A


See Registration page.

Cancellation Policy

See Registration page.

Read these notes before you sign up:

NOTE: The registration and participation policy for each Web PDC is the same as for a fixed location or on-site PDC. Registration is per participant, not per viewing site. Each participant must register.  Only those registered should view and participant in this web PDC.

NOTE: The email address submitted at the time of payment will be used for all email communications and for logging onto the web PDC.

NOTE: This web PDC will presented using GoToMeeting. GoToMeeting must be installed on your computer. To install (usually takes less than two minutes), click on the GoToMeeting link above, scroll to the bottom of the page, and click on the link “Download GoToMeeting (for customers)”. If you do not have administrative privileges for your computer have your IT person install the GoToMeeting software at least the day before the web PDC.

NOTE: The conference call number will not be toll free. You will be responsible for any long distance phone charges if you do not have an unlimited long distance account. However, you may also connect using your computer speakers and microphone or headset (VoIP).

NOTE: See the “Prerequisites” below for software and freeware that will be helpful when taking this web PDC. To download and install the program(s) you must first be a registered member of