Resources to Estimate Risk

Resources to Help Estimate Risk of SARS-CoV-2 Transmission in an Indoor Environment


Tools to estimate exposure or risk in indoor environment (not exhaustive)

Table A1. Tools for estimating exposure or risk for SARS-CoV-2 in indoor environments


Key parameters that can be manipulated

Safe Air Spaces

Oregon Institute for Health in the Built Environment

Risk of SARS-CoV-2 transmission considers “high” or “low” viral emitter, number of occupants sharing air, ventilation, extra air cleaning from filtration.

Portable Air Cleaner Calculator for Schools v1

Harvard-CU Boulder

Considers the number of people and size of space, and risk of SARS-CoV-2 transmission; provides suggestion for how to increase effective air exchange rate through use of portable air cleaning devices.

COVID-19 Aerosol Transmission Estimator

Jose Jiménez CU-Boulder


Aerosol transmission calculator. Considers infectious dose emission rate (quanta), inhalation rate, mask efficiencies for source. control and PPE, building ventilation rate, biological decay of virus and aerosol deposition onto surfaces, chance of encountering an infectious person, proportion of population immune.

Visualization by El País using the Jiménez aerosol transmission estimator.

Estimation of COVID-19 infection risk from airborne transmission during classroom teaching

Duke University

Adding probabilistic Monte Carlo approach to Jose Jiménez transmission risk estimator.

Airborne infection risk calculator

International collaborators (USA, Italy, Australia), hosted by CUNY

Estimates risk as a function of time, viral inactivation/removal, room volume, number of infectious occupants, breathing level based on activity, and estimated quanta generation level based on comprehensive analysis of published findings.

COVID-19 Risk Calculator

Harvard Healthy Buildings

Estimates risk based on model described in analysis of Diamond Princess cruise ship outbreak. Model adjusts risk based on room size, length of exposure, activity type, and controls including face mask use, distancing, ventilation, air cleaning, hand washing, and room cleaning.

FaTIMA (Fate and Transport of Indoor Microbiological Aerosols)



Multizone modeling tool to help predict viral aerosol exposure given exposure within a building. Considers ventilation from building infiltration and mechanical sources, system filtration, portable air cleaner use. Describes exposure and does not make assumptions about the relationship between exposure and infection risk. (Documentation)

Equivalent outdoor air calculator


Estimates time of indoor flush-out period to achieve 3 air changes per hour. The goal of the flush-out is to reduce exposure to contaminants that build up over time with occupants.

Ventilation calculator


Estimates the effect of ventilation on SARS-CoV-2 transmission risk.

COVID Exposure Assessment Tool (CEAT) 

Signature Science, LLC

Considers near-field and far-field exposure associated with numerous factors, including community infection prevalence and adherence to distancing measures. Benchmarks risk associated with inhalation exposure using OSHA “high risk” classification.


Michael Riediker and Christian Monn; SECO (Swiss State Secretariat for Economic Affairs)

Calculates concentration of aerosolized virus in a room and exposure within an arm’s length (60cm) and at room-scale. Considers mask use, variable source emission, physical activity, speech, and room size, air exchange, and air flow velocity.

Facility Infection Risk Estimator v2.1


Estimates number of infected adults and children per exposure scenario. Can build exposure scenarios based on age, activity level, room size, use of GUV, air exchange, filtration, exposure time, level of viral shedding into exhaled breath, mask use. Translates disease estimates into economic value, and associated, hypothetical reproductive ratio values. 

Why Is the Risk of Coronavirus Transmission so High Indoors? Article with visualization and tool.

Zeit Online Publication with advising from a Max Planck Institute for Chemistry research team (Jos Lelieveld et al. 2020)

Estimates transmission given available evidence and assumptions regarding generation of infectious aerosols including through speech, speech volume, singing, coughing, mask efficiency, room size, air exchange rate, and occupancy density, and length of exposure. The concentration of infectious virus contained in respiratory lining fluid is used to estimate infectious material concentration in aerosols. Measured concentrations of exhaled breath particles are used. 

An analysis of three Covid-19 outbreaks: how they happened and how they can be avoided

El País in collaboration with numerous public health agencies advising.

Provides visual models of documented transmission of SARS-CoV-2 in an office, a restaurant, and a bus. Provides suggestion for mitigating transmission based on the hierarchy of controls.

City reduced probability of infection for indoor airborne transmission of COVID-19


Draws on the Jiménez transmission estimator and building archetypes to infer infection transmission risk at the building level across Canada and the United States.


Summary documents and helpful resources

  1. FAQs on Protecting yourself from aerosol transmission (Contributions from Marr, Miller, Prather, Haas, Bahnfleth, Corsi, Tang, Herrmann, Pollitt, Jiménez)
  2. Resources on transmission & prevention of COVID-19 (Compiled by Alex Huffman, University of Denver)
  3. Guide for choosing masks for children (Virginia Tech University)
  4. Guide for making a Corsi-Rosenthal ‘do-it-yourself’ air cleaner for high clean air delivery and low cost.