ABSTRACT
The coronavirus disease 2019 (COVID-19) Exposure Assessment Tool (CEAT) allows users to compare respiratory relative risk to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) for various scenarios, providing understanding of how combinations of protective measures affect risk. CEAT incorporates mechanistic, stochastic, and epidemiological factors including the (i) emission rate of virus, (ii) viral aerosol degradation and removal, (iii) duration of activity/exposure, (iv) inhalation rates, (v) ventilation rates (indoors/outdoors), (vi) volume of indoor space, (vii) filtration, (viii) mask use and effectiveness, (ix) distance between people (taking into account both near-field and far-field effects of proximity), (x) group size, (xi) current infection rates by variant, (xii) prevalence of infection and immunity in the community, (xiii) vaccination rates, and (xiv) implementation of COVID-19 testing procedures. CEAT applied to published studies of COVID-19 transmission events demonstrates the model's accuracy. We also show how health and safety professionals at NASA Ames Research Center used CEAT to manage potential risks posed by SARS-CoV-2 exposures.
ABSTRACT
The COVID-19 Exposure Assessment Tool (CEAT) allows users to compare respiratory relative risk to SARS-CoV-2 for various scenarios, providing understanding of how combinations of protective measures affect exposure, dose, and risk. CEAT incorporates mechanistic, stochastic and epidemiological factors including the: 1) emission rate of virus, 2) viral aerosol degradation and removal, 3) duration of activity/exposure, 4) inhalation rates, 5) ventilation rates (indoors/outdoors), 6) volume of indoor space, 7) filtration, 8) mask use and effectiveness, 9) distance between people, 10) group size, 11) current infection rates by variant, 12) prevalence of infection and immunity in the community, 13) vaccination rates of the community, and 14) implementation of COVID-19 testing procedures. Demonstration of CEAT, from published studies of COVID-19 transmission events, shows the model accurately predicts transmission. We also show how health and safety professionals at NASA Ames Research Center used CEAT to manage potential risks posed by SARS-CoV-2 exposures. Given its accuracy and flexibility, the wide use of CEAT will have a long lasting beneficial impact in managing both the current COVID-19 pandemic as well as a variety of other scenarios.
ABSTRACT
A sampling and analytical method for measuring ethylene oxide (EO) in ambient air was developed and evaluated. The method is based on the use of evacuated canisters and gas chromatography-mass spectrometry (GC-MS). The objectives of this work were to characterize the performance of the method with respect to the following: (1) stability/recovery of ethylene oxide in a canister over a 15-day holding time; (2) detection capability; and (3) measurement of EO in an ambient air matrix. Both electropolished and silica-lined stainless steel canisters were evaluated in this study. The method evaluation involved both laboratory and field tests. The recovery of the EO was evaluated both on an absolute basis and relative to a spiked internal standard of toluene. EO spiked at levels of 2 ppbv and 20 ppbv was found to be stable for holding times of up to 15 days at 25 degrees C in both a humidified nitrogen matrix and in ambient air. The detection limit of the method was found to be 0.25 ppbv using EPA's traditional approach of seven replicate analyses of a low-level standard and 0.20 ppbv using a probability-based approach. EO recoveries in the laboratory stability study generally were 100 +/- 25%, and did not vary by canister type, nor did the EO recoveries decrease with holding time. Field studies demonstrated that the method is capable of detecting EO (as well as benzene and toluene) in an ambient air matrix.
