Evaluation of ventilation, indoor air quality, and probability of viral infection in an outdoor dining enclosure.

In 2020, many cities closed indoor dining to curb rising COVID-19 cases. While restaurants in warmer climates were able to serve outdoors year-round, restaurants in colder climates adopted various solutions to continually operate throughout the colder months, such as the use of single-party outdoor dining enclosures to allow for the continuation of outdoor dining. This study evaluates indoor air quality and the air exchange rate using carbon dioxide as a tracer gas in a dining enclosure (12.03 m3) and models the probability of COVID-19 infection within such an enclosure. The air exchange rates were determined during two trials for the following scenarios: (1) door closed, (2) door opened, and (3) door opened intermittently every 15 min for 1 min per opening. The probability of COVID-19 infection was evaluated for each of these scenarios for 1 hr, with occupancy levels of two, four, and six patrons. The Wells-Riley equation was used to predict the probability of infection inside the dining enclosure. The air exchange rates were lowest in the closed-door scenarios (0.29-0.59 ACH), higher in the intermittent scenarios (2.36-2.49 ACH), and highest in the open-door scenarios (3.61 to 33.35 ACH). As the number of subjects inside the enclosure increased, the carbon dioxide accumulation increased in the closed-door and intermittent scenarios. There was no identifiable accumulation of carbon dioxide in the open-door scenario. The probability of infection (assuming one infected person without a mask) was inversely proportional to the airflow rate, and ranged from 0.0002-0.84 in the open-door scenario, 0.0034-0.94 for the intermittent scenarios, and 0.015-1.0 for the closed-door scenarios. The results from this study indicate that under typical use, the indoor air quality inside dining enclosures degrades during occupancy. The probability of patrons and workers inside dining enclosures being infected with COVID-19 is high when dining or serving a party with an infected person.

Comparing respirator laboratory protection factors measured with novel personal instruments to those from the PortaCount.

A quantitative fit test is performed using a benchtop instrument (e.g., TSI PortaCount) to assess the fit factor provided by a respirator when assigned to a worker. There are no wearable instruments on the market to measure protection factors while the respirator is in use. The aim of this study is to evaluate two new, wearable, quantitative instruments-a dual-channel optical particle counter (DC OPC) and a dual-channel condensation particle counter (DC CPC)-that would enable in-situ, real-time measurement of respirator workplace protection factor. Respirator laboratory protection factors measured by the new instruments were compared to those measured with the TSI PortaCount on one test subject for three test aerosols (sodium chloride, incense, ambient) at target laboratory protection factors of 100, 300, and 1,000 for sodium chloride and ambient, and 75 and 500 for incense. Three replicates were performed for each test condition. Data were analyzed with a two-sided paired t-test at a significance level of 0.05. Laboratory protection factors measured with the DC CPC agree with those measured with the PortaCount whereas those from the DC OPC generally do not. Mean laboratory protection factors derived from the DC CPC are only statistically significantly different for mean values of a laboratory protection factor at ambient conditions for a target laboratory protection factor of 300 (p = 0.02) and for incense at a target laboratory protection factor of 75 (p = 0.03). Although statistically significant, the difference in laboratory protection factors derived from the DC CPC are not substantial in practice and may be explained by systematic uncertainty. In contrast, the DC OPC reports substantially larger mean laboratory protection factors, differing by about half an order of magnitude in extreme cases, and statistically significantly different mean laboratory protection factors for the sodium chloride aerosol for target laboratory protection factors of 100 and 300 (p = 0.01 and p = 0.01).