Efficacy of Ventilation, HEPA Air Cleaners, Universal Masking, and Physical Distancing for Reducing Exposure to Simulated Exhaled Aerosols in a Meeting Room

Abstract

There is strong evidence associating the indoor environment with transmission of SARS-CoV-2, the virus that causes COVID-19. SARS-CoV-2 can spread by exposure to droplets and very fine aerosol particles from respiratory fluids that are released by infected persons. Layered mitigation strategies, including but not limited to maintaining physical distancing, adequate ventilation, universal masking, avoiding overcrowding, and vaccination, have shown to be effective in reducing the spread of SARS-CoV-2 within the indoor environment. Here, we examine the effect of mitigation strategies on reducing the risk of exposure to simulated respiratory aerosol particles within a classroom-style meeting room. To quantify exposure of uninfected individuals (Recipients), surrogate respiratory aerosol particles were generated by a breathing simulator with a headform (Source) that mimicked breath exhalations. Recipients, represented by three breathing simulators with manikin headforms, were placed in a meeting room and affixed with optical particle counters to measure 0.3–3 µm aerosol particles. Universal masking of all breathing simulators with a 3-ply cotton mask reduced aerosol exposure by 50% or more compared to scenarios with simulators unmasked. While evaluating the effect of Source placement, Recipients had the highest exposure at 0.9 m in a face-to-face orientation. Ventilation reduced exposure by approximately 5% per unit increase in air change per hour (ACH), irrespective of whether increases in ACH were by the HVAC system or portable HEPA air cleaners. The results demonstrate that mitigation strategies, such as universal masking and increasing ventilation, reduce personal exposure to respiratory aerosols within a meeting room. While universal masking remains a key component of a layered mitigation strategy of exposure reduction, increasing ventilation via system HVAC or portable HEPA air cleaners further reduces exposure.

Efficacy of Do-It-Yourself air filtration units in reducing exposure to simulated respiratory aerosols

“…Physical distancing has been shown to be important when individuals are facing each other less than 1.8 m apart indoors [ 19 , 20 ]. Beyond physical distance, ventilation in a room becomes the dominant contributor to aerosol dispersion and, therefore, personal exposure [ 21 , 22 ]. Increasing indoor ventilation by increasing outdoor and total airflow through heating, ventilation, and air conditioning (HVAC) systems, using more efficient central HVAC filters [ 23 ], opening windows to increase natural ventilation [ 24 ], and/or adding supplemental air filtration systems help reduce exposure [ 25 ].…”

“…Thus, portable HEPA air cleaners can provide a rapidly deployable alternative to increasing effective ventilation rates where renovating existing HVAC systems is not immediately practical. In three studies using mechanical breathing simulators, the use of commercially available portable HEPA air cleaners that were sized to provide 5 air changes per hour (ACH) of filtered air led to a >50% reduction in exposure to simulated exhaled aerosols [ 21 , 31 , 32 ]. Another study using a calculation model found that the addition of portable HEPA filtration units sized to provide 5.4 ACH can help reduce transmission of SARS-CoV-2 [ 33 ].…”

Between-Occupation Differences in Work-Related COVID-19 Mitigation Strategies over Time: Analysis of the Virus Watch Cohort in England and Wales

“…However, multi-occupation investigation into mitigation methods is currently limited. Modelling, simulation and observational studies of workplace COVID-19 prevention and control strategies indicate that layered packages of mitigation methods -including gradual return to in-person working, asymptomatic testing, reduction of contact, and using personal protective equipment (PPE)appear effective and more likely to reduce worker positivity compared to single measures (7)(8)(9)(10)(11)(12). However, studies thus far have tended to focus on single workplaces, and many sectors outside of health and social care settings are underrepresented in the current literature (9).…”

Assessment of Aerosol Persistence in ICUs via Low-cost Sensor Network and Zonal Models

“…Tracer methods are currently used in indoor air quality investigations; these typically use tracer gases rather than aerosols. [19][20][21][22] For example, both ASHRAE and ASTM International have standardized test procedures. 23,24 While tracer gases are the most common approach for acquiring quantitative data on ventilation rates; however, it may not fully represent bioaerosol behavior.…”