First is an article, Face Shields, Masks with Valves Ineffective Against COVID-19 Spread, that looks at a recently published study evaluating face shields and masks with valves. While these face shields are easier for some to use, they are not effective in controlling aerosols. The same goes with the masks that have vents. These are not effective at controlling aerosols from the person wearing them. One could probably figure that these would not be able to control aerosols, but here is research that proves that they are not effective controls for minimizing the risk of spreading virus.
The second was an article in the Wall Street Journal that looks at the need for good airflow in classrooms and other settings where there are a group of people. The article, Key to Preventing Covid-19 Indoors: Ventilation, discusses the importance of air movement with the need for moving air in the room - bringing in fresh air and expelling air from the room without it blowing from one person to another.
The article discusses a few cases where improper ventilation was a problem
"Five people sitting at tables adjacent to an infected but presymptomatic diner inside a Guangzhou, China, restaurant in January later tested positive for Covid-19, despite video that indicates the separate parties didn’t have close contact, according to an April study published on a preprint server. Some patrons who contracted the virus, the authors said, were seated as far as 15 feet away from the infected diner."
AIP Publishing
https://publishing.aip.org/publications/latest-content/face-shields-masks-with-valves-ineffective-against-covid-19-spread/Face Shields, Masks with Valves Ineffective Against COVID-19 Spread
September 1, 2020
Physics of Fluids - News
From the Journal: Physics of Fluids
Link to article: Visualizing droplet dispersal for face shields and masks with exhalation valves
DOI: 10.1063/5.0022968
WASHINGTON, September 1, 2020 — As countries around the world experience a steep surge in COVID-19 infections, face masks have become increasingly accepted as an effective means for combating the spread of the disease when combined with social distancing and frequent hand-washing.
Increasingly people are using clear plastic face shields and masks with exhalation valves instead of regular cloth or surgical masks, since they can be more comfortable. In a paper published in Physics of Fluids, by AIP Publishing, researchers investigate whether they are as effective.
The visualizations showed face shields block the initial forward motion of a simulated jet of a cough or a sneeze, but the expelled droplets can move around the visor with relative ease and spread out over a large area depending on light ambient disturbances.
The visualizations for a mask equipped with an exhalation port illustrate a large number of droplets pass through the exhale valve unfiltered, which make it ineffective in stopping the spread the COVID-19 virus if the person wearing the mask is infected.
“As students return to schools and universities, some have wondered if it is better to use face shields, as they are more comfortable and easier to wear for longer periods of time,” said Siddhartha Verma, one of the authors. “But what if these shields are not as effective? You would be essentially putting everyone in a tight space with droplets accumulating over time, which could potentially lead to infections.”
The researchers used a hollow manikin head and simulated a cough or sneeze with a pressure impulse from a manual pump. Tracers composed of droplets of distilled water and glycerin were expelled through the mouth opening, and laser sheets visualized the spatial and temporal development of the ejected flow.
“We focused on the smaller droplets, since they can stay suspended for very long times and might contain enough virus particles to transmit COVID-19,” said Verma.
The research suggests that to minimize the community spread of COVID-19, it may be preferable to use high-quality cloth or surgical masks that are of a plain design instead of face shields and masks equipped with exhale valves.
“Even the very best masks have some degree of leakage. It’s still important to maintain physical distance while wearing them to mitigate transmission,” said Verma.
AIP Physics of Fluids
https://aip.scitation.org/doi/10.1063/5.0022968
Visualizing droplet dispersal for face shields and masks with exhalation valves
Physics of Fluids 32, 091701 (2020); https://doi.org/10.1063/5.0022968
Siddhartha Vermaa), Manhar Dhanakb), and John Frankenfieldc)
ABSTRACT
Several places across the world are experiencing a steep surge in COVID-19 infections. Face masks have become increasingly accepted as one of the most effective means for combating the spread of the disease when used in combination with social-distancing and frequent hand-washing. However, there is an increasing trend of people substituting regular cloth or surgical masks with clear plastic face shields and with masks equipped with exhalation valves. One of the factors driving this increased adoption is improved comfort compared to regular masks. However, there is a possibility that widespread public use of these alternatives to regular masks could have an adverse effect on mitigation efforts. To help increase public awareness regarding the effectiveness of these alternative options, we use qualitative visualizations to examine the performance of face shields and exhalation valves in impeding the spread of aerosol-sized droplets. The visualizations indicate that although face shields block the initial forward motion of the jet, the expelled droplets can move around the visor with relative ease and spread out over a large area depending on light ambient disturbances. Visualizations for a mask equipped with an exhalation port indicate that a large number of droplets pass through the exhale valve unfiltered, which significantly reduces its effectiveness as a means of source control. Our observations suggest that to minimize the community spread of COVID-19, it may be preferable to use high quality cloth or surgical masks that are of a plain design, instead of face shields and masks equipped with exhale valves.
The COVID-19 pandemic has deeply affected every aspect of daily life worldwide. Several places across the world, including the United States, Brazil, and India, are experiencing a steep surge in infections. Healthcare systems in the most severely affected locations have been stretched to capacity, which also tends to impact urgent care for cases unrelated to COVID-19.1,2
Researchers have reported steady progress in the development of potential treatments and vaccines; however, it is estimated that widespread inoculation will not be available until sometime in the year 2021. It appears that the likelihood of vulnerable individuals struggling with severe health issues and the debilitating socio-economic ramifications of the pandemic will continue in the foreseeable future. Furthermore, widespread uncertainty regarding the re-opening of schools and universities for in-person instruction has created additional cause for concern, since these institutions have the potential to become focal points for unchecked community spread of the disease. In light of the acute circumstances, it has become crucial to establish clear and specific guidelines that can help mitigate the disease’s spread, especially given the high prevalence of asymptomatic and pre-symptomatic spread.3
A number of recent studies have contributed to this effort by significantly improving our understanding of various physical mechanisms involved in the disease’s transmission.4–7
Face masks have become increasingly accepted as one of the most effective means for source control (i.e., protecting others from a potentially infected wearer) and can help curb the community spread of the disease when used in combination with social-distancing and frequent hand-washing.8–12
Widespread mask-use by the general population has now been recommended or mandated in various places and communities around the world. Several private businesses have also adopted requirements for customers to use face coverings. Importantly, certain cloth-based masks have been shown to be effective in blocking the forward spread of aerosolized droplets13
(supplementary material, Movie 1). Although they are somewhat less capable than well-fitted medical grade masks, homemade masks constructed using certain materials can filter out a large proportion of respiratory droplets and particles.14–18
Moreover, cloth masks have the advantage of being readily available to the wider public in addition to being cost-effective, comfortable, and reusable when washed and disinfected properly. Additionally, they do not divert away from the supply of medical grade masks for healthcare workers.
While broad acceptance regarding the need for face coverings has risen steadily, there is an increasing trend of people substituting regular cloth or surgical masks with clear plastic face shields, and with masks equipped with exhalation valves (Fig. 1). Face shields tend to have noticeable gaps along the bottom and the sides, and are used in the medical community primarily for protecting the wearer against incoming sprays and splashes while in close proximity to patients.19
Moreover, they tend to be used in conjunction with respirators, surgical masks, or other protective equipment. Masks with exhalation ports include a one-way valve, which restricts airflow when breathing in, but allows free outflow of air. The inhaled air gets filtered through the mask material; however, the exhaled breath passes through the valve unfiltered. There has been limited research on how effective face shields and masks with exhalation valves are as a means of source control.20,21
One of the factors driving the increased adoption of shields and exhalation valves is improved comfort compared to regular surgical or cloth masks. Exhale valves allow for improved breathability, and reduce humidity and fogging when wearing prescription glasses. Face shields also offer these benefits, in addition to protecting the eyes from splashes and sprays of infected droplets.19,22
Shields have also been credited with other advantages such as ease of cleaning and disinfecting, long-term reusability (which is also true for well-constructed cloth masks), and allowing visual communication of facial expressions for people who may be hearing-impaired.19,23
Notably, a recent opinion-based article by Perencevich et al.23
suggested that shields may be a better alternative to regular masks for combating the COVID-19 crisis. The authors’ opinion is based on the premise that ejecta from the mouth and nose hit the visor, and their forward motion is arrested completely. While this is true for relatively large respiratory droplets, the effect on the smaller aerosol-sized droplets (diameter less than approximately 5 µm–10 µm) is markedly different, since they act as tracers and have a higher tendency to follow airflow patterns more faithfully. We note that one of the primary studies cited by Perencevich et al. expressly indicates that face shields did not serve as primary respiratory protection for the wearer in experimental tests, since suspended aerosols could flow around the visor and enter the respiratory tract.22
Over an exposure duration of 1 min–30 min, the shield was only 23% effective in reducing inhalation of droplets that were 3.4 µm on average. Although this study by Lindsley et al.22
did not consider face shields as source control methods, they are likely to suffer the same disadvantage in this role, since smaller outgoing droplets will flow around the bottom and the sides of the visor. While the opinion article by Perencevich et al.23
is based on the presumption that transmission of COVID-19 occurs primarily through larger respiratory droplets, recent studies support the possibility of airborne transmission via aerosol-sized droplets.24–27
Current CDC guidelines discourage the use of face shields as a sole means of source control,28
and mention that masks equipped with exhalation valves should not be used when a sterile environment is required.29
At the same time, there are broad variations in recommendations made by states and counties across the US, with some allowing the use of face shields as alternatives to masks,30,31
whereas many others do not address the issue at all. There is a possibility that widespread public adoption of these alternatives to regular masks could have an adverse effect on mitigation efforts. To help increase public awareness regarding the effectiveness of these alternative options, we use qualitative visualizations to examine the performance of face shields and exhale valves in impeding droplet spread.
Wall Street Journal
https://www.wsj.com/articles/key-to-preventing-covid-19-indoors-ventilation-11598953607
Key to Preventing Covid-19 Indoors: Ventilation
Add this to the Covid-19 prevention toolbox: strong ventilation.
After urging steps like handwashing, masking and social distancing, researchers say proper ventilation indoors should join the list of necessary measures. Health scientists and mechanical engineers have started issuing recommendations to schools and businesses that wish to reopen for how often indoor air needs to be replaced, as well as guidelines for the fans, filters and other equipment needed to meet the goals.
“We didn’t focus on it enough initially,” said Abraar Karan, a doctor at Brigham and Women’s Hospital in Boston who treated Covid-19 patients. “We told everyone to stay home. We weren’t thinking about people congregating in public spaces.”
How has your company improved its ventilation systems in preparation for the return to work? Join the conversation below.
Driving the thinking is mounting evidence that the new coronavirus is transmitted through the air among people with prolonged exposure to the pathogen. Especially troublesome, epidemiologists and other scientists say, is evidence from numerous indoor outbreaks suggesting the virus’s ability to spread to others even when close contact is avoided.
The precise role that airborne transmission plays is still being debated by parts of the scientific community. Yet proponents of aerosol transmission say the evidence so far argues for the need to keep clean air flowing in indoor spaces where people gather.
Ideally, they say, public spaces like a standard classroom should aim to have air replaced with clean air between four to six times an hour to dilute Covid-19 particles that might accumulate.
That can be done, aerosol scientists and building engineers say, through strategies that introduce outdoor air and filter indoor contaminants. Those include opening windows and doors, installing window fans, using portable air purifiers with high-efficiency particulate air, or HEPA, filters and upgrading heating, ventilation and air-conditioning systems to meet certain standards.
Keeping Classroom Air Clean
Scientists say schools and businesses should focus on improving ventilation to help prevent Covid-19’s spread. Spaces such as a typical classroom should aim to have air replaced with clean air four to six times an hour, though recommendations can vary by room size and occupancy. That can be done by introducing more outdoor air and enhancing filtration.
Without air conditioning:
Placement Matters
Open Windows and Doors
Place air purifiers centrally and in places without good ventilation to maximize air cleaning.
Open windows and doors to introduce outdoor air. Aim for cross-ventilation via windows on opposite walls. If unsafe to open completely, six inches can still help.
Fresh air
Install Window Fans
Fans placed inside open windows can increase airflow. Two fans, blowing fresh air in from one window, while pushing air out from another, may be helpful. Avoid positioning that would blow air directly from one person to another.
Add Air Purifier
Depending on the model, portable purifiers with HEPA filters can produce several air changes per hour. Most filter only small spaces. Schools should ensure purifiers are appropriately sized relative to the classroom.
With air conditioning:
Start Earlier
Upgrade Air-Conditioning Filters
Keep HVAC systems, such as this unit ventilator, running frequently, and start earlier than usual to allow more time for airflow and filtering before the school-day begins.
Choose HVAC filters that can remove a large portion of airborne particles, such as a MERV 13. If such a filter is incompatible, choose the most efficient filter.
Increase Outdoor Air
Increase the HVAC system’s supply of outdoor air, to as much as the system can handle, in order to reduce reliance on recirculated air.
Establish 6 FEET
Add Air Purifier
Consider several purifiers for larger rooms. Change HEPA filters regularly while wearing a mask, goggles and gloves.
Other Tools to Reduce Spread:
Keep desks spaced at least six feet apart
Reduce class sizes
Have students, teachers and staff wear masks whenever possible
[The graphic would not properly display, contact me for more information]
Rest of article - https://www.wsj.com/articles/key-to-preventing-covid-19-indoors-ventilation-11598953607
No comments:
Post a Comment