Which face mask protects you best in closed places?
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(CNN) —
More than two years into the Covid-19 pandemic, you probably know the basics of protection: vaccinations, boosters, proper handwashing and masks.
But one of the most powerful tools against the coronavirus is one that experts believe is only just beginning to receive the attention it deserves: ventilation.
Respiratory backwash
"The challenge for organizations that improve air quality is that it's invisible," said Joseph Allen, director of the Healthy Buildings Program at the Harvard TH Chan School of Public Health.
It is true: other tools against covid-19 are more tangible.
But visualizing how the virus might behave in poorly ventilated spaces can help people better understand this mitigation measure.
Allen compares it to cigarette smoke.
"If I'm smoking in the corner of a classroom and it's poorly ventilated/filtered, that room will fill with smoke and everyone will be breathing the same air."
The covid-19 is spread by contact of aerosols with the eyes, mouth and nose, according to WHO
Then apply it outdoors.
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"I could be smoking a cigarette, you could be a couple of feet away from me, depending on which way the wind is blowing, you might not even know I'm smoking."
If you're indoors, you might be breathing less fresh air than you think.
"Everyone in a room is constantly breathing air that just came out of the lungs of other people in that room. And depending on the rate of ventilation, it could be as much as 3% or 4% of the air you're breathing just came out." from the lungs of other people in that room," Allen said.
He describes this as respiratory backwash.
"Normally, that's not a problem, right? We do this all the time. We're always exchanging our respiratory microbiomes with each other. But if someone is sick and infectious ... those aerosols can carry the virus. That's a problem."
It is in the air
"We've known for decades how to keep people safe from infections in buildings, from airborne infectious diseases like this," Allen said.
Since the start of the pandemic, Allen and other experts have waved red flags, saying the way we were thinking about COVID-19 transmission (surfaces, large respiratory droplets) was wrong.
"Handwashing and social distancing are appropriate but, in our opinion, insufficient to provide protection against virus-carrying respiratory droplets released into the air by infected people. This problem is especially acute in indoor or closed environments, particularly those that are crowded and have inadequate ventilation," hundreds of scientists stated in an open letter in July 2020.
Finally, the World Health Organization and the US Centers for Disease Control and Prevention acknowledged what experts had been saying all along: that covid-19 could also spread through tiny particles in aerosol that can travel more than 1 meter.
Questions from the audience about the coronavirus: What happens to the antibodies of a person with a complete vaccination schedule and who has contracted covid-19?
The coronavirus itself is very small — about 0.1 microns — but that doesn't affect how far it can travel.
“The size of the virus itself doesn't matter because, as we say, the virus is never naked in the air.
In other words, the virus always travels in respiratory particles that develop in our lungs.
And those are all different sizes," Allen said.
Singing or coughing can emit particles down to 100 microns (about the width of a human hair), he said, but the virus tends to travel in smaller particles, between 1 and 5 microns.
The size of these particles affects not only how far they can travel, but also how deeply we can breathe them into our lungs and how we should approach protection from this virus.
"When you talk about an airborne disease, there's what's around you, you know, the kind of people you know who can cough in your face, the 6-foot thing, and then there's the wider indoor air, because indoor air recirculates," said Max Sherman, leader of the Task Force on Epidemics at the American Society of Heating, Refrigerating, and Air-Conditioning Engineers.
Dilute and clean
"Outside is safer than inside" has become an accepted mantra with covid-19.
Allen points out that protecting ourselves indoors is where our focus should always be, even beyond the pandemic.
"We're [a] closed space kind of thing. We spend 90% of our time indoors. The air we breathe indoors has a huge impact on our health, whether you think about infectious diseases or anything else, but just has escaped public consciousness for a long time," he said.
Making sure our indoor air is healthy isn't that complicated, Sherman said.
"You just want to reduce the number of particles that could be carrying Covid or any other nasty [viruses]."
The way to do this is through ventilation and filtration.
Filtration, just as it sounds, is filtering or cleaning the air, removing infected particles.
But think of ventilation as diluting the air.
You are bringing in more fresh air to reduce the concentration of those particles.
Dilution is exactly why we haven't seen outdoor superspreader events, says Allen.
"We have almost no outdoor transmission. Why is that? Unlimited dilution, because you have unlimited ventilation. And so even at mass protests or outdoor sporting events like the Super Bowl, we just don't see superspreading happening. But if If we did, we'd make the signal loud and clear. We just don't see it. It's all indoors in these underperforming, unhealthy spaces."
healthy spaces
Even before the advent of HVAC systems, ventilation was integrated into many building designs.
New York's Tenement Housing Act of 1901 required that each tenement building, a multifamily dwelling building, have ventilation, running water, and gas lighting.
Builders added ventilation to many of these buildings with a vent down the middle that runs from the ceiling to the ground, allowing for more airflow.
"In the late 1800s, people finally began to understand how disease spreads. So air shafts and the ventilation that goes with them were seen as a solution to the public health crises that were occurring in buildings. of housing," said Katheryn Lloyd, director of programming for the Museum of Housing.
"There were high cases of tuberculosis, diphtheria and other diseases that spread. Now we know that they spread through the air."
Today, we face the same challenge.
"Getting basic ventilation in your home is important, full stop," Sherman said.
One of the easiest and cheapest ways to do this is to open the windows.
Open doors or windows at opposite ends of your house to create cross ventilation, advises the Environmental Protection Agency.
Opening the highest and lowest windows, especially if they are on different floors, in a home can also increase ventilation.
Adding an indoor fan can take you even further.
A gym trainer with covid-19 exposed 50 people, but no one got it due to a ventilation redesign
"If a single fan is used, it should face (and blow air) in the same direction the air naturally moves. You can determine the direction the air naturally moves by watching the movement of curtains or by holding a cloth or by throwing paper clippings and noticing which way they move," says the EPA.
Simply opening a window can help a lot, Allen says: "Even keeping a window open a couple of inches to really facilitate higher air changes, especially if you do it in multiple places in the house, so you can create some pressure differentials.
It's important to note that if you have an HVAC system, it must be running for it to actually circulate or filter the air.
The EPA says that these systems work less than 25% of the time during the heating and cooling seasons.
"Most controls these days have a setting where you can run the fan on low speed all the time. And that's usually the best thing to do because that ensures you're pushing air through the filter all the time. time and mix the air in your house," Sherman advised.
This might be something to consider if you're having visitors or if someone in the household is at higher risk of getting seriously ill.
Choose the most efficient filter your HVAC system can handle, and be sure to change filters routinely.
Filters have a Minimum Efficiency Reporting Value, or MERV, which indicates how well they capture small particles.
The American Society of Heating, Refrigerating, and Air Conditioning Engineers recommends using at least a MERV-13 filter, which it says is at least 85% efficient at capturing 1- to 3-micron particles.
If that's not an option, portable air cleaners can also work just fine, but the EPA says to use one that's made for your intended room size and meets at least one of these criteria:
Designed as High Efficiency Particulate Air (HEPA)
CADR Rating
The manufacturer says the device will remove most particles below 1 micron.
Find a safe space
When you enter a space, there's no good rule of thumb for looking around and assessing how well ventilated it might be, and that can be challenging when people are tasked with assessing their own risk.
Allen suggests starting with the basics: Make sure you're up to date on your vaccinations and know where the numbers for Covid-19 are in your community.
But then it gets harder.
Even the number of people in a space is not an indicator of a higher risk situation.
"The more people inside, the higher the risk because the more likely someone is to be infectious, but if the ventilation is good, it doesn't really matter."
Ventilation standards are based on "an amount of fresh air per person, plus the amount of fresh air per square foot," Allen explained.
"So if you have a good system, the more people that come into the room, the more ventilation that goes into the room."
One tool that can help you assess ventilation in a room is a CO2 monitor, something Allen would like to see more of in public spaces.
He likes to carry a portable one, which can be ordered online for between US$100 and US$200.
"If you see less than 1,000 parts per million, you're generally hitting the ventilation targets that are the design standard. But remember, these are not health-based standards. So we want to see ventilation rates higher." high".
Allen prefers to see CO2 at 800 parts per million or less.
He also points out that just because a space has low levels of CO2, it might not be unsafe if the filtration is high, like on an airplane.
A game changer for schools
Atlanta Public Schools Superintendent Lisa Herring says installing 5,000 air filtration units, enough for every classroom, in her school district is "a game changer."
The district had begun upgrading HVAC systems at several schools even before the pandemic, but federal funding allowed it to add filtration units during a crucial time when masks have become optional.
"It gives us a higher level of confidence as a system to know that our air filtration systems are in place," said Herring.
School districts across the country have seized the opportunity to improve ventilation thanks to the influx of federal funds.
A February analysis by FutureEd, a think tank at Georgetown University's McCourt School of Public Policy, found that public schools had earmarked $4.4 billion for HVAC projects, which could rise to nearly $10 billion if trends continue.
Mask mandates in schools are starting to go away.
It's too soon?
New Hampshire's Manchester School District is spending nearly $35 million on upgrading HVAC systems, and interim superintendent Jennifer Gillis says federal funding is "absolutely key."
"You think of a district our size with all the competing demands and the need to be fiscally responsible, a $35 million project, that's a big project to get into our budget. Having those funds available allows us to do 19 projects -- and 19 projects in a very short time.
For Gillis, ventilation has been an important mitigation strategy and a discreet way to keep people safe.
"It's something that most in the building don't think about, but it's a very passive way of creating safety within schools. From the beginning, the goal was always 'let's get our kids involved, let's get our staff involved, but let's do it a way that is safe for all of them.
Good ventilation isn't just about keeping students safe from Covid-19, Sherman says.
It can also improve your performance in school.
"They're going to learn better, they're going to be more awake, they're going to be more responsive. They're going to be healthier if they have good indoor air quality," he said.
Finally front and center
To help solidify the role of ventilation in the battle against COVID-19, the Biden administration last month announced a Clean Air in Buildings Challenge.
The challenge asks building owners and operators to improve ventilation by following guidelines set forth by the EPA.
Model shows the spread of covid-19 in the air 2:16
Major actions include creating a clean indoor air action plan, optimizing fresh air ventilation, improving air filtration and cleaning, and engaging the building community by reaching out to occupants to increase safety. awareness, commitment and participation.
The message may seem overdue, but Allen received it enthusiastically.
“The White House used its pulpit to say unequivocally that clean air and buildings are important.
That's huge.
Regardless of what you think about what happens next with implementation or what happens with funding.
That is a clear message that is already being conveyed, heard by businesses, nonprofits, universities, and state leaders.
I see that these changes are already happening."
Covid-19