How to Use Ventilation and Air Filtration to Prevent Coronavirus Spreading Indoors
By Shelly Miller
The vast majority of SARS-CoV-2 transmission occurs indoors, most of it from the inhalation of airborne particles that contain the coronavirus. The best way to prevent the virus from spreading in a home or business would be to simply keep infected people away. But this is hard to do when an estimated 40% of cases are asymptomatic and asymptomatic people can still spread the coronavirus to others.
Masks do a decent job at keeping the virus from spreading into the environment, but if an infected person is inside a building, inevitably some virus will escape into the air.
I am a professor of mechanical engineering at the University of Colorado Boulder. Much of my work has focused on how to control the transmission of airborne infectious diseases indoors, and I've been asked by my own university, my kids' schools and even the Alaska State Legislature for advice on how to make indoor spaces safe during this pandemic.
Once the virus escapes into the air inside a building, you have two options: bring in fresh air from outside or remove the virus from the air inside the building.
It’s All About Fresh, Outside Air
The safest indoor space is one that constantly has lots of outside air replacing the stale air inside.
In commercial buildings, outside air is usually pumped in through heating, ventilating and air-conditioning (HVAC) systems. In homes, outside air gets in through open windows and doors, in addition to seeping in through various nooks and crannies.
Simply put, the more fresh, outside air inside a building, the better. Bringing in this air dilutes any contaminant in a building, whether a virus or a something else, and reduces the exposure of anyone inside. Environmental engineers like me quantify how much outside air is getting into a building using a measure called the air exchange rate. This number quantifies the number of times the air inside a building gets replaced with air from outside in an hour.
While the exact rate depends on the number of people and size of the room, most experts consider roughly six air changes an hour to be good for a 10-foot-by-10-foot room with three to four people in it. In a pandemic this should be higher, with one study from 2016 suggesting that an exchange rate of nine times per hour reduced the spread of SARS, MERS and H1N1 in a Hong Kong hospital.
Many buildings in the U.S., especially schools, do not meet recommended ventilation rates. Thankfully, it can be pretty easy to get more outside air into a building. Keeping windows and doors open is a good start. Putting a box fan in a window blowing out can greatly increase air exchange too. In buildings that don't have operable windows, you can change the mechanical ventilation system to increase how much air it is pumping. But in any room, the more people inside, the faster the air should be replaced.
Using CO2 to Measure Air Circulation
So how do you know if the room you're in has enough air exchange? It's actually a pretty hard number to calculate. But there's an easy-to-measure proxy that can help. Every time you exhale, you release CO2 into the air. Since the coronavirus is most often spread by breathing, coughing or talking, you can use CO2 levels to see if the room is filling up with potentially infectious exhalations. The CO2 level lets you estimate if enough fresh outside air is getting in.
Outdoors, CO2 levels are just above 400 parts per million (ppm). A well ventilated room will have around 800 ppm of CO2. Any higher than that and it is a sign the room might need more ventilation.
Last year, researchers in Taiwan reported on the effect of ventilation on a tuberculosis outbreak at Taipei University. Many of the rooms in the school were underventilated and had CO2 levels above 3,000 ppm. When engineers improved air circulation and got CO2 levels under 600 ppm, the outbreak completely stopped. According to the research, the increase in ventilation was responsible for 97% of the decrease in transmission.
Since the coronavirus is spread through the air, higher CO2 levels in a room likely mean there is a higher chance of transmission if an infected person is inside. Based on the study above, I recommend trying to keep the CO2 levels below 600 ppm. You can buy good CO2 meters for around $100 online; just make sure that they are accurate to within 50 ppm.
If you are in a room that can't get enough outside air for dilution, consider an air cleaner, also commonly called air purifiers. These machines remove particles from the air, usually using a filter made of tightly woven fibers. They can capture particles containing bacteria and viruses and can help reduce disease transmission.
The U.S. Environmental Protection Agency says that air cleaners can do this for the coronavirus, but not all air cleaners are equal. Before you go out and buy one, there are few things to keep in mind.
The first thing to consider is how effective an air cleaner's filter is. Your best option is a cleaner that uses a high-efficiency particulate air (HEPA) filter, as these remove more than 99.97% of all particle sizes.
The second thing to consider is how powerful the cleaner is. The bigger the room – or the more people in it – the more air needs to be cleaned. I worked with some colleagues at Harvard to put together a tool to help teachers and schools determine how powerful of an air cleaner you need for different classroom sizes.
The last thing to consider is the validity of the claims made by the company producing the air cleaner.
The Association of Home Appliance Manufacturers certifies air cleaners, so the AHAM Verifide seal is a good place to start. Additionally, the California Air Resources Board has a list of air cleaners that are certified as safe and effective, though not all of them use HEPA filters.
Keep Air Fresh or Get Outside
If you are in control of your indoor environment, make sure you are getting enough fresh air from outside circulating into the building. A CO2 monitor can help give you a clue if there is enough ventilation, and if CO2 levels start going up, open some windows and take a break outside. If you can't get enough fresh air into a room, an air cleaner might be a good idea. If you do get an air cleaner, be aware that they don't remove CO2, so even though the air might be safer, CO2 levels could still be high in the room.
If you walk into a building and it feels hot, stuffy and crowded, chances are that there is not enough ventilation. Turn around and leave.
By paying attention to air circulation and filtration, improving them where you can and staying away from places where you can't, you can add another powerful tool to your anti-coronavirus toolkit.
Shelly Miller is a Professor of Mechanical Engineering, University of Colorado Boulder.
Disclosure statement: Shelly Miller receives funding from the National Science Foundation, Environmental Protection Agency, Centers for Disease Control, National Institutes of Health, and additional nonprofit organizations. She is affiliated with American Association of Aerosol Research and the International Society of Indoor Air Quality and Climate.
Reposted with permission from The Conversation.
- These Are Some of the Highest-Risk Places for COVID-19 - EcoWatch ›
- CDC Recommends Big Changes to Office Life - EcoWatch ›
- Here's Why COVID-19 Can Spread So Easily at Gyms and Fitness ... ›
- New Cooling Technology Protects Against Severe Heat and Viral Spread - EcoWatch ›
- CDC Officially Acknowledges Airborne Transmission of Coronavirus - EcoWatch ›
- 12 Things You Can Do To Help Stop COVID-19 (in Addition To Staying Home for Thanksgiving) - EcoWatch ›
- Would You Eat Indoors At a Restaurant? 5 Health Experts Answer - EcoWatch ›
New fossils uncovered in Argentina may belong to one of the largest animals to have walked on Earth.
- Groundbreaking Fossil Shows Prehistoric 15-Foot Reptile Tried to ... ›
- Skull of Smallest Known Dinosaur Found in 99-Million-Year Old Amber ›
- Giant 'Toothed' Birds Flew Over Antarctica 40 Million Years Ago ... ›
- World's Second-Largest Egg Found in Antarctica Probably Hatched ... ›
EcoWatch Daily Newsletter
- Pruitt Guts the Clean Power Plan: How Weak Will the New EPA ... ›
- It's Official: Trump Administration to Repeal Clean Power Plan ... ›
- 'Deadly' Clean Power Plan Replacement ›
By Jonathan Runstadler and Kaitlin Sawatzki
Over the course of the COVID-19 pandemic, researchers have found coronavirus infections in pet cats and dogs and in multiple zoo animals, including big cats and gorillas. These infections have even happened when staff were using personal protective equipment.
- Gorillas in San Diego Test Positive for Coronavirus - EcoWatch ›
- Wildlife Rehabilitators Are Overwhelmed During the Pandemic. In ... ›
- Coronavirus Pandemic Linked to Destruction of Wildlife and World's ... ›
- Utah Mink Becomes First Wild Animal to Test Positive for Coronavirus ›
By Peter Giger
The speed and scale of the response to COVID-19 by governments, businesses and individuals seems to provide hope that we can react to the climate change crisis in a similarly decisive manner - but history tells us that humans do not react to slow-moving and distant threats.
A Game of Jenga<p>Think of it as a game of Jenga and the planet's climate system as the tower. For generations, we have been slowly removing blocks. But at some point, we will remove a pivotal block, such as the collapse of one of the major global ocean circulation systems, for example the Atlantic Meridional Overturning Circulation (AMOC), that will cause all or part of the global climate system to fall into a planetary emergency.</p><p>But worse still, it could cause runaway damage: Where the tipping points form a domino-like cascade, where breaching one triggers breaches of others, creating an unstoppable shift to a radically and swiftly changing climate.</p><p>One of the most concerning tipping points is mass methane release. Methane can be found in deep freeze storage within permafrost and at the bottom of the deepest oceans in the form of methane hydrates. But rising sea and air temperatures are beginning to thaw these stores of methane.</p><p>This would release a powerful greenhouse gas into the atmosphere, 30-times more potent than carbon dioxide as a global warming agent. This would drastically increase temperatures and rush us towards the breach of other tipping points.</p><p>This could include the acceleration of ice thaw on all three of the globe's large, land-based ice sheets – Greenland, West Antarctica and the Wilkes Basin in East Antarctica. The potential collapse of the West Antarctic ice sheet is seen as a key tipping point, as its loss could eventually <a href="https://science.sciencemag.org/content/324/5929/901" target="_blank">raise global sea levels by 3.3 meters</a> with important regional variations.</p><p>More than that, we would be on the irreversible path to full land-ice melt, causing sea levels to rise by up to 30 meters, roughly at the rate of two meters per century, or maybe faster. Just look at the raised beaches around the world, at the last high stand of global sea level, at the end of the Pleistocene period around 120,0000 years ago, to see the evidence of such a warm world, which was just 2°C warmer than the present day.</p>
Cutting Off Circulation<p>As well as devastating low-lying and coastal areas around the world, melting polar ice could set off another tipping point: a disablement to the AMOC.</p><p>This circulation system drives a northward flow of warm, salty water on the upper layers of the ocean from the tropics to the northeast Atlantic region, and a southward flow of cold water deep in the ocean.</p><p>The ocean conveyor belt has a major effect on the climate, seasonal cycles and temperature in western and northern Europe. It means the region is warmer than other areas of similar latitude.</p><p>But melting ice from the Greenland ice sheet could threaten the AMOC system. It would dilute the salty sea water in the north Atlantic, making the water lighter and less able or unable to sink. This would slow the engine that drives this ocean circulation.</p><p><a href="https://www.carbonbrief.org/atlantic-conveyor-belt-has-slowed-15-per-cent-since-mid-twentieth-century" target="_blank">Recent research</a> suggests the AMOC has already weakened by around 15% since the middle of the 20th century. If this continues, it could have a major impact on the climate of the northern hemisphere, but particularly Europe. It may even lead to the <a href="https://ore.exeter.ac.uk/repository/handle/10871/39731?show=full" target="_blank" rel="noopener noreferrer">cessation of arable farming</a> in the UK, for instance.</p><p>It may also reduce rainfall over the Amazon basin, impact the monsoon systems in Asia and, by bringing warm waters into the Southern Ocean, further destabilize ice in Antarctica and accelerate global sea level rise.</p>
The Atlantic Meridional Overturning Circulation has a major effect on the climate. Praetorius (2018)
Is it Time to Declare a Climate Emergency?<p>At what stage, and at what rise in global temperatures, will these tipping points be reached? No one is entirely sure. It may take centuries, millennia or it could be imminent.</p><p>But as COVID-19 taught us, we need to prepare for the expected. We were aware of the risk of a pandemic. We also knew that we were not sufficiently prepared. But we didn't act in a meaningful manner. Thankfully, we have been able to fast-track the production of vaccines to combat COVID-19. But there is no vaccine for climate change once we have passed these tipping points.</p><p><a href="https://www.weforum.org/reports/the-global-risks-report-2021" target="_blank">We need to act now on our climate</a>. Act like these tipping points are imminent. And stop thinking of climate change as a slow-moving, long-term threat that enables us to kick the problem down the road and let future generations deal with it. We must take immediate action to reduce global warming and fulfill our commitments to the <a href="https://www.ipcc.ch/sr15/" target="_blank" rel="noopener noreferrer">Paris Agreement</a>, and build resilience with these tipping points in mind.</p><p>We need to plan now to mitigate greenhouse gas emissions, but we also need to plan for the impacts, such as the ability to feed everyone on the planet, develop plans to manage flood risk, as well as manage the social and geopolitical impacts of human migrations that will be a consequence of fight or flight decisions.</p><p>Breaching these tipping points would be cataclysmic and potentially far more devastating than COVID-19. Some may not enjoy hearing these messages, or consider them to be in the realm of science fiction. But if it injects a sense of urgency to make us respond to climate change like we have done to the pandemic, then we must talk more about what has happened before and will happen again.</p><p>Otherwise we will continue playing Jenga with our planet. And ultimately, there will only be one loser – us.</p>
By John R. Platt
The period of the 45th presidency will go down as dark days for the United States — not just for the violent insurgency and impeachment that capped off Donald Trump's four years in office, but for every regressive action that came before.
- Biden Announces $2 Trillion Climate and Green Recovery Plan ... ›
- How Biden and Kerry Can Rebuild America's Climate Leadership ... ›
- Biden's EPA Pick Michael Regan Urged to Address Environmental ... ›
- How Joe Biden's Climate Plan Compares to the Green New Deal ... ›