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 ›
A pygmy rabbit rescued from a breeding site in Beezley Hills, Washington, eats owl clover in its new enclosure. Kourtney Stonehouse, WDFW
- 7 Devastating Photos of Wildfires in California, Oregon and ... ›
- California Wildfires Destroy Condor Sanctuary, at Least 4 Birds Still ... ›
EcoWatch Daily Newsletter
By Mark Hertsgaard
What follows are not candidate endorsements. Rather, this nonpartisan guide aims to inform voters' choices, help journalists decide what races to follow, and explore what the 2020 elections could portend for climate action in the United States in 2021 and beyond.
Will the White House Turn Green?<p>Whether the White House changes hands is the most important climate question of the 2020 elections. President Donald Trump rejects climate science, is withdrawing the United States from the Paris Agreement, and has accelerated fossil fuel development. His climate policy seems to be, as he tweeted in January when rejecting a U.S. Army Corps of Engineers proposal to protect New York City from storm surges, "Get your mops and buckets ready."</p><p>Joe Biden, who started the 2020 campaign with a climate position so weak that activists gave it an "F," called Trump a "climate arsonist" during California's recent wildfires. Biden backs a $2 trillion plan to create millions of jobs while slashing emissions—a Green New Deal in all but name. Equally striking, his running mate, California Senator Kamala Harris, has endorsed phasing out fossil fuel production—a politically explosive scientific imperative.</p><p>The race will be decided in a handful of battleground states, five of which already face grave climate dangers: Florida (hurricanes and sea-level rise), North Carolina (ditto), Texas (storms and drought), Michigan (floods), and Arizona (heat waves and drought). <a href="https://climatecommunication.yale.edu/visualizations-data/ycom-us/" target="_blank">Public concern is rising</a> in these states, but will that concern translate into votes?</p>
Will Democrats Flip the Senate, and by Enough to Pass a Green New Deal?<p>With Democrats all but certain to maintain their majority in the U.S. House of Representatives, the Senate will determine whether a potential Biden administration can actually deliver climate progress. Democrats need to pick up three seats to flip the Senate if Biden wins, four if he doesn't. But since aggressive climate policy is shunned by some Democrats, notably Joe Manchin of coal-dependent West Virginia, Democrats probably need to gain five or six Senate seats to pass a Green New Deal.</p><p>Environmentalists, including the League of Conservation Voters, are targeting six Republicans who polls suggest are vulnerable.</p><ul><li>Steve Daines of Montana, who denies climate science</li><li>Martha McSally of Arizona</li><li>Thom Tillis of North Carolina</li><li>Susan Collins of Maine</li><li>Joni Ernst of Iowa (bankrolled by Charles Koch)</li><li>John James of Michigan (also a Koch beneficiary)</li></ul><p>Republican Senators are even at risk in conservative Kansas and Alaska. In both states, the Democratic candidates are physicians—not a bad credential amid a pandemic—who support climate action. In Kansas, Barbara Bollier faces an incumbent funded by Charles Koch. In Alaska, Al Gross urges a transition away from oil, though his openness to limited drilling in the Arctic National Wildlife Preserve dims his appeal to green groups. He faces incumbent Republican Dan Sullivan, who receives an 8 percent lifetime voting record from the League of Conservation Voters.</p>
Will Local and State Races Advance Climate Progress?<h4>THE CLIMATE HAWKS</h4><p>Under Democratic and Republican leadership alike, Washington has long been a graveyard for strong climate action. But governors can boost or block renewable energy; the Vermont and New Hampshire races are worth watching. Attorneys general can sue fossil fuel companies for lying about climate change; climate hawks are running for the top law enforcement seats in Montana and North Carolina. State legislatures can accelerate or delay climate progress, as the new Democratic majorities in Virginia have shown. Here, races to watch include Pennsylvania, North Carolina, and Colorado.</p><h4>THE CLIMATE POLICY MAKERS</h4><p>Perhaps the most powerful, and most overlooked, climate policy makers are public utility commissions. They control whether pipelines and other energy infrastructure gets built; they regulate whether electric utilities expand solar and energy efficiency or stick with the carbon-heavy status quo. Regulatory capture and outright corruption are not uncommon.</p><p>A prime example is Arizona, where a former two-term commissioner known as the godfather of solar in the state is seeking a comeback. Bill Mundell argues that since Arizona law permits utilities to contribute to commissioners' electoral campaigns, the companies can buy their own regulators. Which may explain why super-sunny Arizona has so little installed solar capacity.</p><p>In South Dakota, Remi Bald Eagle, a Native American U.S. Army veteran, seeks a seat on the South Dakota Public Utilities Commission, which rules on the Standing Rock oil pipeline. And in what <em>HuffPost</em> called "the most important environmental race in the country," Democrat Chrysta Castaneda, who favors phasing out oil production, is running for the Texas Railroad Commission, which despite its name decides what oil, gas, and electric companies in America's leading petro-state can build.</p>
Will the Influencers Usher in a Green New Era?<h4>THE UNCOUNTED</h4><p>The story that goes largely under-reported in every U.S. election is how few Americans vote. In 2016, some 90 million, <a href="https://www.pewresearch.org/politics/2018/08/09/an-examination-of-the-2016-electorate-based-on-validated-voters/" target="_blank" rel="noopener noreferrer">roughly four out of every 10 eligible voters</a>, did not cast a ballot. Attorney Nathaniel Stinnett claims that 10 million of these nonvoters nevertheless identify as environmentalists: They support green policies, even donate to activist groups; they just don't vote. Stinnett's <a href="https://www.environmentalvoter.org/" target="_blank" rel="noopener noreferrer">Environmental Voter Project</a> works to awaken this sleeping giant.</p><h4>THE SUNRISE MOVEMENT</h4><p>Meanwhile, the young climate activists of the <a href="http://www.sunrisemovement.org/" target="_blank" rel="noopener noreferrer">Sunrise Movement</a> are already winning elections with an unabashedly Green New Deal message. More than any other group, Sunrise pushed the Green New Deal into the national political conversation, helping Representative Alexandria Ocasio-Cortez and Senator Ed Markey draft the eponymous congressional resolution. In 2020, Sunrise has helped Green New Deal champions defeat centrists in Democratic primaries, with Markey dealing Representative Joe Kennedy Jr. the first defeat a Kennedy has ever suffered in a Massachusetts election. But can Sunrise also be successful against Republicans in the general elections this fall?</p><h4>THE STARPOWER</h4><p>And an intriguing wild card: celebrity firepower, grassroots activism, and big-bucks marketing have converged behind a campaign to get Latina mothers to vote climate in 2020. Latinos have long been the U.S. demographic most concerned about climate change. Now, <a href="https://votelikeamadre.com/" target="_blank" rel="noopener noreferrer">Vote Like A Madre</a> aims to get 5 million Latina mothers in Florida, Texas, and Arizona to the polls. Jennifer Lopez, Salma Hayak, and Lin-Manuel Miranda are urging mothers to make a "pinky promise" to vote for their kids' climate future in November. Turning out even a quarter of those 5 million voters, though no easy task, could swing the results in three states Trump must win to remain president, which brings us back to the first category, "Will the White House Turn Green?"</p>
- Climate Activists Prepare for November Election - EcoWatch ›
- The Next Election Is About the Next 10,000 Years - EcoWatch ›
- Latino Voters Worried About Climate Change Could Swing 2020 ... ›
- Climate Crisis Could Change Permafrost Soil Microbes, With ... ›
- Zombie Fires Could Be Awakening in the Arctic - EcoWatch ›
- The Arctic Is on Fire and Warming Twice as Fast as the Rest of the ... ›
By Tony Carnie
South Africa is home to around 1,300 of the world's roughly 7,100 remaining cheetahs. It's also the only country in the world with significant cheetah population growth, thanks largely to a nongovernmental conservation project that depends on careful and intensive human management of small, fenced-in cheetah populations. Because most of the reserves are privately funded and properly fenced, the animals benefit from higher levels of security than in the increasingly thinly funded state reserves.
Vincent van der Merwe at a cheetah translocation. Endangered Wildlife Trust
Under Pressure<p>Cheetah populations elsewhere in Southern Africa have not prospered over the past 50 years. In Zimbabwe, cheetah numbers have crashed from 1,500 in 1975, to just 170 today. Botswana's cheetah population has held steady at around 1,500 over the same period, but illegal capture for captive breeding and conflicts with farmers and the growing human population are increasing. In Namibia, there were an estimated 3,000 cheetah in in 1975; roughly 1,400 remain today.</p><p>In contrast, South Africa's cheetah numbers have grown from about 500 in 1975 to nearly 1,300 today. Van der Merwe, who is also a Ph.D. student at the University of Cape Town's Institute for Communities and Wildlife in Africa (iCWild), says he's confident that South Africa will soon overtake Namibia and Botswana, largely because the majority of South African cheetahs are protected and managed behind fences, whereas most of the animals in the neighboring countries remain more vulnerable on mainly unfenced lands.</p><p>Wildlife researchers Florian Weise and colleagues have reported that private stock owners in Namibia still trap cheetahs mainly for translocation, but there are few public or private reserves large enough to contain them. Weise says that conservation efforts need to focus on improving tolerance toward cheetahs in commercial livestock and game farming areas to reduce indiscriminate trapping.</p><p>Van der Merwe says fences can be both a blessing and a curse. While these barriers prevent cheetahs and other wild animals from migrating naturally to breed and feed, they also protect cheetahs from the growing tide of threats from humanity and agriculture.</p><p>To simulate natural dispersion patterns that guard against inbreeding, the trust helps landowners swap their animals with other cheetah reserves elsewhere in the country. The South African metapopulation project has been so successful in boosting numbers that the trust is having to look beyond national boundaries to secure new translocation areas in Malawi, Zambia and Mozambique.</p><p>Cheetah translocations have been going on in South Africa since the mid-1960s, when the first unsuccessful attempts were made to move scores of these animals from Namibia. These relocations were mostly unsuccessful.</p>
Charli de Vos uses a VHF antenna to locate cheetahs in Phinda Game Reserve. Tony Carnie for Mongabay
Swinging for the Fences<p>But other wildlife conservation leaders have a different perspective on cheetah conservation strategy.</p><p>Gus Mills, a senior carnivore researcher retired in 2006 from SANParks, the agency that manages South Africa's national parks, after a career of more than 30 years in Kalahari and Kruger national parks. He says the focus should be on quality of living spaces rather than the quantity of cheetahs.</p><p>Mills, who was the founder of the Endangered Wildlife Trust's Carnivore Conservation Group in 1995, and who also spent six years after retirement studying cheetahs in the Kalahari, says it's more important to properly protect and, where possible, expand the size of existing protected areas.</p><p>He also advocates a triage approach to cheetah conservation, in which scarce funds and resources are focused on protecting cheetahs in formally protected areas, rather than diluting scarce resources in an attempt to try and save every single remaining cheetah population.</p><p>"People have an obsession with numbers. But I believe that it is more important to protect large landscape and habitats properly," Mills said.</p><p>He suggests that cheetahs enclosed within small reserves live in artificial conditions: "It's almost like glorified farming."</p><p>"In the long run we have to focus on consolidating formally protected areas," he added. "Africa's human population will double by 2050, so cheetah populations in unfenced areas will become unsustainable if they are eating people's livestock."</p>
Scientists are on the brink of scaling up an enzyme that devours plastic. In the latest breakthrough, the enzyme degraded plastic bottles six times faster than previous research achieved, as The Guardian reported.
- Mutant Enzyme Recycles Plastic in Hours, Could Revolutionize ... ›
- Scientists Find Bacteria That Eats Plastic - EcoWatch ›
- Plastics: The History of an Ecological Crisis - EcoWatch ›
- Scientists Accidentally Develop 'Mutant' Enzyme That Eats Plastic ... ›