Can a portable air cleaner protect you from COVID?

Can a portable air cleaner protect you from COVID?

Coronavirus is spreading across the country, and the cold weather is pushing more Americans into their homes, increasing the hours most of us spend in closed homes against the cold.

Makers of home air cleaners have noticed, with product streams suddenly appearing like autumn leaves.

But can a portable air cleaner really protect you from corona virus?

The short answer is yes, according to experts like Joseph Allen, associate professor of exposure assessment sciences and director of the Sanitary Buildings Program at Harvard University.

But there are caveats.

“A portable air cleaner, equipped with a HEPA filter, can definitely help reduce the risk of airborne transmission of COVID-19,” Allen says.

For a few hundred dollars, you can purchase a quality home unit that can remove 99.97% of pollutants from the air, including respiratory droplets that spread the virus.

But before you rush to buy one, here are some things you need to know:

    Not all air cleaners work as well.
    Room size matters when it comes to air hygiene efficiency.
    There is no single strategy - including the top-rated air cleaner - that is a foolproof panacea to combat the spread of the virus.
"The air cleaner should be used as part of a multi-layered defense strategy," notes Allen. "It must be combined with other strategies and a comprehensive approach to risk reduction."

Portable air cleaners are getting more attention as infectious disease experts warn that coronavirus cases may continue to rise in the coming months.

The reopening of schools and colleges has already led to numerous outbreaks of disease in recent weeks, as students have returned to classrooms in several regions of the country.

As temperatures drop, more Americans are retreating indoors, keeping doors and windows closed and spending less time visiting family and friends on outdoor balconies or patios.

And with the winter break approaching, health experts are concerned that the increase in travel, family meetings and festive parties will bring more people into close contact - leading to an increase in COVID-19 cases along with outbreaks of cold and seasonal flu.

One thing that has increased the focus on portable air cleaners in recent weeks has been an increased interest in the role that microscopic respiratory droplets play in the spread of the virus.

Linsey Marr, Ph.D., a Virginia Tech scientist who specializes in transmitting viruses through the air, notes that these tiny droplets are smaller, hang in the air for longer, and can travel more than 6 feet indoors.
As a result, these small aerosols present a greater transmission risk from respiratory droplets, experts say.

When we breathe, sing, sneeze or cough, we release respiratory droplets that range in size from about 100 microns (the thickness of a human hair) all the way to microscopic levels (1 micron, which is a millionth of a meter), says Marr. .

Usually, we only emit a few large respiratory droplets, which can only travel about 6 feet before falling to the ground. But at the same time, we're expelling hundreds to thousands of smaller microscopic droplets - aerosols - that can float in the air for minutes to hours like smoke or fog, and travel 16 feet or more, studies show.

Allen says that respiratory volatile droplets are generally in the range of 1 to 10 microns. Although viral particles are much smaller than that - 0.1 to 0.3 microns or so - they generally "cut" large dust or small water droplets to become airborne, "so the virus is not naked," he says.

Mar and Allen agree that the good news is that portable air cleaners are very good at filtering out these smaller, more dangerous aerosols.

"It's actually more efficient at picking up smaller particles than larger particles - 99.97 per cent for particles as small as 0.3 microns, but it's more effective with smaller particles," Allen says.
The development of science and politics

The important role played by microdroplet aerosols in spreading the Coronavirus has evolved since the beginning of the epidemic.

Allen, Marr and dozens of other experts have been arguing since last February that aerosols can significantly transmit the virus. But the World Health Organization (WHO) and the Center for Disease Control (CDC) initially resisted the idea.

In July, 239 scientists pressed the World Health Organization to change its stance in a comment published in Clinical Infectious Diseases.

The World Health Organization has since changed its stance, and the CDC agreed, earlier this month, as well.

Allen says it is "shocking" that it took so long for the Centers for Disease Control and Prevention to acknowledge scientific evidence of aerosol transmission, despite previous support from Anthony Fauci, a physician, the nation's main infectious disease specialist.

But he's glad the agency has finally come.

 "It's something we've been paying for since early February," he says, "and it was just shocking that they didn't acknowledge the science [earlier]."
Portable Air Cleaners: A Buyer's Guide

Shelly Miller, Ph.D., an environmental engineer at the University of Colorado Boulder, agrees that portable air cleaners are very good at removing viral particles from indoor air.

But before you decide if this device is right for you, it suggests first finding out if you really need one.
"The most important thing to consider, when purchasing an air cleaner, is whether the space you want to use is really well ventilated - so the air cleaner won't add much," says Miller, whose work focuses on airborne disease transmission.

But for rooms that don't get enough fresh air, such as basements or dorm rooms, the mobile device "will really improve the cleaning of the air," she says.

If you decide you need an air cleaner for your home, she recommends choosing one with a High Efficiency Particulate Air (HEPA) filter.

You will also need to ensure that the unit you purchase can handle the size of the room it will be used in.

Most devices on the market rely on mechanical filtration to clean the air and are categorized by what's called the CADR system - short for Clean Air Delivery Rate. They work by using fans to draw air out of the room, pass it through a filter to remove particles, and then expel the filtered air back into the room.

Note that some devices use electrostatic precipitators or ionization to trap particles. But for home use, experts say this isn't necessary, and they recommend against using these types of units because they generate ozone, which is a harmful respiratory pollutant.
CADR - A guide to unit classifications

The CADR classification system for portable air cleaners measures both the efficiency of the filter the device uses and the amount of air that moves through it.

Cleaners that use a HEPA filter - a type of pleated mechanical air filter - can remove at least 99.97% of dust, pollen, mold, bacteria, pathogens and other particles as small as 0.3 microns, according to the U.S. Environmental Protection Agency.

This rating of 0.3 microns is the worst case scenario; Allen explains that larger or smaller particles are better captured.

He also says the filters don't destroy the virus, as UV rays do, but this is not critical to clearing the air of COVID-19 particles.

"You don't need UV rays or any other process, because the virus is picked up in the filter media," he says. "Once you pick up the [viral] particles, they don't grow and can't be released. So, you don't need anything other than a portable air cleaner with a HEPA filter.

"It's really simple, just like washing hands is really simple and essential."
Room size matters

The second main thing to consider, when choosing a portable air cleaner, is the size of the room in which you plan to use it.

"If you buy a portable air cleaner and put it in the corner of a gymnasium, it won't be very effective," Allen says. "So, you need to resize it appropriately for your living room or other rooms."

The higher the CADR, the more space it will serve. Generally speaking, the product packaging will tell you the largest area or room the detergent can handle.

If you're willing to do a little math, here's the equation to match a device, based on its CADR, with the room it's used in:

Let's say you're looking to purchase an air cleaner for a 500 square foot room - with 8-foot ceilings - and you want to see if a 300 CADR unit will do the trick.

First, you have to multiply CADR (300) by the number of minutes per hour (60) - for a total of 18,000.

Then it divides 18,000 by the size of the space in the room (500 square feet, multiplied by 8) - for a total of 4,000.

Finally, you divide 18000 by 4000 and get 4.5 - that's the ACH that the air cleaner will pass, which falls between the four to six recommended for indoor spaces.

For ease of reference, Allen offers this backstory guideline: "Just keep in mind that we recommend four to six air changes per hour, so a quick rule of thumb is to look for a portable air cleaner with a CADR of at least 300 per 500 square feet of space." .

The Environmental Protection Agency also provides a guide to minimum CADR levels for rooms of various sizes in their "Home Air Cleaners Guide" online. For rooms with 8-foot ceilings, she recommends:

    65 CADR for 100 square feet
    130 Canadian dollars for 200 square feet
    $ 195 CAD per 300 sq ft
    $ 260 CAD for 400 Square Feet
    $ 325 CAD for 500 square feet
    390 Canadian dollars for 600 square feet

Additionally, the Harvard-CU Boulder Portable Air Cleaner Calculator for Schools Online, created by Allen and Miller to help teachers choose effective air cleaners for the classroom, can give you a rough estimate for different-sized rooms in your home.

Bear in mind: You need to clean or replace the filters regularly for the air cleaners to work well. So follow manufacturers' recommendations on maintenance and replacement if you buy a device with a HEPA filter.
Not a silver bullet solution

One final point Allen and Miller stresses: Portable air cleaner is not the only solution to combating COVID-19 at home.

"It is not a panacea," Miller says, noting that it should be used in combination with other measures recommended by health experts to prevent the virus.

"We have to focus on defenses," Allen says. “We should wear masks indoors, open our windows, bring in more air outside, and increase the level of air purification, whether it be through mechanical systems ... or portable air cleaners with HEPA filters. We must keep our social circles small, and we must We wash our hands. "

In fact, if you do all of these things already, and stay home without a lot of visitors, you might not even need an air cleaner.

The same goes for people who live in apartment buildings or apartment complexes, Allen says.

"But if you have people, adding a portable HEPA filter air cleaner is a good strategy," he notes. "It also makes sense to open windows, even if only two inches away, and wearing a mask is a must."

Allen bought two air cleaners for his home this year. But he does not consider them a cure-all.

"We don't use it now because the weather was nice, we had our windows open as much as possible, we didn't have too many people, and if we had people, we were outdoors and separated and wearing masks."

Environmental engineers measure indoor air quality by means of air changes per hour (ACH). This refers to the number of times the air inside the room is filtered every 60 minutes.

As a general rule, Allen says experts recommend four to six air changes per hour for indoor spaces. This means that the entire volume of air in the room is cleaned or replaced every 10 to 15 minutes. This is sufficient to remove the spray of COVID-19 from the air and reduce the risk of transmission.


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