How to keep the coronavirus at bay indoors

As the autumn chill ushers people back into homes, classrooms and offices, the coronavirus may resurge even in states that so far have restrained its spread.

Why? The virus poses a greater threat in crowded indoor spaces than it does outdoors. Southern states, for example, saw a spike in infections when the temperatures soared this summer, prompting people to remain inside with the air conditioners humming.

“I’m a little concerned we’re going to see that shift to the northern latitudes as the weather gets cold,” said Linsey Marr of Virginia Tech in Blacksburg, who studies how viruses move through the air.

In poorly ventilated indoor settings, like most restaurants and bars, the virus can remain suspended in the air for long periods and travel distances beyond 6 feet, Marr and other researchers said.

This summer, scientists isolated live virus from tiny droplets called aerosols floating in the air as far as 16 feet from an infected patient in a hospital.

Unless you are living with an infected person — in which case the Centers for Disease Control and Prevention offers specific guidelines to follow — protecting yourself at home does not particularly require extraordinary measures, Marr said.

And when you venture elsewhere, wearing a face covering and washing your hands are still the best ways to protect yourself indoors.

But fear of the risk of transmission indoors has fuelled a market for expensive devices that promise to scrub surfaces — and even the air — clean of the virus. But most of those products are overkill and may even have unintended harmful consequences, experts warned.

“Anything that sounds fancy and isn’t tried and true — those are all things to avoid,” said Delphine Farmer, an atmospheric chemist at Colorado State University in Fort Collins. “Soap and water work beautifully.”

We asked experts which strategies people should embrace and which ones to avoid as the weather cools.

It’s not just about ventilation.

Some school districts have focused on virus-proofing their ventilation systems, and the CDC has produced an exhaustive set of recommendations for businesses trying to keep employees from becoming infected with the virus.

But “the conversation on risk reduction is beyond ventilation,” said Joseph Allen, an expert on building safety at the Harvard TH Chan School of Public Health. “It’s a layered defence approach where no one strategy in and of itself is sufficient, but collectively they can reduce risk.”

Allen proposed these measures for managing larger buildings:

— Eliminate exposure whenever possible — for example, by encouraging staff to work from home.

— Permit entry only to those who need to be physically present in the building.

— Adopt strategies like adding air filters and disinfecting surfaces.

— Manage the flow of people going through the building — for example, the number of those in elevators at a time.

— Require the use face coverings and other personal protective equipment as appropriate indoors.

Researchers at the Massachusetts Institute of Technology have created an app to determine how many people can safely congregate in a given space and for how long.

But regardless of these precautions, the optimal strategy is simply to wear a mask indoors, said Martin Bazant, a chemical engineer at MIT, adding, “That’s a much bigger effect than any of those strategies would provide.”

There are simple solutions to try now.

Here’s one that’s easy and free: If possible, open your windows, “especially during the shoulder season when the conditions are more mild,” Allen said.

Schools are required to have enough ventilation to fully exchange the air in a room every 20 minutes, but most barely manage to do so once every hour. “Even just opening windows 6 inches can dramatically change the air exchange rate,” Allen said.

The trick is useful for car travel, too. Just cracking open a window a little can help disperse any coronavirus that may be exhaled by other riders.Oscillating fans can be helpful or harmful indoors, depending on how they’re used. Ideally, they should not be placed in any spot where they might push virus-laden exhalations from an infected person around a room or into another occupant’s face.

A nonoscillating fan placed in a window and away from people may increase the airflow in a room without these risks.

Basic air filters are often the best.

HEPA, MERV, HVAC — conversations about air systems can devolve into an alphabet soup of acronyms. Relax and take a deep breath: Even the most stripped-down devices can help bring down the microbial burden in the air.

For a classroom or office, a portable air cleaner suited to the room’s size “is a great low-cost, plug-and-play strategy to give you several air changes per hour of clean air,” Allen said. These are compact devices that can be plugged into any outlet; effective models are available for less than $200.

The American Society of Heating, Refrigerating and Air-Conditioning Engineers, a professional society that sets standards for such devices, recommends air filters that qualify as MERV 13 or higher to filter out the coronavirus. Not all ventilation systems can handle a MERV 13 filter, Marr said, but most can at least handle MERV 11, which can keep out 60% of viral droplets.

HEPA filters are also generally considered to be excellent, although some experts said the research on the extent of their effectiveness was limited.

Beware those “air cleaners.”

The best way to clean the air in a room is to replace it with air from outside or run through an air filter.

But some air filters offer features that experts referred to as “gimmicks” — useless at best and dangerous at worst. So-called exotic cleaners are not regulated by any federal agency, but they have been aggressively marketed to schools and businesses, Farmer, the atmospheric chemist, said.

“There’s a lot of potential for damaging side effects,” she said.

Some devices generate ozone — yes, that ozone, a respiratory hazard — while others produce dangerous hydroxyl radicals that may injure cells. There are products that claim to rely on “bipolar ionisation” to break down the coronavirus, but they may also produce ultrafine particles that are dangerous when inhaled.

Ultraviolet lights are a step too far.

The experts had the most concerns about UV lights, which are used in many hospitals to disinfect instruments, gear and even entire rooms. But now UV lights are marketed to businesses, schools and even residential buildings as indoor disinfectants.

Unlike portable air filters that are inexpensive and can simply be plugged into an electrical outlet, UV lights need to be carefully engineered by trained individuals in order to disinfect. Installed incorrectly, they can cause skin burns and damage eyesight, said Saskia Popescu, a hospital epidemiologist at the University of Arizona in Tucson.

UV lights are regulated mostly for use as pesticides and are not well studied for use around people, she added. “I get really nervous when I see people pushing UV disinfection.”

UV light generally does not penetrate deep into a surface and will not destroy virus that’s buried beneath other microscopic detritus.

It takes time for UV light to kill the coronavirus, and experts cautioned against using UV devices unless you’re willing to spend the time and money to purchase models that can be installed by a skilled professional.

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