In the age of a deadly airborne virus, air purification devices now come in every shape and size. At the consumer electronics trade show CES last month, companies debuted new portable air filtration devices for your bedside, your cup holder, your desktop, your conference room and even one that even hangs around your neck. While each of these devices may be capable of purifying air, the problem is none are capable of ventilation. Science is increasingly showing that if you’re serious about stopping the spread of coronavirus, masks, social distancing and opening a window likely do more than expensive electronic purification devices.
Most air purifiers are designed the same basic way. There’s a filter and fan. The fan sucks in and circulates the air through the filter. Filters in these types of devices are usually made of paper, fiber (often fiberglass), or some type of mesh, making them good at removing pollutant particles like dust and pollen but unable to remove gases or smaller particles. It’s important to remember in lab tested scenarios, the efficacy rates air purifier purveyors claim is accurate, but recreating specific lab conditions is nearly impossible. A purifier’s location, installation, flow rate and operational hours can all drastically impact how well they work. Ventilation is usually a big problem. Once the air is ‘cleaned,’ the fan circulates it out, but the air is not ventilated to other areas of the space. So more often than not, air purifiers are repeatedly purifying the same air in their immediate vicinity. The smaller device, the bigger that fundamental issue is.
The medical community is still undecided on just how much air purification devices actually help to stop the spread of the coronavirus. No doubt they can help allergy sufferers, they have been for years, but the specifics of filtering out particles as small as those containing COVID-19 is much more difficult. No doctor is saying portable air purification devices are a solution to the spread, experts recommend a mask and social distancing as a first line of defense. Making sure COVID-19 particles never make it into the air is far easier than filtering them out once they’ve dispersed. Most air purification devices are not hurting the situation though.
More useful than the filtration is the increased ventilation. Studies have shown keeping air ‘fresh’ is one of the best ways to stop the spread. Known as air changes, the rate at which air is fully replaced within a space is a key indicator of covid risk levels. The more air changes the better. In our recent Resilient Workplaces report Mayo Clinic professor and researcher Dr. Mark Ereth explained how much air is needed to move through a room to help eliminate ultrafine particulates like COVID-19 “Just to give you an idea, in operating rooms the air is replaced every three to six minutes, in office buildings it is more like a few times an hour,” he said. Evidence shows that air purification devices increase the rate or air change when assisted by a central ventilation system. But so does opening a window.
Just to give you an idea, in operating rooms the air is replaced every three to six minutes, in office buildings it is more like a few times an hour.
Dr. Mark Ereth, Mayo Clinic professor and researcher
“The most important thing to consider, when purchasing an air cleaner, is whether the space you want to use it in already has good ventilation—then, the air cleaner isn’t going to add much,” Shelly Miller, PhD, an environmental engineer at the University of Colorado-Boulder, whose work focuses on airborne disease transmission, told Webmd.
Exactly how opening a window changes ventilation is hard to study. Airflow in indoor spaces is hard to model and even harder to predict. The world’s best building models have trouble accounting for open windows because airflow systems are so complex. The bottom line is opening a window is likely just as effective, if not more effective, than an air purification device. Diluting indoor air which may contain COVID-19 with outdoor air that doesn’t contain the virus makes the virus less concentrated in the air, lowering the chance of infection. How much ventilation and what type is best is something researchers are still trying to figure out. The medical community simply doesn’t have enough consensus on the subject.
“There’s no perfectly ‘safe’ level of ventilation because we don’t actually know what ‘safe’ is, since we don’t know how much exposure leads to transmission,” Angela Rasmussen, a Columbia University virologist, told Vox.
Not having all the answers isn’t ideal but it’s better than pretending to have them. Being honest about what may or may not work helps people make better personal choices about how to stay safe. Gimmicks, like those associated with many air purifiers, do not. At best, they lull people in a false sense of security. At worst, ionizers, plasma generators and electrostatic precipitators can be actively harmful. The devices electrically charge particles so they stick to surfaces instead of floating through the air, generating ozone as a byproduct.
ASHRAE, a professional association that sets standards for ventilation and air conditioning, says that ‘extreme caution is warranted’ when using units that may produce significant ozone, a respiratory irritant, as a by-product of their operation. The EPA and the ASHRAE recommend avoiding the use of any air purification devices that produce ozone as a byproduct of cleaning indoor air in occupied spaces.
Best practices for cleaner air revolve around ventilation. In the modern office, opening windows may not be feasible for a variety of reasons. Often the window simply cannot open. In that case, high-quality air filtration devices may be warranted. With no harmful side effects from non-ozone based air filtration, the only downside to a portable air filtration device is the cost and the noise. A devices’ Clean Air Delivery Rate (CADR) tells you most of what you need to know about its effectiveness. The rating takes into account the efficiency of the filter and the power of the fan to determine how much air moves through it. The higher the CADR, the large the space it can purify. Buying the right device is all about getting the room size right. Keep in mind, the larger the device, the louder it will be as powerful fans keep air moving. In an office setting, loud noise is particularly important to consider. A quality HEPA air purifier starts at around $200, going up in price as the CADR rating increases. Some people have even built their own air purifier for less than $30 by strapping a MERV filter to a box fan.
When dealing with devices that have medical claims attached, it’s always important to separate fact from fiction and benefits from marketing. Product manufacturers looking to cash in on the immense demand for COVID-19 mitigation devices have flooded the market with portable air purification devices. Expert opinion says quality devices certainly can’t hurt. Spending hundreds, even thousands, on air purification devices does make the air cleaner, but by how much, we likely may never know. A better answer is to wear masks and, if possible, open a window instead.