The most effective way to make indoor air safer during a viral pandemic: Reflow Labs Airsafe White Paper

tl;dr ventilation is needed to combat aerosol transmission, which is the primary risk factor after other preventive measures are put into place. Traditional UVC devices have ridiculous mark-ups since they were focused on selling into the health care industrial complex where we all know prices are detached from reality, so the best option was previously HEPA purifiers. Our device beats them on cost, electricity consumption, and noise. This is is possible because pushing air through a dense filter require a high pressure centrifugal fan (instead of axial), which is more expensive to make, uses more electricity for a given amount of air flow, and produces more noise. The power difference is larger than the extra power from UVC since we actually leverage the fact that UVC can be efficiently reflected (theoretical maximum is 10x amplification given 90% reflectivity of mirror-polished aluminum), and HEPA filters cost a lot more to replace than UVC bulbs, which really adds up after a few years.

This tl;dr is more up-to-date than the rest of the white paper. Just like you, we got a bit bamboozled with the many gimmicky products so other comparisons are unintentional strawmen, whereas HEPA purifiers are our steelman, which we still beat hands-down.


We know that pandemics are only able to spread when people are close together and the primary way people find themselves close to each other is inside buildings. It is only inside buildings that we are likely to touch surfaces someone else has touched or breath the air someone has exhaled. While there are numerous precautions that can be taken to nearly eliminate surface contact risk with little inconvenience (alcohol, chlorine, soap+water, handwashing, etc), removing the risk of airbone transmission has proven more challenging. Although masks are effective, many people use them improperly, with materials that only protect against larger aerosols, or refuse to wear them all together. Masks are absolutely critical now, but most people do not expect to wear them forever, whereas handwashing and wiping surfaces regularly is not as great an inconvenience. Therefore, we have developed a system to drastically cut down on the airborne transmission risk by rapidly reducing the viral load from aerosols that are known to linger in the air for hours.


There are various devices to make indoor air safer to reduce the risk of spreading hamrful pathogens, but they all have one critical flaw in common: they were designed with bacteria in mind as the priority, not viruses. Up until 2020, bacterial infections were a far larger threat -- the optimal methods of killing bacteria are not only different, but the ways in which bacterial risk increases in an indoor environment is different from the ways a virus spread. This does not mean those approaches are useless against viruses, only that they will cost more, be slower, and often both. Operating more slowly means you maintain a higher level of viruses, which increases the risk of transmission. We have written various articles covering the machines and approaches developed prior to 2020 that people are considering.

By and large there are two classes of methods to indoor air safety: 1) treat all the air continuously throughout your space, or 2) move your air through a device that treats it. The challenge with the 1st approach is that it requires whatever treatment is being done to the air be safe for long term human exposure, while still being potent enough to rapidly inactive viruses. The challenge with the 2nd approach is that the air in the room can only be processed so fast, but the treatment can be isolated such that the risk to human health from chronic exposure is 0 since there is no exposure. Rather than being pinned between the tradeoff of efficacy and safety (we prefer to not directly irradiate your customers, or have them breathing hydrogen peroxide or ozone), we decided to focus on approach 2, asking ourselves just how much faster can we make this work?

The Airsafe Design Philosophy

It turns out we can make something that processes air a lot faster and this is the key principle behind the Reflow Labs Airsafe. Previously, processing all the air in the room every hour or two was fine, but we make it possible to process all the air within minutes if you want. There are a couple design elements that make this possible. First, we eliminate the high density HEPA-grade filters you find in many traditional air filters, opting instead for a lower density 5-micron pre-filter (eliminates only the larger particles that may pose a sneeze risk), or even no physical filter at all. HEPA filtration is a sort of catch-all system, catching at least 99.97% of particles that are 0.3 microns or larger. Although the cross-sectional area of an individual coronavirus is over 6 times smaller, this is not too much of a problem since they are often carried in agglomerated aerosols that are caught. The problem is that dense filters require high static pressure to move air through them. Maintaining a high air flow rate with high static pressure requires a far more powerful fan that produces far more noise, or, a prohibitively large machine that can spread out the force needed over a large area. UV light is more effective, inactivating individual viruses as well as larger aerosol particles, and obviating the need for physical filtration.

But what about the UV lights that are used in filters or air sanitization systems today? These are often used in conjunction with physical filters, or they are designed to offer a similar functionality as a physical filter, treating the air in a room on the order of an hour. There are also UV air treatment systems that were designed for ultra-high-risk environment systems such as hospitals. These systems sometimes do more than what is needed to inactivated >99.9% of viruses, but they do this by moving air more slowly. These systems cost far more up front for comparable air flow, take up a lot more space, and might have expensive installation costs that do not enable fast deployment. Moreover, these systems may focus on achieving near-whisper-quiet sound levels.

Airsafe Design Details

The Reflow Labs Airsafe line of devices all share a few things in common. Air flow rate is maximized with a slightly relaxed acceptable upper bound on noise of 60-65 decibels. We achieve a UVC light dose on the air is 3-5x the amount that is estimated to inactivate 99.9% (log-3) of SARS-CoV-2 based on tightly clustered data showing UVC on 2 coronavirus strains as well as UVC inactivation on other structurally similar enveloped viruses such as influenzas (see our [research archive] for more details). However, these studies usually use a much lower power level and it would be reasonable to expect non-linear effects in inactivation rate with the same energy delivered faster (you'll find it more painful to have 1000 marbles dropped on your head than 1 at a time), in which case maybe our devices have tens of times the power needed to achieve 99.9% activation. If we determine this to be the case, we will not lower the power we use, but leverage this data so your customers can feel even safer.

We combine baffles with optical elements to ensure that practically all the UV light stays inside the Airsafe. An interesting aspect of using UV light in air as a disinfectant is that there is nearly no energy loss as the light passes through the air. This means that if you take the light you just passes across a chunk of air and could pass it back through a second time, you would nearly double the effective energy dose that hits the air. You are probably familiar with a technology that can do just this -- it is called a mirror. While it is possible to simply surround a light bulb with a cheap reflector without considering the overall geometry, this wastes a lot of the potential air-irradiance that can be achieved with a given amount of initial UV power. Instead of steel or brushed aluminum, we use mirror-polished aluminum, which has several times less energy loss on each reflection. With around 90% reflectivity, a system that reflects light back and forth perfectly can achieve a 10x effective amplification effect. By collimating our light source into a parallel 'sheet' of light, and slightly angling it in conjunction with parallel plates, we conservatively assume we are at least doubling our effective output when determing how much irradiance is needed in our machines.

Although the various optical, acoustic, and fluidic approaches we are taking are patent-pending (#63048295), we are prepared to scale to meet whatever quantity of Airsafes your business needs so that there is no bottlneck. We are continuously working to improve our offerings to increase air flow rate, decrease noise, and improve aesthetics. However, our primary focus in launching is on scale and we have achieved that. Unlike hydrogen peroxide machines relying on specialized catalyst materials, Reflow Labs Airsafe machines are 100% built with standard parts and materials. Whether you are a small business owner with half a dozen location or whether you are Starbucks, we can quickly meet your needs.

If you want to learn more about our thinking, please take a look at the rest of our articles. Additionally, we have curated a set of research papers that informed our approach, and we have summarized these papers so you can easily skim through them.

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See our other articles or take a look at our research paper summaries.

Learn more about the landscape of technologies marketed as making air safer: 1) Far UVC; 2) Radical Oxides e.g. Hydrogen Peroxide; 3) Ozone; 4) Violet and UVA

See the key FAQ pages provided by a team of scientists on COVID-19 transmission and preventive approaches:

Learn more about our board of reviewers.

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