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Indoor Air Filtration and COVID-19

On September 2, 2020, in news, by Melanie

It is important to think about filtration, ventilation and air cleaning in order to mitigate risk of COVID-19 transmission.

Indoor confined space with closed window
Indoor properly ventilated space with open window

Let’s define some terms :

Droplets are propelled through the air, visible but fall to the ground after traveling 3-6 feet. Published research which has been replicated shows that droplets are only important when coughing and sneezing

Aerosols are much smaller than droplets (generally considered to be anywhere from 1 to 10 microns). They can be generated by talking, or by evaporation of droplets.

Aerosol (also referred to as “airborne”) transmission is similar to droplet transmission, except that the bits of fluid are so small that they can linger in the air for minutes up to 16 hours. Fears AC, Klimstra WB, Duprex P, et al. Comparative dynamic aerosol efficiencies of three emergent coronaviruses and the unusual persistence of SARS-CoV-2 in aerosol suspensions. medRxiv 2020:2020.04.13.20063784. doi: 10.1101/2020.04.13.20063784

Appropriate air filtration and ventilation ensures that adequate dilution is achieved where and when needed, avoiding the build-up of viral contamination

Ventilation is the replacement of stale or noxious air with fresh air to a space or building by natural or mechanical means (ISO, 2017). It controls how quickly room air is removed and replaced over a period of time. Ventilation plays a critical role in removing exhaled virus-laden air, thus lowering the overall concentration and therefore any subsequent dose inhaled by the occupants.

HEPA is a type of pleated mechanical air filter. It is an acronym for “high efficiency particulate air [filter]” (as officially defined by the U.S. Dept. of Energy). This type of air filter can remove at least 99.97% of dust, pollen, mold, bacteria, and any airborne particles with a size of 0.3 microns (µm).

Public health messaging can be confusing. Scientists have issued a global statement through the World Health Organization stating that when it comes to COVID-19, the evidence overwhelmingly supports aerosol transmission.

With infectious diseases transmitted through aerosols, HVAC systems can have a major effect on the transmission from the primary host to secondary hosts. Decreasing exposure of secondary hosts is an important step in curtailing the spread of infectious diseases. HVAC systems impact the distribution and bio-burden of infectious aerosols.

It is important to visualize the mechanism by which COVID-19 is transmitted, in order that individuals and institutions can understand how to protect themselves.

The closer you are to someone releasing virus-carrying aerosols, the more likely you are to breathe in larger amounts of virus. We know from detailed, rigorous studies that when individuals talk in close proximity, aerosols dominate transmission.

Talking increases aerosol exhalation by a factor of 10. It has been found that outbreaks occur when people gather in crowded, insufficiently ventilated indoor spaces

Superspreading events, where one person infects many, occur almost exclusively in indoor locations and are driving the pandemic. These observations are supported and explained by aerosols, and are very difficult or impossible to explain by droplets.

Contact tracing shows that, when it comes to COVID-19, being outdoors is 20 times safer than being indoors, which argues that aerosol transmission is much more important than droplets. Outdoors, there’s plenty of air in which aerosols can become diluted; not so indoors.

As we move from warm weather outdoor activity season into autumn and winter indoor season, the Airscape HEPA.Tower provides an excellent ventilation solution to create fresh air indoors.


Using Humidity to mitigate Covid-19

On September 2, 2020, in news, by Melanie

Since coronavirus is spread by breathing in respiratory aerosols from infected people, it stands to reason that avoiding breathing those aerosols is key to not getting COVID-19. One way to do that, according to a new study, is to keep humidity levels in indoor settings at 40 to 60 percent.

Researchers came to this conclusion after analyzing 10 international studies that were done between 2007 and 2020 looking at the rate of survival and infections of coronaviruses and influenza based on humidity levels in the air.

It was discovered that at higher humidity, the droplets grow faster, fall to the ground earlier and have less chance of inhalation by healthy people, meaning that viruses cannot spread as easily in humid conditions.

Although low humidity causes the droplets containing viruses to dry out more quickly, the survivability of the viruses still seems to remain high. Research concluded that other processes are more important for infection. If the relative humidity of indoor air is below 40 percent, the particles emitted by infected people absorb less water, remain lighter, fly further through the room and are more likely to be inhaled by healthy people. In addition, dry air also makes the mucous membranes in our noses dry and more permeable to viruses.

From the researchers’ point of view, more attention should be paid to indoor air to prevent future outbreaks of viral disease.

HRV/ERV exhausts stale indoor air to the outside, and brings in fresh air from outside. This fresh air is then distributed throughout the home either by the HRV/ERV or by your furnace fan.

In the winter, the warm indoor air passes through the HRV/ERV core as its being exhausted and warms up the incoming fresh outside air. The the summer, the cycle is reversed and the cool indoor air cools down the hot outdoor air recovering the energy. The 2 airstreams never mix when passing through the HRV/ERV core.

During cold and inclement weather, high efficiency filter ventilation systems that recirculate some of the air are an excellent solution.

Buy our humidifiers


Airscape HEPA Tower Air Purifiers : Now Available

On July 22, 2020, in news, by Melanie

Arising out of our personal and professional need for high quality portable air filtration during the COVID-19 pandemic, the inspiration and launch of the the newest member of the Airscape family was born.

We noticed an absence of cost effective and high quality portable indoor air filtration products utilizing critical core attributes:

*high number of air exchanges

*quality filtration media: MERV pre-filter and HEPA filtration

*particulate level filtration appropriate for airborne size micro-droplets (i.e. COVID-19, influenza etc.

*quiet operation (suitable for conference rooms during meetings)

*efficient energy utilization (speed controllable, low energy use ECM motor)

We utilize this product in our headquarters and trust it to keep our team safe.

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If you’ve been following our blog entries about viruses, micropdroplets, and Covid-19, or just reading the news, you’re coming to the conclusion that air filtration is getting to be very important.

It’s important to cut the “viral load” or amount of viruses that one is exposed to, and micro droplets that can contain Covid can remain aloft for up to 10 hours.

Masking and source capture (see our blog on dental aerosols) are good ideas, but there are many reasons why we still want to filter our air. Masks are not 100% effective (nothing is), and people make mistakes.

Just the facts: Why Filtration?

  • Masks are not 100% effective
  • People are not 100% effective at masking
  • Microdroplets stay in the air for up to 10 hours
  • Toilets can be a source of pathogens (including Covid 19)

Just the facts: What does my filtration system need to do ?

  • Capture microdroplets and viruses
  • Have airflow capable of 12 + air changes per hour (12 ACH)
  • Filtered air should flow from high to low
  • Have directed vents to avoid stagnant areas
  • Be quiet
  • Efficient
Clean air should be delivered high and returned low to the unit.

How to calculate required airflow

Airflow in cubic feet per minute (CFM) = # Air changes per hour (ACH) x Room Volume / 60

Example: Conference room 10’x20’x12′, with desired 12 ACH. CFM = 12 x (10x20x12) / 60 = 480 CFM


  • 2 Sizes: 500 CFM and 900 CFM
  • Low power use: 128 watts and 164 watts
  • Footprint of 18″ x 26″ x 72″ high (with casters)
  • Prefilter MERV11 with carbon impregnation
  • HEPA H13 (EU standard) 99.95% efficient, with individual test certificate.
  • HEPA is 24″x24″ x 12″ deep. This means it has a lot of holding capacity.
  • Electronically commutated motor (ECM), very efficient
  • Full range speed control with no motor hum (it’s ECM)
  • Customizable discharge: Front, Side, Top

Availability and Cost

  • We have a few of our initial batch available
  • We’re taking reservations for units to be ready in 6 weeks.
  • Check for updated price and availability.

Talking can launch thousands of droplets so small they can remain suspended in the air for ten hours for one micro particles.

Scientists agree that the coronavirus jumps from person to person most often by hitching a ride inside tiny respiratory droplets. These droplets tend to fall to the ground within a few feet of the person who emits them. They may land on surfaces like doorknobs, where people can touch lingering virus particles and transfer them to their face. But some droplets can remain aloft, and be inhaled by others.

Droplets become microdroplets and are formed by people by breathing talking, sneezing, coughing and toilet flushing. These tiny particles evaporate, stay afloat and do not drop down nor exhaust on their own.

How droplets become aerosols:

When people breathe, cough and sneeze, they release respiratory droplets and smaller aerosols less than five millionths of a meter in size. Compared with respiratory droplets, the smaller aerosols can remain in the air for longer periods of time. The current data suggest the novel coronavirus is primarily transmitted through contact with larger droplets, but tiny aerosols can also harbor the virus and may pose a threat to people, especially indoors. To establish a sound defense against these aerosols, informed management of airflow and airborne contaminants could be critical.

Three factors seem to be particularly important for aerosol transmission: proximity to the infected person, air flow and timing.

Larger droplets are heavy and float down quickly — unless there’s a breeze or an air-conditioning blast — and can’t penetrate surgical masks. But droplets less than 5 microns in diameter, called aerosols, can linger in the air for hours. They travel further, last longer and have the potential of more spread than the large droplets,” Dr. Barouch said.

Researchers from the National Institutes of Health used lasers to illuminate and count how many droplets of saliva were flung into the air by a person talking with and without a face mask. The paper was only recently published officially. When the researcher used a simple cloth face cover, nearly all the droplets were blocked.

This evidence is only relevant if COVID-19 is transmitted by droplets from a person’s mouth. It is. There are many documented super-spreading cases connected with activities – like singing in enclosed spaces – that create a lot of droplets.he light-scattering experiment cannot see “micro-droplets” that are smaller than 5 microns and could contain some viral particles.

How far does the virus move? And is it stable and concentrated enough at the end of its journey to harm someone’s health?

Solutions include source capture of airborne viral and bacterial pathogens (including influenza, COVID-19, SARS, MERSA) utilization filtration by increasing number of air exchanges through HEPA and MERV media, mixing with fresh air and exhausting externally.

Bringing in fresh air and stratify it utilizing high efficiency portable fan units to reduce viral and bacterial load in shared air spaces:

  • Conference rooms
  • Bars
  • Restaurants
  • Medical / Dental office waiting rooms
  • Hospital clean rooms
  • Patient Isolation Units
  • Doctor/Nurse break areas


We all know that aerosolized particles, particularly COVID-19 hang in the air for long periods of time.

Now, to add to the concerns, researchers have found that toilet flushing can trigger release of pathogens. In particular, COVID-19 carrying microdroplets from pre-symptomatic or symptomatic carriers can occur via fecal shedding . Ick !

How do we fix it ?

You guessed. Good. Bathroom. Ventilation.

Who knew. We did. This has been our job for the last 20 years.

Here’s a couple places to start:

More information:

Sources for further research:


The best way to remove aerosols created by dental procedures is to create a stream of air focused close to the source. Source capture as it’s known is more efficient since we’re pulling a concentrated source of contaminants. Each unit of air that you are paying for “works harder” in this manner.

From this point, there are 2 choices: exhaust the air, or recirculate it. Here’s a list of pros/cons for each system.

ExhaustNo worries about viral and other contaminants being spread inside
Exhausts conditioned air
Requires Installation
Very Quiet
Can be designed with lots of airflow to provide a purge between patients
RecirculationRequires expensive HEPA filters
More expensive
No Installation Required

The system shown below exhausts to the outdoors.

Typical Aerosol Exhaust System Installed in Attic or Interstitial Space (click image to expand)

Let’s go through the parts starting from the intake (left to right):

  • Intake cone: A plastic cone to pull aerosol from around the patient’s mouth
  • Self supporting flex duct: Typically a 4″ diameter flexible duct that “self supports” – holds its last position
  • Thimble: This is just a neat way to allow the inside duct to be removed and cleaned without system disassembly
  • Flexible insulated duct: This duct has a plastic liner and can be easily installed
  • Filter box: The CFB-6-OS contains a prefilter and a MERV15 filter. Even though we’re exhausting outdoors, it’s good practice to remove most of the particulates. The MERV15 filter is in the range of a N95 face mask.
  • Inline fan: We really like this powerful fan that is capable of high static pressure (sucking ability) and high flow (CFM or cubic feet per minute). The fan can be adjusted for flow for two modes: a) Patient aerosol removal b) Room purge between patients [VERY USEFUL AND PROBABLY WILL BE CODE MANDATED]


More Information

There is an invisible problem in the dental profession which has the potential to be harmful to medical professionals, patients, office staff and family members. Indoor air within dental offices may contain unhealthy and infectious airborne particulate resulting from transmittable bacteria and viruses. Dental offices are high traffic, publicly accessible, commercial spaces and the multiple daily interactions between patients and staff, can introduce bacterial, viral and fungal infections into the air. Ultrasonic instruments, along with the constant cleaning and disinfection of contact surfaces can create bio-aerosols which contaminate the indoor air and degrade the air quality of air in a dental office.

Risk vs. Income — Looks at Dentists !
(courtesy — click image to expand)

Indoor air quality contamination has been a known concern for many years, especially within hospital and dental manufacturer’s environments. Operating rooms of all hospitals and surgery centers have a cooler and filtered positive air flow within each surgical suite. Manufacturers of surgically implanted hardware (orthopedic) and dental implants have source capture devices on their equipment and “Clean Rooms” as part of the final sterilization process to preserve the surfaces of the implants before packaging. The manufacturers of these products invest heavily in the design of air quality controls to ensure they meet industry, regulatory and governmental standards and to protect their staff and the end user of their final product.

Source capture of dental bio-aerosols effectively collects airborne contaminants that are often present in dental offices; including such as oral aerosols, ultra-fine particles, disinfectant odors, mercury vapor, drill aerosols and abrasion powder and provide an added layer of safety by improving air quality in the immediate vicinity of interaction between individuals. This “source capture” feature helps protect doctors, dental technicians and patients alike.

During a regular dental visit, patients and providers are exposed to bio-aerosols which can originate from contaminated patient care items. In dental offices, the oral cavity constitutes the highest reservoir of infectious organisms with over 350 different types of bacteria. During dental treatments, the use of high and low speed instruments drilling into teeth, bones and tissues create hazardous bio-aerosols. Aerosols containing microbes from the saliva, blood, and sub-gingival fluids are dispersed in the air. The dispersal of fine droplets, which may contain pathogens, can stay airborne for hours. These pathogens are easily inhaled and become a potential source of infection for everyone within the dental office. The amount of time these droplets remain suspended in the air, how far they travel, and their level of contamination should be a concern for everyone, and especially when treating highly vulnerable patients – children, pregnant women, older people, and patients with COVID specific co-morbidity factors, hypertension, obesity, COPD.

A typical dental office can see 40-50 patients in a day. These patients are another source of air pollution from the tiny particulates of skin which that are continually exfoliated from the skin. Researchers believe that the majority of Staphylococcus aureus, one of the leading causes of infection, is transported mainly on these shed skin particles, readily disturbed from floors and other surfaces as microscopic specks of dust which thousands of pathogens use as a transmission vehicle.

Despite the SARS (Severe Acute Respiratory Syndrome) and MRSA (Multi-Resistant Staphylococcus Aureus) epidemics which profoundly affected healthcare mortality and infection rates, concrete actions to prevent the spread of aerobiological viral and bacterial infections have not been taken.

The Occupational Safety and Health Administration (OSHA) mandates that every employer, including medical and dental offices, has a general duty to protect employees. OSHA industrial hygiene includes references to ventilation and replacement air for the protection of the workers. There should be adequate ventilation by either natural or mechanical means, in order that the atmosphere does not endanger the health and safety of workers. The replacement air shall be free from contamination with any hazardous dust, vapor, smoke, fumes, mist or gas. The discharge of air from any exhaust system shall be in such a manner so as to prevent the return of contaminants into any workplace.

Microbial air pollution is a health hazard and source capture filtration units can play a role in significantly reducing the transmittable bio-aerosols. In many medical and dental office environments, the most practical and convenient solution is to have source capture systems.


More Information

In case you were wondering why we should wear a mask in public and filter the air around us, check out this demonstration of suspended micro droplets.

Micro droplets suspending in air from MixonK on Vimeo.

Our CFB HEPA Filters are currently being used by a number of hospitals to create negative pressure isolation rooms for COVID-19 patients. They are typically paired with an inline fan to exhaust the contaminated air from those areas, filter and then discharge it safely outside. Discharging the air without any filtration is considered risky since you are spreading/distributing the virus particles extracted from the patient areas. If you have questions on how to build negative pressure isolation rooms give us a call.

What is a HEPA?

HEPA stands for high-efficiency particulate arrestance. To be classified as a HEPA, the air filter must remove at least 99.97% of particles whose diameter is equal to 0.3 μm. Classification at 0.3 μm is important because this is the weakest point in the filter’s performance – typical HEPA filtration efficiency increases for particle diameters both less than and greater than 0.3 μm.

Image courtesy of the National Institute for Occupational Safety and Health (NIOSH)

Virus particles, due to their small size, typically fall in the diffusion regime of HEPA collection efficiency. Specifically, the virus that causes COVID-19 is approximately 0.125 μm in diameter. That diameter is perfectly within the particle-size range that HEPA filters capture with great efficiency: 0.01 μm and bigger (see the NIOSH diagram above).

Want to ready more about HEPA and how they filter particles the size of viruses? We found the Submicron and Nanoparticulate Matter Removal by HEPA-Rated Media Filters by NASA study is a great source of reliable technical info. Page 7 of the paper has an excellent illustration of filter efficiency as a function of particle diameter for sizes 0.01 μm and above.

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HEPA Filtration for Hospitals

On April 13, 2020, in covid, filtration, IAQ, news, by radek

How times change…

A few weeks ago our sister company AirScape Fans ( was ramping up whole house fan production for the summer season. Now they are very busy making HEPA filtration units for hospitals, and yes, observing Covid safety protocols. Masks [check], distancing [check], good ventilation [check], doors open for extra air dilution [check], hand sanitizer [check], outdoor breaks in the sun [check]. They (as did we!) spent a lot of time writing procedures on how to stay safe.

Stay safe and healthy out there!

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