Questions and answers

about the corona pandemic in schools

Sources of information and general definitions

There are numerous information sites worldwide with recommendations regarding the COVID-19 pandemic. How its spread, how to avoid the disease and what measurements to be taken in society in general to stop spreading the virus. We are working with air cleaning and have focused on the area where we and our products can create a safer environment. Our base are the leading information sites – WHO, ECDC (EU), RKI (DE), CDC (USA) and Folkhälsomyndigheten (SWE).

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How does SARS-CoV-2 virus spread?

According to WHO and major health organizations the SARS-CoV-2 virus is mainly spread by direct contact or droplets/aerosols, and less commonly by indirect contact from contaminated surfaces.

Read more from WHO, CDC, ECDC and RKI in the end of this document.

Droplet infection, airborne infection, or aerosol infection?

It is important to point out that the term droplet infection is not the same as airborne infection, even though the droplets are in the air for a certain period. If the droplets can dry up into microscopically small grains, the virus can travel much longer distances in the air. This significantly increases the risk of spread and inhalation and is called airborne infection. Measles and chickenpox are examples of such viruses. Sometimes the term aerosol infection is also used. Aerosols are a term for small particles that are atomized in a gas, usually air. Consequently, both droplet infection and airborne infection can be included when using the term aerosol infection.

What is the size of aerosols and SARS-CoV-2 virus?

The influenza B virus is estimated to be about 0.12 μm and the new coronavirus at most, 0.16 μm. They may for some time be encapsulated in the droplets (about 10 μm) that spread in the air when we cough and sneeze as well as in the aerosols (about 1 μm) in our exhaled air. A single breath can contain anywhere from 1,000 up to 50,000 micro droplets.

What is an µm?

µm is an abbreviation of micrometer and is a unit of length used for particle size. 1 µm is 0.000 001 meter (one millionth of a meter).

How long can the SARS-CoV-2 virus stay in the air?

Droplets that we are emitting when talking, sneezing, or coughing stays in the air from a few seconds for the larger droplets to some minutes for the smallest droplets. Aerosols are smaller than droplets and stays from some minutes to several hours.

Is the risk to get infected higher indoor or outdoor?

For direct transmission via droplets the distance is the most important factor regardless if you are indoor or outdoor. For indirect transmission via aerosols indoors has a higher risk since aerosols can accumulate. Crowded, poor ventilated areas should be avoided.

What are the current recommendations to reduce aerosol transmission for SARS-CoV-2 virus indoors?

WHO - “There should be fresh, clean air in all workplaces. For jobs and work tasks at medium or high risk of exposure, WHO recommends an increased ventilation rate through natural aeration or artificial ventilation, preferably without re-circulation of the air. In case of air recirculation, filters should be cleaned regularly.”

How can I protect myself from aerosol transmission indoors from SARS-CoV-2 virus?

If possible, make sure the building is properly ventilated through a ventilation system or by opening windows. Air cleaners will add further circulation of the air and HEPA filters will reduce the amount of airborne particles, such as pathogens, contaminated dust, and aerosols as well as other harmful particles like soot from combustion etc.

Are freestanding air cleaners useful against aerosol transmission of the SARS-CoV-2 virus?

Yes, the built-in ventilation is not always effective enough to provide healthy air quality and to control the spread of airborne microorganisms. Freestanding air purification solutions are an effective complement to the existing ventilation. Equipped with adequate filters and correctly dimensioned, air cleaners are an efficient solution for reducing the concentration of airborne particles, virus and bacteria. A HEPA 14 has a filtration efficiency of at least 99.995% for particles of size 0.1–0.2 µm which is in the range for SARS-CoV-2 virus.

How is the air filtrated in general in schools and other public buildings?

In older buildings, fresh air is either provided via window ventilation, which means no filtration or via a ventilation system that uses low-grade filtration, typically ePM Coarse or ePM10 according to ISO16890 filter standard. More modern buildings are normally equipped with a ventilation system and filters of higher grads, i.e. ePM2,5 or in some cases ePM1 filtration. Normally it is difficult to increase the filtration or airflow in the ventilation system substantially due to the construction of the system. Design is normally based on the number of persons the building is built for, times X liters of fresh air per second. (example for new buildings in SWE – 7 liters/second/person + 0,35l/second/m²). The air in the building is constantly diluted over time as fresh air is pumped into the building.

Can you change the existing air filters in the building to HEPA filters?

No, a HEPA 13/14 filter has much denser filter media than comfort filters for ventilation systems and the pressure drop (resistance) in the HEPA filter is much higher. The ventilation unit is not designed for the density of the HEPA filter and therefore not strong enough and the result are very low airflow in the system.

If I want to reduce aerosols and particles of the SARS-CoV-2 virus size in a secure and efficient way, what do I need?

Air cleaners with HEPA 13 or 14 filters is an efficient and secure way to reduce aerosols and particles in the indoor air. Pay attention to the room size and how much air the air cleaner can process per hour. It is also advisable to have a look on the sound level of the unit. To run any air cleaner on its max velocity is normally perceived as noisy.

How shall I calculate my need?

This depends on the size of the room, the desired air changes per hour, and how sensitive sound and airflow is for the comfort in the room. When you know how big the room is in cubic meters (L x B x H), the number of air changes needed per hour is determined. Using the maximum speed on the air cleaner results in higher noise levels and a greater risk of the draft. In environments where comfort may be affected, the air should be set up in a silent operation. In environments with high noise levels and a lot of movement, the air cleaners can have a higher airflow without being perceived to be disturbing. As an example, we recommend operating our FS 70 on 800- 1200m³/h in schools where the sound is critical. You can operate the same unit on 3000 m³/hour in a noisy environment. Maximum speed of the unit is 4000m³/hour.

What is the definition of a HEPA air cleaner?

A HEPA air cleaner contains a certified filter according to EN 1822-1. They exist in two classes: HEPA 13 and HEPA 14. QleanAir applies only HEPA 14 which has the highest degree of separation. According to our definition, air cleaners must also have a completely airtight construction and an air flow adapted to the filter.

Is there an alternative technology to a HEPA air cleaner to prevent indoor aerosol transmission of SARS-CoV-2 virus?

Mechanical filters of HEPA quality are recommended, by all major hospitals and other stakeholders connected to medical care, to reduce indoor aerosol transmission of SARS-CoV-2 virus. There are other technologies; filter charging techniques, ionizers, UV lights etc., but these are normally not recommended in hospitals or other sensitive areas. For ISO classified Clean rooms HEPA14 filters are the only filters approved by FDA (USA) and Läkemedelsverket (SWE).

Where should I place a HEPA air cleaner to prevent aerosol transmission of SARS-CoV-2 virus indoors?

As close as possible to potential sources or areas in direct connection to critical areas. It is also important to think about where you want to direct the outlet air from the air cleaner. An air cleaning specialist can guide you to the optimal placement of air cleaners. A particle measurement as well as control of the air movement in the room are tools to ensure optimal placements according to the circumstances in the room.

How long does/can the SARS-CoV-2 virus “live” on a surface of an air filter?

“It is not yet clear how long the virus can survive outside the body. Research on related coronaviruses shows that they can live for several days on surfaces and items, under particular conditions. Their survival depends on temperature, humidity, and sunlight. Coronaviruses are sensitive to dehydration,” according to Folkhälsomyndigheten, Public Health agency in Sweden.

In general, the softer material the shorter time the SARS-CoV-2 virus is viable according to several studies. All this in consideration, it is most likely that SARS-CoV-2 virus is only viable a few hours after captured in an air filter.

How and when should filters be replaced?

For professional use we recommend signing up for a full-service concept. This ensures that filters are changed in a correct way according to regulations and guidelines and that the unit is maintained by trained technicians.

Do all QleanAir air cleaners have HEPA 14 filters?

All QleanAir products (except the new industrial unit FS 90) can be equipped with HEPA 14 filters. We use HEPA 14 filters as the main filters in air purifiers that will be installed in environments where it is important to minimize the spread of particles, viruses, and bacteria. HEPA 14 is part of the standard setup for our smoking cabins and cleanrooms. The filter composition in our standalone air cleaners is adapted to the specific environment and the customer’s needs, and HEPA 14 is included as an option.

For schools, what is QAS recommendation to prevent aerosol transmission of SARS-CoV-2 virus?

A standard classroom is normally around 60m² and is easily covered with a FS 30 or a FS 70 HEPA. Silent operation is important in schools and FS 70 HEPA can be operated under 35db and still cover a complete classroom. For school cantinas and gyms we recommendFS 70 HEPA. For changing rooms and teacher's rooms we recommend FS 30 HEPA.

For smaller meeting rooms and offices (up to approx. 15m²) or rooms that are shared by 2-3 persons, a smaller air cleaner like AirQlean Low 115 HEPA or FS 30 HEPA is a good solution.

For public outdoor areas, what is QAS recommendation to prevent aerosol transmission of SARS-CoV-2 virus?

In general, there is no effect of air cleaners outside, space is too large so you will not reach any effect.

For direct transmission, via droplets, the distance is the most important factor regardless if you are indoor or outdoor. Indirect transmission via aerosols outdoors is quite unlikely since aerosols cannot accumulate. Crowds where people are close together and sing, shout or talk loudly should be avoided.

WHO - World Health Organization

“The virus can spread from an infected person’s mouth or nose in small liquid particles when they cough, sneeze, speak, sing or breathe heavily. These liquid particles are different sizes, ranging from larger ‘respiratory droplets’ to smaller ‘aerosols’. Other people can catch COVID-19 when the virus gets into their mouth, nose or eyes, which is more likely to happen when people are in direct or close contact (less than 1 metre apart) with an infected person. Current evidence suggests that the main way the virus spreads is by respiratory droplets among people who are in close contact with each other. Aerosol transmission can occur in specific settings, particularly in indoor, crowded and inadequately ventilated spaces, where infected person(s) spend long periods of time with others, such as restaurants, choir practices, fitness classes, nightclubs, offices and/or places of worship.”

RKI - Robert Koch Institute - Germany

“SARS-CoV-2 can be transmitted easily from person to person. The risk of infection depends heavily on individual behavior (physical distancing, hygiene measures and community masks), on the regional distribution and on living conditions. In this regard, contacts in situations with increased risks (such as face-to-face contact for a longer time) play a special role. This also holds for situations with contact to family members and friends outside the household and in occupational settings. Aerosol emission is increased markedly when speaking loudly, singing or laughing. Indoors, this significantly increases the risk of transmission, even if a distance of more than 1.5 m is maintained. If the minimum distance of 1.5 m is not complied with among persons without community/face masks, e.g. when groups of people sit at a table or in large gatherings, there is also an increased risk of transmission outdoors.” nightclubs, offices and/or places of worship.”

“A transmission of SARS-CoV-2 by aerosols is possible in certain situations over longer distances, e.g. when many people come together in insufficiently ventilated indoor rooms and there is an increased production and accumulation of aerosols”.

ECDC - European Center for Disease Prevention and Control - EU

“SARS-CoV2 spreads from person to person (human-to-human transmission) through direct contact. It is currently estimated that, in the absence of physical distancing and other preventive measures, one infected person will on average infect between two and three other people. The virus is mainly transmitted via small respiratory droplets, through sneezing, coughing or when people interact with each other for some time in close proximity (usually less than two metre apart). These droplets can be inhaled or can land on surfaces that others come into contact with and are then infected when they touch their nose, mouth or eyes. We know that the virus can be transmitted when people who are infected show symptoms such as coughing. A person who is infected can also transmit the virus up to two days before they show symptoms; the extent to which such asymptomatic infections contribute to the overall transmission is not currently clear.”

CDC - Center for Disease Control and Prevention - USA

“COVID-19 most commonly spreads during close contact from person to person including people who are physically near (within 6 feet) a person with COVID-19 or have direct contact with that person are at greatest risk of infection. When people with COVID-19 cough, sneeze, sing, talk, or breathe they produce respiratory droplets. These droplets can range in size from larger droplets (some of which are visible) to smaller droplets. Small droplets can also form particles when they dry very quickly in the airstream. Infections occur mainly through exposure to respiratory droplets when a person is in close contact with someone who has COVID-19. Respiratory droplets cause infection when they are inhaled or deposited on mucous membranes, such as those that line the inside of the nose and mouth. As the respiratory droplets travel further from the person with COVID-19, the concentration of these droplets decreases. Larger droplets fall out of the air due to gravity. Smaller droplets and particles spread apart in the air. With passing time, the amount of infectious virus in respiratory droplets also decreases.”

“COVID-19 can sometimes be spread by airborne transmission”

“There is evidence that under certain conditions, people with COVID-19 seem to have infected others who were more than 6 feet away. These transmissions occurred within enclosed spaces that had inadequate ventilation. Sometimes the infected person was breathing heavily, for example while singing or exercising. Under these circumstances, scientists believe that the amount of infectious smaller droplet and particles produced by the people with COVID-19 became concentrated enough to spread the virus to other people. The people who were infected were in the same space during the same time or shortly after the person with COVID-19 had left.”

“Spread from touching surfaces is not thought to be a common way that COVID-19 spreads”

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