Interesting facts from studies and scientific experiments with air purifiers.
Air purifiers significantly reduce the risk of infection in classrooms
Study of the Frankfurt Goethe University from 19th, Nov. 2021
There is no need to freeze!
Room air purifiers with Hepa filters are considered an alternative to regular ventilation. A new preliminary study by Frankfurt's Goethe University shows that the air purifiers can remove 90% of aerosols from classrooms in 30 minutes. This significantly reduces the risk of infection.
Even with superspreaders in the room, the risk of contagion is reduced
"Based on our measurement data, we made a model calculation that can be used to estimate: An air purifier reduces the amount of aerosols so much that in a closed room, even the risk of infection from a highly infectious person - a superspreader - would be very significantly reduced," Curtius says. Noise measurements and a survey of students and teachers showed that the noise from the devices was overwhelmingly not considered annoying, as long as they were not running at the highest level, he said. "That's why we're recommending that schools use Hepa air purifiers with a high enough air flow rate this winter."
High efficiency of mobile air purifiers and masks
Study of the effectiveness of indoor aerosol reduction using air purifiers. A simulated session with 4 participants and simulated exhaled SARS-CoV-2 aerosols from 9th, July 2021, U.S. Department of Health and Human Services, CDC.gov.
What is already known about this topic?
Air purifiers should be supplemented with mobile high-efficiency particulate air (HEPA) purifiers to reduce the number of infectious particles in the air.
What is determined by the study?
A simulated infected meeting attendee who exhaled aerosols was placed in a room with two simulated uninfected attendees and a simulated uninfected speaker. The use of two HEPA air purifiers near the aerosol source reduced aerosol exposure to the uninfected attendees and speaker by up to 65%. A combination of HEPA air purifiers and worn surgical mask reduced aerosol exposure by up to 90%.
What are the implications for public health practice?
Mobile HEPA air purifiers can significantly reduce exposure to simulated SARS-CoV-2 aerosols indoors, especially when combined with an additional surgical mask.
SARS-CoV-2: Air purifiers remove 90% of aerosols in school classrooms
Experimental study of the medRxiv from 6th, Oct. 2020 (published on aerzteblatt.de)
Placement of 4 commercially available air purifiers reduced the concentration of aerosols in a classroom by 90% within half an hour in an experimental study. According to the study in medRxiv (2020; DOI: 10.1101/2020.10.02.20205633), students and teachers found the noise pollution from the air purifiers to be mostly non-annoying.
SARS-CoV-2 and other respiratory viruses are transmitted via droplets, aerosols, and by touching objects or people. Droplets are retained by mouth-to-nose coverage. Hand disinfection helps against transmission by touch. Air purifiers can be a protective measure against aerosols, which are only incompletely retained by an oral-nasal covering.
The air cleaners accelerated the drop in aerosols. The devices together converted between 760 and 1.460 m3 of air per hour, which means that the room air was filtered about 5.5 times per hour. According to the measurements, this resulted in a continuous drop in aerosol concentration. It dropped by more than 90% within 37 minutes compared to the beginning of the lesson. According to the study, the reduction affected all particle sizes equally.
Schooling during the SARS-CoV-2 pandemic.
Study of the University of the Federal Armed Forces Munich, Institute of Fluid Mechanics and Aerodynamics from 22nd, Sept. 2020
- The content of the study was to examine whether mobile air purifiers are suitable to contribute to the reduction of the risk of infection, when free ventilation is no longer possible due to energy wastage at the latest in winter or due to the dwindling of people's well-being.
- By using mobile air cleaners with high quality filters of class H14 the aerosol concentration in a room with 80m² could be reduced to a low level everywhere within a short time.
- Mobile air purifiers are a very useful technical solution to reduce the indirect risk of infection by aerosols in schools, offices, stores, waiting rooms, community and club houses, recreation and dining rooms (canteens), etc.
- Daily heating of the filter is necessary to destroy the viruses and prevent the formation of biofilms, bacteria and fungi.
- During permanent operation of such systems "no human being will manage to create an aerosol concentration of infectious level in a room" (Prof. Dr. Kähler)
- Prof. Dr. Kähler from the University of the Federal Armed Forces in Munich recommends a 6-fold air exchange rate to keep rooms at a low aerosol level.
- To achieve fast and highly efficient filtration, a filter combination of classes F7 and H-14 is recommended.
- Due to the high air circulation, depending on the room size, a halving of aerosol concentrations can be achieved within 3 -15 minutes and easily maintained at a low level.
- In contrast to free ventilation, mobile room air cleaners also ensure a real reduction of the virus load.
- In buildings/rooms (e.g. waiting areas, fitness studios) where large aerosol quantities are generated due to large crowds and high workloads, the units can also be used in support of air handling RTL-units