Since HEPA filters were developed in the early 1940s for the Manhattan Project to contain the spread of airborne radioactive contaminants, there have been numerous studies to show how it successfully traps all particles including nano-particles like the virus.
However since the spread of COVID-19, there has been reluctance to use the word 'airborne' so the solution of filtration has been hampered and even rejected outright.
Ventilation dilutes airborne particles but filtration removes it. A combination of the two helps reduce long-range transmission, it cannot prevent short-range transmission. That said, the more places that offer filtration, the lower the community transmission rates will be until spread is no longer endemic.
We have compiled a list of research to help you spread the word. Not all of this research is about infection control, some will also identify the benefits of breathing in cleaner air in both our physical and mental health.
Schools and universities
- Cath Noakes and Henry Burridge's paper on dynamic thermal modelling to assess the potential impacts of standalone HEPA filter units in classrooms
- Working Paper by London School of Economics looking at the improvements made in Key Stage 2 test results since LEZs were introduced in 2016. Improvements at a level similar to reducing class size by 10 students!
- Study looking at various research reports to identify the benefit of air purifiers on our health. Results found reduced PM2.5 concentrations by between 22.6 and 92.0% in homes and 49% in the schools
- In 2015, a big leak at a natural gas facility in the US resulted in the company paying for air filters in every classroom, office and common area in ALL schools within a five mile radius. After 4 months, Math scores went up by 0.20 and English scores by 0.18 standard deviations. These same results could be achieved by cutting class sizes by 1/3rd
- London School of Economics studied university studentsโ test performance relative to air pollution levels on the day of the test alone. Results showed that taking a test in a filtered rather than unfiltered room would raise test scores by 0.09 standard deviations
- Air filters and scheduled window opening can reduce classroom pollution by up to 36% โ University of Surrey study
- Natural ventilation supplemented with the use of HEPA filters is the most effective way to reliably improve indoor air quality year-round, balancing the need to have easy to enact approaches to reduce the buildup of PM2.5, airborne viruses and carbon dioxide
- A study by the University of Amsterdam found that the use of professional air purifiers can lead to a 90% less chance of indirect Covid-19 infection.
- Forthcoming studies
- Do air purifiers and fans reduce circulating virus particles in schools? Project CLAIRE (Clean Air for Everyone), which includes the Blast from Smart Air, is due for completion in 2025
- Bradford 'Class Act' study is awaiting peer review but is currently showing a 20% reduction in absences as a result of air cleaners
- Preliminary results found that daycare centres where air purification had been added, absence reduction was about 30% - results due 2025
Healthcare industries
- Research at Addensbrooke Hospital in Cambridge on Covid wards found that air filter machines removed almost all traces of airborne Covid virus
- Correct use of Portable Air Cleaners can reduce the clearance half-life of aerosols by 82% compared to the same indoor-environment without any ventilation, and at a broadly equivalent rate to built-in mechanical ventilation
- Research at a hospital swamped by people with COVID-19 has confirmed that portable air filters effectively remove SARS-CoV-2 particles from the air - the first such evidence in a real-world setting.
- Use of portable air cleaners to reduce aerosol transmission on a hospital coronavirus disease 2019 (COVID-19) ward. With 2 small domestic air cleaners in a single patient room of a hospital ward, 99% of aerosols could be cleared within 5.5 minutes
- The single-bed hospital room had an excellent ventilation rate (โผ14 air changes per hour) and cleared the aerosols in 20 min. However, with the addition of two air cleaning devices, the clearance time was three times faster!
- A study looking at the rate of suspended particles during dental procedures with and without air purifiers found 93% higher efficacy of pollution abatement with air purifiers. Additionally, the contamination was reduced by 69โ80%.
- The air purification systems realised a 97-99% reduction in viral load in air in 1 hour.
- If you would like to approach your GP or other healthcare provider to discuss clean air options, we have created a template that may help.
Offices and businesses
- The use of multiple HEPA air cleaners spread out around the room provides a faster and better mixing and cleaning of the room air, thereby reducing the overall concentrations for participants in the room and reducing the probability of SARS-CoV-2 transmission.
- A study looking at office workers with and without air purifiers near them. It found a significantly better performance for 9 out of the 16 cognitive skills with air purifiers, with the most consistent effect in the memory domain
- Finnish study looking at filtration in nurseries and the impact on parents to the economy, due 2025. Preliminary results show the the cost of one day of sick leave is approximately EUR 370 for the employer.
- A study by Stantec looking at 22 variations of ventilation and filtration: 18 adaptations of HVAC system, 4 with portable air cleaners. They found the best case scenario for HVAC (ventilation) was up to 17% particle reduction yet combined with portable air cleaners, the particle reduction was up to 45%.
General
- Lessons from the COVID-19 pandemic for ventilation and indoor air quality addressing 'open window' solutions and equivalent ventilation through portable air cleaners
- An assessment of the effectiveness of air purifiers (HEPA) for controlling indoor particulate pollution found The result showed that the air purifier reduced PM levels of different sizes ranged from 37โ64% in general indoor air
- Researchers gave 35 healthy Shanghai university students real or fake air purifiers and tracked several health markers for two days. They found that after 48 hours, the students had significantly lower inflammation in their blood vessels. They also had lower blood coagulation (a marker of blood clotting) and less constricted blood veins
- This study concluded that adding portable air cleaners to achieve equivalent of 12 ACH averted 54 infections in a 1000 square feet (92 m2) restaurant & produced cost savings of more than $150,000 per year
- A study in a gym found that combining ventilation and air cleaners can reduce aerosol particle concentrations within 80 to 90%, depending on aerosol size.
There are, of course, numerous more studies out there but this should give you some information to persuade your employer, school, healthcare setting to invest in filtration. A good source of research links can be found here: https://medium.com/@carlvank/luchtreiniging-air-purification-hepa-5dd2c728ef8f.
