While awareness of ventilation and fresh, healthy air in schools has increased considerably, there is still one weak link in the hygiene chain: transport from home to school and back. Students spend a lot of time on older buses, especially in rural areas, where the air is often as stuffy and as firm as cheesecake.

In the morning, many parents wonder: Will my child really leave their mask on in the bus, or will they catch something in this space without parents, teachers or chaperones watching? Even the bus driver, whose concern used to be the stink bombs from the last row, wants to spend the day safely on the bus. She wonders: Will enough fresh air get in and bacteria get out if I open the doors for about 20 seconds every two to three minutes?

Fresh air filters on buses are just the beginning

Should we let our children on buses? How safe are they from COVID-19 infections in the busses? Parents as well as transportation and hygiene officials in the U.S. were also asking this question. They were after pragmatic solutions. One pioneer was the Prince George County School District in the US state of Virginia. As early as November 2020, the district equipped all buses for all of its 119 bus routes with air filters.

The choice fell on a filter solution from Webasto: "We were looking at filter solutions for other public transportation vehicles such as ambulances and fire trucks," says Dustin Nase, the district's transportation director. "That's how we came across Webasto and their air filtration system for ambulances." It could fit in buses, too, Nase thought, and in no time, mechanics were installing Webasto's fans in all the district's buses. 

The advantage of Webasto's HFT 300 air filter system installed in the buses is that it can be operated independently from the bus's air conditioning system on a 12V power source. This simplifies and speeds up installation. In addition, it can be mounted vertically or horizontally in the interior of the school bus. "The unit moves a very high volume of air at a high pressure drop," explains Webasto’s Paul Baczewski, USA National Account Manager Bus Products.

"The pressure drop means that a large volume of air is coming into the filter, but only a minimal amount is coming out of the filter," Baczewski says. It is this combination of a high volume of air with a high pressure drop that is needed to remove, for example, COVID-19 particles in a single ventilation pass. "This is important because otherwise the contaminated air would circulate in the vehicles for too long,“ Baczewski explains.

Not every filter achieves the desired effect

What are the benefits of air filters in buses and which filter system is the most effective? That's what the independent Dutch research company TNO wanted to find out in a study. TNO examined the particle concentration in two bus types (city and intercity bus) with different air filter technologies over one hour. The first finding was that the concentration was significantly higher in the city bus without filter measures than in the intercity bus. Measurements of the air volume flow showed that additional air extraction is more effective than air supply via open doors or windows.

The tests also showed that not every filter is effective. For example, a passive HEPA filter in the recirculating air supply of the bus did not produce any effect. Only the combination of return air and active filter units were able to significantly reduce particle levels after a short time.

"There are enormous differences in the filtering effect of HEPA filters," says Webasto’s Product Line Manager, Andrea Zironi. "With our HEPA filter of class H14, 99.995 percent of particles with a size of up to 0.3 μm can be filtered. This meets the requirements in sterile medical rooms such as operating rooms or even ambulances." Only a true HEPA-H14 system filters these small objects out of the air within one pass.

With HEPA-H14 filter, better air and more safety

While HEPA-14 was previously only required in medical facilities, this standard is thus slowly establishing itself in other areas, such as in aircrafts. Until now, Webasto offered the modular air filtration systems with HEPA-H14 filters mainly for ambulances. But this is now changing: "HEPA H14 filters provide more safety in many situations: starting in school buses, in trains, but also in stationary usage, for example in doctors' offices or hotel lobbies; everywhere where many people sit close together. This is where we want to ensure fresh and healthy air with our HEPA 14 filters," explains Zironi.

When a "new normal" is declared almost every day, it is impossible to plan how further COVID-19 variants will effect  the operation of schools and buses. Masks will likely be a part of our daily lives for some time to come. Now is the time to think about accompanying technical measures to make our lives are as safe and healthy as possible. The Webasto air filter systems with HEPA H14 can contribute to this. And that pleases the bus driver and all other passengers: The filters not only grab the smallest particles out of the air, but they also filter out the stench of stink bombs from the last row in no time.