Carroll County Times

Spurred by coronavirus pandemic, Westminster-based Knorr Brake Company devises air filtration system for train cars

A full unit that sits on the train car roof it displayed, on its end, in the lab at Knorr Brake Company in Westminster.

Westminster engineers are leading an effort to make public transportation safer during the coronavirus pandemic by developing an air filtration system for train cars.

The engineers from Knorr Brake Company, which is headquartered in Westminster, have developed a technology that can be installed in HVAC units on metro, train and light rail cars, and continually cleanse the air.


The Carroll County company has found itself among the throngs of businesses rushing to adapt to a changing world with technological innovation. The firm, which typically traffics in braking systems, passenger doors and climate-control equipment for train cars, has found a new avenue as cities across the country grapple with how to revive public transportation during the COVID-19 pandemic.

The company’s technology works in three stages. First, particles in the air pass through a charging grid. Once charged, they’re attracted to a dielectric air filter. Then, the particles are treated with an ultraviolet light placed behind the charging grid in the HVAC unit. Finally, the system ionizes the particles in the air, just before they pass out into the ductwork that flows into the car.


The ions travel through the air and attack pollutants in the car and on handrails, poles and seats.

“It’s not like wiping it down with disinfectant, but it helps to neutralize the virus on surfaces in the car,” said Derek Hurst, the company’s director of RailServices.

The system, which can be retrofitted into existing HVAC units on train cars, helps supplement the cleaning that takes place while trains are out of service, by cleaning the air while the train is in operation.

“The rail industries are doing tons of things between running the trains,” said Tyler Bowie, a RailServices sales application engineer at the company. “They’re cleaning all the surfaces, they’re spraying everything. But the interesting part is, as soon as one person gets on the train between those cleanings, they could infect the whole train again. So having these technologies applied in the recirculated air brings the greatest safety.”

Then-Gov. Martin O'Malley, right, views the factory floor with Richard Bowie, Knorr Brake Corporation's president and CEO until December 2019, during the grand opening ceremony for the new Knorr Brake building in Westminster in 2013.

The engineers in Westminster worked alongside groups in China and Australia to develop the three-part technology.

Segments of the system, including the UV light component, were previously in use in train cars in other parts of the world.

“This is the first time that we’ve pulled together the three individual technologies into a single package in this way, which was what makes it novel and why we filed for a patent for it.” Hurst said.

The system is capable of eliminating 99.9% of airborne particulates, bacteria, and viruses, “including PM10, PM2.5, and smaller; plus pollutants such as TVOC, ammonia, toluene, formaldehyde, and acetaldehyde. It also targets viruses and bacteria — including COVID-19, natural bacteria, H1N1 influenza, E. Coli, Staph, H3N2 influenza, plus the fungus that causes black mold,” according to a Knorr Brake Company news release.


It’s crucial to evaluate how quickly the system is able to remove airborne virus particles, said Jelena Srebric, a mechanical engineering professor at the University of Maryland, College Park, who focuses on ventilation technology.

“It’s not possible to eliminate all risk,” she said. “If you are standing next to somebody who has the pathogen and you are not wearing appropriate protection, then there is no system that can protect against that, right? But for a reasonable set-up with people wearing masks and maybe some of them wearing shields and so on, the question is then how quickly this can remove the pathogen from the space.”

Because train cars are small, and therefore the HVAC unit is typically in closer proximity to individuals than in, say, a building, the HVAC system could remove virus particles fairly quickly. But, they could still linger in parts of the car. That’s why personal protective gear remains so important, Srebric said.

After recent lab tests in Texas, the team discovered that after 15 minutes, the system achieves 99.99993% elimination of virus particles. As part of the test, scientists filled a chamber with the MS2 bacteriophage virus, and ran the Knorr Brake Company technology, evaluating its efficacy by taking samples at various time intervals.

The system, which weighs less than ten pounds, takes about two hours to install, the news release said.

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As it was undergoing testing, the system garnered plenty of interest from transit operators, Hurst said.


“All of the major cities of the country are interested in this product and interested in doing something to protect their passengers,” Hurst said. “The New York area is certainly one where we have activity underway.”

Some large operators, though, were hesitant about the new technology, Hurst said, so the company made them an offer: It would install the prototype on one of their vehicles, free of charge, so that they could test it out, Hurst said.

The company, which is a member of the German Knorr-Bremse Group, has long worked in HVAC and braking systems, but this was its first major foray into a public health issue of this magnitude, Hurst said.

“It’s been a really extraordinary experience,” he said. “I think from my 34 years of experience in the rail industry it has been unique for me.”

The technology could prove even more critical as the flu season approaches, the engineers said, and as concerns mount about future waves of COVID-19.

“Maybe the brake system is not something everybody thinks about, but it’s our job to get people from point A to point B safely and get home to their families,” Bowie said. “Doing another thing to actually improve safety to me is really rewarding.”