[9][10][11] Some microorganisms, for example, Aspergillus niger, Penicillium citrinum, Staphylococcus epidermidis, and Bacillus subtilis are captured by HEPA filters with photocatalytic oxidation (PCO).

[14] HEPA filters are used in applications that require contamination control, such as the manufacturing of hard disk drives, medical devices, semiconductors, nuclear, food and pharmaceutical products, as well as in hospitals,[15] homes, and vehicles.

The smallest particles have very little inertia and move randomly as a result of collisions with individual air molecules (Brownian motion).

[23] In such setup, the first stage in the filtration process is made up of a pre-filter which removes most of the larger dust, hair, PM10 and pollen particles from the air.

[citation needed] HEPA filters, as defined by the United States Department of Energy (DOE) standard adopted by most American industries, remove at least 99.97% of aerosols 0.3 micrometers (μm) in diameter.

[24] The filter's minimal resistance to airflow, or pressure drop, is usually specified around 300 pascals (0.044 psi) at its nominal volumetric flow rate.

Failing to change a HEPA filter in a timely fashion will result in it putting stress on the machine or system and not removing particles from the air properly.

Typically, medical use HEPA filtration systems also incorporate high-energy ultraviolet light units or panels with anti-microbial coating to kill off the live bacteria and viruses trapped by the filter media.

[citation needed] Some of the best-rated HEPA units have an efficiency rating of 99.995%, which assures a very high level of protection against airborne disease transmission.

[citation needed] HEPA filters are capable of removing viruses including COVID-19 (particles of 60-140 nanometer diameter) from the air, and as such saw a surge in adoption during the pandemic in order to mitigate infection risks.

To combat supply chain and cost issues hindering adoption of HEPA filters during the COVID-19 pandemic, a professor at University of California, Davis, created a simple do-it-yourself air purifier design called crbox(Corsi–Rosenthal Box).

In addition, the COVID-19 Pandemic resulted in a surge of new air purifier products from new and established brands such as Dyson or Xiaomi hitting the markets.

So, a true HEPA filter is effectively trapping particles several hundred times smaller than the width of a human hair.

[citation needed] Modern airliners use HEPA filters to reduce the spread of airborne pathogens in recirculated air.

[38] The idea behind the development of the HEPA filter was born from gas masks worn by soldiers fighting in World War II.

A piece of paper found inserted into a German gas mask had a remarkably high capture efficiency for chemical smoke.

The British Army Chemical Corps duplicated this and began to manufacture it in large quantities for their own service gas masks.

The Army Chemical Corps developed a combination mechanical blower and air purifier unit, which incorporated cellulose-asbestos paper in a deeply-pleated form with spacers between the pleats.

[40] The US Army Chemical Corps and National Defense Research Committee needed to develop a filter suitable for removing radioactive materials from the air.