PROCESS

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Knowlege about High-Efficiency Particulate Air

Filter efficiency standard
 

HEPA-High-Efficiency filter

HEPA(High-Efficiency Particulate Air) is a kind of equipment used for air purification. HEPA is used in a wide range of applications like medical equipment, vehicle, water filter, and air filter. The filter standard is set by the United States Department of Energy. The high-efficiency filter like standard H14 can remove at least 99.99% of aerosols 0.3 micrometers (μm) in diameter

 

HEPA Class


According to the United States Department of Energy, HEPA filters should filter at least 99.97% of particles in the air with a diameter of ≧ 0.3 microns (µm). This is also the standard adopted by most American industrial sectors. In EU countries, this technical specification is usually also presented as EN 1822:2020. 

 
 HEPA Class  Retention(total)
E10(H10) > 85%
E11 (H11) > 95%
E12 (H12) > 99.5%
H13 > 99.95%
H14 > 99.995%
U15 > 99.9995%
U16 > 99.99995%
U17 > 99.999995%
 

Dangerous 0.3 microns


The HEPA filter can prevent air particles of 0.3 microns, so why not 0.1 microns? Wouldn't it be better to filter the smaller air particles?In fact, 0.1 micron air particles will produce Brownian motion, which is easily filtered by the HEPA, while the size of 0.3 micron does not produce Brownian motion, and it is not as easy to be filtered by a general filter as 0.4 micron or more. 

Aerosol Technology. Properties, behaviour, and measurement of airborne particles.
(From Anesthesia Key, Fig 11.2 accessed 8/6/20, Adapted from Hinds WC. Aerosol Technology. Properties, behaviour, and measurement of airborne particles. 2nd ed. New York: John Wiley and Sons; 1999.)