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Clinical Associate & Chief clinical Coordinator - Dr. Sushma Sanghvi
HEPA is a type of pleated mechanical air filter. It is an acronym for high efficiency particulate air filter (as officially defined by the U.S. department). This type of air filter can theoretically remove at least 99.97% of dust, pollen, mold, bacteria, and any airborne particles with a size of 0.3 microns (µm)
Filters meeting the HEPA standard must satisfy certain levels of efficiency. Common standards require that a HEPA air filter must remove—from the air that passes through at least 99.95% (European Standard) or 99.97% (ASME, U.S. DOE) of particles whose diameter is equal to 0.3 μm, with the filtration efficiency increasing for particle diameters both less than and greater than 0.3 μm. HEPA filters
capture pollen, dirt, dust, moisture, bacteria (0.2-2.0 μm), virus (0.02-0.3 μm), and submicron liquid aerosol (0.02-0.5 μm). Some microorganisms, for example, Aspergillus niger, Penicilliumcitrinum, Staphylococcus epidermidis, and Bacillus subtilis are captured by HEPA filters with photocatalytic oxidation (PCO). HEPA is also able to capture some viruses and bacteria which are ≤0.3 μm. HEPA is also able to capture floor dust which contains bacteroidia, clostridia, and bacilli.
HEPA was commercialized in the 1950s, and the original term became a registered trademark and later a generic trademark for highly efficient filters. 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, homes and vehicles.
HEPA filters are composed of a mat of randomly arranged fibres. The fibers are typically composed of polypropylene or fiberglass with diameters between 0.5 and 2.0 micrometers. Most of the time, these filters are composed of tangled bundles of fine fibers. These fibers create a narrow convoluted pathway through which air passes. When the largest particles are passing through this pathway, they behave like a kitchen sieve which is blocked physically passing through. However, when the smaller particles pass with air, as the air twist and turns, the smallerparticles can’t keep the same motion of air up and they crush with the fibers. The smallest particles have very little inertia and they always move around the air molecules like they are bombarded by these molecules (Brownian motion). Because of their movement, they end up crashing into the fibers. Key factors affecting its functions are fiber diameter, filter thickness, and face velocity. The air space between HEPA filter fibers is typically much greater than 0.3 μm. HEPA filters in very high level for smallest particular particles. Unlike sieves or membrane filters, where particles smaller than openings or pores can pass through, HEPA filters are designed to target a range of particle sizes. These particles are trapped (they stick to a fiber) through a combination of the following three mechanisms:
HEPA filters are critical in the prevention of the spread of airborne bacterial and viral organisms and, therefore, infection. 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.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.
SARS CoV 2 is approximately 0.125 µm. Airborne droplets of SARS-CoV-2 could be captured by HEPA filters, even if they are on the floor.