Analysis reveals that the particle measurement of SARS-CoV-2, the virus that causes COVID-19, is round 0.1 micrometer (µm). Nevertheless, the virus typically doesn’t journey by the air by itself. These viral particles are human-generated, so the virus is trapped in respiratory droplets and droplet nuclei (dried respiratory droplets) which might be bigger. A lot of the respiratory droplets and particles exhaled throughout speaking, singing, respiratory, and coughing are lower than 5 µm in measurement. By definition, a Excessive Effectivity Particulate Air (HEPA) filter is at the least 99.97% environment friendly at capturing particles 0.3 µm in measurement. This 0.3 µm particle approximates probably the most penetrating particle measurement (MPPS) by the filter. HEPA filters are much more environment friendly at capturing particles bigger and smaller than the MPPS. Thus, HEPA filters are a minimum of 99.97% environment friendly at capturing human-generated viral particles related to SARS-CoV-2.
Transportable HEPA filtration items that mix a HEPA filter with a powered fan system are a fantastic possibility for auxiliary air cleansing, particularly in larger threat settings equivalent to well being clinics, medical testing areas, exercise rooms, or public ready areas. Different settings that would profit from moveable HEPA filtration might be recognized utilizing typical threat evaluation parameters, equivalent to neighborhood incidence charges, facemask compliance expectations and room occupant density. In selecting a transportable HEPA unit, you need to choose a system that’s appropriately sized for the world wherein it’s put in. A method to do that for room air cleaners is to pick a HEPA fan system with a Clear Air Supply Charge (CADR) [See EPA’s Guide To Air Cleaners In The Homepdf iconexternal icon] that meets or exceeds the sq. footage of the room wherein it is going to be used. The bigger the CADR, the sooner it can clear the room air. If the room wherein the air cleaner shall be used is taller than 8 ft, select an air cleaner with a proportionally larger CADR than that primarily based merely on sq. footage. Whereas these programs don’t usher in outside dilution air, they’re very efficient at cleansing air inside areas to cut back the focus of airborne particulates, together with SARS-CoV-2 viral particles. Thus, they offer efficient air exchanges with out the necessity for conditioning outside air.
HEPA fan programs can be utilized as stand-alone items, or many bigger items permit versatile ductwork to be connected to the air inlet and/or outlet (notice that bigger ducted items don’t fall below the “room air cleaner” description and will not have a CADR score). Utilizing ductwork and putting the HEPA system strategically within the area might help present desired clean-to-less-clean airflow patterns the place wanted. Ducted HEPA programs may also be used to determine direct supply seize interventions for affected person remedy and /or testing eventualities (See CDC/NIOSH dialogue on Ventilated Headboard). Relying on the dimensions of the HEPA fan/filter items and the way the ability wherein they’re getting used is configured, a number of small moveable HEPA items deployed to excessive threat areas could also be extra helpful than one massive HEPA unit serving a mixed area.
Instance 2: The room described in Instance 1 is now augmented with a transportable HEPA air cleansing gadget with a CADR of 145 cfm (Qhepa = 145 cfm). The added air motion inside the room improves general mixing, so assign ok = 3. How a lot time is saved to attain the identical 99% discount in airborne contaminants by including the moveable HEPA gadget to the room?
The addition of the HEPA filter gadget gives further clear air to the room. Right here, the clear volumetric air movement fee (Q) is: Q = Qe + Qhepa = 72 cfm + 145 cfm = 217 cfm.
ACH = [Q x 60] / (room quantity) = (217 cfm x 60) / (12’ x 10’ x 9’) = 13,020/1080 = 12.06 ACH (spherical right down to 12).
Utilizing Desk B.1, the right mixing wait time primarily based on 12 ACH and a 99% discount of airborne particles is 23 minutes.
Utilizing the blending issue of three, the estimated wait time for 99% discount of airborne contaminants within the room is 3 x 23 = 69 minutes. Thus, the elevated ACH and decrease ok worth related to the moveable HEPA filtration unit decreased the wait time from the unique 5 hours and 45 minutes to only one hour and 9 minutes, saving a complete of 4 hours and 36 minutes earlier than the room might be safely reoccupied.
In conclusion, including the moveable HEPA unit elevated the efficient air flow fee and improved room air mixing, leading to an 80% discount in time for the room to be cleared of potentially-infectious airborne particles.