Array ( [0] => {{short description|Efficiency standard of air filters}} [1] => {{Other uses|HEPA (disambiguation)}} [2] => {{Use British English|date=October 2020}} [3] => [4] => [[File:HEPA Filter diagram en.svg|thumb|300px|right|HEPA filter corrugated internal structure and aluminium support along with the description of its functioning principle (interception, impact and diffusion of dust particles through a dense non-woven fiber material)]] [5] => [6] => '''HEPA''' ({{IPAc-en|ˈ|h|ɛ|p|ə}}, '''high-efficiency particulate air''') filter,{{Cite web |title=GLOSSARY |url=https://www.hepa.com/glossary |url-status=live |access-date=2021-05-14 |website= |publisher=[[HEPA Corporation]] |archive-date=2020-04-20 |archive-url=https://web.archive.org/web/20200420065929/https://www.hepa.com/glossary}} also known as '''high-efficiency particulate absorbing''' filter{{Cn|date=October 2023}} and '''high-efficiency particulate arrestance''' filter,{{Cite web |title=HEPA |url=https://www.thefreedictionary.com/HEPA |url-status=live |access-date=2021-05-14 |website=[[The Free Dictionary]] |archive-date=2020-04-20 |archive-url=https://web.archive.org/web/20200420235158/https://www.thefreedictionary.com/HEPA}} is an [[efficiency]] standard of [[air filter]]s.{{Cite web |title=Efficiency of the HEPA air filter: HEPA filter quality and bypassing |url=http://www.air-purifier-power.com/hepa-air-filter.html |url-status=live |access-date=2021-05-14 |website=Air-Purifier-Power |archive-date=2020-04-20 |archive-url=https://web.archive.org/web/20200420070844/http://www.air-purifier-power.com/hepa-air-filter.html}} [7] => [8] => 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% ([[International Organization for Standardization|ISO]], European Standard)European Standard EN 1822-1:2009, "High efficiency air filters (EPA, HEPA and ULPA)", 2009 or 99.97% ([[American Society of Mechanical Engineers|ASME]], [[United States Department of Energy|U.S. DOE]])American Society of Mechanical Engineers, ASME AG-1a–2004, "Addenda to ASME AG-1–2003 Code on Nuclear Air and Gas Treatment", 2004{{Cite web |url=https://www.standards.doe.gov/standards-documents/3000/3020-astd-2015 |title=Specification for HEPA Filters Used by DOE Contractors — DOE Technical Standards Program |last=Barnette |first=Sonya |website=www.standards.doe.gov |language=en |access-date=2019-06-05 |archive-date=2020-04-20 |archive-url=https://web.archive.org/web/20200420065034/https://www.standards.doe.gov/standards-documents/3000/3020-astd-2015 |url-status=live}} of [[particle]]s whose diameter is equal to 0.3 [[micrometre|μm]], with the filtration efficiency increasing for particle diameters both less than and greater than 0.3 μm.{{Cite book |url=https://www.cdc.gov/niosh/docs/2003-136/pdfs/2003-136.pdf?id=10.26616/NIOSHPUB2003136 |title=Guidance for Filtration and Air-Cleaning Systems to Protect Building Environments from Airborne Chemical, Biological, or Radiological Attacks |publisher=[[National Institute for Occupational Safety and Health]] |date=April 2003 |location=Cincinnati, OH |pages=8–12 |access-date=2020-02-09 |doi=10.26616/NIOSHPUB2003136 |archive-date=February 10, 2020 |archive-url=https://web.archive.org/web/20200210042751/https://www.cdc.gov/niosh/docs/2003-136/pdfs/2003-136.pdf?id=10.26616%2FNIOSHPUB2003136 |url-status=live}} 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).{{Cite journal |last1=Godoy |first1=Charlotte |last2=Thomas |first2=Dominique |date=2020-07-02 |title=Influence of relative humidity on HEPA filters during and after loading with soot particles |journal=Aerosol Science and Technology |volume=54 |issue=7 |pages=790–801 |doi=10.1080/02786826.2020.1726278 |bibcode=2020AerST..54..790G |s2cid=214275203 |issn=0278-6826 |doi-access=free }}{{Cite journal |last1=Payet |first1=S. |last2=Boulaud |first2=D. |last3=Madelaine |first3=G. |last4=Renoux |first4=A. |date=1992-10-01 |title=Penetration and pressure drop of a HEPA filter during loading with submicron liquid particles |url=https://dx.doi.org/10.1016%2F0021-8502%2892%2990039-X |journal=Journal of Aerosol Science |language=en |volume=23 |issue=7 |pages=723–735 |doi=10.1016/0021-8502(92)90039-X |bibcode=1992JAerS..23..723P |issn=0021-8502 |access-date=2021-03-05 |archive-date=2021-05-16 |archive-url=https://web.archive.org/web/20210516175110/https://www.sciencedirect.com/science/article/abs/pii/002185029290039X?via%3Dihub |url-status=live}}{{Cite book |last1=Schentag |first1=Jerome J. |url=https://www.ncbi.nlm.nih.gov/books/NBK92445/ |title=SARS: CLEARING THE AIR |last2=Akers |first2=Charles |last3=Campagna |first3=Pamela |last4=Chirayath |first4=Paul |date=2004 |publisher=National Academies Press (US) |language=en |access-date=2021-03-04 |archive-date=2021-01-05 |archive-url=https://web.archive.org/web/20210105082920/https://www.ncbi.nlm.nih.gov/books/NBK92445/ |url-status=live}} Some [[microorganism]]s, for example, ''[[Aspergillus niger]]'', ''[[Penicillium citrinum]]'', ''[[Staphylococcus epidermidis]]'', and ''[[Bacillus subtilis]]'' are captured by HEPA filters with [[Photocatalysis|photocatalytic]] oxidation (PCO). A HEPA filter is also able to capture some viruses and bacteria which are ≤0.3 μm.{{Cite journal |last1=Chuaybamroong |first1=P. |last2=Chotigawin| first2=R. |last3=Supothina |first3=S. |last4=Sribenjalux |first4=P. |last5=Larpkiattaworn |first5=S. |last6=Wu |first6=C.-Y. |date=2010 |title=Efficacy of photocatalytic HEPA filter on microorganism removal |journal=Indoor Air |language=en |volume=20 |issue=3 |pages=246–254 |doi=10.1111/j.1600-0668.2010.00651.x |pmid=20573124 |issn=1600-0668|doi-access=free |bibcode=2010InAir..20..246C }} A HEPA filter is also able to capture floor dust which contains [[bacteroidia]], [[clostridia]], and [[bacilli]].{{Cite journal |last1=Guo |first1=Jianguo |last2=Xiong |first2=Yi |last3=Kang |first3=Taisheng |last4=Xiang |first4=Zhiguang |last5=Qin |first5=Chuan |date=2020-04-14 |title=Bacterial community analysis of floor dust and HEPA filters in air purifiers used in office rooms in ILAS, Beijing |url= |journal=Scientific Reports |language=en |volume=10 |issue=1 |pages=6417 |doi=10.1038/s41598-020-63543-1 |issn=2045-2322 |pmc=7156680 |pmid=32286482 |bibcode=2020NatSR..10.6417G}} 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,{{Cite web |url=http://hepa.com/about-us-overview |title=About HEPA |website=hepa.com |access-date=2019-06-05 |archive-date=2020-04-20 |archive-url=https://web.archive.org/web/20200420071752/http://hepa.com/about-us-overview |url-status=live}} homes, and vehicles. [9] => [10] => ==Mechanism== [11] => [[File:Filter collection mechanisms.svg|alt=Four diagram each showing the path of small particle as it approaches a large fiber according to each of the four mechanisms|thumb|The four primary filter collection mechanisms: [[diffusion]], interception, inertial impaction, and [[Electrostatics|electrostatic]] attraction (air flow direction from right to left)]] [12] => [[File:Filteration Collection Mechanisms-en.svg|thumb|400x400px|alt=|Classic Collection Efficiency Curve with Filter Collection Mechanisms]] [13] => HEPA filters are composed of a [[depth filter|mat of randomly arranged fibers]].{{Cite book |last1=Gupta |first1=Shakti Kumar |title=Modern Trends in Planning and Designing of Hospitals: Principles and Practice |last2=Kant |first2=Sunil |date=2007-12-01 |publisher=[[Jaypee Brothers]] |isbn=978-8180619120 |pages=199 |oclc=1027907136}} 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 [[fiber]]s. These fibers create a narrow convoluted pathway through which air passes. When the largest particles are passing through this pathway, the bundles of fibers behave like a kitchen sieve which physically blocks the particles from passing through. However, when smaller particles pass with the air, as the air twists and turns, the smaller particles cannot keep up with the motion of the air and thus they collide 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.{{Cite journal|last1=Christopherson|first1=David A.|last2=Yao|first2=William C.|last3=Lu|first3=Mingming|last4=Vijayakumar|first4=R.|last5=Sedaghat|first5=Ahmad R.|date=July 14, 2020|title=High-Efficiency Particulate Air Filters in the Era of COVID-19: Function and Efficacy|journal=Otolaryngology–Head and Neck Surgery|volume=163|issue=6|pages=1153–1155|doi=10.1177/0194599820941838|pmid=32662746|doi-access=free|s2cid=220518635}} Key factors affecting its functions are fiber diameter, filter thickness, and [[Face velocity is the measured air speed at an inlet or outlet of a heating ventilation and air conditioning (HVAC) system. ... Face velocity is measured in m/s and can be calculated as the volume flow rate (m3/s) divided by the face area (m2).#Face velocity|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 particulate matter. Unlike [[sieve]]s or [[Membrane technology|membrane filter]]s, 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: [14] => [15] => # Diffusion; particles below 0.3 μm are captured by [[diffusion]] in a HEPA filter. This mechanism is a result of the collision with [[gas]] [[molecule]]s by the smallest particles, especially those below 0.1 μm in diameter. The small particles are effectively blown or bounced around and collide with the filter media fibers. This behavior is similar to [[Brownian motion]] and raises the probability that a particle will be stopped by either interception or impaction; this mechanism becomes dominant at lower [[airflow]]. [16] => # Interception; particles following a line of flow in the air stream come within one [[radius]] of a fiber and adhere to it. Mid size particles are being captured by this process. [17] => # Impaction; larger particles are unable to avoid fibers by following the curving contours of the air stream and are forced to embed in one of them directly; this effect increases with diminishing fiber separation and higher air flow velocity. [18] => [19] => Diffusion predominates below the 0.1 μm diameter particle size, whilst impaction and interception predominate above 0.4 μm.{{cite web|last1=Woodford|first1=Chris|author1-link=Chris Woodford (author)|date=May 21, 2008|title=How do HEPA air filters work?|url=https://www.explainthatstuff.com/hepafilters.html|url-status=live|access-date=May 15, 2021|website=Explain That Stuff|archive-date=2020-04-20|archive-url=https://web.archive.org/web/20200420203811/https://www.explainthatstuff.com/hepafilters.html}} In between, near the most penetrating particle size (MPPS) 0.21 μm, both diffusion and interception are comparatively inefficient.{{Cite journal|last=da Roza|first=R. A.|date=December 1, 1982|title=Particle size for greatest penetration of HEPA filters—and their true efficiency.|url=https://www.osti.gov/servlets/purl/6241348-a5wL4J/|url-status=live|access-date=May 15, 2021|website=[[U.S. Department of Energy Office of Scientific and Technical Information]]|doi=10.2172/6241348|osti=6241348|doi-access=free|archive-date=May 16, 2021|archive-url=https://web.archive.org/web/20210516175118/https://www.osti.gov/biblio/6241348-a5wL4J/}} Because this is the weakest point in the filter's performance, the HEPA specifications use the retention of particles near this size (0.3 μm) to classify the filter. However it is possible for particles smaller than the MPPS to not have filtering efficiency greater than that of the MPPS. This is due to the fact that these particles can act as [[nucleation]] sites for mostly [[condensation]] and form particles near the MPPS. [20] => [21] => ===Gas filtration=== [22] => HEPA filters are designed to arrest very fine particles effectively, but they do not filter out gasses and [[odor]] molecules. Circumstances requiring filtration of [[volatile organic compound]]s, chemical vapors, or [[cigarette]], pet or [[flatulence]] odors call for the use of an [[activated carbon]] (charcoal) or other type of filter instead of or in addition to a HEPA filter.{{cite journal|last1=Khan|first1=Faisal I|last2=Ghoshal|first2=Aloke Kr.|date=November 2000|title=Removal of Volatile Organic Compounds from polluted air|url=http://beta.chem.uw.edu.pl/people/AMyslinski/nowy/zarzadzanie_01/literature_HWW/02.pdf|journal=[[Journal of Loss Prevention in the Process Industries]]|publisher=[[Elsevier]]|volume=13|issue=6|pages=527–545|doi=10.1016/S0950-4230(00)00007-3|issn=0950-4230|access-date=May 15, 2021|archive-date=February 15, 2017|archive-url=https://web.archive.org/web/20170215081514/http://www.chem.uw.edu.pl/people/AMyslinski/nowy/zarzadzanie_01/literature_HWW/02.pdf|url-status=live}} Carbon cloth filters, claimed to be many times more efficient than the granular activated carbon form at [[adsorption]] of gaseous [[pollutant]]s, are known as high efficiency gas adsorption filters (HEGA) and were originally developed by the British Armed Forces as a defense against [[chemical warfare]].{{cite journal|last=Glover|first=Norman J.|date=May 2002|title=Countering chemical and biological terrorism|journal=Civil Engineering|location=New York City|publisher=[[American Society of Civil Engineers]]|volume=72|issue=5|pages=62–67|issn=0885-7024|oclc=926218714|id={{ProQuest|228557557}}}}{{cite web|last=Jonathan|date=August 19, 2016|title=Air Purifier Acronyms - Stripping Out The Tech Jargon|url=https://www.airenhancing.com/air-purifiers-acronyms-explained/#HEGA_8211_High-Efficiency_Gas_Assistance_or_High-Efficiency_Gas_Absorption_or_High-Efficiency_Gas_Adsorption|url-status=live|access-date=May 16, 2021|website=Air Enhancing|archive-date=2020-04-20 |archive-url=https://web.archive.org/web/20200420073627/https://www.airenhancing.com/air-purifiers-acronyms-explained/#HEGA_8211_High-Efficiency_Gas_Assistance_or_High-Efficiency_Gas_Absorption_or_High-Efficiency_Gas_Adsorption}} [23] => [24] => ===Pre-filter and HEPA filter=== [25] => A HEPA bag filter can be used in conjunction with a pre-filter (usually carbon-activated) to extend the usage life of the more expensive HEPA filter.{{Cite web|title=Air Purifier Pre-Filter Replacement: The Prefilter Experiments|url=http://www.air-purifier-power.com/replacementprefilter.html|url-status=live|access-date=May 16, 2021|website=Air-Purifier-Power|archive-date=2020-04-20 |archive-url=https://web.archive.org/web/20200420075902/http://www.air-purifier-power.com/replacementprefilter.html}} 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. The second stage high-quality HEPA filter removes the finer particles that escape from the pre-filter. This is common in [[Air handler|air handling units]].{{cn|date=March 2024}} [26] => [27] => ==Specifications== [28] => [[File:HEPA filter unit.jpg|thumb|A portable HEPA filtration unit used to clean air after a fire, or during manufacturing processes]] [29] => 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.{{Cite web|last=Perryman|first=Oliver|date=December 3, 2020|title=Do HEPA filters or air purifiers remove carbon monoxide?|url=https://dehumidifiercritic.com/do-hepa-filters-remove-carbon-monoxide/|url-status=live|access-date=May 16, 2021|website=Dehumidifier Critic|archive-date=May 16, 2021|archive-url=https://web.archive.org/web/20210516175103/https://dehumidifiercritic.com/do-hepa-filters-remove-carbon-monoxide/}} The filter's minimal resistance to airflow, or [[pressure drop]], is usually specified around {{convert|300|Pa}} at its nominal [[volumetric flow rate]]. [30] => [31] => The specification used in the [[European Union]]: European Standard EN 1822-1:2019, from which ISO 29463 is derived,{{cite web|date=October 15, 2011|title=INTERNATIONAL ISO STANDARD 29463-1—High-efficiency filters and filter media for removing particles in air|url=https://www.sis.se/api/document/preview/913826/|url-status=live|access-date=May 16, 2021|publisher=[[International Organization for Standardization]]|archive-date=March 8, 2021|archive-url=https://web.archive.org/web/20210308162337/https://www.sis.se/api/document/preview/913826/}} defines several classes of filters by their retention at the given most penetrating particle size (MPPS): ''Efficient Particulate Air filters'' (EPA), ''High Efficiency Particulate Air filters'' (HEPA), and ''[[Ultra-low particulate air|Ultra Low Particulate Air filters]]'' (ULPA). The averaged efficiency of the filter is called "overall", and the efficiency at a specific point is called "local": [32] => [33] => {| class="wikitable" [34] => ! Efficiency !! EN 1822 !! ISO 29463 !! Retention (averaged) !! Retention (spot) [35] => |- [36] => | rowspan="3" align="center" | EPA [37] => | align="center" | E10 || align="center" | — || ≥ 85% || align="center" | — [38] => |- [39] => | align="center" | E11 || align="center" | ISO 15 E
ISO 20 E || ≥ 95%
≥ 99% || align="center" | — [40] => |- [41] => | align="center" | E12 || align="center" | ISO 25 E
ISO 30 E || ≥ 99.5%
≥ 99.9% || align="center" | — [42] => |- [43] => | rowspan="2" align="center" | '''HEPA''' [44] => | align="center" | H13 || align="center" | ISO 35 H
ISO 40 H || ≥ 99.95%
≥ 99.99% || ≥ 99.75%
≥ 99.95% [45] => |- [46] => | align="center" | H14 || align="center" | ISO 45 H
ISO 50 U || ≥ 99.995%
≥ 99.999% || ≥ 99.975%
≥ 99.995% [47] => |- [48] => | rowspan="3" align="center" | ULPA [49] => | align="center" | U15 || align="center" | ISO 55 U
ISO 60 U || ≥ 99.9995%
≥ 99.9999% || ≥ 99.9975%
≥ 99.9995% [50] => |- [51] => | align="center" | U16 || align="center" | ISO 65 U
ISO 70 U || ≥ 99.99995%
≥ 99.99999% || ≥ 99.99975%
≥ 99.9999% [52] => |- [53] => | align="center" | U17 || align="center" | ISO 75 U || ≥ 99.999995% || ≥ 99.9999% [54] => |} [55] => See also the different classes for [[Air filter#Filter classes|air filters]] for comparison. [56] => [57] => Today, a HEPA filter rating is applicable to any highly efficient air filter that can attain the same filter efficiency performance standards as a minimum and is equivalent to the more recent [[National Institute for Occupational Safety and Health]] P100 rating for respirator filters. The United States Department of Energy (DOE) has specific requirements for HEPA filters in DOE-regulated applications.{{cn|date=March 2024}} [58] => [59] => === Marketing === [60] => Some companies use a marketing term known as "True HEPA" to give consumers assurance that their air filters meet the HEPA standard, although this term has no legal or scientific meaning.{{cite web|last=Bretag|first=Scott|date=March 18, 2020|title=Air Conditioners, HEPA Filters, And Airborne Allergens|url=https://www.pulseelectrical.com.au/air-conditioners-hepa-filters-and-airborne-allergens/|url-status=live|access-date=May 16, 2021|work=Pulse Electrical|archive-date=March 10, 2021|archive-url=https://web.archive.org/web/20210310161225/https://www.pulseelectrical.com.au/air-conditioners-hepa-filters-and-airborne-allergens/}} Products that are marketed to be "HEPA-type," "HEPA-like," "HEPA-style" or "99% HEPA" do not satisfy the HEPA standard and may not have been tested in independent laboratories. Although such filters may come reasonably close to HEPA standards, others fall significantly short.{{Cite web|title=HEPA-Type Filter: The Great Pretender|url=http://www.air-purifier-power.com/hepatypefilter.html|url-status=live|access-date=May 16, 2021|website=Air-Purifier-Power|archive-date=February 25, 2021|archive-url=https://web.archive.org/web/20210225051425/http://www.air-purifier-power.com/hepatypefilter.html}} [61] => [62] => == Efficacy and safety == [63] => In general terms (and allowing for some variation depending on factors such as the air-flow rate, the physical properties of the particles being filtered, as well as engineering details of the entire filtration-system design and not just the filter-media properties), HEPA filters experience the most difficulty in capturing particles in the size range of 0.15 to 0.2 µm.{{Cite journal |last1=Christopherson |first1=David A. |last2=Yao |first2=William C. |last3=Lu |first3=Mingming |last4=Vijayakumar |first4=R. |last5=Sedaghat |first5=Ahmad R. |date=2020-07-14 |title=High-Efficiency Particulate Air Filters in the Era of COVID-19: Function and Efficacy |journal=Otolaryngology–Head and Neck Surgery |volume=163 |issue=6 |pages=1153–1155 |doi=10.1177/0194599820941838 |issn=0194-5998 |pmid=32662746 |doi-access=free |s2cid=220518635}} HEPA filtration works by mechanical means, unlike ionic and [[ozone]] treatment technologies, which use negative [[ion]]s and ozone gas respectively. So, the likelihood of potential triggering of pulmonary side-effects such as [[asthma]]{{Cite web |last=Dunkin |first=Mary Anne |date=2010-04-30 |others=Reviewed by Nayana Ambardekar |title=HEPA Filter Benefits for Allergy Relief |url=https://www.webmd.com/allergies/hepa-filters-for-allergies|url-status=live |access-date=2021-05-16 |website=[[WebMD]] |archive-date=2021-03-29|archive-url=https://web.archive.org/web/20210329204924/https://www.webmd.com/allergies/hepa-filters-for-allergies}} and [[Allergy|allergies]] is much lower with HEPA purifiers.{{Cite web |last= |first= |date= |title=How do HEPA Filters Help in Cleaning Indoor Air - Complete Guide |url=http://www.pureairhub.com/guide-hepa-air-purifiers/ |url-status=dead |archive-url=https://web.archive.org/web/20191020213512/http://www.pureairhub.com/guide-hepa-air-purifiers/ |archive-date=2019-10-20 |access-date=2021-05-16 |website=Pure Air Hu}} [64] => [65] => To ensure that a HEPA filter is working efficiently, the filters should be inspected and changed at least every six months in commercial settings. In residential settings, and depending on the general ambient air quality, these filters can be changed every two to three years. 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. Additionally, depending on the gasketing materials chosen in the design of the system, a clogged HEPA filter can result in extensive bypassing of airflow around the filter.{{Cite web|last=Kelly|first=Tammy|date=March 14, 2018|title=How Often Should A HEPA Filter Be Changed|url=https://www.janitized.com/how-often-should-a-hepa-filter-be-changed/|url-status=live|access-date=May 16, 2021|website=Janitized|archive-date=March 8, 2021|archive-url=https://web.archive.org/web/20210308145354/https://www.janitized.com/how-often-should-a-hepa-filter-be-changed/}} [66] => [67] => == Applications == [68] => [[File:Portable HEPA filter.jpg|thumb|right|180px|Hospital staff modelling a [[powered, air-purifying respirator]] (PAPR) fitted with a HEPA filter, used to protect from airborne or aerosolised pathogens such as [[tuberculosis]]]] [69] => [70] => === Biomedical === [71] => 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.{{Citation needed|date=June 2019}} [72] => [73] => Some of the best-rated HEPA units have an efficiency rating of 99.995%, which assures a very high level of protection against [[Airborne transmission|airborne disease transmission]].{{cn|date=March 2024}} [74] => [75] => ==== COVID-19 ==== [76] => [[Severe acute respiratory syndrome coronavirus 2|SARS‑CoV‑2]] is approximately 0.125 µm. Airborne [[Drop (liquid)|droplets]] of SARS-CoV-2 could be captured by HEPA filters, even if they are on the floor.{{clarify|date=May 2021}}{{Cite web|last1=Elias|first1=Blake|last2=Bar-Yam|first2=Yaneer|date=March 9, 2020|title=Could Air Filtration Reduce COVID-19 Severity and Spread?|url=https://necsi.edu/could-air-filtration-reduce-covid19-severity-and-spread|url-status=live|access-date=May 16, 2021|website=[[New England Complex Systems Institute]]|archive-date=March 21, 2021|archive-url=https://web.archive.org/web/20210321111716/https://necsi.edu/could-air-filtration-reduce-covid19-severity-and-spread}}{{Cite web|last=Heffernan|first=Tim|date=November 18, 2020|title=Can HEPA Air Purifiers Capture the Coronavirus?|url=https://www.nytimes.com/wirecutter/blog/can-hepa-air-purifiers-capture-coronavirus/|url-status=live|access-date=May 16, 2021|website=[[Wirecutter (website)|Wirecutter]]|archive-date=May 11, 2021|archive-url=https://web.archive.org/web/20210511185635/https://www.nytimes.com/wirecutter/blog/can-hepa-air-purifiers-capture-coronavirus/}} [77] => [78] => === Vacuum cleaners === [79] => [[File:PHILIPS HEPA H10 air filter for vacuum cleaner.JPG|thumb|left|HEPA original filter for Philips FC87xx-series vacuum cleaners]] [80] => Many [[vacuum cleaner]]s also use HEPA filters as part of their filtration systems. This is beneficial for asthma and allergy sufferers, because the HEPA filter traps the fine particles (such as pollen and [[house dust mite]] [[feces]]) which trigger allergy and asthma symptoms. For a HEPA filter in a vacuum cleaner to be effective, the vacuum cleaner must be designed so that ''all'' the air drawn into the machine is expelled through the filter, with none of the air leaking past it. This is often referred to as "Sealed HEPA" or sometimes the more vague "True HEPA". Vacuum cleaners simply labeled "HEPA" may have a HEPA filter, but not all air necessarily passes through it. Finally, vacuum cleaner filters marketed as "HEPA-like" will typically use a filter of a ''similar construction'' to HEPA, but without the filtering efficiency. Because of the extra density of a true HEPA filter, HEPA vacuum cleaners require more powerful motors to provide adequate cleaning power.{{cn|date=March 2024}} [81] => [82] => Some newer models claim to be better than the earlier ones with the inclusion of "washable" filters. Generally, washable true HEPA filters are expensive. A high-quality HEPA filter can trap 99.97% of dust particles that are 0.3 microns in diameter. For comparison's sake, a human hair is about 50 to 150 microns in diameter. So, a true HEPA filter is effectively trapping particles several hundred times smaller than the width of a human hair.{{Cite web|last=Anand|first=Mohit|date=November 23, 2020|title=Understanding the Home Air Purifier Technology in Use Today|url=https://honeywellconnection.com/blog/understanding-the-home-air-purifier-technology-in-use-today/|url-status=live|access-date=May 16, 2021|website=Honeywell Connection|archive-date=May 16, 2021|archive-url=https://web.archive.org/web/20210516175132/https://honeywellconnection.com/blog/understanding-the-home-air-purifier-technology-in-use-today/}} Some manufacturers claim filter standards such as "HEPA 4," without explaining the meaning behind them.{{cn|date=February 2023}} This refers to their [[Minimum efficiency reporting value|Minimum Efficiency Reporting Value]] (MERV) rating.{{cn|date=February 2023}} These ratings are used to rate the ability of an air cleaner filter to remove dust from the air as it passes through the filter. MERV is a standard used to measure the overall efficiency of a filter. The MERV scale ranges from 1 to 16, and measures a filter's ability to remove particles from 10 to 0.3 micrometer in size. Filters with higher ratings not only remove more particles from the air, but they also remove smaller particles. [83] => [84] => ===Heating, ventilation, and air conditioning=== [85] => [[File:Display VSON WP6910 (air detector) - pm2,5 at Verona (Borgo Milano) Italy - (particulate pollution, polveri sottili) - 2020 01 30 (hour 22-37) - OUTdoor and INdoor (HEPA H13 filter) - first publication commons.wikimedia.org.webm|thumb|HEPA filter effect inside home [[Heating, ventilation, and air conditioning|HVAC]] system: without (OUTdoor) and with filter (INdoor)]] [86] => [[Heating, ventilation, and air conditioning]] (HVAC){{Cite dictionary|title=Hvac|publisher=[[Merriam-Webster]]|url=https://www.merriam-webster.com/dictionary/HVAC|access-date=May 16, 2021|date=|archive-date=January 15, 2021|archive-url=https://web.archive.org/web/20210115194334/https://www.merriam-webster.com/dictionary/HVAC|url-status=live}} is technology that uses air filters, such as HEPA filters, to remove pollutants from the air either indoors or in vehicles. Pollutants include smoke, viruses, [[powder]]s, etc., and can originate either outside or inside. HVAC is used to provide environmental comfort and in [[Pollution|polluted]] cities to maintain health.{{citation needed|date=February 2021}} [87] => [88] => ===Vehicles=== [89] => [90] => ====Airlines==== [91] => Modern airliners use HEPA filters to reduce the spread of airborne [[pathogen]]s in recirculated air. Critics have expressed concern about the effectiveness and state of repair of air filtering systems, since they think that much of the air in an airplane cabin is recirculated. Almost all of the air in a [[Pressurization|pressurized]] aircraft is, in fact, brought in from the outside, circulated through the cabin and then exhausted through outflow valves in the rear of the aircraft.{{Cite web|last=Smith|first=Patrick|date=July 22, 2012|title=The truth about cabin air|url=https://askthepilot.com/questionanswers/cabin-air-quality/|url-status=live|access-date=May 16, 2021|website=AskThePilot.com|archive-date=May 6, 2021|archive-url=https://web.archive.org/web/20210506161935/http://askthepilot.com/questionanswers/cabin-air-quality/}} About 40 percent of the cabin's air goes through a HEPA filter and the other 60 percent comes from outside the plane. Certified air filters block and capture 99.97 percent of airborne particles.{{Cite magazine|last=Read|first=Johanna|date=August 28, 2020|title=How clean is the air on planes?|url=https://www.nationalgeographic.com/travel/article/how-clean-is-the-air-on-your-airplane-coronavirus-cvd|magazine=[[National Geographic]]|publisher=[[National Geographic Partners]]|access-date=May 16, 2021|archive-date=May 6, 2021|archive-url=https://web.archive.org/web/20210506132052/https://www.nationalgeographic.com/travel/article/how-clean-is-the-air-on-your-airplane-coronavirus-cvd|url-status=dead}} [92] => [93] => ====Motor vehicles==== [94] => In 2016, it was announced that the [[Tesla Model X]] would have the world's first HEPA-grade filter in a Tesla car.{{cite web |date=2016-05-02 |title=Putting the Tesla HEPA Filter and Bioweapon Defense Mode to the Test |url=https://www.tesla.com/blog/putting-tesla-hepa-filter-and-bioweapon-defense-mode-to-the-test |url-status=live |access-date=2021-05-16 |website=[[Tesla, Inc.]] |archive-date=2021-04-27 |archive-url=https://web.archive.org/web/20210427150211/https://www.tesla.com/blog/putting-tesla-hepa-filter-and-bioweapon-defense-mode-to-the-test}} Following the release of the Model X, Tesla has updated the [[Tesla Model S|Model S]] to also have an optional HEPA air filter.{{Cite news |last=Völcker |first=John |date=2016-04-12 |title=2016 Tesla Model S gets styling update, 48-amp charger, new interior options, $1,500 price increase (updated) |work=[[Green Car Reports]] |url=https://www.greencarreports.com/news/1103380_2016-tesla-model-s-gets-styling-update-48-amp-charger-new-interior-options |access-date=2021-05-16 |archive-date=2021-02-24 |archive-url=https://web.archive.org/web/20210224154947/https://www.greencarreports.com/news/1103380_2016-tesla-model-s-gets-styling-update-48-amp-charger-new-interior-options |url-status=live}} [95] => [96] => ==History== [97] => [98] => The idea behind the development of the HEPA filter was born from [[gas mask]]s 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. They needed another solution for operational headquarters, where individual gas masks were impractical. 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. It was referred to as an "absolute" air filter and laid the groundwork for further research to come in developing the HEPA filter.{{cite journal|last1=First|first1=Melvin W.|date=March 1, 1998|title=HEPA Filters|url=https://www.liebertpub.com/doi/pdf/10.1177/109135059800300111|journal=[[Journal of the American Biological Safety Association]]|publisher=[[American Biological Safety Association]]|volume=3|issue=1|pages=33–42|doi=10.1177/109135059800300111|issn=1091-3505|s2cid=207941359|access-date=May 16, 2021|archive-date=May 16, 2021|archive-url=https://web.archive.org/web/20210516175101/https://www.liebertpub.com/doi/pdf/10.1177/109135059800300111|url-status=live}} [99] => [100] => The next phase of the HEPA filter was designed in the 1940s and was used in the [[Manhattan Project]] to prevent the spread of airborne [[Radioactive decay|radioactive]] contaminants.{{Cite book|last=|first=|url=https://books.google.com/books?id=XtXJzogLCecC&pg=PA13|title=Green Health: An A-to-Z Guide|date=2011|publisher=[[SAGE Publishing]]|isbn=9781412996884|editor-last=Ogunseitan|editor-first=Oladele|location=Los Angeles|pages=13|oclc=793012578|editor-last2=Robbins|editor-first2=Paul|access-date=2016-12-18|archive-date=2021-05-17|archive-url=https://web.archive.org/web/20210517182333/https://books.google.com/books?id=XtXJzogLCecC&pg=PA13|url-status=live}} The US Army Chemical Corps and National Defense Research Committee needed to develop a filter suitable for removing radioactive materials from the air. The Army Chemical Corps asked Nobel Laureate [[Irving Langmuir]] to recommend filter test methods and other general recommendations for creating the material to filter out these radioactive particles. He identified 0.3 micron size particles to be the "most penetrating size"—the most difficult and concerning.{{cite web|date=November 21, 2019|title=The History of HEPA Filters|url=https://www.apcfilters.com/the-history-of-hepa-filters/|url-status=live|access-date=May 16, 2021|website=APC Filters|archive-date=March 26, 2021|archive-url=https://web.archive.org/web/20210326084208/https://www.apcfilters.com/the-history-of-hepa-filters/}} [101] => [102] => It was commercialized in the 1950s, and the original term became a registered trademark and later a generic trademark for highly efficient filters.{{Cite book|url=https://books.google.com/books?id=QSNfCrpcSCAC&q=HEPA+filter+registered+trademark&pg=PA128|title=The Vacuum Cleaner: A History|last=Gantz|first=Carroll|date=2012-09-21|publisher=McFarland|isbn=9780786493210|page=128|language=en|access-date=2020-11-11|archive-date=2021-05-16|archive-url=https://web.archive.org/web/20210516175103/https://books.google.com/books?id=QSNfCrpcSCAC&q=HEPA+filter+registered+trademark&pg=PA128|url-status=live}} [103] => [104] => Over the decades filters have evolved to satisfy the higher and higher demands for air quality in various high technology industries, such as aerospace, pharmaceutical industry, hospitals, health care, nuclear fuels, nuclear power, and [[integrated circuit]] fabrication.{{cn|date=March 2024}} [105] => [106] => ==See also== [107] => * {{annotated link|Air purifier}} [108] => * {{annotated link|Clean air delivery rate}} [109] => * {{annotated link|Cleanroom}} [110] => * {{annotated link|Electrostatic precipitator}} – trap particles with high voltage [111] => * {{annotated link|Hypoallergenic vacuum cleaner}} – vacuum cleaner with high efficiency air filter [112] => * {{annotated link|Minimum efficiency reporting value}} (MERV) [113] => * {{annotated link|Respirator}} [114] => * {{annotated link|ULPA}} – Removes 99.999% of dust, pollen, mold, bacteria, and particles larger than 120 nm (0.12 μm) [115] => * {{annotated link|Ultraviolet germicidal irradiation}} [116] => * [[Corsi–Rosenthal Box]] [117] => [118] => ==References== [119] => {{reflist|30em}} [120] => [121] => ==Further reading== [122] => * [https://web.archive.org/web/20170829125133/http://www.tsi.com/uploadedFiles/Product_Information/Literature/Application_Notes/ITI-041.pdf TSI Application Note ITI-041: Mechanisms of Filtration for High Efficiency Fibrous Filters] [123] => [124] => ==External links== [125] => {{commons category|High-Efficiency Particulate Arresting}} [126] => [127] => {{HVAC}} [128] => [129] => {{DEFAULTSORT:Hepa}} [130] => [[Category:Building biology]] [131] => [[Category:Air filters]] [132] => [[Category:Cleanroom technology]] [133] => [[Category:Gas technologies]] [134] => [[Category:Indoor air pollution]] [] => )
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HEPA

High Efficiency Particulate Air (HEPA) is a type of air filter that is capable of filtering out a wide range of particle sizes, including small particles and airborne contaminants. HEPA filters are commonly used in industries such as healthcare, aerospace, and manufacturing to maintain clean air quality and prevent the spread of pollutants and pathogens.

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HEPA filters are commonly used in industries such as healthcare, aerospace, and manufacturing to maintain clean air quality and prevent the spread of pollutants and pathogens. The term HEPA refers to the standard set by the United States Department of Energy. According to this standard, a HEPA filter must be able to capture at least 99. 97% of particles that are 0. 3 microns in diameter or larger. However, HEPA filters can also trap smaller and larger particles with varying levels of efficiency. HEPA filters work by using multiple layers of fine fibers to capture particles as they pass through the filter. These filters are designed to be highly efficient and are capable of removing particles such as dust, pollen, pet dander, bacteria, viruses, and even some chemicals from the air. HEPA filters can be found in various applications, including air purifiers, vacuum cleaners, HVAC systems, cleanrooms, and medical devices. These filters are essential in environments that require high levels of cleanliness and air quality, such as hospitals, laboratories, and spaces for sensitive manufacturing processes. While HEPA filters are highly effective in removing airborne particles, it is important to note that they do not eliminate gases, odors, or volatile organic compounds. Additional filtration methods, such as activated carbon or zeolite filters, may be needed to address these specific pollutants. Overall, HEPA filters play a vital role in maintaining clean and healthy air in various settings. They are widely recognized and utilized for their ability to significantly reduce the presence of airborne contaminants and improve indoor air quality.

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