Air filters for hospitals

This is an excerpt from the published technical article entitled “Air Filtration and Its Practical Application in the Hospital Environment,” written by Kristian Kirwin (B.ENG Mechanical) and Shannon Roger (B.Ed) for Airepure Australia (a Camfil Group company), and published in Healthcare Facilities Volume 41, No 3, September 2018.

For detailed information regarding filtration mechanisms, filtration performance, filter efficiency/ratings/standards, hospital filtration requirements, filter maintenance and testing please refer to https://www.airepure.com.au/air-filters-for-hospitals-and-healthcare-facilities/.

Common air filters in hospital environments

Particulate pre-filters

Metal framed flat-panel filter (20–25 mm deep G4)

Flat-panel filters are the most basic type of air filter, whereby a panel of flat surface air-filtration media is enclosed within a metal frame. Commonly used in hospital applications as a pre-filter for terminal-mounted exhaust HEPA housings where there is limited space for pre-filtration (such as isolation room ensuite areas), they serve to protect the HEPA filter and prevent large particles from entering the system.

Cardboard pleat filter (100 mm deep G4–F7)

Cardboard disposable filters are constructed from pleated air-filtration media bonded to a cardboard frame (typically moisture-resistant beverage-grade cardboard). Diagonal cardboard supports across the filter face are included for rigidity and durability. Typically used in hospital applications as a pre-filter for inline containment exhaust filtration systems where there is sufficient space for higher-grade, high-capacity pre-filters, which protect high-capacity HEPA filters.

Glass-fibre pleated panel filter (100 mm deep F8–F9)

Glass-fibre pleated panel filters are constructed from fine, paper-thin micro glass-fibre media, formed into packs of closely spaced pleats and bonded to a cardboard frame (typically moisture-resistant beverage-grade cardboard). Suited to variable air volume systems or turbulent flow conditions, they typically provide high pressures for a given airflow. Commonly used in hospital applications as a final filter within FCUs, where space is a premium due to size and media limitations.

Multi pocket bag filter (380 mm deep F8/F9)

Multi pocket bag filters are constructed from a six/eight pocket (full size) or three/four pocket (half size) deep bed bags, constructed from electrostatically charged filter media bonded to a metal header frame, and generally have excellent contaminant holding capacities and reasonable pressure resistance. They are bulky, and take a significant duct length to house them. Commonly used in hospital AHUs.

Rigid/hybrid media filter (100 mm deep F8/F9)

Rigid, formed hybrid media filters are constructed from self-supporting, layered filter media that uniquely incorporates pre filtration, medium and fine filtration layers, bonded to a metal frame. These filters have excellent contaminant holding capacities and reasonable pressure resistance — particularly for high-efficiency grades. Within hospital applications, these filters are selected to replace glass-fibre pleated panel filters as a final filter within restricted space locations (bed bays or location-specific FCUs).

HEPA (high efficiency particulate air) filters

Constructed from finely pleated air filtration media with high surface area properties for high-efficiency filtration, HEPA filters are typically manufactured from the highest quality of materials under strict quality control conditions, and are factory certified to ensure filtration performance to EN 1822:2009 standards.

Specialty separator-style and dimple-pleat/separator-less-style HEPA filters are factory tested to meet the requirements of IEST RP-CC001.3 for Type A, B, C, D, E or F filters (industrial grade, nuclear grade, laminar flow grade, bio/hazard grade, VLSI, ULPA or pharmaceutical grade); and can be certified to UL586 or UL900 standards.

Mini-pleat HEPA (H14)

Mini-pleat HEPA filters are constructed from fine, paper-thin, micro glass-fibre media, formed into packs of closely spaced pleats that are separated by a continuous thermoplastic cord and bonded to a metal frame. Typically used within every supply or exhaust HEPA housing within hospital applications.

Separator-style HEPA (H14/U15 or specialty)

Separator-style HEPA filters are constructed from fine, paper-thin, micro glass-fibre media, formed into packs of closely spaced pleats that are separated by corrugated aluminium separators and bonded to a metal frame. Within hospital applications, these filters are used within i-line HEPA housings, AHU-mounted HEPA housings or high-efficiency exhaust BIBO (bag/in-bag/out) airborne containment systems.

V-form mini-pleat HEPA (F9–H10, 95% DOP and H14)

V-form mini-pleat HEPA filters are constructed from fine, paper-thin, micro glass-fibre media, formed into mini-pleat media packs that are arranged into a V-bed configuration and bonded to a box style metal frame that provides strength and durability for high-velocity applications. F9–H10 and 95% DOP-rated V-form mini-pleat HEPA filters are typically used as a final filter within critical care areas, or as a final pre-filter for HEPA-filtered areas. H14-rated V-form mini-pleat HEPA filters are typically used in high-volume duct-mounted HEPA applications (within a supply AHU or exhaust plenum).

Dimple pleat, separator-less HEPA (H14/U15 — specialty)

Dimple pleat, separator-less HEPA filters are constructed from a self-supporting and self-separating layered filter media bonded to a metal or wooden frame. These filters are typically used in high-efficiency exhaust BIBO (bag/in-bag/out) airborne containment systems or nuclear medicine/cyclotron areas, due to their relatively low pressure and high-volume characteristics. Subject to the application, the filter media packs and frames can be incinerated if required.

Gas-phase/carbon filters

Activated carbon filters

Activated carbon filters, which use activated carbon filter media are typically available in flat-panel style, cardboard pleat style and V-form mini-pleat style. Some filter types use hybrid particulate/activated carbon media for combined particle and gas filtration. Commonly used to remove VOCs and other inorganic gases that are generated from indoor and outdoor sources to improve IAQ. They are particularly useful when outdoor air intakes are near roads, loading docks or helicopter pads.

High-mass carbon/chemical-infused media filters

High-mass carbon or chemical-infused media filtration is available through carbon/chemical media pellets installed into housings/canisters. Typically used where bulk or high-percentage gas/odour removal is required, these filters are commonly used within animal laboratory areas and helipad areas to remove odours and jet/diesel fumes.

HEGA (high-efficiency gas adsorption) filters

HEGA filters are manufactured from the highest quality of materials under strict quality control conditions as custom targeted high-mass carbon media installed into V-bank-style housings, and are factory tested to meet the requirements of IES RP-CC-008-84, “Recommended Practice for Gas Phase Adsorber Cells”. HEGA filters are commonly used in conjunction with HEPA filters in high-efficiency exhaust BIBO (bag/in-bag/out) airborne containment systems or radioactive dispensing/cyclotron areas. They are typically type tested and media is batch tested. Where required, field testing to confirm performance can be undertaken. The primary thing to consider is the handling of these filters — they are bulky and extremely heavy due to their construction and carbon mass.