HEPA air filters are classified according to their retention at the given MPPS (most penetrating particle size):

1. H13 with a total retention of >99.95%
2. H14 with an overall retention of >99.995%
3. U15 with overall retention of >99.9995%
4. U16 with overall retention of >99.99995%
5. U17 with overall retention of >99.999995%

The location or primary function of different hospital areas and departments determine the type of HEPA filters that will be used.

Camfil Airepure is national air filtration company that provides high-performing, accredited and integrated air filtration solutions, advice in the specification and design stage, and offer compliant HEPA systems with purification levels:

1. 95% air purity
2. H13-rated HEPA filters (99.97% at 0.3 micrometres)
3. H14-rated HEPA filters (99.995 at 0.3 microns)
4. U15-rated HEPA filters (99.9995% at 0.3 microns)
5. ULPA filters from 99.999% at 0.12 microns

With many HVAC air filters and grades available in the market today, there can be a tendency to opt for cheap products or undersized systems in the building and renovation stages. However, this is not a wise option for the high-risk environment of a hospital or clinical setting. Substandard HVAC air filters often lead to expensive consequences, including high, long term operation costs and non-compliant performance levels. Sub-par filters can compromise the air integrity in hospital settings that can even lead to "life and death situations".

The Gel Seal Ducted Terminal CS HEPA Module/ULPA Modules from Camfil Airepure are one of the most commonly used types of HEPA air filter module in hospital settings. They ensure optimum leak-free protection, essential for hospital areas where a cleanroom like environment is required.

Design Advice for HEPA Filters

Correct sizing and design of HEPA filters are important factors for the filters to handle the right airflow rates and to meet the required air changes per hour specified by AS 1668.2:2012.

The requirements for face velocity, physical filter and housing size of HEPA filters is different when compared to filters used in general HVAC applications. Pleated HEPA filter media have a massive surface area - with every 1m2 of face area containing roughly 20m2 of media surface area. As such, the space required for HEPA filters and housings in hospital applications are much larger than standard HVAC pre filtration units.

The correct sizing is needed for a HEPA filter to function effectively at the right face velocity. The required face velocity then determines the physical size of the filter media that will be used. This factor is crucial in intercepting the elusive 0.3-micron airborne particles.

Therefore, allocating adequate space for the HEPA filter and housing construction should be done in the design phase. Otherwise, it becomes an expensive issue for architects and builders if adequate space is not provided for HEPA filters / housings and walls need to be relocated or areas need to be redesigned.

Test ports and access hatches should be included in the design and building phases, to accommodate verification of HEPA performance during commissioning and for its annual HEPA integrity testing.

Correct Sequencing of HEPA Filters

The nanoscale, fibrous material of HEPA filters forms an accordion-like shape that creates a dense mat. It captures and restrains contaminants through air filtration mechanisms as the air flows through the filter.

HEPA filters are designed to capture the elusive 0.3 micron particles, so it is important that pre filters are installed to protect the HEPA from premature clogging by larger particles and allow it to fulfil its intended purpose. As a visual comparison to understand the size of large standard particles - a typical vacuum cleaner bag is rated F5, which fills quite quickly with dust and particulates (1.0 micron or larger).

Proper HEPA sequencing appears as follows:

1. Pre-filter (G4 pleated filter) - to seize larger particles, such as dust, lint, etc.

2. Intermediate filter (F8 multi-pocket bag filter) - to intercept small to medium sized particles, such as some bacteria, mould, etc.

3. Final filter (HEPA filter) - to capture the fine, elusive particles at 0.3 microns, such as viruses.

Without the sacrificial filters, HEPA filters will not be able to perform its function of intercepting sub 1 micron airborne particles. Also, it will get clogged immediately, shortening its service life to days or weeks instead of three to five years.

Maintenance Procedure for HEPA Filters

For maximum protection and performance, HEPA filters are re-tested after installation. HEPA filters in general, are checked and tested annually by certified, independent NATA testing authority. Hence, test ports and access hatches should also be included in the design and building of HVAC systems. This measure provides easy access for verification of HEPA air filter performance during commissioning and routine annual check-ups.

Routine maintenance and regular check-ups of HVAC components and HEPA filters enable early detection of faulty air control systems. It also helps prolong the service life of HEPA filters and maximises its functionality.

Camfil Airepure's Air Purification Solutions

Camfil Airepure aims to provide its clients with a wide variety of infiltration air products that meets Australian Standards and complies with major accreditation bodies. For hospitals, these include ACHS, DHS VIC Guidelines (and equivalent for QLD, WA and NSW), ISO/IEC 17025:2005 Requirements, AS 1668.2, AS/NZS 2243.3:2010 and AS/NZS 2243.8:2014.

Camfil Airepure offers a broad spectrum of high-quality HEPA air filters for HVAC systems suitable for hospital applications.

Contact Camfil Airepure or visit their website at www.airepure.com.au for more information on HVAC air filters and HEPA air filters today. In New Zealand, contact www.airepure.co.nz.