09 April 2020

In-Line HEPA Filter Servicing for Hospitals

Containment housing filter

In-Line HEPA Filter Change-out Procedure Guidelines for Service Technicians

Given the current climate and precautionary regulations in-place to reduce the spread of the coronavirus known as COVID-19, there are several highly important and potentially lifesaving steps that must be considered before attempting to service conventional in-line HEPA filtration systems within hospitals and healthcare facilities.

What are conventional in-line HEPA filtration systems?

In-line HEPA containment exhaust filtration systems may be used within hospital and healthcare areas such as isolation rooms, cytotoxic areas, research laboratories, pathology areas and cyclotron or nuclear medicine areas.

Inline containment exhaust filtration systems are typically located in plant or roof spaces away from the isolation room – allowing for filter change-out and integrity testing access outside of patient areas. They can be larger in size than terminal HEPA modules, and in turn provide sufficient space for higher grade, high capacity pre-filters and high capacity HEPA filters.

Types of inline containment systems can vary greatly, depending on the potential risk and housing location. An inline system may be as simple as an upstream injection port for introducing challenge aerosol in the duct system and an inline HEPA housing, containing a HEPA filter and an access door for scan testing. As the potential risks increase, and the system requirements become more complex and laboratory type Bag-In / Bag-Out (BIBO) systems are used.

For more information, refer to Airepure article Design Considerations for Hospital Class-N isolation Rooms.

Considerations prior to in-line HEPA filter change-out

The change out of the filters also needs to be considered with other functional procedures;

  • Internal risk assessments
  • Decontamination
  • Shutdown and restart of the system
  • HEPA testing
  • Waste disposal

By default the filters should not be changed out unless the conditions are safe to do so.

It is also recommended that when changing out filters that are considers “safe”, minimum Personal PPE, safety glasses, gloves and face masks should still be used.

The “safe” status needs to take into consideration the whole of the system, including the area served and the associated duct systems.

In-line HEPA filter change-out procedure (indicative only – subject to site specific SWMS)

Assuming that there is not a duty standby filtration system, and the system does not have isolation dampers on either side of the housing:

  • Prepare all change-out procedures and undertake associated risk assessments with all involved personnel.
  • Ensure that the isolation room is “safe” and that deviation from the control pressures can be undertaken.
  • Ensure that the interconnecting duct is “Safe”.
    –  Written advice from the facility operator stating the system has not been exposed to any hazardous substances/biologicals etc.
    –  Written advice from the facility operator stating the system has been decontaminated and that there are no hazardous substances/biologicals etc.
    –  If this cannot be provided the method of filter change out will need to be reviewed.
  • Ensure that the correct replacement filters are available (and ready to be changed out).
  • Ensure that Waste disposal bags are available (for disposal of filters as hazardous waste).
  • Wind back the supply and exhaust of the plant serving the isolation room (maintaining a negative pressure in the system). Technically the supply can be shut off, and the exhaust should be running to just maintain the duct at a negative pressure (more than -10Pa to adjacent spaces).
  • Ensure the plantroom is positive to the exhaust system (you do not want air to be sucked out of the housing and into any other systems or outside air intakes).
  • While wearing the appropriate, “and agreed”, PPE, (minimum of facemask, goggles, gloves – it may also be prudent to wear coveralls, Tyvek suits).
    –  Open the housing filter access door, remove gradually to ensure that there is a slight flow of air being drawn into the housing, place to the side. (if airflow is excessive, wind back the fan or restrict the airflow further).
    –  Remove the appropriate filters (pre-filter and/or HEPA filter) if removing and replacing both, please remove the pre-filter first (this allows any loose dust to be picked up by the HEPA).
    –  Place the removed filters into waste disposal bag.
    –  Wipe down internal HEPA filter mating faces. Dispose of cleaning materials with the dirty filter.
    –  Reinstall filters (if both filters are being changed out, reinstall the pre-filter first).
    –  Ensure the HEPA filter is centered correctly and tighten the mounting fixture (nuts/bolts/clamps), so that the filter gasket seals.
    *  For gel seal the knife edge only needs to embed in the gel 2-5 mm. Do not use excessive force.
    *  For gasket seal filters, the entire gasket should be pressed up firmly but not compressed excessively as this can damage the gasket and filter. Do not use excessive force.
    –  Check all fittings and fixtures are firmly fitted and secure.
    –  Close the filter installation access panel.
    –  Remove any airflow restrictions (dampers) and start to ramp up the exhaust fan system. The supply air fan will need to be brought on line to maintain the required pressures within the isolation room.
    –  Once at design, or a satisfactory test velocity (0.5 m/s through filter) the HEPA filter can be tested/scanned AS1807.7 to confirm integrity (please refer to separate NATA test procedure for this).
    –  Discard disposable PPE and wipe down any other equipment with IPA, dispose of with hazardous waste.
  • Reinstate system back to original room pressure set points.
  • Record initial speed drive set points and room and filter pressure readings.
  • Submit Final NATA test results.

Important Notes

  •  Some of the above mentioned steps form part of other functions (i.e. NATA filter testing, but have been included).
  • Some steps may be moved around to suit individual systems.
  • It is possible to undertake filter change-outs with all fans off, however it is desirable to maintain a slightly negative pressure to reduce the risk of any dust or potential contaminants escaping to the area the inline housing is located in (be aware of internal hospital pressures and stack effects).
  • It is suggested that the HEPA filter be integrity tested prior to removal to confirm performance up to the date of its replacement. The new filter will also need to be tested to confirm its integrity.
  • We recommend the used of hand tools, and not power tools for removal and replacement of fixings, due to the potential for thread damage.
  • Ensure any threads are lubricated with acceptable thread lubricant (Vaseline may be all that is accepted).

For information please refer to Airepure Filter Servicing for PC3/PC4 Facilities.

Terminal exhaust HEPA filtration systems

Terminally mounted exhaust HEPA filtration systems allow contaminants to be contained within their locations (isolation rooms, cytotoxic areas, research laboratories, pathology areas and cyclotron or nuclear medicine areas).  Typically, room exhaust HEPA are located at low level, at a bio-cabinet discharge level or at high level in Isolation room ensuites.

Locating the HEPA filters within exhaust terminal housings/units does pose a testing/validation access issue that needs to be overcome.

Terminal mounted HEPA housings/units can also pose decontamination and removal issues, and when needed can rule fumigation out as a valid decontamination option.

Terminally mounted exhaust HEPA filtration systems pose additional challenges for HEPA filter service and testing personnel.

Further Information

A more detailed article entitled “Filter Service Considerations for Hospital and Healthcare Facilities” written by Kristian Kirwin (B.ENG Mechanical) & Shannon Roger (B. Ed) has been published in the official IHEA journal – Healthcare Facilities Magazine Vol 43, No 3, September 2020.

Airepure specialised filter servicing

Airepure design and supply containment filtration systems for PC3/PC4 (QC3/QC4) rated facilities and hospital or healthcare facilities that include isolation rooms.

We also supply relevant national support services, including product installation, routine maintenance / filter change-out and NATA accredited on-site testing and certification of HEPA filters, and on-site fumigation and testing of biological safety cabinets.

Contact Airepure for further details on these services.

About the Author

Kristian Kirwin

Kristian Kirwin
Engineering Director
Camfil Airepure

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