Practical advice for reducing the risk of airborne transmission via HVAC systems - Part 3

Action Prioritisation

As with any risk to personnel and product quality, a considered approach is vital to prioritise appropriate and practicable actions to mitigate the risk. This is especially the case in the current changing global situation and the subsequent impact on production sites, particularly with low resource levels for critical manufacturing and supporting utilities staff.

Before making practical changes to HVAC systems, you should

List higher risk areas in your facility (see section 4)
List higher risk HVAC systems in these areas (see section 4.)
Prioritise areas for HVAC actions based on risk
Plan reasonably practicable HVAC actions and review with your team (see sections 0 and 7)

Local Specific Requirements

It has been noted that governments may be starting to recommend or insist (set laws) on more specific requirements HVAC Systems to try and prevent the spread of Coronvirus-19 through ventilation systems.

Please note any regional variations to the advice below and request support. It is unlikely that any recommendations will specifically relate to cleanroom (manufacturing) environments. Guidance for general ventilation should not be adopted for cleanrooms for the reasons detailed in this document.

Practical HVAC Actions during epidemic/outbreak

These actions are focused on HVAC/AHU systems only during and after returning from outbreak periods. It is assumed that all personnel will also follow government and company guidelines on surface cleaning, personal hygiene, physical distancing & separation measures.

Once areas and systems are prioritised, assess which actions can be implemented as far as is reasonably practicable and prepare a plan for review.

Many actions will be temporary in nature with respect to regional epidemic levels, and plans should include considerations for long term “normal” operations.

Limit Access

Limit access to unventilated areas to prevent transmission risks.
Manage occupancy levels to reduce density.
Maintain Social distancing through control.

Check filter type:

Primary & Secondary (bag, panel) and final level of filtration: If it is possible to upgrade to ePM1 / F7 / MERV 13 or higher, this should be prioritised on recirculation systems. (This level is already recommended to protect occupants from harmful contaminants)
Ensure that systems will not suffer significantly reduced airflows by improving filtration levels
Ensure filter suppliers have provided documented effectiveness for your filters (% filtration efficiency) according to the latest standards, e.g. ISO 16890

Check filter status

Pressure drop on BMS or Magnehelic gauges: If reading is very low (less than starting pressure drop, close to zero), this could indicate failed or ruptured filter. Prioritise filter change.
If filters are very dirty outside of the safe operating range, prioritise change of filters in case of rupture due to high pressure.
Dirty filters restrict airflows where no automatic fan speed controls are utilised. Changing filters will increase ventilation.
Avoid the use of re-usable filters where possible. Replace re-usable filters with new, or re-clean if necessary, taking adequate precautions to protect operatives

Increase Outside Airflow (OA) / Reduce Recirculation

Central HVAC Systems:

Where possible, increase Outside (Fresh) Airflow, especially in systems where filter improvement to ePM1 / F7 / MERV 13 or higher is not reasonably practicable.
If systems cannot increase Outside (Fresh) Airflow rates, consider reducing recirculation to a minimum or lower level. Reducing recirculation may lower the risk of transmission to other spaces served by the same system, but you should also consider filtration effectiveness.
Switch off economiser mode where possible and fix to increase Outside (Fresh) Airflow.

For these actions, you should consider the impact on temperature and humidity control. In addition, reducing flow rates will limit the ability of the system to remove airborne virus particles in the space through filtration and dilution effect.

Local AC Systems (Fan Coils, DX, split systems)

For Local AC Systems with poor levels of filtration, switch off temporarily if possible. The impact on space temperature control should be considered as a consequence of this action.

For GMP Cleanrooms, please refer to the previous section - do not adjust Outside Air % in any area which may impact a GMP pressurisation strategy without a full understanding of the risks and following change control measures required.

Increase Exhaust airflow (EA)

Increase exhaust airflow in systems where possible. This particularly applies to restrooms and WC areas.

Run systems more frequently.

If systems currently switch off in evenings or weekends with a timer or BMS/BAS control, consider running systems continuously during this period, with reduced flowrate during unoccupied periods.
night setback back should be managed according to section 5.1.4.

Provide natural ventilation

If offices or other areas have access to openable windows, these can remain open, where practicable and secure, even if HVAC systems are running.

Room Air Cleaners

Additional room air cleaners can be introduced to spaces to remove particles and increase ACPH. To be effective, they need to have HEPA filtration and to have a substantial part of the room air pass through them. Locating cleaners or multiple cleaners in the centre of a space would be required.

Frequently Asked Questions

Q1. Will switching off the HVAC system reduce the risk of transferring and spreading the virus to other areas?

Answer: There have been some suggestions that switching off recirculating systems reduces the risk of spreading the virus. In general, switching off systems is not recommended, provided the system has adequate filtration (at least ePM1 / F7 / MERV13 final filtration stage). Switching off the system will stop the air from being passed through filters and therefore not being cleaned. HVAC systems rely on dilution effect to replace dirty air with clean air in order to clean up the space.

Q2. How do I risk assess the impact of recirculation systems?

Answer: In high-risk areas/rooms where recirculation systems do not have adequate filtration (at least ePM1 / F7 final filtration stage), workarounds should be employed to re-engineer the system to add appropriate filtration or avoid the need to use these areas.

Q3. Is Ultraviolet radiation (light) effective in killing the virus, and can this be used in an HVAC system?

Answer: There is no evidence yet on the effectiveness of UV light on inactivating the SARS-CoV-2 virus. Some research has been done on similar viruses (SARS and MERS) that did show that these viruses can be inactivated on surfaces by exposure to UVC radiation for 60 mins. The effectiveness of UVC radiation depends on the intensity of the radiation, the virus's resistance to UVC radiation and the exposure time. Some UVC light systems are available for installing in AHU’s, and these are generally employed to manage microbial growth and bio-burden on coils and other surfaces within the AHU. They are not intended to treat the air passing through the AHU. In EECO2’s opinion, they are ineffective in treating the air because the residence time (exposure time) of the air to the UV radiation is likely to be a few seconds at most. This is not long enough to have a measurable effect on the virus in the air stream. The most effective means of control of both virus and microbial contamination is through filtration.

Q4. I have a system supplying mainly outside (fresh) air. Is there a need to increase the filtration levels?

Answer: In general, increasing the amount of outside (fresh) air is advisable to manage the current risks associated with SARS-CoV-2. If your system is supplying largely outside air (>80% approximately), then the existing levels of filtration should be adequate. It is worth checking that this filtration is in place and is functioning correctly. It is not unusual that primary filtration (panel filters) can become loaded and fail due to excess pressure.

Q5. Can I increase the airflow to improve air circulation and reduce risk?

Answer: Where you are able to turn up systems to full speed this may be beneficial in high-risk areas. However, you should not increase flow in any area that adjoins a GMP or pressurised space, as this may disrupt the pressure balance and could lead to airflow reversal. In any case, you should conduct an impact assessment and follow your local change control process before actioning any change.

Q6. Should I be worried about the impact to classified or unclassified GMP areas?

Answer: In general, classified or unclassified GMP spaces have very good levels of filtration and very good airflows. They are designed to remove many types of contamination, including viruses. If you are not sure, review your risk assessment. There may be other areas (GMP and non-GMP) of your site that do not have the same level of scrutiny and control. These may need to be prioritised.

Q7. Should I use portable room air cleaners?

Answer: You can if reasonably practicable. Portable room air cleaners with HEPA filters can be used to increase the filtration rate of rooms. If possible, these may be best positioned near the return air inlets (if at ground level) or generally near working areas/ breathing zone. The effectiveness of these very much depends on the airflow, smaller commercial units typically have low airflows. Therefore lower filtration capacity and can only reasonably filter a small work area. Larger industrial or office commercial units are available but at a higher cost.

Q8. Should I turn off thermal wheel (rotary heat exchanger) heat recovery systems?

Answer: Not necessarily. The advice is to check the seals and pressure between supply and extract to ensure leakage is below 2% and to adjust the pressure balance if possible. If leakage is suspected in the heat-recovery sections, pressure adjustment or bypassing can be an option to avoid a situation where higher pressure on the extract side causes air leakages to the supply. If this situation can not be corrected, you should temporarily turn off rotary heat exchangers during SARS-CoV-2 episodes.

Transmission via heat-recovery devices is not an issue when an HVAC system is equipped with a twin-coil (‘run around’ coil) or other heat-recovery devices that guarantees air separation between return and supply side.

Q9. What about floor drains or other drainage traps?

Answer: Waterborne aerosols are recognised as a possible transmission route, so in areas served by mechanical ventilation systems or frequently occupied areas, check that drain traps (floor drains, HVAC traps) are charged with water and continue with any ongoing dosing maintenance regime.

Q10. Do I need to get ducts cleaned to prevent transmission?

Answer: No, duct cleaning is not effective against room-to-room infection because the ventilation system is not a contamination source if guidance about heat recovery and recirculation is followed. Viruses attached to small particles will not deposit easily in ventilation ducts and normally will be carried out by the airflow.

Q11. What about recirculating fan coil units or induction units? Do I need to switch these off?

Answer: Ideally, yes, Some systems (fan coil and induction units) work with local (room level) circulation. If possible (no significant cooling need), these units are recommended to be turned off to avoid resuspension of virus particles at room level (esp. when rooms are used normally by more than one occupant). Fan coil units have coarse filters which practically do not filter small particles but still might collect particles. On the fan coil heat exchanger surface, it is possible to inactivate the virus by heating up fan coils to 60ºC (140ºF) for one hour or 40 ℃ (100ºF) for one day.

If fan coils cannot be switched off, it is recommended that their fans are operated continuously. When the air is in continuous circulation, virus particles can be removed with general exhaust ventilation.

Q12. My facility has had potential cases of Covid-19; what precautions should staff take when dealing with HVAC systems?

Answer: HVAC maintenance personnel could be at risk when filters (especially extract air filters) are not changed in line with standard safety procedures. To be on the safe side, always assume that filters have active microbiological material on them, including viable viruses. This is particularly important in any building where there recently has been an infection. Filters should be changed with the system turned off while wearing gloves, with respiratory protection, and disposed of in a sealed bag. Use a secondary bag (double bag) as an additional precaution if considered appropriate.

Appendix A – Space Definitions

Classified, Unclassified & Other

Please note that GMP areas should be considered Extremely Low to Low risk for airborne transmission via HVAC due to multiple levels of filtration, including G4 / F7(ePM1, MERV 13) HEPA (H13-H14 and Higher) within these systems. It is not foreseen that any immediate changes should be made to any HVAC system that directly serves classified areas or indirectly impacts via pressure cascades. Any proposed change should follow standard change control procedures.

Cleanroom (classified and unclassified) spaces are inherently designed to control and clean the external environmental particulate contaminants (outside air) and internally generated contaminants (people, processes) of all sizes from large dust down to minute sub-micron particle sizes, along with associated microbes and bacteria.

These facilities are already designed to manage these particles, microbes and bacteria that can cause contamination, and SARS-CoV-2 should be treated the same as any other virus or bacteria within in production space.
Facilities are verified against stringent global standards and have regular repeat testing based on their classification, including continuous monitoring in higher classification environments.

All cleanrooms should have adequate and continuous validated cleaning activities with IPA & Biocides that will deal with SARS-CoV-2 and many other infectious diseases. These chemicals should be checked for efficacy and rotated according to manufacturers' advice and Standard Operating Procedures (SOPs).

The primary SARS-CoV-2 risk factor for cleanrooms is people; therefore, the primary risk mitigation measure is the continued and effective use of PPE (gowning), personal hygiene and room sterilisation to minimise bacteria & particulates within these spaces.

Operative & SOP training should be checked and refreshed to reduce the risk of spreading SARS-CoV-2 and any other virus or bacteria that people can carry. We recommend that the Primary Checks prior to entry to the cleanroom are robust and follow or exceed the requirements of each Corporate / Government / WHO or regional requirements.

We would recommend that gowning & cleanroom entry procedures be reviewed and improved before any HVAC modifications such as an increase of outside air, an increase of air change rates, or removing unoccupied airflow setback modes. Increasing outside air and air change rates will not guarantee an improvement to the ventilation effectiveness of the cleanroom HVAC systems.

Cleanroom spaces are usually classified in accordance with ISO 14644. Most GMP classified spaces have HEPA grade filters that are tested regularly and monitored for pressure and failure.

Classified: ISO 5 / Grade A /Class 100 – Extremely Low HVAC Risk Potential

These spaces are reserved for final fill and exposed product protection and will have validated ‘uni-directional airflow with HEPA or ULPA quality air designed to remove all contaminants from the working area. H14 filters have an efficiency of 99.997% and ULPA 99.9997% for the defined MPPS (Most Penetrating Particle Size). Effectiveness will be better for larger or smaller particle sizes if airflows are within the defined limits for each type of filter.

In general, ISO 5 areas have dedicated local air recirculation systems. Outside air connections will be provided from the HVAC systems serving the Grade B area generally or dedicated systems for controlling conditions & pressure.

Classified: ISO 6 / Grade B - Extremely Low HVAC Risk Potential

These spaces usually surround the ISO 5 / Grade A area as a ‘buffer zone for carrying out ancillary activities to the Grade ‘A’ Area. These areas will be supplied with the same quality air, usually with H14 final filtration. Often there will be two stages of H14 filtered air in these systems.

Air Changes within these spaces will often far exceed 30 ACPH. Recovery times from airborne particulate contamination are very short, often under 10 minutes.

Classified: ISO7 / Grade C / Class 10,000 – Extremely Low HVAC Risk Potential

These spaces will surround the Grade ‘B’ Areas in Sterile manufacturing facilities and often be the highest class in ‘Oral Solid Dose’ (OSD) or similar later stage manufacturing or packaging facilities. ISO 7 / Grade C HVAC systems will have final/terminal filtration within the cleanroom boundary.

These systems will have high air change rates within the space, typically 10 to >30 air changes per hour (ACPH) which capture, dilute and remove airborne particulate contamination. Recovery times will be 0- 20 minutes from airborne particulate contaminants in most cases.

These areas will be pressure controlled to protect from contamination infiltration from lower grade areas.

Classified: ISO 8 / Grade ‘D’ / Class 100,000 – Very Low HVAC Risk Potential

Grade ‘D’ is the lowest GMP classification, but rooms will generally still be provided with H13/H14 filtration to the spaces. ACPH will be lower but designed to contain and control airborne contaminates from both outside air and inside the room. Greater than 5 ACPH and often much greater. The gowning level in these areas may be reduced from the other higher Grades. These areas will be pressure controlled to protect from contamination infiltration from lower grade areas.

Unclassified: CNC (Controlled Not Classified) – Low HVAC Risk Potential

These areas are not GMP and typically used for secondary packaging facilities after the product is encapsulated /sealed and as transfer routes for production materials. In general, there will be positive pressure to the external environment to assist with protection from lower grade areas. There will likely be airlocks and change rooms protecting these areas.

These areas will have cleaning SOP’s more in line with GMP areas than general ‘Black’ areas. The filtration level for these areas should be F7/F9 but should be checked in line with the recommendations for non-GMP areas Below. These areas are often engineered to ISO8 cleanrooms but not certified as GMP.

Other Areas (GMP) – Low / Moderate HVAC Risk Potential

These areas will be reserved for primary material transportation. Warehouses, corridors, stores, and may have an HVAC system with low-grade filtration, low or no recirculation, very low ACPH and low PPE requirements from a product or microbial contamination perspective.

For these areas, the Other Areas guidance should be followed below.

Other Areas (non-GMP) – Low / Moderate HVAC Risk Potential

These areas will be common with most industrial & commercial business operations reserved for primary material transportation. Offices, Food Services Spaces, Restaurants, Technical Spaces, may have an HVAC system with low-grade filtration, low or no recirculation, very low ACPH and no routine requirement for additional PPE.

For these areas, the Other Areas guidance should be followed.

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