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Influenza A/H1N1 »Swine flu« - Recommendations for the Operation of HVAC Systems
The speed of the worldwide spread of the new Influenza A/H1N1, also called Swine or Mexican flu, has lead the WHO to announce the highest pandemic level. This new influenza virus can be transferred by inhalation of infectious droplet aerosols (e.g. generated by sneezing), by contact with infectious surface liquids (e.g. residue on door-handles), or by direct contact to infectious persons. For example, very fine aerosols are generated by a sneezing person, where the single droplets carry the infectious viruses, if these droplets are inhaled, it may lead to an infection of the inhaling person. Such aerosols can be spread over an entire building by the ventilation system, and potentially expose and endanger a large number of people.
This potential risk can be minimized by means of applying suitable air filtration and using the correct mode of operation of the HVAC systems.
The new influenza virus has a size of approximately 100 nm which equals to 0.1 μm. As an example, this means that 10.000 viruses fit into the length of one millimetre. However, viruses cannot diffuse in air without being adhered to droplets or particles. The mean diameter of these aerosols typically is a multiple of the size of the viruses. Aerosols of this kind, possibly with viruses or germs adhering, are arrested in air filters to a certain percentage. Air filter systems are accordingly suitable for reducing, with differing degrees of efficacy, the concentrations of airborne pathogens and thus the risk of infection as a result of inhaling the viruses or germs. High efficiency particulate air (HEPA) filters as used for example in cleanrooms in the pharmaceutical industry (e.g. for the production of the vaccine) or in operating theatres in hospitals, are filtering out particles in a size of 100 nm to an efficiency of at least 99.995%.
Reliable protection when handling pathogens is offered only by those air-conditioning systems which have been designed and approved specifically for this purpose, such as the microbiological safety workbenches to EN 12469 (specified Filter Class H14 acc. to EN 1822) approved by an official authority like the TÜV (German Technical Inspectorate) Applications Engineering Information [05/2009 E].
Freudenberg Filtration Technologies gives the following recommendations for the operation of HVAC systems:
- The proportion of fresh air shall be increased as much as possible to reduce potential airborne pathogen diffusion by recirculated air.
- In case a certain proportion of recirculated air has to be maintained, it shall be filtered through HEPA filters (e.g. Viledon MX100 filters of class H11 to EN 1822) or at least through fine filters of high efficiency (e.g. Viledon MX98 filter of class F9 acc. to EN 779).
The maximum pressure of the HVAC fan should be considered as well as the leakage rate usual for standard ventilation systems (see EN 1886). The use of higher-efficiency filters may increase the resistance in the ventilation system and thus foster the escape of unfiltered air through leaks. The actual leakage rate can vary markedly depending on the system involved, and needs to be checked for each individual case. -
The requirements of EN 13779 or the German VDI guideline 6022 for a hygienic operation of HVAC systems shall be strictly applied.
Additionally, special attention shall be paid to any damage or leakage the filters may have suffered during installation. At this point, attention should be drawn to the importance of using self-supporting or rigid air filters (e.g. Viledon Compact pocket filters or Viledon MaxiPleat filters), since dimensionally stable filters provide more reliable and lasting retention of particles already stored. Insufficient rigidity of the pockets in pocket filters may lead to previously trapped particles being shaken free, particularly during volume flow changes (known as shedding effect). -
Used filters shall be changed by trained personnel, wearing appropriate personal protective equipment. Additionally, used filters shall be sealed into air tight plastic bags, and shall be disposed by incineration.
Following these instructions can reduce the potential risk of pathogen diffusion throughout a building by the ventilation systems to a minimum.
HVAC systems cannot reduce the risk of direct infection as a result of a person sneezing in close proximity to other persons, or by direct body contact to a source of contamination. The instructions given above should be regarded as accompanying actions and do not replace the recommendations given by the WHO or the national health authorities.
This document provides non-binding product information. Freudenberg Filtration Technologies KG cannot accept any liability for the completeness and correctness of the statements made. Liability and warranty questions shall be governed solely by the provisions of the delivery relationships involved.