UV-C Lethal Doses for Sars-Cov-2

COVID-19 and Ventilation System Filter Improvements

In building heating, ventilation, and air conditioning (HVAC) systems, filtration may be part of a general risk reduction approach, but not generally seen as a solution in itself. There is no direct scientific evidence of benefit, but some lower risks may arise due to the ability of some filters to trap particles and droplets of the respective size.

For air filters to have any impact on infectious diseases, filters must be chosen carefully, properly installed and maintained in appropriate systems to treat recirculating air. More importantly, in most buildings and most cases, filters may not be as effective as other infection control measures such as social distancing and hand washing.

What filters should be used in the building to protect from COVID-19?

There is no clear answer to this question due to insufficient data on the nature of the particles and droplets containing COVID-19. However, we know that low-efficiency filters are very unlikely to make a difference.

Properly fitted high-efficiency filters can handle particles of various sizes depending on their capture efficiency. The size of pathogens such as viruses and bacteria has been determined. Filter selection should be made by considering this information.

Should the highest efficiency filters be used?

High-efficiency filters may be suitable for your building, but they can also be inefficient. A high-efficiency filter can have a high initial pressure drop or accumulate dust and particles very quickly, so it requires frequent filter changes.

If the high-pressure drop filter is not installed properly and well sealed, it may cause more air to bypass the filter. Depending on the design of your system, a high-pressure drip filter may also reduce the amount of air released into the environment, making the filter less effective and causing other problems with other parts of the ventilation system.

Most importantly, in many residential and some light commercial systems, the fan in the system does not run very often and the efficiency of the filter may not be as important as it could be.

Why are hospital filters not used everywhere?

Hospitals have specially designed mechanical systems that can meet the filtration levels they need. Often rely on other systems and control strategies (eg UV lamps, humidity control, airflow management) to maximize the filtering advantage. Most importantly, it has dedicated personnel operating and maintaining this equipment to ensure the best possible protection.

Are ultraviolet lamps (UV Systems) effective in fighting the virus?

Yes. A properly designed and maintained UV system in harmony with filtration, humidity control and airflow management reduces infections from other viruses.

However, the details of the system are very important (eg design of luminaires, lamp type, lamp placement, amount of airflow and mixing, etc.). Adding a UV system to an existing system without considering these factors has not proven to be a benefit.

Are ionizers, ozone generators, plasma and other air-cleaning technologies useful?

Each of these technologies is useful, but their effectiveness, strength, and time vary. The most powerful of these technologies are Ozone Generators, which are very powerful oxidizers. They provide a successful result with the right calculation, the right product selection and the correct control instruments.

Are portable air purifiers effective?

There is much evidence of the effectiveness of portable air purifiers to reduce the risk of infectious diseases. To achieve maximum efficiency from an air purifier, it is necessary to check the technologies it contains and choose accordingly. Room conditions and dimensions should be determined well and a sufficient ACH (Air Exchange Per Hour) rate should be provided.

As with building filtration, they are only likely to be efficient in combination with other measures.

Can filters trap the droplets causing COVID-19?

Most public health guidance suggests that COVID-19 transmission is predominantly associated with large droplets. Air filtration is therefore only a small part of a solution as it does not address the transmission from surface contact or close contact between individuals.

However, the distinction between droplet transmission and airborne transmission is due to particle size. If the droplets are small enough, they can turn into the air and even stay for hours under the right conditions. Also, droplets change size depending on several factors, including their composition and the relative humidity of the air around them: low relative humidity often causes droplets and particles to be smaller. DNA and RNA from other viruses are often associated with droplets found in the air filters used.

High-grade HEPA filters (H13 and above)can effectively trap the droplets and aerosols.

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