Higher Efficiency Filters Rather than Dilution are the Cost Effective Approach to Mitigate COVID

H 13 Filters are Likely the Best Option for Many Applications

Droplets on Filter Media Evaporate and Form Smaller Droplets

What Do We Conclude from Studies that Not Many Particles are Aerosolized in Mask Reuse?

Most COVID Transmission is Airborne

Fibertex has HEPA 13 Nanofiber Filter Media

Sandler will Start Operating New Nonwovens Face Mask Line This Month

A Minnesota Biker who Attended the Sturgis Motorcycle Rally has Died of COVID-19 —

Airborne Transmission on a Bus in China 

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Higher Efficiency Filters Rather than Dilution are the Cost Effective Approach to Mitigate COVID

This is the conclusion of enVerid. While it has yet to be definitively demonstrated that aerosolized SARS-CoV-2, the virus behind COVID-19, can be transmitted through HVAC systems, ASHRAE has stated that the “Transmission of SARS-CoV-2 through the air is sufficiently likely that airborne exposure to the virus should be controlled.” The latest commercial guide from ASHRAE’s Epidemic Task Force recommends several strategies to mitigate any airborne transmission of SARS-CoV-2 including the use of mechanical filtration, ultraviolet germicidal irradiation (UVGI), humidity control, and dilution through increased outdoor air (OA) ventilation. Some of these strategies lead to the same outcome but at widely varying costs.

HVAC engineers need to design cost-effective HVAC systems that reduce the potential airborne transmission of SARS-CoV-2 in new commercial buildings, so enVerid has reviewed the most recent research and has developed a cost/benefit model for assessing the relative efficacy and cost of various OA ventilation and filtration approaches in the age of COVID-19. The model confirms that increasing filtration is preferable to increasing ventilation based on relative risk of infection and cost.

High-efficiency filters were found to be as effective at preventing the spread of bioaerosols, minuscule airborne droplets that carry the virus, as increased ventilation, and could do so with a far less energy-intensive impact than ventilation. Upgrading current buildings with high-efficiency HVAC filtration to address virus transmission is a simple and immediate solution. For new build and major retrofits, enVerid’s models show that when advanced filtration is combined with ASHRAE’s Indoor Air Quality Procedure (IAQP) and air scrubbing technology, substantial savings can be realized. For example, in an analysis of a 100,0000 ft² commercial building in New York City using this approach, a savings of $500,000 was projected for combined first cost and 20-year operating cost.

 

The graph shows little benefit of increased efficiency beyond  MERV 13.  However if filters capture 5 micron and larger droplets but then  become aerosol generators the analysis changes.

The MERV 13 filter may have an initial capture of 85% but if it is creating droplets 1 micron and smaller and or creating even smaller droplet nuclei which penetrate the filter it will be desirable to consider MERV 16  or HEPA filters.

H 13 Filters are Likely the Best Option for Many Applications

MERV 13 filters will not capture more than half the particles in the 0.3 to 1 micron range.  MERV 16 filters will catch 95%.

MERV 16 is roughly equivalent to E 10-E 11 in the European EN 1822:2009.  The H and U HEPA filters are more efficient. So where an E 11 would be emitting 50 particles an H 13 filter would only be emitting 2.5.

 

In the rating system presented in the Alert on August 31 we did not include H 13 filters. Given the higher effectiveness of an H 13 filter and the assumption that the economic cost will be less than 10% greater than MERV 16 the net value will be 63.

 

This will make the H 13 filter the highest rated option after the N95 mask.

 

 

Droplets on Filter Media Evaporate and Form Smaller Droplets

The studies on droplet evaporation in the air are instructive as to what happens on the surface of filter media.

In one study the airborne particles were about 4 µm in diameter and had dehydrated from respiratory droplets that the authors estimate were larger than 12 µm in diameter when they left the speaker’s mouth. The SARS-CoV-2 viral particles range from 0.6 to 0.14 µm in diameter.

https://www.the-scientist.com/news-opinion/droplets-from-speech-can-float-in-air-for-eight-minutes-study-67538

The amount by which a droplet shrinks upon dehydration depends on the fraction of nonvolatile matter in the oral fluid, which includes electrolytes, sugars, enzymes, DNA, and remnants of dehydrated epithelial and white blood cells. Whereas pure saliva contains 99.5% water when exiting the salivary glands, the weight fraction of nonvolatile matter in oral fluid falls in the 1 to 5% range. Presumably, this wide range results from differential degrees of dehydration of the oral cavity during normal breathing and speaking and from decreased salivary gland activity with age. Given a nonvolatile weight fraction in the 1 to 5% range and an assumed density of 1.3 g⋅mL⁻¹ for that fraction, dehydration causes the diameter of an emitted droplet to shrink to about 20 to 34% of its original size, thereby slowing down the speed at which it falls.

https://www.pnas.org/content/117/22/11875

The conclusion from these two papers is that droplets will evaporate to form smaller droplets.  Since only 5% is nonvolatile the conclusion has to be that the diameter of residue is very small even if it remains intact. More than likely it is not going to remain intact due to the movement air through the filter media.

 

What Do We Conclude from Studies that Not Many Particles are Aerosolized in Mask Reuse?

In the following paper it was shown that not much  virus retained on a used mask would be aerosolized with reuse.  this does nothing to dissuade one from the thesis that masks are aerosol generators.  It is not surprising that reside remaining after the generation would not be easily aerosolized

In this study, reaerosolization of virus particles from contaminated FFRs was examined using bacteriophage MS2 as a surrogate for airborne pathogenic viruses. MS2 was applied to FFRs as droplets or droplet nuclei. A simulated cough (370 l min−1 peak flow) provided reverse airflow through the contaminated FFR. The number and size of the reaerosolized particles were measured using gelatin filters and an Andersen Cascade Impactor (ACI). Two droplet nuclei challenges produced higher percentages of reaerosolized particles (0.21 and 0.08%) than a droplet challenge (<0.0001%). Overall, the ACI-determined size distribution of the reaerosolized particles was larger than the characterized loading virus aerosol. This study demonstrates that only a small percentage of viable MS2 viruses was reaerosolized from FFRs by reverse airflow under the conditions evaluated, suggesting that the risks of exposure due to reaerosolization associated with extended use can be considered negligible for most respiratory viruses. However, risk assessments should be updated as new viruses emerge and better workplace exposure data becomes available. https://academic.oup.com/annweh/article/56/3/315/168940

 

Most COVID Transmission is Airborne

Last week we reported on the two day conference on airborne transmission. The recording is now available. To view the webcast recording, click here or on this link:

https://www.nationalacademies.org/event/08-26-2020/airborne-transmission-of-sars-cov-2-a-virtual-workshop  

 

Fibertex has HEPA 13 Nanofiber Filter Media

Fibertex Nonwovens has introduced a new fully synthetic non charged HEPA 13 filter media based purely on mechanical filtration by nanofibres and with near to half the pressure drop of glass media. Designed for use in various applications, including vacuum cleaners, air purifiers, HVAC systems and respirators, Pleatex 80AH13NP6 is made from durable non-shredding nonwovens, which can replace hazardous glass fibres that are a risk when processing or when replacing filters in HVAC systems. Fibertex Pleatex 80AH13NP6 is easy to process on all types of pleating machines, including rotary pleaters, knife and blade pleaters. Advantages of this 100% synthetic material over commercially available glass fibre products include faster pleating, a low pressure drop and long-term efficiency. This material also adheres to the lowest energy consumption standards in ventilation systems.

Fibertex Pleatex 80AH13NP6 is based purely on mechanical filtration by nanofibres which are non-charged and is most commonly available as an 80 gsm HEPA 13 pleatable filter media. The benefit is that Fibertex Pleatex 80AH13NP6 works efficiently in all conditions and has a longer shelf life compared to charged melt-blown media,

 

Sandler will Start Operating New Nonwovens Face Mask Line This Month

On Aug. 26, Sandler formally inaugurated a new production line for nonwovens for face masks. Hubert Aiwanger, Bavarian Minister of Economic Affairs, was personally on site together with other guests from politics and business.

In early April, the nonwovens manufacturer from Schwarzenbach/Saale had announced the investment in a new line to increase production of nonwoven filter media for face masks and thereby expand its contribution to the security of supply of these products. The new nonwovens line enables the production of filter media for about 600 million mouth-nose-protection masks a year and had started production on schedule in mid-August. Among many investment initiatives announced in response to the bottlenecks caused by the pandemic, this line is the first of its kind to come on stream to establish German supply chains for medical protective masks. With a small celebration under hygiene conditions, the production line was formally inaugurated.

CEO Dr. Christian Heinrich Sandler welcomed the about 50 guests, emphasizing that it was and continues to be a matter of course for the company to contribute to overcoming the pandemic. "The main reason for investing in a new production line was our goal to increase our production capacity for nonwovens for face masks as quickly as possible. On Aug. 14, as we promised our Federal Minister of Health Mr. Jens Spahn, we began putting the new line into operation. In September, we will commence 24/7 operation.“

In May, Sandler AG, PIA Automation (automation specialist from Amberg), and Zettl Group (leading supplier of products for automotive interiors from Weng) had established the "Mask-Alliance-Bavaria.” Together, they set up an entire value chain for the manufacture of face masks in Bavaria. Management representatives of both partner companies were also guests at the inauguration of the new production line in Schwarzenbach.

 

A Minnesota Biker who Attended the Sturgis Motorcycle Rally has Died of COVID-19 —

A Minnesota biker who attended the Sturgis Motorcycle Rally has died of COVID-19 — the first fatality from the virus traced to the 10-day event that drew more than 400,000 to South Dakota.

The man was in his 60s, had underlying conditions and was hospitalized in intensive care after returning from the rally, said Kris Ehresmann, infectious-disease director at the Minnesota Department of Health. The case is among at least 260 cases in 11 states tied directly to the event, according to a survey of health departments by The Washington Post.

 

Airborne Transmission on a Bus in China 

A person on a poorly ventilated Chinese bus infected nearly two dozen other passengers with coronavirus even though many weren't sitting close by, according to research published on Tuesday that offers fresh evidence the disease can spread in the air.

Health authorities had initially discounted the possibility that simply breathing could send infectious micro-droplets into the air but did a U-turn as experts piled on pressure and evidence mounted.

The article published Tuesday in JAMA Internal Medicine probes the threat of airborne infection by taking a close look at passengers who made a 50-minute trip to a Buddhist event in the eastern Chinese city of Ningbo aboard two buses in January before face masks became routine against the virus.

Researchers believe a passenger, whose gender was not identified, was likely patient zero because the person had been in contact with people from Wuhan, the city where the contagion emerged late last year.

The scientists managed to map out where the other passengers sat, and also test them for the virus, with 23 of 68 passengers subsequently confirmed as infected on the same bus.

What is notable is that the sickness infected people in the front and back of the bus, outside the perimeter of 1-2 meters (three-six feet) that authorities and experts say infectious droplets can travel.

On top of that, the sick passenger was not yet showing symptoms of the disease, such as a cough, when the group made their trip to a religious event.

Researchers also noted the air conditioning simply recirculated the air inside the bus, which likely contributed to spreading of the virus.

"The investigations suggest that, in closed environments with air recirculation, SARS-CoV-2 is a highly transmissible pathogen," they wrote, referring to the name of the virus.

"Our finding of potential airborne transmission has important public health significance."

Their study, which includes a diagram showing where each infected passenger sat, adds to the evidence of airborne transmission, including research into how the virus spread between diners' tables at a restaurant in the southern Chinese city of Guangzhou.

More information: Ye Shen et al. Community Outbreak Investigation of SARS-CoV-2 Transmission Among Bus Riders in Eastern China, JAMA Internal Medicine (2020). DOI: 10.1001/jamainternmed.2020.5225