With the resumption of work and commercial activities around the world, Zhifeng Ren, director of the University of Houston’s Center for Superconductivity, recalls the urgent need to develop technologies that prevent contagion in indoor environments. A study carried out in China two months ago, for example, showed that air conditioning in a Wuhan restaurant contaminated customers who had lunch in the same sector as a family who did not know they had the disease. Another survey, also Chinese, detected considerable amounts of Sars-CoV-2 particles in the room where doctors at a referral hospital for the treatment of covid-19 change clothes.
In a study now published in the journal Materials Today Physics, the Houston researchers demonstrated that, in a single filter, 99.8% of the new coronavirus was eliminated, as well as 99.9% of the anthrax spores, an infection caused by the bacteria Bacillus anthracis. These tests were carried out at the Galveston National Laboratory, of the university’s Medical Department. The filter made with a nickel foam – sound absorbing material – heated to 200ºC.
For the researchers, the equipment can be used in airports, airplanes, schools, offices and cruise ships, avoiding the spread of covid-19. “The filter’s ability to help control the spread of the virus can be very useful for society,” believes Zhifeng Ren. He says that the medical equipment company that manufactured the prototype already wants to develop a table model to protect workers at their stations.
Suspended for hours
Previous studies by other teams of researchers indicate that Sars-CoV-2 is in the air for about three hours. Since the virus has also been shown to be unable to survive temperatures above 70 ° C, Houston scientists theorized that a heated filter could remove the microorganism from circulation and kill it. In laboratory tests, the applied temperature was 200ºC – under this heat, the pathogen died instantly. The material chosen to filter the air was nickel foam, widely used commercially in acoustic insulation. It is porous, flexible and, as a conductor of electricity, can be heated.
An initial problem was the resistance of the material to the intense heat, necessary to eliminate the virus instantly. To get around it, Ren decided to fold the foam and connect the filter compartments with electrical wires. That was enough for it to support up to 250ºC. “This internal wiring eliminated the need for an external source to heat the filter, and this minimizes the amount of heat escaping. The system made the device efficient: the air conditioning works well, without much effort ”, he says.
“This new indoor air protection technology offers the first prevention against the air transmission mediated by the Sars-CoV-2 environment. It will be at the forefront of the technologies available to combat the current pandemic and any future biological threats ”, said, in a note, one of the study’s co-authors, Faisal Cheema. Considering the initial production capacity, the researchers suggest that, at first, the equipment should be installed in priority locations, where there is a high risk of exposure, such as schools and hospitals.
At the beginning of the week, a letter signed by more than 200 scientists asked WHO to issue a public alert on the aerial spread of Sars-CoV-2. “There is a significant potential for exposure by inhalation to viruses in microscopic respiratory droplets (microdroplets) over short and medium distances (up to several meters, indoors and without ventilation), and we advocate the use of preventive measures to mitigate this airborne pathway. ”, Says the text.
“Preventing airborne transmission of covid-19 should be the next front in the battle against the virus,” argues Prashant Kumar, a researcher at the Global Clean Air Research Center in Surrey, Australia, author of a study on air contamination in indoor environments. He explains that, like many viruses, Sars-CoV-2 is less than 100mn in size, but the droplets expired by people who coughed or sneezed contain water, salts and other organic materials, in addition to the microorganism itself. As this content evaporates, the microscopic matter becomes small and light enough to remain suspended in the air and, over time, the virus concentration increases, as does the risk of infection.
As the indoor air stagnates, the danger is much greater. “We must turn this global tragedy into an opportunity to improve preparedness for similar threats,” says Kumar. “Improved internal ventilation is an important step that can be taken to reduce the risk of infection. However, more needs to be done to recognize and understand the air transmission of Sars-CoV-2 and similar viruses, to minimize the accumulation of virus-laden air in places that normally contain high densities of people, ”he observes.